Effects Of Three Kinds Of Exogenous Substances On Reactive Oxygen Species Metabolism And Chlorophy Ⅱ Fluorescence In Tomato Seedlings Under NaCl Stress

Soil secondary salinization is becoming worse in tomato protected culture, which causes decline of yield and quality, brings a severe effect on sustainable development of vegetable production. The paper investigated the effect of exogenous cytokinins ( CTK ) and GABA(γ-aminobutyric acid) application to salinized nutrient solution on physiological metabolism in the leaves and roots of tomato cultivar'Jin Peng No.1'under NaCl stress. The index of growth and reactive oxygen species ( ROS ) are determined when the seedings are having 5 leaves, meanwhile Chlorophyâ…¡fluorescence were measured by chlorophyâ…¡f luorescence spectrometer (MINI-IMAGING-PAM). Therefore, the effects of exogenous substances on the relationship between ROS metabolism and photosynthesis under NaCl stress in tomatos were investigated ,which clarify the possible mechanisms of enhancing salt-tolerance in tomatos. The main results werepresented as follows.1. The paper investigated the effects of exogenous cytokinins ( CPPU and 6-BA ) in different concentration ( 10-30mg·L-1 ) application to salinized nutrient solution on ROS metabolism and chlorophyâ…¡fluorescence parameters in the seedlings of tomato under NaCl stress. The results showed that seedlings grown in nutrient solution salinized with 150mM NaCl for 2 d displayed increased superoxide anion radical ( O2—·) productive rate, malondialdehyde ( MDA ) content and antioxidant enzyme ( SOD, POD, CAT ) activities both in roots and shoots, while the increasing range of antioxidant enzyme activities was lower than ROS productive rate, which lead to decrease the capability of photosystemâ…¡in tomato seedlings. Exogenous CPPU and 6-BA application to salinized nutrient solution alleviated the NaCl on tomato seedlings damage to some extent, but there was significant concentration effect, in which 20mg·L-1CPPU treatment effect was best, followed by 30mg·L-1 6-BA treatment. In the 20mg·L-1CPPU and 30mg·L-16-BA treatments, O2—·productive rate and MDA content in leaves and roots were significantly lower than NaCl treatment, while the SOD, POD, CAT activities and photosystemâ…¡performance had improved significantly.2. Hydroponic experiments were performed to investigate the effects of exogenous CPPU application on growth, Na⁺ and Cl^- concentrations, ROS metabolism and chlorophyâ…¡fluorescence parameters in tomato seedlings subjected to salt stress ( 150 mmol·L-1 NaCl ). The results showed that exogenous CPPU application significantly improved the growth of seedlings, obviously decreased the Na⁺ and Cl^- concentrations in roots under salt stress. Meanwhile, the addition of CPPU obviously decreased the O2一productive rate, contents of hydrogen peroxide ( H₂O₂), MDA, ascorbic acid (AsA) in leaves and roots, and reduced glutathione (GSH) content in leaves through significant increasing activities of antioxidant enzymes (SOD,POD,CAT),ascorbate peroxidase (APX) and glitathione reductase (GR) of leaves and roots in the salt-stressed plants. In addition, the addition of CPPU to the salinized nutrient solution could enhanced chlorophyâ…¡fluorescence parameters, maximal photochemical efficiency of photosystemâ…¡(Fv/Fm),actual photochemical efficiency (Ñ„PSâ…¡),electron transport rate (ETR),photochemical quenching coefficient (qP) and chlorophyâ…¡content, but decreased non-photochemical quenching coefficient ( NPQ ).3. The purpose of this paper was to study the effects of exogenous GABA in different concentration on seed germination, ROS metabolism and chlorophyâ…¡fluorescence parameters in seedlings of tomato under NaCl stress. The results showed that exogenous GABA could increase germination of seeds and salt tolerance of seedlings, but there was variance among GABA concentrations, in which 10 mmol·L-1 GABA soaking treatment was best. In comparison to NaCl stress, exogenous 10 mmol·L-1 GABA soaking treatment led to a marked increase in germination and growth of tomato seeds, as well as decrease in accumulation of O2一, H₂O₂ and content of MDA, but antioxidant enzymes ( SOD, POD and CAT ) activities significantly increased in leaves and roots of tomato seedlings. Meanwhile, 10 mmol·L-1GABA soaking treatment could maintain higher PSâ…¡activity through significantly improving Fv/Fm,ΦPSâ…¡, ETR and qP, as well as decreasing NPQ.4. The purpose of this paper was to study the effects of exogenous 5 mmol/L GABA application on growth, ROS metabolism, chlorophyâ…¡contents and chlorophyâ…¡fluorescence parameters in tomato seedlings under NaCl stress and to investigate the physiological mechanism of GABA-enhancement of salt tolerance in tomato. It was found that exogenous GABA slightly affected on growth , activities of CAT in leaves,contents of ASA in leaves , contents of H₂O₂ and MDA, but significantly increased SOD, POD, CAT in roots, APX, GR acitivity in tomato leaves under normal nutrient solution. On the other hand, exogenous GABA application to normal nutrient solution had no significant effects on chlorophyâ…¡contents, Fv/Fm and NPQ, but ETR,ΦPSâ…¡and qP significant increased in tomato leaves. In comparison to NaCl stress, exogenous GABA application led to a marked increase in leaves growth, activities of SOD in leaves, POD in roots, CAT in roots, APX in leaves and GR in leaves, contents of AsA in leaves, as well as decrease in accumulation of O2一, H₂O₂ and contents of MDA, but the little influence on SOD in roots, POD in leaves, CAT activity in leaves, APX in roots , GR in roots and contents of GSH .Meanwhile, the addition of GABA to the salinized nutrient solution could maintain higher PSâ…¡activity through significantly improving chlorophyâ…¡content, Fv/Fm, ETR,ΦPSâ…¡and qP, as well as decreasing NPQ.