Response Of Photosynthetic Apparatus In Apple Peel To High Temperature And High Light Stress

Prompt chlorophyll fluorescence(PF), delayed fluorescence(DF) and modulated 820 nm reflection(MR) were measured simultaneously in ‘Golden Delicious’(Malus domestica Borkh) apple fruit peel, to explore the effects of high temperature or high light stress alone or the crossed stresses of high temperature coupled with high light on PSII, PSI and the whole photosynthetic electron transport chain. The main results are as follows:1. With the increase of treated temperature and light intensity, the PF and DF signals decreased. Under high temperature(42℃, 45℃) stress, the minimum of modulated 820 nm reflection increased with the increase of light intensity.2. High temperature stress alone(45℃) showed a clear “K” step in the PF transients, indicating that the doner side P680 was damaged. With the increase of the treated temperature, the appearance of the time of “K” step occurred earlier, suggesting that the electron transport capacity at the donor side of PSII decreased. High light nearly has no effect on “K” step. The signals of I1 and I2 of DF decreased, while the ratio of I2/I1 increased, which indicate that high temperature coupled with high light stresses inhibited the two systems capacity, especially that of PSII. The PSI capacity was inhibited relatively smaller than that of PSII. From PSII to PSI, the electron transport from the primary quinine electron acceptor of PSII(QA) to plastoquinol(PQH2) was the most sensitive part to high temperature and high light. With the increase of treated temperature or light intensity, especially at 42℃ and 45℃, the maximum quantum yield of PSII(FV/FM) decreased. The change of the absorption of antenna chlorophylls per PSII reaction center(ABS/RC) and the density of PSII reaction center per excited cross section(at t=0)(RC/CSO) indicate that high temperature is the main factor which triggered the degradation of PSII reaction center and antenna. High temperature alone significantly inhibited the electron transport at PSII accepter side, but had a small effect of PSI activity. When the treated temperatures was below 45℃, low light may increase the activity of PSI. However, the low light could exacerbate the inhibition of PSI at 45℃.In general, our study demonstrates that high temperature and high light stress significantly inhibited the activity of PSII, PSI and the photosynthetic electron transport chain between PSII and PSI. Compared to PSI, PSII was damaged more severely. The light irradiation may increase the damage to PSI at high temperature stress. The three techniques, PF, DF, and MR could support each other and provide more information on the response of photosynthetic apparatus in apple peel to high light or high temperature stress alone or the crossed stresses.