GAS-EXCHANGE AND CHLOROPHYLL FLUORESCENCE DURING WATER AND HIGH-TEMPERATURE STRESSES AND RECOVERY - PROBABLE PROTECTIVE EFFECT OF CARBAMIDECYTOKININ 4-PU30

Two-weeks-old Phaseolus vulgaris plants were subjected to increasing w ater deficit (WD) and to combination of WD + high temperature (HT). Th e possible protective or reparatory effect of carbamide cytokinin 4-PU 30 [N-(2-chloro-4-pyridyl)-N-phenylurea] applied before and after the stress was studied. The photosynthetic gas exchange and chlorophyll fl uorescence induction kinetics excited by low (60 mu mol m(-2) s(-1)) a nd saturating (3000 mu mol m(-2) s(-1)) photon flux densities at 25 an d 45 degrees C were measured on the primary leaves. The WD (17-20 % af ter 3 d) caused significant decrease in rates of CO2 uptake and O-2 ev olution, and its combination with HT (40-44 % WD and leaf temperature of 45 degrees C) led to an almost complete inhibition of them. The eff ects in the parameters characterizing the state of photosystem 2 react ion centres were less expressed. The dynamics of recovery of CO2 uptak e and O-2 evolution were different in plants under WS or WS + HT. The carbamide cytokinin 4-PU30 in 10(-6) M concentration favourably affect ed the recovery and not so noticeably actioned during the stress.