Specific inhibition of cell wall-bound ATPases by fungal suppressor from mycosphaerella pinodes

Activities of phosphatases were found in the fractions which were solubilized from cell walls of both pea and cowpea seedlings with 0.5 M NaCl. These phosphatases hydrolyzed triphosphonucleotides in the order: UTP=CTP>GTP>ATP; and UTP=GTP>CTP=ATP, respectively. The activities of a pyrophosphatase and a p-nitrophenylphosphatase were also detected in these fractions. The suppressor in the spore germination fluid of a pea pathogen,Mycosphaerella pinodes, inhibited all of these phosphatase activities in the fraction solubilized from pea cell walls, but it rather enhanced only the activity of the ATPase among those phosphatases from the cowpea cell wall. Hydrolysis of ATP by a cell wall fraction of pea was also markedly inhibited by the suppressor, while hydrolysis of ATP by similar fractions from cowpea, kidney bean and soybean were rather enhanced by the suppressor, as well as by the elicitor. Thus, the cell wall-bound ATPases responded to the suppressor species-specifically. These cell wall-bound ATPases seemed to be different from the plasma membrane ATPases in several respects. The results suggest that plants recognize the fungal signals not only on their plasma membranes but also on their cell walls and, moreover that putative receptors for the fungal signals might be located close to cell wall-bound ATPases or might even be these ATPases themselves.