Photosynthetic responses of sun- and shade-grown barley leaves to high light: is the lower PSII connectivity in shade leaves associated with protection against excess of light?

Abstract

In this study, we have compared photosynthetic performance of barley leaves (Hordeum vulgare L.) grown under sun and shade light regimes during their entire growth period, under field conditions. Analyses were based on measurements of both slow and fast chlorophyll (Chl) a fluorescence kinetics, gas exchange, pigment composition; and of light incident on leaves during their growth. Both the shade and the sun barley leaves had similar Chl a/b and Chl/carotenoid ratios. The fluorescence induction analyses uncovered major functional differences between the sun and the shade leaves: lower connectivity among Photosystem II (PSII), decreased number of electron carriers, and limitations in electron transport between PSII and PSI in the shade leaves; but only low differences in the size of PSII antenna. We discuss the possible protective role of low connectivity between PSII units in shade leaves in keeping the excitation pressure at a lower, physiologically more acceptable level under high light conditions.Electronic supplementary materialThe online version of this article (doi:10.1007/s11120-014-9969-8) contains supplementary material, which is available to authorized users.

Photosynthetic proton and electron transport in wheat leaves under prolonged moderate drought stress

“…The faster J-I rise in ChlF transient supports the idea of reduced PSI content, but the surprisingly symmetrical response at PSII and PSI (increase in Q À A accumulation balanced with the slow-down of P700 + re-reduction) argued against this possibility, as reduced number of PSI is expected to be re-reduced faster (or by the same rate), not slower. The more probable was an increase of limitation of electron transport between PII and PSI (''the bottleneck effect''), which can be due to decrease in content of electron key electron transport components [75]. A possible explanation is the decrease in cyt b6/f content in chloroplasts, which was previously observed in severely drought stressed plants [28].…”

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“…non-photochemical quenching of chlorophyll fluorescence) is a feedback regulatory mechanism induced upon exposure to high irradiance exceeding that which may be used at maximum quantum yield by photosystem II (PSII) [20,[22][23][24][25][26]. Previous studies have shown that low irradiance protects the photosynthetic apparatus from the adverse effects of high temperature, while photoinhibition protects against both high irradiance and high temperature stress [7,27,28].…”

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