Drought-Induced Changes in Xylem Sap pH, ABA and Stomatal Conductance

Upstream signals potentially regulating evaporation and stomatal conductance wereinvestigated using 6-8-leaf-old maize (Zea may L.) seedlings which were grown in agreenhouse. Pressure chamber was used to measure leaf water potential and to collectxylem sap. The pH of xylem sap in stems was higher than that in root, and the abscisicacid (ABA) concentration in stems was the highest in well-watered seedlings. The ABAconcentration and pH of xylem sap in roots, stems and leaves increased, and the ABAconcentration in leaves reached the maximum during drought stress. The treatment ofroots with exogenous ABA solution (100molL-1) increased xylem sap ABA concentration inall organs measured, and induced stomatal closure, but did not change ABA distributionamong organs of maize seedlings. The combined effects of external pH buffer on pH, ABAof xylem sap and stomatal behavior indicated that pH, as a root-source signal to leavesunder drought stress, regulated stomatal closure through accumulating ABA in leaves orguard cells.

Relationship Between Ca ^(2+)-CaM and Ethylene-Induced PG Activity in Tomato Fruit

Polygalacturonase (PG) was studied during ripening and senescence of postharvest tomato fruit at pink stage at low and normal temperature. The results showed that the PG activity increased, then decreased during ripening and senescence of tomato. Low temperature inhibited but ethylene enhanced PG activity. Ethylene also enhanced calmodulin content, which was dependent on Ca 2+concentration in cell. When EGTA(Ca 2+chelator), verapamil(Vp) and LaCl 3(Ca 2+channel blockers), trifluoperazine and chloropromaize (two CaM antagonisms) were used to treat tomato fruit at green mature stage with ethylene, they could reverse ethylene-induced increase in PG activity, but Vp, chloropromaize (CPZ), trifluoperazine (TFP) could not directly influence PG activity, which indirectly indicated that influx of Ca 2+ from the extracellular space including the cell wall via the Ca 2+ channel localized in plasma membrane and CaM were required for ethylene-induced PG activity increase and that ethylene signal transduction may be related to Ca 2+CaM messenger system.

Effects of Ca^(2+)/CaM Messenger System Inhibitors on Ethylene-Induced Increase in Lycopene Content

The changes of lycopene content during ripening and senescence of tomato fruit and the relationship between ethylene glycol-bis (EGTA, Ca 2+ chelator), verapamil (Vp, Ca 2+ channel blockers), trifluoperazine (TFP), chloropromaize (CPZ) (CaM antagonism) and ethylene-induced increase in lycopene content in tomato fruit were investigated. Lycopene content accumulated obviously during ripening and senescence of tomato fruit after harvest at pink stage. Low temperature inhibited but ethylene enhanced the lycopene content. Meanwhile, ethylene also promoted calmodulin (CaM) content in tomato fruit, which was related to the concentration of ethylene. When EGTA, Vp, TFP and CPZ with ethylene were used to treat tomato fruit, ethylene-induced increase in lycopene content could be reversed, indicating that blocking Ca 2+ channel in plasma membrane or chelating extracellular Ca 2+ or inhibiting the activity of CaM could decrease the action of ethylene, and suggesting that Ca 2+-CaM messenger system may be involved in lycopene increase induced by ethylene.