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Part III, continued:

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

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

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

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

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

  These results show that the radioactive (S³⁵ ) vitamin B₁ 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 vitamin concentration in the roots and stems in the late growth phase of the plant may be explained by the fact that the vitamin is absorbed in the early phase of the growth when the vitamin synthesis by the shoot is inadequate. Later on the plant begins to synthesize the required amount of the vitamin. and the latter, under favorable conditions, enters the stem and roots. It has been shown that plants can obtain vitamins from microorganisms. This was demonstrated by the use of radioactive isotopes. If bacteria or yeasts were saturated with an amino acid or vitamin labeled with phosphorus P³² or sulfur S³⁵ and inoculated into a medium where plants were being grown, the radioactive substances were soon detected in the tissues of plants. Shavlovskii (1954) grew buckwheat in sand with a culture of Ps. aurantiaca or yeasts (Torlopsis utilis, T. latvica and Rhodotorula rubra). All the cultures were previously saturated with radioactive vitamin B_l (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 microbes in detectable amounts. The greatest amount went to, the plant (8.5 % of the total activity) 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

 

  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. According to 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 assimilate leucine, glycine, aspartic acid and tyrosine. Klein and Kisser (1925) have shown that during growth in sterile conditions, oats can assimilate arginine not less than they can assimilate nitrates. According to Virtanen and Lathe (1937, 1946), peas and clover assimilate aspartic acid well, while wheat and barley react negatively to this substance, Steinberg (1947) showed that isoleucine has a harmful effect on the growth of tobacco. Tanaka (1931) has shown that the plant Sysirinchium bermudianum utilizes asparagine, glycine, and cystine. Miller (1947) followed the absorption of dimethionine by tobacco and tomatoes growing under sterile conditions. The sap of roots and aerial parts contained 1.0- 2.5 mg methionine per 5 ml. Miller is of the opinion that amino acids are assimilated by plants.

  Riker and Gütsche (1948) have shown that some amino acids suppress the growth of isolated tissues of sunflower. The authors think that the deleterious action 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 favorable effect 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 (decarboxylation product of phenylalanine) strongly affect the growth of peas, in the same way as the 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 excreted various amounts of the vitamin depending on the species. The data given below should be considered as approximate and possibly lower than in reality. This amino acid was added to the medium of Knopp in which these plants were grown. After 11 days of growth the plant tissues were examined for the presence of radioactive sulfur. The results are given in Table 57.

  As can be seen from the table, the absorption of this amino acid by plants 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 and external conditions.

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

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

  The distribution of the radioactive sulfur of methionine is different from that of radioactive inorganic sulfur. In the former came sulfur is concentrated in 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 other amino acids are assimilated by plants without any change in their molecules and are being used by them for protein synthesis. Shavlovskii extracted protein from the roots of peas which had grown in the presence of radioactive methionine and showed that they contained the major part of the methionine absorbed by the roots. One gram of 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. aurantiaca and yeasts Sacchar. cerevisiae, in a medium containing radioactive sulfur S³⁵ in the form of (Na₂ S³⁵0₄). The bacteria were then autolyzed and the autolysates containing radioactive (S³⁵) amino acids were added to the medium where plants were grown, Radioactive sulfur was then found 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 cotyledon tissues was 137 cpm, in the stems--356 cpm, and in the roots--720 cpm; in the presence of yeast autolysate the corresponding figures were: 43 cpm, l99 and 569 cpm.

  In his subsequent experiments Shavlovskii grew buckwheat in a medium with living cultures of Ps. aurantiaca previously grown in a medium containing radioactive sulfur. Seeds of the buckwheat were infected with these cells before sowing (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 the plant: cotyledons--228, stems--181, roots--132 cpms. Consequently, on the second day the plants had taken up about 0.4 % of the bacterial radioactivity. A direct relationship between the amount of bacteria and the absorption of radioactivity was noted. Upon introduction of 3.45 billion cells per seed, about 1% of the total radioactivity of the cells was detected in the plants (after 7 days growth).

  The capacity of microorganisms to transfer their metabolic products to 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 containing P³² as a source of phosphorus nutrition. The cultures of microorganisms thus grown were carefully washed with water and inoculated into the sand in which saplings of oak and ash trees were grown.

  Experiments had shown that radioactive phosphorus is taken up by the plants in considerable amounts; it is emitted at a different rate and in different amounts by the various microbial species. The greatest effect is obtained in experiments with yeasts. About 43 % of the radioactive phosphorus from yeast was taken up by plants in the first days of their growth. Oak saplings absorbed more radioactivity than 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.

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

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

  Antibiotics are very specific. They are not present in plant tissues and are not formed by them. They are easily detected and differentiated from other organic substances including phytocides. In our experiments we have employed antibiotics in their native state as well as in the form of chemically pure preparations. Antibiotics produced by different representatives of soil microorganisms were used: penicillin (mold product), streptomycin, globisporin, aureomycin, terramycin, and others (products of 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 had shown that antibiotics were taken up by roots rapidly and in considerable amounts and were more or less uniformly distributed in all plant tissues and organs.

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

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

  The antibiotics are known to be rather complex organic substances of 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 and vitamins are absorbed it may be assumed that many other carbon and nitrogen compounds present in the soil are also absorbed by plants.

  A voluminous work was performed in the laboratory of the famous French botanist Bonne to determine the absorption of organic compounds by plants. Laurent J. 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 capacity of plants to assimilate amino acids and other nitrogenous compounds. Ravin (1913), experimenting with horse radish came to the conclusion that plants can assimilate the organic acids--succinic, citric, malic, tartaric and oxalic.

  Maze and Perrier (1904) grew corn in a methanol-sugar solution. In 30 days of growth these plants absorbed 10-14 g of saccharose, their dry weight was 14-21.9 g. Approximately the same amount of glucose was absorbed by plants in another series 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 presence of levulose.

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

  Seliber (1944) brings results of his own studies and those of others on the growth of potatoes at the expense of starch and other substances present in the 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 reserves of the mother nodule. Organic compounds of the latter pass into the embryo and into the daughter tuber.

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

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

  Studies show that under conditions of sterile growth of plants these substances 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 the absorption of penicillin, streptomycin, aureomycin and other antibiotics in the presence and absence of various bacterial species.

  Bacterial cultures were chosen which did not inactivate or decompose the above-listed antibiotics and were at the same time resistant to them for the inoculation of the nutrient solution. We have tested and chosen more than 10 cultures belonging 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 bacteria was determined by the rate of disappearance of the antibiotics from the solution and their uptake by the plants. The presence of antibiotics in the plants was determined by the conventional microbiological tests. The indicator microbes were cultures of the sporiferous bacillus Bact. subtilis and staphylococcus--Staph. aureus.

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

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

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

  Analogous data were obtained in experiments with plants growing in sand. The uptake of antibiotics was highest in the presence of Azotobacter and root-nodule. bacteria and the smallest in the presence of the nonsporiferous bacillus 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 plant roots under the influence of the microflora. He grew oats, sunflower, buckwheat and other plants in vessels with sterile and nonsterile soil, in the presence and absence of bacteria. Phosphates, soluble. insoluble and sparsely soluble in water, were introduced into the soil (bi- and tricalcium, phosphate, phosphoric powder, etc).

  The experiments have shown that under sterile conditions, without bacteria, the uptake of phosphates proceeds at a lower rate than in the presence of 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 radioactive phosphorus by bacteria. Under sterile conditions the radioactive phosphorus was taken up at a slower rate and in smaller amounts. The plants showed only 4% of the total radioactivity when grown under sterile conditions, in the presence of bacteria the radioactivity of the plants increased to 13%.

  Experiments with labeled (P³²) lecithin gave analogous results. Lecithin was added to the solution used for wetting sand in which barley was grown. The experiments were carried out in the presence and in the absence of bacteria. In the absence of bacteria 1.9% of the radioactive phosphorus was taken up, 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 plants from granules prepared with radioactive superphosphate. Barley sprouts grown under sterile conditions gave 400--500 cpm, but 1,000-1,500 cpm, when grown under nonsterile conditions (cpm. per 10 mg of plant dry weight) (Kotelev, 1955).

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

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 accumulation of organic phosphorus in the tissues of barley grown under sterile conditions, and in the presence of bacteria. It can be seen from the figure and Table 58 that bacteria have a considerable effect on the uptake and accumulation of phosphorous compounds in the tissues of plants. Under the influence of the bacteria a formation of quite different 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 evaporated to 1-2 ml and subjected to chromatography. The results are given In Table 61.

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 amino acids in plants grown in the presence of 2 bacterial cultures (lp and 2p). It can be seen from the figure, that the presence of bacteria in the substrate causes formation and accumulation of amino acids of a different nature to those formed in the absence of bacteria. Some amino acids (serine, glycine, alanine, valine, cysteine) cannot be 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 amounts in plants grown in the presence of bacteria. Different bacterial cultures have a varying 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 (heavy loam chernozem), although considerable. was somewhat different to that noticed when the plants were grown in pure sand. The quantitative and qualitative relationship of amino acids was different. Neither lysine nor alanine could be found in the barley sprouts grown in the presence of lp and 2p bacteria, asparagine and glycine were found only in traces (Figure 68 B).

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

  Ratner and Kozlov (1954) grew corn under sterile conditions, according to 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 of phosphorus and nitrogen were found in larger amounts than when the plants were grown without bacteria. In the sterile vessels the plants contained the following: amides and amines--1.300 mg; organic nitrogen--1.191 mg (32.33%); in nonsterile vessels the respective figures were 1.562 mg and 1.960 mg (44.22%).

  The difference in composition of the amino acids is well defined on the 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 the phosphorus and nitrogen content of their exudate. The microbial metabolic products increase not only the uptake of these substances by the roots but also the synthetic capacity of the roots. The increased incorporation of the radioactive phosphorus P³² into the lipides and nucleoproteins, as well as the increased content of amide and amine nitrogen in the exudate confirms these assumptions.

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

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

  Numerous papers have stressed the point that mere contact of roots with 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 in their hyphae. It is known that protoplasm moves along the hyphae at high speed. In mucor fungi it is as much as 50-80 µ and more per minute. Various inorganic and organic compounds, including nutrients move together with the protoplasm from the site of their concentration to the site of demand in the growing mycelium of the fungus. It is well known that many fungi grow abundantly on roots and around them, forming the mycorhiza.

  Not only fungi but also bacteria promote the transportation of nutrients in the soil. Kotelev (1955) employed tracer techniques in the following manner. He introduced grains of radioactive P³² in the form of superphosphate into the soil and followed the diffusion of the phosphorus in the presence and absence of bacteria. The diffusion of phosphorus in sterile soil was very slow and uptake by roots was either lacking or negligible. The diffusion of phosphorus in the presence of bacteria was much more rapid.

  The above indicates that it is not permissible to consider the problem of plant nutrition only from the point of view of autotrophy. Alongside the assimilation of inorganic compounds, plants also assimilate various organic-carbonaceous and nitrogenous substances. Some of these are utilized to meet the plant's energy requirements, others serve as biocatalysts. The latter are taken up by the roots and aerial parts of the plant and increase the intensity of the biochemical and biological processes in the cells and tissues. They enhance the growth of plants and increase the absorption capacity of the roots the assimilation of absorbed substances and other vitally important functions.

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

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

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

  Plants can indeed be grown in mineral media and yield seeds without the participation of microbes. Is it possible, however. to secure the vitality of such plants in subsequent generations?

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

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

  We cannot understand the assumption of certain authors that microorganisms by their assimilation of inorganic substances preclude the utilization of the latter by plants. This, according to some authors, leads to plant starvation. The saprophytes of 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 their competition for soluble salts (Peterburgskii, 1954).

  Bacterial life in the soil is known to be very short; it is counted in hours. Even during their life, the dying cells are subjected to autolysis. At the end of the enzymatic lytic processes, processes of solubilization of their residues by enzymes of other microbes ensue. The process of bacterial cell destruction is rapid, The metabolism of living cells is an endless sequence. The elements absorbed from the substrate are soon excreted. Experiments with radioactive elements have shown that phosphorus (P³²), for example, appears in the substrate after a 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 a special zone--the rhizosphere. Soil in this zone differs in its physical, chemical and biological properties from the soil outside the root zone. It possesses different conditions, for the absorption and excretion of substances by the roots.

  The interaction between microorganisms and plants on one hand, and between individual microbial species and their metabolites, on the other hand, is the basis for the different transformations of inorganic and organic compounds. As a result, compounds which serve as nutrients for plants are formed. These are absorbed by the roots.

  Substances present in the soil are subjected to a greater or lesser extent of processing before their absorption by the roots. The plants do not absorb those compounds which are characteristic for this or other soil, but metabolic products of the rhizosphere. The rhizosphere microflora prepares various organic and inorganic nutrients for the plants.

  The role of the rhizosphere microflora reminds one of the digesting organs of animals. Microorganisms in the final account serve the same function in the 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 same work as do the intestines of animals. Academician Lysenko (1955) is even more definite in this respect. He thinks that the microflora of the root zone acts as the digestive organ of plants. We can agree with such a comparison if we recall the function of the microflora of the intestines. In recent years, the microflora of the intestines has more and more come to be considered as a factor of supplementary nutrition for animals and human beings. Many intestinal bacteria are known to produce substances which enter the organism of the animal and play an essential role in biological processes as biocatalysts.

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

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