ROOT EXUDATES IN RELATION TO THE RHIZOSPHERE-EFFECT

BY (MIss) K. BHUVANESWARI AND N. S. SUBBA-RAO (University Botany Laboratory, Madras.5)

Received May 3, 1957 (Communicated by Prof. T. S. Sadasivan, v.A.sc.)

INTRODUCTION

IN the course of analyses of rhizosphere microflora of several crop plants, it was observed that while sorghum plants (Sorghum vulgate, var. dochna) showed increased microbial population of the rhizosphere (positive rhizo- sphere-effect), mustard plants (Brassica ]uncea) showed a definite decrease (negative rhizosphere-effec0 when compared to the microbial numbers of the unplanted soil. Since it is now generally accepted that stimulation or inhibition of micro-organisms around roots depend on the nature of root oxudates, a study of root excretions of these plants was made and reported hereunder.

MATERIALS AND I~ETHODS

Root exudates from 4-day old seedlings were collected by the technique described earlier from this laboratory (Andal, Bhuvaneswari and Subba-Rao, 1956) and examined for the presence of organic acids and sugars by the cir- cular paper chromatographic technique (Lakshminarayanan, 1954), using n-Butanol]Acetic acid/Water::4: 1:5 for sugars and n-Butanol/Formic acid/Water:: 10: 2 :5 for organic acids as the developing solvent mixtures. The developed ehromatograms were sprayed with B.D.H. 4.5 indicator for detection of organic acids and aniline hydrogen phthalate for sugars (Patridge, 1949).

RESULTS AND DISCUSSION

Several organic acids and sugars were present in the root exudates of both the plants (Table I). Of these tartaric and oxalic acids were common to both sorghum and mustard; likewise, d-xylose and d-fructose were present in the exudates of both the plants. However, mustard had malie and citric adds, d-glucose and maltose in addition.

i t is now known that plantroots exude various amino acids (Katznelson, l~ouatt and Payne, 1955; Parkinson, 1955; Rovira, 1956; Andal ot aL, loc. cit.), vitamins (West, 1939; Bhuvaneswari and Sulochana, 1955)~ flavones

299

300 (MIss) K. BHUVANESWARI AND N. S. SUBBA-RAo

TA~LF I

Organic acids and sugars in the root exudates of sorghum and mustard

Exuded organic acids Mustard Sorghum and sugars

Malic acid

Citric acid

Tartaric acid

Oxalic acid

d-xylose

d-fructose

d-glucose

Maltose

~ Q

Q D

O I

D •

@ •

-=•

+

+ +

+ +

+ +

+ +

+

+

+ ---- P r e s e n t . - - = A b s e n t .

and nucleotides (Lundeg~rdh and Stenlid, 1944) and hydrocyanic acid (Timonin, 1941). The present report, however, has demonstrated the libera- tion of organic acids and sugars by actively growing roots. R is quite possible that malic and citric acids contained in the root exudate of mustard might be responsible for the observed negative rhizosphere-effect of these plants and indeed intensive work on the role of these organic root excretions in controlling the microbial population of the rhizosphere is bound to be fruitful.

SUMMARY Chromatographic study of the root exudates of Sorghum vulgate, vat.

dochna (Sorghum) and Brassica juncea (Mustard) revealed the presence of several organic acids and sugars in them. Although tartaric and oxalic acids, d, xylose and d-fructose were common to both, mustard had malic and citric acids, d-glucose and maltose in addition. The possibility of malic and citric acids as factors influencing the observed depression of the rhizo- sphere microflora of mustard plants has been suggested.

ACKNOWLEDGMENTS

We are grateful to Prof. T. S. Sadasivan for guidance and Dr. C. V. Subramanian for his keen interest in the present investigation.

Root Exudates in Relation to Rhizosphere-Effect 301

REFERENCES

Andal, R., Bhuvaneswari, K. and "Root exudates of paddy," Nature, Land., 1956, 178, 1063. Subba-Rao, N. S.

Bhuvaneswari, K. and Sulochana, "Assay of root exudates," Curr. Sci., 1955, 24, 376. C.B,

Katznelson, H., Rouatt, J. W. and Payne, T. M.

Lakshminarayanan, K. . .

Lundeg~rdh, H. and Stenlid, G.

Parkinson, D. ..

Partr id~, S .M. . .

Rov/ra, A . D . ..

Timonin, M. J.

West, P. M.

"Liberation of amino acids by plant roots in relation to desic- cation," Nature, Lend., 1954, 174, 1110.

"A simple technique in paper disk chromatography," Arch. Biochem. and Biophys., 1954, 49, 396.

"On the exudation of nucleotides and flavonones from living roots," Ark. Bet., 1944, 31 A, 1.

"Liberation of amino acids by oat seedlings," Nature, Lend., 1955, 176, 35.

"Aniline hydrogen phthalate as a spraying reagent for sugars," Ibid., 1949, 164, 443.

"Plant root excretions in relation to the rhizosphere effect. I. The nature of root exudat¢ from oats and peas," Plant &Soil, 1956, 7, 178.

"The interaction of higher plants and soft micro-organisms, III. Effect of by-products of plant growth on the activity of fungi and actinomycetes," Soil ScL, 194I, 52, 395.

"Excretion of biotin and thiamin by roots of higher plants,'" Nature, Lend., 1939, 144, 1050.