CHANGES IN LASER-INDUCED CHLOROPHYLL FLUORESCENCE RATIO F690 F735 IN THE POIKILOCHLOROPHYLLOUS DESICCATION TOLERANT PLANT XEROPHYTA-SCABRIDA DURING DESICCATION/

The degradation of chlorophylls, carotenoids and the photosynthetic ap paratus in photosynthetically active leaves of Xerophyta scabrida was studied during slow desiccation using chlorophyll fluorescence inducti on kinetics measured at two wavelengths, at 690 nm (F690) and 735 nm ( F735). Breakdown of the photosynthetic apparatus in X. scabrida was in dicated by a decrease in both the chlorophyll a+b and carotenoid x+c c ontents and by decreasing values of the ratio chlorophylls/carotenoids (a+b)/(x+c). During desiccation, the total carotenoid content decreas ed less than the total chlorophyll content (63% and 78% loss respectiv ely). The rising value of the chlorophyll fluorescence ratio F690/F735 during desiccation was inversely proportional to the decrease in chlo rophyll content and to the decline of the ratio of chlorophylls/carote noids (a+b)/(x+c). Our results indicate that the fluorescence ratio F6 90/F735 is a reliable parameter for monitoring and following the loss of chlorophylls and the breakdown of the photosynthetic apparatus in p oikilochlorophyllous desiccation tolerant (PDT) plants in a non-invasi ve manner. The results also provide evidence that slow chlorophyll flu orescence induction kinetics and its parameters (fluorescence ratio F6 90/735 and the variable fluorescence decrease ratio Rfd) can provide a useful alternative to gas exchange measurements for screening the pho tosynthetic activity in the PDT plants and other desiccation tolerant plane during desiccation.