THE ROLE OF ENDOGENOUS PHENOLIC-COMPOUNDS IN INFECTION OF PEA ROOTS BY RHIZOBIUM-LEGUMINOSARUM AT LOW-TEMPERATURE

The effect of phenolic compounds (PC) extracted from pea (Pisum sativu m L.) roots on the growth of the bacteria Rhizobium leguminosarum in m inimal nutrient medium was investigated. Phenolic compounds were extra cted from noninfected roots of etiolated seedlings as well as from roo ts with structurally developed colorless nodules after growing plants at a 16-h photoperiod. The effects of extracted PC on bacterial growth were compared for plant roots grown at optimum and low temperatures. The PC fraction obtained with ethyl acetate stimulated bacterial growt h, whereas the fraction obtained with rt-butanol had no effect. Irresp ective of the plant growth conditions, PC extracted from noninfected r oots were more effective than PC from nodulous roots. Low temperature potentiated the effects of PC extracted from noninfected and infected roots. Bacterial growth depended on the concentration of PC in the med ium. Analysis of the PC content in root tissues showed that the level of active compounds decreases at low temperature during the period of nodulation. It is proposed that such a decrease may have a negative ef fect on the propagation of the rhizobia that are released at this stag e from the infective threads into the cytoplasm of bacteroid tissue. W e hypothesize that the involvement of endogenous PC in earlier stages of infection is largely restricted at low temperature. This restrictio n is presumably due to a certain mechanism that prevents the immediate action of PC on bacteria residing at this stage within the infective threads.