Photosynthetic Physiological Of Tomato Seedlings Response To Exogenous Salicylic Acid And Nitric Oxideunder Salt Stress

Soil salinization is a global issue of ecological environment and agricultural production. In recent years, with the development of vegetable production in china, the area of facility vegetable cultivation is continuously expanding. In a relatively closed facility, soil could not get the rain washed out for a long time, coupled with high temperature and large evaporation, leading to salt accumulation to the surface soil and serious soil secondary salinization gradually, which restricts the healthy and sustainable development of Chinese facilities for vegetable production. Tomato ?Lycopersicon esculentum Mill.? is one of the most popular and a consumption quantity facility vegetable for many years, and the study of tomato salt resistance is the academic hot issue of common concern. Salicylic acid ?SA? and nitric oxide ?NO? are the two common kinds of biological activity of signal molecules in plants, both of which participate in the signal transduction process to biological and abiotic stress. Studies showed that appropriate concentration of exogenous SA, NO single or compound processing can effectively alleviate any adverse effects of the non-biological adversity stress on plant, and the effect of compound treatment is better. At present, studies on exogenous SA, NO application regulating plant photosynthetic physiological mechanism of salt tolerance are still lack of in-depth report. Therefore, Researches on regulations of the SA single, SA and NO compound to photosynthetic physiological characteristics of tomato seedling under the NaCl stress resistance were carried on with the nutrient solution culture through the method of root applied induced resistant agent using salt sensitive tomato varieties'Qin Feng Bao Guan'as the test material. And aiming at excessive accumulation of Ca?NO₃?₂ leading to secondary salinization of soil, researches on the effects of NO and Ca?NO₃?₂ sprayed on the leaf on photosynthetic physiological characteristics of tomato seedling were also studied using the same material and cultivation methods. The main results are as follows:1. Studies on photosynthetic physiological characteristics of tomato seedlings to exogenous SA under the NaCl stressRoot application SA can make light saturation point ?LSP? and light saturation ?maximum?, net photosynthetic rate ?Pnmax?, apparent quantum efficiency ?AQY?, dark respiration rate ?Rd? and CO₂ saturation point ?CSP?, carboxylation efficiency ?CE?, the largest RuBP regeneration rate, light respiration rate ?Rp? and CO₂ release the light/dark ratio ?LID? of tomato seedlings rise in different degree and light compensation point ?LCP?, CO₂ compensation point ?CCP? and light respiration rate/carboxylation efficiency ?Rp/CE? decreas significantly under the NaCl stress, which showed that exogenous SA could alleviate the damage of NaCl stress on photosynthetic carbon cycle and reduce the occurrence of photo-inhibition by enhancing photorespiration ways.Under the NaCl stress, the unbalance of excitation energy distribution between PSI and PSII ??/?-1? of tomato seedling leaves of SA root application processing decreased obviously, and PSII excitation energy pressure ?1-qP? decreased while the photochemical operation efficiency ?Fv'/Fm', ?PS? and qP? significantly enhanced so as to promote the linear electron transfer ?JF?, which make the light energy share used to photochemical reaction of share ?P? increase and invalid dissipation ?Ex and D? reduce and improve the utilization efficiency of light energy.Under the NaCl stress, the leaf photosynthetic rate ?Pn?, transpiration rate ?Tr?, stomatal conductance ?Gs?, the apparent mesophyll conductance ?AMC? and light energy use efficiency ?LUEapp? and chlorophyll content ?Chla, Chlb, Chla+b? of tomato seedling of root application SA treatment improve obviously while the stomatal limitation ?Ls?, the intrinsic water use efficiency ?WUEi?, transient water use efficiency ?WUEt? and the Car/Chla+b reduce to different degrees; at the early stage of the stress ?0-4 d? make the intercellular CO₂ concentration ?Ci? increase while in the later ?6-8 d? the Ci decline in different degrees, which indicated that exogenous SA reduced the stress on the degradation of photosynthetic pigments, and the leaf photosynthetic gas exchange performance was improved, the growth of tomato seedling was promoted, and increased the distribution of photosynthetic products in the leaves ?SSR increase?, to facilitate the photosynthesis.2. Researches on photosynthetic physiological mechanism of regulation of exogenous SA and NO to the NaCl stress resistance of tomato seedlingsUnder the NaCl stress, content of proline, soluble sugar, free amino acids and soluble protein of the tomato seedling root and leaf treated by single or compound exogenous SA, NO increase to different degree, and the abilities of plant selective absorption and upwards transport of K⁺, Ca²⁺, and Mg²⁺ also significantly enhanced at the same time so that the content of Cl-, Na⁺ in leaf and Na⁺/K⁺, Na⁺/Ca²⁺, Na⁺/Mg²⁺ value decrease significantly while the content of K⁺, Ca²⁺ and Mg²⁺ increases to different degree, which makes the osmotic regulation work, maintain photosynthetic membrane stability and ease the photosynthetic pigment degradation. Stress 8 d, the content of photosynthetic pigment ?Chla, Chlb, Chla+b and Car? increased significantly, and the combination of treatment effect is the best. At his point, the leaf proline content of combined treatment is obviously less than the cause of the individual treatment related to proline in chlorophyll synthesis.Application of exogenous SA, NO single or combined can significantly improve superoxide dismutase ?SOD?, peroxidase ?POD? and catalase ?CAT? activity of seedling leaves under the NaCl stress, and also improve the activities of peroxidase ?APX? and glutathione reductase ?GR?, single dehydrogenation ascorbic acid reductase ?MDAR?, dehydrogenation of ascorbic acid reductase ?DHAR? participating in AsA-GSH cycle ascorbic acid, add the content of ascorbic acid ?AsA?, oxidized glutathione ?GSSG? and reduced glutathione ?GSH?, dehydrogenation ascorbic acid ?DHA? and reduce content of reactive oxygen species ?ROS? and malondialdehyde ?MDA?, low electrolyte permeability as well. The comprehensive effect of combined application of exogenous SA, NO is better.Under the NaCl stress, the unbalance of excitation energy distribution between PS? and PS? ??/?-1? of tomato seedling leaves of exogenous SA, NO single or combined processing decreased obviously, and PS? excitation energy pressure ?1-qP? decreased while the photochemical operation efficiency ?Fv'/Fm',?ps? and qP? significantly enhanced so as to promote the linear electron transfer ?JF?, which make the quotient of absorbed luminous energy used for photochemical action ?P? increase and invalid dissipation ?D and Ex? reduce and improve the utilization efficiency of light energy, and the combined treatment effect is better.The Rp and JO/JF of tomato seedling leaves improved different degrees by the Exogenous SA, NO single or combined application treatment under the NaCl stress. while the differences between three treatments of SA, NO single or combined application was not significantly. This result indicated that Exogenous SA and NO has synergies effect on photosynthetic mechanism protecting, but its not through the pathway of strengthening the photorespiration cycle and dissipating more excess light energy. Compared to SA, NO single application, the combined treatment was not reduce JC/JF?VC/JC and VTPU/VC obviously, while increased the VO?VC and VTPU significantly. This result also indicated that SA and NO combined application has synergies effect on relieveing the damage of photosynthetic dark reaction of tomato seedling leaves under the NaCl stress.Exogenous SA, NO single or combined application can significantly inhibit the damage of the NaCl stress on xanthophyll cycle library ?V+A+Z? of seedling leaves, and significantly reduce the de-epoxidation ability of xanthophyll cycle ?DEPS?=?A+Z?/?V+A+Z?, which makes share of V increase in the library, share of A and Z decrease, and the combined application treatment effect is more apparent, which indicates that exogenous SA, NO single or combined processing cannot depend on blade by enhancing the heat dissipation of xanthophyll cycle to protect the photosynthetic mechanism.Exogenous SA, NO single or combined processing can effectively relieve the damage of the NaCl stress on PSII reaction center in seedling leaves. By increasing the unit number by light cross section contains active reaction center ?RC/CS? lighten the burden of light energy dissipation of each reaction center ?ABS/RC, TR0/RC and DI0/RC decrease?, to absorb the light energy is used to transfer the quantum yield of electronic ??E0? increased significantly, quantum for heat dissipation ratio ??D0? significantly reduced. Simultaneous determination of 820 nm light absorption results show that, the seedling leaves AMR/MR and VPS? were significantly increased by exogenous SA, NO single or combined application under the NaCl stress, which indicates that exogenous SA, NO single or combined processing can reduce the damage of NaCl stress on inhibition of P700, and the combined treatment effect is better.Under the NaCl stress, PItotal, ?PS?/PS? and VPS?-PS? of seedling leaves of exogenous SA, NO single or combined processing all rise to different degree, which indicates that exogenous SA, NO single or combined processing can improve photochemical properties of the whole optical system including PS? and PS?, thus improve photosynthetic gas exchange performance ?Pn, Tr and Gs, WUEt, LUEapp and CUEapp rise, Ci decrease?, and the effect of the combined treatment is the best. The results showed that exogenous SA, NO has synergies effect on alleviating damage ?or inhibit? leaves blade light system under the NaCl stress and improving the photosynthetic efficiency of tomato seedling.3. Researches on photosynthetic physiological mechanism of regulation of exogenous NO to the Ca?NO₃?₂ stress resistance of tomato seedlingsSpraying exogenous NO can make leaf Pn?Gs?Tr?AMC?LUEapp and chlorophyll content ?Chla, Chlb, Chla+b? rise by different level under the Ca?NO₃?₂ stress while Car/Chla+b value significantly reduced; 6 d of Ca?NO₃?₂ stress, Ci of tomato seedling leaves treated by exogenous NO significant rise while the Ls, WUEt, Car content and Chla/b value significantly reduced; 12 d of Ca?NO₃?₂ stress, Ci tomato seedling leaves treated by exogenous NO significantly reduced, WUEt has no significant change, Ls, WUEt, Car content and Chla/b a significant rise in value. NO can through regulating stomatal opening and closing ?6 d?, but also by improving the mesophyll cell ?12 d? photosynthetic activity to relieve the Ca?NO₃?₂ stress on tomato seedling inhibition of photosynthesis.Spraying exogenous NO can significantly increase the the activity of SOD, POD and CAT, improve the activity of APX, GR, MDAR, DHAR participating in AsA-GSH cycle, and increase the amount of AsA, GSSG, GSH, DHA, reduce the content of ROS and MDA, reduce the electrolyte permeability under Ca?NO₃?₂ stress in seedling leaves. These results suggest that exogenous NO can alleviate the Ca?NO₃?₂ stress on tomato seedling photosynthetic organs induced oxidative damage.Under the stress of Ca ?NO₃?₂, SNP could effectively increase the photochemical efficiency of leaf PSII. The quotient of absorbed luminous energy used for photochemical action ?P? and the non-cyclic electron transport rate ?JF? were significantly increased. The reason is not only related to the improvement of the equilibrium distribution of excitation energy between PSI and PSII, but also the increase of the non-photochemical energy dissipation in the PSII reaction center. On the 6 d of Ca ?NO₃?₂ stress, no significant changes were observed in the ?V+A+Z?, DEPS and each component of xanthophyll cycle accounts for the ?V+A+Z? share of tomato seedlings leaves treated by exogenous NO; On the 12 d after Ca ?NO₃?₂ stress, the value of ?V+A+Z? and V accounted for ?V+A+Z? share of tomato seedlings increased significantly, and DEPS, A, Z accounted for ?V+A+Z? share decreased significantly, which indicated that NO could alleviate the damage of Xanthophyll cycle of tomato seedling leaves under Ca ?NO₃?₂ stress, but it could not promote the xanthophyll cycle Running.The number of active reaction centers in the cross section of the light receiving unit of seedlings was significantly increased by spraying SNP on the 6 d or the 12 d after Ca ?NO₃?₂ stress, and the ET0/RC increased significantly, ABS/RC, TR0/RC and DI0/RC decreased significantly, which indicated that exogenous NO could increase the quantum yield of electron transfer ??E0?, reduce the quantum ratio ??D0? for heat dissipation by increasing the number of active reaction centers per unit leaf area and reducing the excitation energy in unit reaction. In addition, exogenous nitric oxide ?NO? could stabilize the structure of thylakoid structure, and increase the probability of PG in the center, so as to facilitate the transfer and efficient use of excitation energy in photosynthetic apparatus.The results of 820 nm light absorption showed that the ?MR/MRo, VPS? and VPS?-PS? in seedlings treated with exogenous NO were significantly increased under Ca ?NO₃?₂ stress, which indicated that the exogenous NO could alleviate the Ca?NO₃?₂ stress on the P700 inhibition or damage, while improving the coordination of the two photosystems.