caa a22 4500 397522304 CHVBK 20180308164636.0 cr unu---uuuuu 161202e199512 xx s 000 0 eng 10.1093/jxb/46.12.1825 doi (NATIONALLICENCE)oxford-10.1093/jxb/46.12.1825 Summer survival of leaves in a soft-leaved shrub (Phlomis fruticosa L., Labiatae) under Mediterranean field conditions: avoidance of photoinhibitory damage through decreased chlorophyll contents [Elektronische Daten] [A. Kyparissis, Y. Petropoulou, Y. Manetas] Photosynthetic pigments and relative water content of young leaves of P. fruticosa decreased considerably with the onset of the summer dry period and stabilized at low values for the last two summer months, while leaf growth was arrested. Corresponding decreases in photochemical efficiency of photosystem II, as judged by chlorophyll fluorescence measurements of predarkened leaves, were, however, negligible. Following the first autumn heavy rains, growth was restored and photosynthetic pigments and relative water content increased to the pre-drought values. The results indicate that the reduction of chlorophylls does not result from severe photoinhibitory damage but, instead, it may be an adaptive response against the adverse conditions of the Mediterranean summer. Some photosynthetic and photoprotective characteristics of P. fruticosa leaves at two stages of their development, i.e. at the severely dehydrated state with arrested growth during late summer and after their revival following the first heavy autumn rains were compared. Apart from the chlorophyll loss, the photon yield of O2 evolution and the photosynthetic capacity at saturated CO2 were considerably suppressed during the summer, indicating that the extremely low net photosynthetic rates observed in the field were the combined result of stomatal and mesophyll limitations. Epoxidation state was low at midday during the summer, indicating an active, photodissipative xanthophyll cycle. Although zeaxanthin content did not increase at midday after the rains, the potential of the cycle was maintained in the revived leaves, as judged by the high concentrations of the cycle components. After the rains, the activities of the anti-oxidant enzymes (superoxide dismutase, ascorbate peroxidase) remained relatively unchanged on a chlorophyll basis, but increased when expressed on a leaf surface area or protein basis. It may be concluded that P. fruticosa leaves avoid severe photoinhibitory and oxidative damage during the long, warm, dry and sunny Mediterranean summer by reducing light harvesting and electron flow capacity, whilst maintaining an adequate photoprotective ability. The preservation of a remarkable photodissipative and anti-oxidative potential after the rains may be related to the low predictability of precipitation even during the rainy winter. © Oxford University Press Research Papers nationallicence Chl loss nationallicence anti-oxidant enzymes nationallicence xanthophyll cycle nationallicence photosynthesis nationallicence water stress nationallicence Kyparissis A. Laboratory of Plant Physiology, Department of Biology, University of Patras, 26500 Patras, Greece aut Petropoulou Y. Laboratory of Plant Physiology, Department of Biology, University of Patras, 26500 Patras, Greece aut Manetas Y. Laboratory of Plant Physiology, Department of Biology, University of Patras, 26500 Patras, Greece aut Journal of Experimental Botany Oxford University Press 46/12(1995-12), 1825-1831 0022-0957 46:12<1825 1995 46 exbotj https://doi.org/10.1093/jxb/46.12.1825 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1093/jxb/46.12.1825 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Kyparissis A. Laboratory of Plant Physiology, Department of Biology, University of Patras, 26500 Patras, Greece aut NATIONALLICENCE 700 1- Petropoulou Y. Laboratory of Plant Physiology, Department of Biology, University of Patras, 26500 Patras, Greece aut NATIONALLICENCE 700 1- Manetas Y. Laboratory of Plant Physiology, Department of Biology, University of Patras, 26500 Patras, Greece aut NATIONALLICENCE 773 0- Journal of Experimental Botany Oxford University Press 46/12(1995-12), 1825-1831 0022-0957 46:12<1825 1995 46 exbotj Metadata rights reserved CC BY-NC-4.0 http://creativecommons.org/licenses/by-nc/4.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-oxford