The Mechanism Of Photoinhibition Of Peanut (arachis Hypogaea L.) Under Abiotic Stress

Peanut (Arachis hypogaea L.) is one of the important oil crops of China and the world. It is subjected to many abiotic stresses during growth period. Luhua 14 was used as materials to study the response mechanisms of peanut photosystems to different stresses in the experiments. By measuring chlorophyll fluorescence, chlorophyll a fluorescence transient and light absorbance at 820 nm, etc., effects of different stresses on photosynthetic apparatus in peanut leaves were investigated. The main results are as follows:1. At the end of chilling stress, the photoinhibition of PSII was aggravated relative to that of high light stress alone. The PSII reaction center was seriously damaged by chilling temperature, and the activity of PSI also decreased significantly, which showed that the PSI of peanut leaf was more sensitive than PSII. JIP-test analysis showed that the degradation of the antenna system and the light absorption at chilling temperature were significant. Deactivation of some reaction centers led to the reduction of TR/CSm, and the part of energy dissipated in form of thermal increased correspondingly. Photons which were absorbed, captured, used to electron transport increased in per active reaction center. The increase of 1-qP at chilling temperature showed that the increase of the close of PSII and photochemical reaction decreased significantly. The increase of NPQ showed that xanthophyll cycle was triggered by photosynthetic system to consume superfluous excitation energy. The decreased activity of SOD enzyme under chilling stress induced accumulation of reactive oxygen species (ROS) in photosynthetic system, which destroyed the system of cell membrane reflected by the higher content of MDA, higher permeability of membrane and the accumulation of proline relative to those of CK.2. Under High temperature stress, the acceptor side of PSII of peanut was damaged, but the OEC was not damaged because of no appearance of K-step;The change of the rapid chlorophyll induction curve and the increase of Vj implied that the electron flow from QA to QB was blocked. The accumulation of ROS under high temperature stress might be related to the decreased activity of SOD enzyme, and ROS destroyed the system of cell membrane reflected by the higher content of MDA, higher permeability of membrane and the accumulation of proline relative to those of CK. The increase of NPQ showed that xanthophyll cycle was also effectively triggered under high temperature stress to dissipate excess excited energy.3. Under drought stress, the maximal photochemistry of PSII in dark-adapted leaves (Fv/Fm) decreased by 68.5%, which implied that the photoinhibition of PSII had occurred during this treatment. But the activity of PSI was affected slightly. The changes of the rapid chlorophyll induction curve, PIABS, Vj,ΦEo,ΨO and Mo suggested that the electron flow of photosysterm had a significant decrease. The accumulation of the reduced QA increased. Drought stress also deceased the activity of SOD enzyme and caused the accumulation of ROS, which further destroyed the system of cell membrane. Under drought stress, the xanthophyll cycle also could be effectively triggered to dissipate excess excited energy in peanut leaves.4. Salt stress seriously damaged the receptor side of PSII, however, the donor side of PSII was not affected. The content of MDA, permeability of membrane and the accumulation of proline increased in peanut leaves under salt stress. The increase of 1-qP in this salinity showed that the close of PSII increased and photochemical reaction decreased significantly. The xanthophyll cycle also could be effectively triggered under salt stress to dissipate excess excited energy in peanut leaves.