Abscisic acid and turgor pressure regulation in tomato roots

The intact root systems of hydroponically-grown seedlings of tomato (Lycopersicon esculentum) cv. Ailsa Craig (wild-type) and the ABA-deficient mutant notabilis (not) were stressed by immersion in varying concentrations 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 pressure below an initial steady state value appeared to be a sufficient signal for ABA synthesis. Compared with wild-type, not exhibited limited increases in ABA regardless of the level of the applied stress. Following osmotic stress, the recovery of turgor pressure in roots were shown to correlate with the endogenous ABA concentrations; in that turgor pressure 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 with the wildtype. This was, however, presumably as a result of the passive turgor-pressure dependence of these parameters. These findings support the hypothesis that ABA plays a role in turgor pressure regulation.