| In this study, prompt fluorescence, delayed fluorescence and modulated light reflection at820nm in apple leaves were measured simultaneously, to explore the damage of droughtstress and light stress on PSII, PSI and the whole photosynthetic electron transport chain, andthe mechanism of improving drought tolerance of apple leaves by Si-application. The mainresults are as follows:1. At day2of drought stress, the capacity of Q_Areduction by the trapping light in PSIIreaction centers was lower than that of electron transfer from Q_A-to the downstream electroncarriers, and the capacity of electron transfer from Q_A-to the downstream intermediate carriessuch as QBand PQ was also lower than that from QBand PQ to PSI acceptor side. at day5ofdrought stress, the above electron transfer capacities changed contrary with the changes beingmore significantly, compared with that at day2. In general, the electron transport capacitydecreased gradually under severe drought stress and the degradation of PSII and PSI reactioncenters was faster than that of their antenna pigments.2. Under high light, the capacity of Q_Areduction by the trapping light in PSII reactioncenters, the self-oxidation of P700, the content of P700, and the contents of microsecond andsub-millisecond DF components all decreased. This results suggest that during diurnalvariation, high light significantly inhibited the activities of PSII, PSI and the wholephotosynthetic electron transport chain, with the damage to PSII being more severe than toPSI. The redox capacity at P680donor side was not changed during diurnal variation.3. The response to drought stress in the photosynthetic apparatus of leaves betweenSi-treatment and control was compared. The result showed that Si-treatment could alleviatethe degradation of PSII and PSI. Si-treatment also increased the capacity of Q_Areduction bythe trapping light in PSII reaction centers, the cyclic electron transport around PSI, and thenon-photochemical quenching at PSII antenna. |
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