INTERACTIVE EFFECT OF WATER-DEFICIT AND HIGH-TEMPERATURE ON PHOTOSYNTHESIS OF SUNFLOWER AND MAIZE PLANTS .1. CHANGES IN PARAMETERS OF CHLOROPHYLL FLUORESCENCE INDUCTION KINETICS AND FLUORESCENCE QUENCHING

Effects of high temperature (HT, 42 degrees C) and water stress (WD) a pplied separately and in combination, on the chlorophyll fluorescence kinetics and photochemical (q(P)) and non-photochemical (q(N)) quenchi ng in 21-d-old sunflower and maize plants were studied. The WD was cre ated by addition of polyethylene glycol (M-r 6000) to the nutrient sol ution. When the fluorescence was measured at 47 degrees C, the F-V/F-0 ratio in sunflower considerably increased in plants under combined st ress, whereas in maize plants it remained practically unchanged. The c ombined action of HT+WD led also to a noticeable (in sunflower) or a w eaker (in maize) increase of F-0(25 degrees C)/F-0(47 degrees C) ratio (a criterion for stability of the light-harvesting complex LHC2 at HT ) and a decrease of the F-V(25 degrees C)/F-V(47 degrees C) ratio (tol erance of the photochemical activity and O-2-evolving system). The q(P ) and q(N) values measured at 47 degrees C in maize were different fro m those of sunflower. The q(P) values were high, but practically not i nfluenced by HT and WD. In both plant species most of the effects indu ced by stress treatments disappeared after a 72 h recovery.