Effects Of Exogenous Abscisic Acid On Physiologocal And Biochemical Characteristics Of Cucumber Seedlings Under Na₂CO₃-Stress

By spraying abscisic acid on cucumber (Cucumis sativus L.) seedlings leaves, effects of exogenous abscisic acid on growth index, membrane lipid peroxidation, protective enzymes activities, gas exchange parameters, chlorophyll contents and chlorophyll fluorescence parameters in leaves of cucumber seedlings under alkaline stress were studied in this paper in order to provide scientific bases for ABA appliance in cucumber production. The results were showed below:1. The height of cucumber seedlings were significantly decreased under alkaline stress, and fresh and dry weight of root, stem and leaf and root activity as well, but significantly increased proline contents. It could alleviate the decrease of the height of cucumber seedlings, fresh and dry weight of root, stem and leaf and root activity, and increased proline contents when cucumber seedlings were treated with different concentrations of abscisic acid, which 5×10-5 mol·L-1 is the best for cucumber seedlings.2. Malondialdehyde content and membrane permeability of cucumber seedlings were increased under alkaline stress. After spraying 5×10-5 mol·L-1 abscisic acid on cucumber seedlings leaves, membrane lipid peroxidation was significantly decreased and membrance damage was alleviated.3. With the increasing of alkaline stress time, the activities of superoxide dismutase and catalase were significantly decreased, while the activities of peroxidase and ascorbate peroxidase were increased firstly and then decreased. After spraying 5×10-5 mol·L-1 abscisic acid on cucumber seedlings leaves, the activities of superoxide dismutase, peroxidase, catalase and ascorbate peroxidase were increased and the antioxidant capacity was enhanced.4. Alkaline stress caused net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate(Tr) of cucumber seedlings were decreased and its intercellular CO2 concentration(Ci) was increased. After spraying 5×10-5 mol·L-1 abscisic acid on cucumber seedlings leaves, net photosynthetic rate and transpiration rate were increased and stomatal conductance and intercellular CO2 concentration were decreased.5. With the increasing of alkaline stress time, the contents of chlorophyll a, chlorophyll b and total contents of chlorophyll were increased firstly and then decreased, but chlorophyll a/b dropped dramticly and then increased slightly. After spraying 5×10-5 mol·L-1 abscisic acid on cucumber seedlings leaves, the contents of chlorophyll were increased.6. After spraying 5×10-5 mol·L-1 abscisic acid on cucumber seedlings leaves, it could efficiently alleviate the decrease of photochemical maximum efficiency of PSⅡ(Fv/Fm), photochemical efficiency of PSⅡ(Fv'/Fm'), actual photochemical efficiency of PSⅡ(ФPSⅡ), photochemical quenching coefficien(tQp), the electron transport rat(eETR), photochemistry rate(PCR)and the ration of absorbed light in photochemistry(P)as well as the increase of minimal fluorescence(Fo), non- photochemical quenching coefficient(NPQ), the ration of thermal dissipation(D)and excess energy(E)in cucumber seedlings induced by alkaline stress.