The Response Mechanisms Of Photoinhibiton And Photoprotection Intomato (Solaunm Lycopersicum L.) Leaves To Sub-high Temperature And High Light Intensity Stress

Protected vegetable cultivation has become an important part of China's modern agricultural production. As one of the major greenhouse cultivation vegetable crops in north China, tomato ?Solanum lycopersicum L.? often encounters high temperature and high light intensity stresses which resulting in decreased ability of photosynthesis capacity, yield and quality, and serious restriction of the sustainable development of protected tomato over-summer cultivation. Therefore, it is of great significance to study the effects of high temperature and high light intensity on protected vegetables, especially the effects of sub-high temperature and high light intensity on the photosynthesis of the protected tomato in Northeastern China.In this study, a tomato cultivar "Liaoyuanduoli" was used to study the photoinhibition mechanism and the photoprotection mechanism of D1 protein turnover, the xanthophyll cycle, the cyclic electron flow and the linear electron flow. We aim to provide a theoretical basis for mitigation sub-high temperature and high light intensity stress disorders glare. The main study findings are as follows:1. The decline of tomato photosynthetic performance is mainly determined by non-stomatal factor under sub-high temperature and high light intensity. In present, compared with that of control, the net photosynthetic rate ?Pn?, the stomatal conductance ?Gs?, the transpiration ratio ?Tr? and the stomatal limitation value ?Ls? decreased substantially, and the intercellular CO₂ centration increased highly. Additionally, the activity of Rubisco and the relative expression of rbcL and rbcS were significantly lower than control, illustrating the leading of stomatal factor.2. Sub-high temperature and high light intensity stress could affects PS ?. In this study, the maximal photochemical efficiency of PS ? ?Fv/Fm?, light-adapted maximum quantum yield of PS ? ?Fv'/Fm'?, potential activity of PS ? ?Fv/Fo?, effective quantum yield of PS ? [Y???], electron transport rate of PS ? [ETR?I?] decreased significantly under HH stress, while non-photochemical efficiency of PS ? [Y?NPQ?] and photochemical efficiency of PS ? [Y?NO?] increased significantly. Maximum fluorescence ?Fm? and Minimal fluorescence ?Fo? which reflecting inactivation state of PS ? reaction center and qP which reflecting degree of PS ? openness decreased significantly, suggesting that HH caused the closure and irreversible inactivation of PS ? reaction center, thus, the photochemical efficiency of PS ? was decreased, resulting in photoinhibition and photodamage of PS ?. Meanwhile, PS ? photoinhibition and photodamage aggravated with prolong stress time.3. Sub-high temperature and high light intensity stress could affects PS ?. The results showed that, HH caused photoinhibiton of PS ? as the significant decline of photochemical yield of PS ? [Y???] and effective quantum yield of PS ? [Y???]. Since the decline of Y??? was caused by significant decrease of quantum yield of non-photochemical energy dissipation in PS ? due to acceptor side limitation [Y?NA?] and significant increase of quantum yield of non- photochemical energy dissipation in PS I due to donor side limitation [Y?ND?], we inferred that PS II electron transfer was blocked by excess light energy and the electron accumulated in donor side of PS I, resulting in PS I photoinhibiton in donor side; meanwhile, the decline of Rubisco activity led electron accumulated in the acceptor side of PS I, leading to PS I photoinhibiton in acceptor side.4. ROS metabolism is affected by sub-high temperature and high light intensity. In this research, the content of malondiadehyde ?MDA? and H₂O₂, cell relative electric conductivity ?K? and membrane damage degree ?a? were both increased under HH, however, the content of soluble protein ?Sp? and free proline ?Pro? were decreased, implying that HH caused a large number of ROS which seriously damaged cell membrane and lead to outflow. What's more, we found that the activity of superoxide dismutase ?SOD? and peroxidase ?POD?, the gene expression of ?Cu/zn?SOD and GR were significantly inhibited, while catalase ?CAT? activity, ?Mn?SOD and APX gene expression were promoted, suggesting that adversity induced ROS removal system to remove ROS, but the related antioxidant enzymes activity was inhibited by HH, which leading to imbalance of ROS metabolism and destruction of photosynthetic systems.5. D1 protein turn over and xanthophyll cycle affect photosynthesis and guard cells of tomato leaves under HH. The results showed that, compare to that of control, streptomycin sulphate ?SM? and dithiothreitol ?DTT? treatment led to the decline of Pn and apparent quantum yield ?AQY?, at the same time, stomatal number, width and area of guard cells and stomata were decreased, but length and length-width ratio were increased, implying that the damage of D1 protein turnover or xanthophyll cycle induced the closure of stomata and reduced the number of stomata, resulting in the inhibition of light utilization ability, finally caused the inhibition of photosynthesis.6. D1 protein turn over and xanthophyll cycle affect photoinhibiton of tomato leaves under HH. In present, Fv/Fm, Fv/Fo, Y?II? and qP were significantly reduced by SM and DTT, as well as down-regulated expression of psbA and D1 protein. We inferred that the damage of D1 protein turnover or xanthophyll cycle induced core protein of PS ? was damaged at the transcription and translation level respectively, which caused net loss of D1 protein, eventually led to destruction of PS II reaction center and serious photoinhibition of PS ?. In addition, we found that SM and DTT treatment decreased total chlorophyll content significantly and increased Cha/Chb, suggesting that the damage of D1 protein turnover or xanthophyll cycle made the light harvest complex of PS II more sensitive to oxidative stress, leading to the destruction of antenna pigment.7. D1 protein turn over and xanthophyll cycle affect ROS of tomato leaves under HH. In our study, fluorescent dyes DHE and DCFH-DA were utilized respectively to the observation of O2·- and H₂O₂ in guard cells of tomato. Combined with its vital staining, we found that HH led to ROS accumulation in guard cells and leaves, the fluorescence intensity of ROS in guard cells and dyeing level were greatly deepened by SM and DTT. Additionally, antioxidant enzymes activity such as CAT, POD and SOD were highly inhibited by SM and DTT as well as total antioxidant capacity ?T-AOC?. We deduced that the damage of D1 protein turnover or xanthophyll cycle reduced the inhibition of plant antioxidant capacity, once ROS cannot be cleared in time, the accumulation of ROS led to closure of stomata.8. The cyclic and linear electron flow ?CEF & LEF? affect energy distribution of tomato seedlings under HH. In our research, methyl violet ?MV? and diuron ?DCMU? treatment enhanced the energy of allocation to PS ???? and the fraction of light absorbed in PSII antennae that is dissipated thermal ?D? sharply, while the light energy distribution of PS ? ?a?, the fraction of light absorbed in PS ? antennae that is uses in PS ? photochemistry ?P? and the fraction of light absorbed in PS ?antennae that is detained in the PS ? center as excessive energy ?E? were decreased significantly, suggesting that the suppression of CEF and LEF led to imbalance of excitation energy distribution, most excitation energy distributed to PS ? broke down the reaction center, the damaged reaction centers cannot do photochemical reaction.9. CEF and LEF affect photoinhibition of tomato leaves under HH. In present, Fv/Fm, Fv'/Fm'and qP were declined greatly in MV and DCMU treated plants, and ?1-qP? which reflecting excitation voltage of PS ?was rose highly, inferring that the suppression of CEF and LEF caused inactivation of PS ?reaction center, importantly, PS?reaction center may be degraded and cannot recover its activity. Thus, CEF and LEF play an important photoprotection role to reaction center of PS ? and PS ? in tomato seedlings under sub-high temperature and high light intensity stress.10. CEF and LEF affect trans-thylakoid membrane proton motive force ?pmf? in tomato leaves under HH. In present, P515 signal which reflecting pmf in vivo was measured. Rusults showed that, MV and DCMU treatment significantly decreased pmf and its components transmembrane proton gradient ?? pH? and transmenbrane potential ?? ??. Our observations of faster decay after dark adaptation and a slower decay, after illumination in P515 signal on MV and DCMU stressed plant indicated that both the thylakoidmembrane was damaged and ATP-ase activity was reduced seriously.