ABSCISIC-ACID AND TURGOR PRESSURE REGULATION IN TOMATO ROOTS

The intact root systems of hydroponically-grown seedlings of tomato (L ycopersicon esculentum) cv. Ailsa Craig (wild-type) and the ABA-defici ent mutant notabilis (not) were stressed by immersion in varying conce ntrations of mannitol. This promoted abscisic acid (ABA) synthesis in wild-type roots. It was shown that a drop to zero turgor pressure was not required for ABA production. Instead, a decrease in turgor pressur e below an initial steady state value appeared to be a sufficient sign al for ABA synthesis. Compared with wild-type, not exhibited limited i ncreases in ABA regardless of the level of the applied stress. Followi ng osmotic stress, the recovery of turgor pressure in roots were shown to correlate with the endogenous ABA concentrations; in that turgor p ressure recovered to a great er extent in wild-type roots than in not. Differential changes in the instantaneous elastic modulus (epsilon(i) ) and the hydraulic conductivity (L(p)) following osmotic stress were noted. These effects tended to be more apparent in not as compared wit h the wildtype. This was, however, presumably as a result of the passi ve turgor-pressure dependence of these parameters. These findings supp ort the hypothesis that ABA plays a role in turgor pressure regulation .