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Part III, continued:

  

The assimilation of biotic and other substances by plants

  The problem of plant absorption of biotic substances-vitamins. auxins,and other organic substances, has interested investigators for a long time.

 

Assimilation of vitamins

  Many investigators have studied the uptake of vitamins and auxinsthrough the root system or leaf surface. Carpenter (1943) introduced riboflavin byspraying the crowns of decapitated plants such as tomatoes, tobacco, fuchsia andcarrots, which were subsequently kept in a dark room. The analysis of their sap showedthe presence of riboflavin in much higher concentrations than that in the controlplants, sprayed only with water. Plants sprayed with a thiamine solution containedthiamine in higher concentrations than the control plants (Hurni, 1944; Schopfer,1943).

  Bonner et al., (1939) analyzed plant tissues grown in a solution containingvitamin B1. The results of these experiments are given in Table 54.

Table 54
Thiamine concentration in leaves of plants after its artificial application, in mg/kg of dry weight
(according to Bonner at al., 1939)

Plants

Treated Plants

Control Plants

Brassica alba Schmalh.

15.8

6.0

Brassica nigra Koch

6.4

3.9

Agrostia tenuia L.

8.6

5.8

Poa trivalis L.

7.2

4.4

Cosmos Gay

6.0

5.0

  Radioactive vitamins are being used in recent years for the detectionof their uptake by plants.

  Shavlovskii (1954) employed vitamin B1 containing radioactivesulfur S35. The plants were grown under sterile conditions on an agarmedium of Knopp, supplemented with the mentioned radioactive vitamin at a concentrationof 0. 1 y/ ml. The activity of this medium was 4,400 counts / minute (cpm) per 1ml. The amount of vitamin in the tissues of the plant was determined after variousperiods of time. The number of cpm showed the amount of absorbed vitamin. The resultsare given in Table 55.

Table 55
Absorption of radioactive vitamin B1 by plants, from sterile agar substrate
(according to Shavlovskii, 1954)

Plant organs

Buckwheat: cpm per plant after 11 days

Buckwheat: cpm per plant after 38 days

Peas: cpm per planlt after 11 days

Peas: cpm per plant after 38 days

Corn: cpm per plant after 11 days

Leaves

3,458

4,920

1,110

1,326

6,993

Stems

1,655

13,288

1,486

2,912

--

Roots

505

1,601

455

3,360

783

  These results show that the radioactive (S35 ) vitaminB1 enters the plant is the roots, is initially concentrated in the leaves,and then gathers in the stem and in the roots. Apparently, the increase of the vitaminconcentration in the roots and stems in the late growth phase of the plant may beexplained by the fact that the vitamin is absorbed in the early phase of the growthwhen the vitamin synthesis by the shoot is inadequate. Later on the plant beginsto synthesize the required amount of the vitamin. and the latter, under favorableconditions, enters the stem and roots. It has been shown that plants can obtain vitaminsfrom microorganisms. This was demonstrated by the use of radioactive isotopes. Ifbacteria or yeasts were saturated with an amino acid or vitamin labeled with phosphorusP32 or sulfur S35 and inoculated into a medium where plantswere being grown, the radioactive substances were soon detected in the tissues ofplants. Shavlovskii (1954) grew buckwheat in sand with a culture of Ps. aurantiacaor yeasts (Torlopsis utilis, T. latvica and Rhodotorula rubra). Allthe cultures were previously saturated with radioactive vitamin Bl (S35).After 11 days the plants were analyzed for the S35 content of their tissues.Simultaneously the excretion of the radioactive vitamin by the bacteria was measured.The analyses showed that buckwheat takes up the vitamin excreted by the microbesin detectable amounts. The greatest amount went to, the plant (8.5 % of the totalactivity) from Ps. aurantiaca (Table 56).

Table 56
Transfer of vitamin B1 from microbes to buckwheat
(according to Shavlovskii, 1954)

Part of plants

S35 (of vitamin B1) cpm/plant
Ps. aurantiaca
8,100 cpm

S35 (of vitamin B1) cpm/plant
T. latvica
45,000 cpm

S35 (of vitamin B1) cpm/plant
Rh. rubra
9,100 cpm

S35 (of vitamin B1) cpm/plant
T. utilis
10,230 cpm

Cotyledons

294

252

144

150

Stems

217

161

96

114

Roots

180

109

77

77

Total per 1 plant

691

522

317

341

Given up by microbes to plant, in percent

8.5

1.2

4.0

3.3

 

Assimilation of amino acids

  The capacity of roots to absorb amino acids has been proven experimentally.Petrov (1912) gives data on the absorption of asparagine by plants (corn). Shulov(1913), Pryanishnikov (1952) and Byalosuknya (1917) confirmed these data. Accordingto them, asparagine is a good source of nutrition for peas, corn, cabbage, mustard,and other plants.

  Hutchinson and Miller (1911) showed that pea plants can assimilateleucine, glycine, aspartic acid and tyrosine. Klein and Kisser (1925) have shownthat during growth in sterile conditions, oats can assimilate arginine not less thanthey can assimilate nitrates. According to Virtanen and Lathe (1937, 1946), peasand clover assimilate aspartic acid well, while wheat and barley react negativelyto this substance, Steinberg (1947) showed that isoleucine has a harmful effect onthe growth of tobacco. Tanaka (1931) has shown that the plant Sysirinchium bermudianumutilizes asparagine, glycine, and cystine. Miller (1947) followed the absorptionof dimethionine by tobacco and tomatoes growing under sterile conditions. The sapof roots and aerial parts contained 1.0- 2.5 mg methionine per 5 ml. Miller is ofthe opinion that amino acids are assimilated by plants.

  Riker and Gütsche (1948) have shown that some amino acids suppressthe growth of isolated tissues of sunflower. The authors think that the deleteriousaction of the amino acids is caused by their excess, which interferes with the metabolism.Sanders and Burkholder (1948) noted that a mixture of amino acids has a more favorableeffect than each of them separately.

  Virtanen and Lincol ascribe a stimulating role to the amino acids.According to them, small concentrations of alanine and phenylethylamine (decarboxylationproduct of phenylalanine) strongly affect the growth of peas, in the same way asthe heteroauxin. The plant parts change markedly, becoming stronger and greener.

  In order to demonstrate the uptake of amino acids by plants, Shavlovskii(1955) studied the absorption of, radioactive methionine S35 by buckwheat,corn, and peas.

  This culture excretes more vitamin than the others. Yeasts excretedvarious amounts of the vitamin depending on the species. The data given below shouldbe considered as approximate and possibly lower than in reality. This amino acidwas added to the medium of Knopp in which these plants were grown. After 11 daysof growth the plant tissues were examined for the presence of radioactive sulfur.The results are given in Table 57.

Table 57
The absorption of radioactive methionine S35 by plants (cpm per plant)
(according to Shavlovskii, 1955)

Plants

Specific activity:
Leaf

Specific activity:
Stem

Specific activity:
Root

Activity, (dry weight) of:
Leaf

Activity, (dry weight) of:
Stem

Activity, (dry weight) of:
Root

Buckwheat

56

81

625

389

759

1,389

Corn

65

--

124

5,814

--

3,452

Peas

46

31

628

828

992

7,530

  As can be seen from the table, the absorption of this amino acid byplants is quite vigorous. The highest concentration of the amino acid in in the roots.The intensity of absorption varies according to the composition of the medium andexternal conditions.

  The absorption of methionine is more rapid and more pronounced inthe presence of vitamins B1 and B6.

  Ratner and Dobrokhotova (1956) have shown the activating effect ofthiamine pyridoxine and pantothenic acid on the synthesis of glutamic acid and alaninein the roots of sunflower.

  The distribution of the radioactive sulfur of methionine is differentfrom that of radioactive inorganic sulfur. In the former came sulfur is concentratedin the roots and in the latter, in the aerial parts (Thomas and Hendricks, 1950,and others). This gives grounds for the assumption that methionine as well as otheramino acids are assimilated by plants without any change in their molecules and arebeing used by them for protein synthesis. Shavlovskii extracted protein from theroots of peas which had grown in the presence of radioactive methionine and showedthat they contained the major part of the methionine absorbed by the roots. One gramof fresh roots gave 23,171 cpm, and the proteins isolated from them--13,220 cpm.

  Plants absorb the amino acids synthesized and excreted by microbes.This was shown by Shavlovskii who used methionine containing radioactive sulfur S35.As in experiments with vitamins, Shavlovskii grew bacteria Ps. aurantiacaand yeasts Sacchar. cerevisiae, in a medium containing radioactive sulfurS35 in the form of (Na2 S3504). The bacteriawere then autolyzed and the autolysates containing radioactive (S35) aminoacids were added to the medium where plants were grown, Radioactive sulfur was thenfound in the plant tissues; the roots showed more radioactivity than the aerial parts.In the presence of autolysate of Ps. aurantiaca the activity in the cotyledontissues was 137 cpm, in the stems--356 cpm, and in the roots--720 cpm; in the presenceof yeast autolysate the corresponding figures were: 43 cpm, l99 and 569 cpm.

  In his subsequent experiments Shavlovskii grew buckwheat in a mediumwith living cultures of Ps. aurantiaca previously grown in a medium containingradioactive sulfur. Seeds of the buckwheat were infected with these cells beforesowing (700 million cells per seed, with a total activity of 125,000 cpm).

  The following activity was found on the second day of growth in theplant: cotyledons--228, stems--181, roots--132 cpms. Consequently, on the secondday the plants had taken up about 0.4 % of the bacterial radioactivity. A directrelationship between the amount of bacteria and the absorption of radioactivity wasnoted. Upon introduction of 3.45 billion cells per seed, about 1% of the total radioactivityof the cells was detected in the plants (after 7 days growth).

  The capacity of microorganisms to transfer their metabolic productsto the plants was shown in a paper by Akhromeiko and Shestakova (1954). These authors,in their studies, employed radioactive phosphorus P32. They grew Az.chroococum, Ps. fluorescens and yeasts (isolated from soil) in media containingP32 as a source of phosphorus nutrition. The cultures of microorganismsthus grown were carefully washed with water and inoculated into the sand in whichsaplings of oak and ash trees were grown.

  Experiments had shown that radioactive phosphorus is taken up by theplants in considerable amounts; it is emitted at a different rate and in differentamounts by the various microbial species. The greatest effect is obtained in experimentswith yeasts. About 43 % of the radioactive phosphorus from yeast was taken up byplants in the first days of their growth. Oak saplings absorbed more radioactivitythan ash-tree saplings.

  These experiments show that biotic substances formed by microbes,in addition to the amino acids and other metabolites, are excreted into the substrate,and from the substrate are absorbed by plant roots.

Assimilation of antibiotics

  Higher plants absorb not only vitamins, auxins and amino acids butalso many other organic compounds present in the soil and formed by microorganisms.

  Of all the metabolites which can serve as indicators of absorptionby plants, antibiotics, in our opinion, are the most outstanding.

  Antibiotics are very specific. They are not present in plant tissuesand are not formed by them. They are easily detected and differentiated from otherorganic substances including phytocides. In our experiments we have employed antibioticsin their native state as well as in the form of chemically pure preparations. Antibioticsproduced by different representatives of soil microorganisms were used: penicillin(mold product), streptomycin, globisporin, aureomycin, terramycin, and others (productsof actinomycetal metabolism), subtilin, gramicidin, and others (of bacterial origin).

  The crude as well as the chemically pure preparations were added,in various concentrations, to substrates where plants were grown. Experiments hadshown that antibiotics were taken up by roots rapidly and in considerable amountsand were more or less uniformly distributed in all plant tissues and organs.

  In a manner similar to that of biotic substances and amino acids theantibiotics concentrate in the root system more than in other parts. From there theyenter the aerial parts.

  Antibiotics are absorbed by plants directly from the soil where theyare formed by microorganisms. The latter, as it will be shown below, developing insoil under certain conditions, produce and accumulate considerable amounts of theseactive metabolites, These naturally formed substances enter the plant tissues viathe root system in the same way as the chemically pure antibiotics.

  The antibiotics are known to be rather complex organic substancesof high molecular weight. For example, streptomycin consists of three basic groups:N-methyl, S-methyl and also carbonyl group. Its formula is C21H39O12N7.Its molecular weight is more than 500. No less complex are aureomycin, terramycin,penicillin and other antibiotics.

  If such complex organic compounds as antibiotics, amino acids andvitamins are absorbed it may be assumed that many other carbon and nitrogen compoundspresent in the soil are also absorbed by plants.

  A voluminous work was performed in the laboratory of the famous Frenchbotanist Bonne to determine the absorption of organic compounds by plants. LaurentJ. and Laurent J. (1903). studied assimilation of many organic compounds by plants.According to their data, peas, lentils. corn, rice, and wheat utilize glucose, saccharose,glycerol, dextrin, starch and potassium humate. Lefevre (1905, 1906) noted the capacityof plants to assimilate amino acids and other nitrogenous compounds. Ravin (1913),experimenting with horse radish came to the conclusion that plants can assimilatethe organic acids--succinic, citric, malic, tartaric and oxalic.

  Maze and Perrier (1904) grew corn in a methanol-sugar solution. In30 days of growth these plants absorbed 10-14 g of saccharose, their dry weight was14-21.9 g. Approximately the same amount of glucose was absorbed by plants in anotherseries of experiments.

  According to Pryanishnikov, 1952; Shulov, 1913; Byalosuknya, 1917;and others, peas, corn, cabbage, buckwheat and other plants assimilate well glucose,saccharose and lactose. Especially good growth of plants was obtained in the presenceof levulose.

  Klein and Kisser (1925) had shown that oat cultures assimilate organiccompounds well without preliminary clevage of their molecules. Arginine is assimilatedless than nitrate nitrogen. Similar data were obtained by a Japanese investigatorTanaka (1931). This author studied the assimilation of organic nitrogenous co poundsby higher plants under conditions of sterile growth and obtained positive results.

  Seliber (1944) brings results of his own studies and those of otherson the growth of potatoes at the expense of starch and other substances present inthe tubers. The sprouts of potatoes grow worse if the mother tubers are removed.The author describes cases of formation of sprouts and tubers inside the mother tuber.The growth of sprouts in those cases proceeds completely at the expense of food reservesof the mother nodule. Organic compounds of the latter pass into the embryo and intothe daughter tuber.

  Numerous experimental data as well as agrobiological observationsexist which confirm the possibility of heterotrophic nutrition of plants.

 

Effect of bacteria on the assimilation of nutrients by plants

  The assimilation of mineral and organic nutrients by plants proceedsat various intensities and depends not only on the composition and properties ofthe compounds in question but also on the quantitative and qualitative compositionof the microflora around the root system.

  Studies show that under conditions of sterile growth of plants thesesubstances are not absorbed to the same extent as in the presence of microorganisms.We have grown wheat, peas and corn in a sterile nutrient solution and followed theabsorption of penicillin, streptomycin, aureomycin and other antibiotics in the presenceand absence of various bacterial species.

  Bacterial cultures were chosen which did not inactivate or decomposethe above-listed antibiotics and were at the same time resistant to them for theinoculation of the nutrient solution. We have tested and chosen more than 10 culturesbelonging to different species: 3 cultures of root-nodule bacteria (Rh. trifolii,Rh. meliloti and Rh. phaseoli), 2 strains of azotobacter (Az. chroococcum),4 strains of Ps. fluorescens, isolated from the rhizosphere of different plants,and 2 strains of the genus Bacterium (Bact. denitrificans and Bact.sp.) also isolated from the rhizosphere of wheat a nd peas. The effect of the bacteriawas determined by the rate of disappearance of the antibiotics from the solutionand their uptake by the plants. The presence of antibiotics in the plants was determinedby the conventional microbiological tests. The indicator microbes were cultures ofthe sporiferous bacillus Bact. subtilis and staphylococcus--Staph. aureus.

  Tables 58 and 59 bring data on the uptake of streptomycin and penicillinby wheat and peas in the presence of 5 bacterial cultures and their mixture. Experimentswith corn and other plants gave similar results.

Table 58
The effect of bacteria on the uptake of streptomycin by wheat
(units per g of plant tissue; the initial solution contained 2,500 units-100 units/ml)

Bacteria

Roots after 1 day

Stems after 1 day

Leaves after 1 day

Roots after 3 days

Stems after 3 days

Leaves after 3 days

Az. chroococcum

100

20

10

160

20

75

Rh. trifolii

150

30

40

200

20

100

Ps flourescens No 4

30

0

0

50

20

30

Bacterium sp. 25

20

0

0

50

10

10

Oligonitrophil

100

30

50

150

20

50

Bacterial mixture

200

50

100

200

30

120

Control (without bacteria)

20

10

0

100

10

60

Table 59
The effect of bacteria on the uptake of penicillin by peas
(units per g of plant tissue; initial solution in the vessel contained 5,000 units--200 units/ml)

Bacteria

Roots after 10 hours

Stems after 10 hours

Leaves after 10 hours

Roots after 2 days

Stems after 2 days

Leaves after 2 days

Az. chroococcum

120

30

40

200

120

180

Rh. trifolii

100

20

40

250

100

150

Ps flourescens No 4

10

0

0

50

10

20

Bacterium sp. 25

5

0

0

30

5

10

Bacterial mixture

250

50

100

250

120

210

Control (without bacteria)

50

5

0

150

50

100

  As can be seen from the table, the bacteria have a considerable effecton the uptake of antibiotics by tissues of plants. The various bacterial specieshave different effects. Some of them enhance the uptake (Az. chroococcum andRh. trifolii) others (Ps. fluorescens No 4 and Bacterium sp.No 25) inhibit the uptake of antibiotics by the plants. The largest amounts of streptomycinand penicillin were absorbed in the presence of a bacterial mixture and the leastabsorption was in the vessels containing the culture of Bacterium sp. No 25.

  The analyses have shown that the increased concentration of antibioticsin the plants is accompanied by decreased concentration of antibiotics in the solution.

  Analogous data were obtained in experiments with plants growing insand. The uptake of antibiotics was highest in the presence of Azotobacterand root-nodule. bacteria and the smallest in the presence of the nonsporiferousbacillus Bacterium sp. No. 25 (Figure 66).

 

Figure 66. The effect of bacteria on the uptake of streptomycin (from sand) by plants (peas). The analysis was performed 10 hours after the introduction of the antibiotic into the vessel:

I--bacteria of the group of oligonitrophils (strain 25 and others); II--Azotobacter (the same results with Rhizobium); III--control without bacteria. 1--roots, 2--lower part of stem, 3--middle part of stem, 4--upper part of stem, 5--leaves.

 

  Gerretsen (1948) described the enhancement of nutrient uptake by plantroots under the influence of the microflora. He grew oats, sunflower, buckwheat andother plants in vessels with sterile and nonsterile soil, in the presence and absenceof bacteria. Phosphates, soluble. insoluble and sparsely soluble in water, were introducedinto the soil (bi- and tricalcium, phosphate, phosphoric powder, etc).

  The experiments have shown that under sterile conditions, withoutbacteria, the uptake of phosphates proceeds at a lower rate than in the presenceof bacteria. The greatest effect was obtained in the experiments with buckwheat.in the presence of specially chosen bacteria.

  Kotelev and Garkovenko (1954) studied the uptake of inorganic radioactivephosphorus by bacteria. Under sterile conditions the radioactive phosphorus was takenup at a slower rate and in smaller amounts. The plants showed only 4% of the totalradioactivity when grown under sterile conditions, in the presence of bacteria theradioactivity of the plants increased to 13%.

  Experiments with labeled (P32) lecithin gave analogousresults. Lecithin was added to the solution used for wetting sand in which barleywas grown. The experiments were carried out in the presence and in the absence ofbacteria. In the absence of bacteria 1.9% of the radioactive phosphorus was takenup, while in the presence of bacteria 16.6-18.6% of the phosphorus was taken up,i. e., 8-9 times more.

  Bacteria markedly increase the rate of phosphorus uptake by plantsfrom granules prepared with radioactive superphosphate. Barley sprouts grown understerile conditions gave 400--500 cpm, but 1,000-1,500 cpm, when grown under nonsterileconditions (cpm. per 10 mg of plant dry weight) (Kotelev, 1955).

  We employed the tracer-atom technique to carry out a number of experimentson the uptake of phosphorous compounds from a substrate in the presence and in theabsence of different bacterial species. Plants (barley) were grown in a nutrientsubstrate (solution, sand and soil), previously sterilized and then inoculated withpure cultures of bacteria. Radioactive phosphorus (P32) was then addedto the substrate. After 15-20 days of growth the plants were analyzed. We determinedthe presence of organic and inorganic phosphorus, as well as sparsely soluble (inwater) phospholipides, and phosphoproteins. In addition, amino acids were determined(by the use of paper chromatography) in the fraction containing organic water-solublecompounds (Krasil'nikov and Kotelev, 1956). Bacteria isolated from the rhizosphereof corn, grown in Moldavia, were used in these experiments. All of them belongedto the nonsporiferous bacteria of the genera Bacterium and Pseudomonas.One culture (10-A) was isolated from podsol soil of the Moscow Oblast'. Each vesselfilled with sand was supplemented with 465 mg P205 (P32). The total activityper vessel was 6,400,000 cpm. Counting was performed after 17 days growth. The resultsof the first series of experiments are given in Table 60.

Table 60
The effect of soil bacteria on the uptake of radioactive phosphorus by plants

Experiment

cpm/100g of dry plant substance

Uptake of P32, %

Fraction of organic P, cpm/100g plant mass in aqueous solution

Fraction of organic P, cpm/100g plant mass in lipides

Fraction of organic P, cpm/100g plant mass in proteins

Control (without bacteria)

3,000

0.7

375

450

1,700

Infected with Bacterium sp.

3,830

1.4

475

575

2,300

Infected with Bacterium sp

4,300

1.3

578

675

2,300

Infected with Bacterium sp

--

1.2

650

700

2,900

Infected with Bacterium sp

--

0.6

300

400

2,000



 

Figure 67. Radiochromatograms of organic and inorganic phosphorus compounds in the soil and in plant tissues. The plants were grown in sterile and nonsterile soil (in the presence of natural microflora).

1--phosphorus compounds in the soil (sterile soil); 2--phosphorus compounds in plants (barley), grown in sterile soil; 3--phosphorus compounds in plants grown in nonsterile soil; a--organic phosphorus; b--inorganic phosphorus.

 

  The radiochromatogram, (Figure 67) represents the process of accumulationof organic phosphorus in the tissues of barley grown under sterile conditions, andin the presence of bacteria. It can be seen from the figure and Table 58 that bacteriahave a considerable effect on the uptake and accumulation of phosphorous compoundsin the tissues of plants. Under the influence of the bacteria a formation of quitedifferent phosphorous substances takes place.

  The results of the determination of amino acids are not loss demonstrative.We have determined the amino acids present in extracts of 70% alcohol by paper chromatography.Five hundred-mg samples of the dry mass of plants were extracted for 4 hours at 45°C with 25 ml of alcohol. The extracts were then filtered, the filtrate was evaporatedto 1-2 ml and subjected to chromatography. The results are given In Table 61.

Table 61
The effect of bacteria on the composition of amino acids in plant tissues

Experiment

Dry weight of plants, mg

Uptake of P32 per 100 g

Lystine

Aspara- gine

Aspartic acid

Serine

Glycine

Glu- tamic acid

Alanine

Valine

Control (without bacteria)

545

465

++

+

+/-

-

-

-

-

-

bacteria 1p

573

700

++++

+++

+++

+++

+/-

+/-

++

-

bacteria 2p

710

786

+++

++

++

++++

+

+/-

+++

-

bacteria 125

--

--

+/-

-

-

+++

++++

++++

+/-

+

bacteria 151-A

--

--

+

++

++

++

-

+++

+/-

+/-

Legend: 4 pluses--very intense color; 3 pluses--intense color; 2 pluses--moderatecolor; 1 plus--weak color; plus--minus-color hardly detected, on the border of accuracy;minus--absence of the amino acid.



 

Figure 68. Radiochromatograms of the amino acid composition of plants grown in sterile conditions after artificial contamination with bacteria:

A) amino acids of plants grown in sand; B) amino acids of plants grown in the soil (chernozem). a-- amino acids of plants grown in the absence of bacteria; b--amino acids of plants grown in the presence of Bacterium sp 1; c--amino acids of plants grown in the presence of a strain of Bacterium sp. 2; 1--lysine; 2-3--asparagine and aspartic acid; 4--serine; 5--glycine; 6--glutamic acid; 7--alanine; ?--unknown compound.

 

  The radiochromatogram (Figure 68) shows the distribution of aminoacids in plants grown in the presence of 2 bacterial cultures (lp and 2p). It canbe seen from the figure, that the presence of bacteria in the substrate causes formationand accumulation of amino acids of a different nature to those formed in the absenceof bacteria. Some amino acids (serine, glycine, alanine, valine, cysteine) cannotbe detected, in the control sprouts of the barley grown under sterile conditions,only their traces can be found. These amino acids are present in considerable amountsin plants grown in the presence of bacteria. Different bacterial cultures have avarying effect on the formation and concentration of amino acids in plant tissues.In our experiments cultures 125 and 151-A favored the accumulation of glutamic acid,and bacteria lp and 2p favored the accumulation of alanine, lysine and asparagine.

  The effectivity of the same bacteria to plants growing in soil (heavyloam chernozem), although considerable. was somewhat different to that noticed whenthe plants were grown in pure sand. The quantitative and qualitative relationshipof amino acids was different. Neither lysine nor alanine could be found in the barleysprouts grown in the presence of lp and 2p bacteria, asparagine and glycine werefound only in traces (Figure 68 B).

  According to Akhromeiko and Shestakova (1954), microorganisms inhibitthe uptake of phosphorus (P32) by woody plants. Saplings of oak and ashtree were grown in sterile and nonsterile soil and the uptake of radioactive phosphoruswas determined. The authors have noticed that bacteria of the rhizosphere at firsttake up the tracer phosphorus and subsequently release it.

  Ratner and Kozlov (1954) grew corn under sterile conditions, accordingto the method of Shulov, in the presence and in the absence of bacteria in the solution.They found that when bacteria were present in the solution, organic compounds ofphosphorus and nitrogen were found in larger amounts than when the plants were grownwithout bacteria. In the sterile vessels the plants contained the following: amidesand amines--1.300 mg; organic nitrogen--1.191 mg (32.33%); in nonsterile vesselsthe respective figures were 1.562 mg and 1.960 mg (44.22%).

  The difference in composition of the amino acids is well defined onthe chromatogram. The addition of microbial metabolic products, or a dead culture,to plants in their early growth stage on sterile medium, causes an increase in thephosphorus and nitrogen content of their exudate. The microbial metabolic productsincrease not only the uptake of these substances by the roots but also the syntheticcapacity of the roots. The increased incorporation of the radioactive phosphorusP32 into the lipides and nucleoproteins, as well as the increased contentof amide and amine nitrogen in the exudate confirms these assumptions.

  Microorganisms and their metabolic products affect the process ofnitrogen transformation in the root. In the presence of microorganisms the rate ofmetabolism of amino acids in the roots increases as well as the process of transformationof the inorganic to organic nitrogen. In the presence of microorganisms the uptakeof inorganic and organic compounds--microbial metabolites--is increased.

  Besides, microorganisms promote the transport of nutrients in thesoil. They are carriers of nutrients, supplying the root system with various nutrients.

  Numerous papers have stressed the point that mere contact of rootswith the soil is not sufficient to secure the nutrient requirements of the plant.Mediators between nutrient sources of the soil and the root system exist in soils.Such mediators are the microbes.

  Khudyakov (1953 b) has shown that molds can transport nutrients intheir hyphae. It is known that protoplasm moves along the hyphae at high speed. Inmucor fungi it is as much as 50-80 µ and more per minute. Various inorganicand organic compounds, including nutrients move together with the protoplasm fromthe site of their concentration to the site of demand in the growing mycelium ofthe fungus. It is well known that many fungi grow abundantly on roots and aroundthem, forming the mycorhiza.

  Not only fungi but also bacteria promote the transportation of nutrientsin the soil. Kotelev (1955) employed tracer techniques in the following manner. Heintroduced grains of radioactive P32 in the form of superphosphate intothe soil and followed the diffusion of the phosphorus in the presence and absenceof bacteria. The diffusion of phosphorus in sterile soil was very slow and uptakeby roots was either lacking or negligible. The diffusion of phosphorus in the presenceof bacteria was much more rapid.

  The above indicates that it is not permissible to consider the problemof plant nutrition only from the point of view of autotrophy. Alongside the assimilationof inorganic compounds, plants also assimilate various organic-carbonaceous and nitrogenoussubstances. Some of these are utilized to meet the plant's energy requirements, othersserve as biocatalysts. The latter are taken up by the roots and aerial parts of theplant and increase the intensity of the biochemical and biological processes in thecells and tissues. They enhance the growth of plants and increase the absorptioncapacity of the roots the assimilation of absorbed substances and other vitally importantfunctions.

  The biologically active substances of the soil not only enhance thegrowth and increase the yield of plants but also confer on the plant better nutritionalqualities.

  Plants which obtain vitamins and other organic compounds from thesoil in adequate amounts, yield crops of higher quality and their seeds are of ahigher vitality.

  The fact that plants can grow in pure mineral nutrient media in theabsence of microorganisms cannot serve as proof of the uselessness of the latterin the nutrition of plants.

  Plants can indeed be grown in mineral media and yield seeds withoutthe participation of microbes. Is it possible, however. to secure the vitality ofsuch plants in subsequent generations?

  We have presented our observations on the growth of green algae andduckweeds. Grown under sterile conditions, in mineral media without the additionof composts or metabolic products of bacteria, these plants lose their viabilityand eventually die out. Plants grown in the same media but supplemented with compostsor metabolic products of bacteria, as well as plants grown in the presence of livingbacterial cells (nonsterile conditions) have been kept in our laboratory for morethan 20 years without any visible decrease of vitality.

  The assumptions of some authors concerning the fact that soil containsonly small amounts of organic compounds of phosphorus and nitrogen (in the form ofvitamins, amino acids and phytin) which cannot, therefore, be considered as nutrientsof any great importance, are also groundless. Our knowledge of forms of organic compoundsand of the dynamics of their transformations in the complex microbial coenoses, isinadequate. The knowledge we do possess, however, allows us to assume that the processesof synthesis of various organic compounds proceed incessantly in the soil. Owingto such uninterrupted synthesis (be as it may in small amounts) the total productionof these compounds may be sufficient to meet the needs of plants.

  We cannot understand the assumption of certain authors that microorganismsby their assimilation of inorganic substances preclude the utilization of the latterby plants. This, according to some authors, leads to plant starvation. The saprophytesof the soil are looked upon as a harmful factor. They do such harm to plants that,according to some specialists, they should be separated from plants because of theircompetition for soluble salts (Peterburgskii, 1954).

  Bacterial life in the soil is known to be very short; it is countedin hours. Even during their life, the dying cells are subjected to autolysis. Atthe end of the enzymatic lytic processes, processes of solubilization of their residuesby enzymes of other microbes ensue. The process of bacterial cell destruction israpid, The metabolism of living cells is an endless sequence. The elements absorbedfrom the substrate are soon excreted. Experiments with radioactive elements haveshown that phosphorus (P32), for example, appears in the substrate aftera few minutes.

  The microflora of the root zone is of great importance in plant nutrition.Growing near or on the roots, microorganisms, together with the plants, create aspecial zone--the rhizosphere. Soil in this zone differs in its physical, chemicaland biological properties from the soil outside the root zone. It possesses differentconditions, for the absorption and excretion of substances by the roots.

  The interaction between microorganisms and plants on one hand, andbetween individual microbial species and their metabolites, on the other hand, isthe basis for the different transformations of inorganic and organic compounds. Asa result, compounds which serve as nutrients for plants are formed. These are absorbedby the roots.

  Substances present in the soil are subjected to a greater or lesserextent of processing before their absorption by the roots. The plants do not absorbthose compounds which are characteristic for this or other soil, but metabolic productsof the rhizosphere. The rhizosphere microflora prepares various organic and inorganicnutrients for the plants.

  The role of the rhizosphere microflora reminds one of the digestingorgans of animals. Microorganisms in the final account serve the same function inthe plant nutrition as the digestive system of animal organisms (Krasil'nikov, 1940).

  The same point of view is held by the American specialist Prof. Clark(1949). He considers that microorganisms living in the rhizosphere perform the samework as do the intestines of animals. Academician Lysenko (1955) is even more definitein this respect. He thinks that the microflora of the root zone acts as the digestiveorgan of plants. We can agree with such a comparison if we recall the function ofthe microflora of the intestines. In recent years, the microflora of the intestineshas more and more come to be considered as a factor of supplementary nutrition foranimals and human beings. Many intestinal bacteria are known to produce substanceswhich enter the organism of the animal and play an essential role in biological processesas biocatalysts.

  In many animals, microorganisms of the digestive tract participatedirectly the digestion of food. For example, the cellulose bacteria in the intestinaltract of ruminants, decompose cellulose into digestible products.



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