Specific features of plastid pigment apparatus and photosynthesis in the leaves of ephemeroid and summer plants as related to photoinhibition

The state of the pigment apparatus and potential photosynthesis (PP) was compared in the leaves of plants failing into two ecological groups, ephemeroids (three species) and summer plants (two species). For the first time, the organization of the plastid pigment apparatus was investigated in ephemeroids using the data on chlorophyll and carotenoid distribution between the major photosynthetic pools. The molar ratio between xanthophylls and chlorophyll in the light-harvesting complex of plastids in the ephemeroids (0.5 to 0.6) considerably exceeded that in the summer plants (0.3-0.4). By using salicylaldoxime, an inhibitor of the reverse reaction of the violaxanthin cycle, we were able to calculate the active pool of violaxanthin on its way to zeaxanthin. This pool was shown to amount to 85% of the sum total of xanthophylls of the violaxanthin cycle in the ephemeroid leaf plastids as compared to 60% in the summer species. Thus, potentially, the photosynthetic apparatus in the ephemeroid leaves is better provided with the pigments essential for photoprotective function and for maintaining, a high photosynthetic rate under early spring conditions. Under chilling temperatures of 5-10degreesC and full insolation, PP in ephemeroids was as high as in the summer plants at 20degreesC.