Effects Of LED Lighting And Melatonin Priming On Photoinhibition Of Tomato Seedling

Facilities vegetables are an important part of modern agriculture, the precise environmental regulation is the guarantee of high-yield, high-quality production. Facilities cultivation of crops are still hard to avoid suffering from low temperature, weak light, drought and other environmental stresses, the occurrence of these environmental stresses can cause photo-inhibition of leaf, reduce the photosynthetic efficiency, resulting in a decline in yield and quality. A lot of advantage of LED light source make it is widely used in light environment regulation of horticultural facilities in recent years, but the influence of different light quality on plant photosynthesis still need further exploration; In the study of plant resistance, melatonin is sensitivity to light and has a strong antioxidant activity and may participate in regulating the efficiency of photosynthesis, but seldom reported. So this article using photosynthetic fluorescence measurement technology such as infrared gas detection, chlorophyll fluorescence, the change of the optical signal of 820nm and 515nm, comprehensive analysis the influence of different light quality LED (Wight W, combination of Red and Blue(1:1) RB, Blue B, Purple P and Red R) lighting on photosynthetic electron transport activity of tomato seedling, and preliminary exploration the regulation of melatonin priming on tomato leaf photo-inhibition under low temperature and drought stress, respectively. The main results were as follows:(1) Plant height of tomato seedlings under B, P treatment were significantly higher than other treatments, stem diameter lower than other treatment, the angle of stem to leaf significantly lower than plants under R and RB, to plant more compact. Leaf photosynthetic pigment content and net photosynthetic rate Pn of B and P treatment is significantly lower than W; The leaf NBT and DAB staining of other treatment was junior than W and R processing, indicate that treatment of RB, B and P have the ability to remove oxygen free radicals; JIP-test analysis showed that performance index (PIabs) of tomato seedling is the lowest under B and P, compared with W processing was reduced by 24.1% and 9.8%, respectively; Oxidation speed of leaf P700 is the slowest under B and P, and the largest oxidation value is lower than other light quality processing, PQ pool of seedling under R was significantly lower than W, the content of leaf functional PSI (Zmax) under B, P treatment was significantly lower than W; Y(Ⅱ), Y(Ⅰ) and ETR(Ⅱ), ETR(Ⅰ)under B and P treatment are lower than other light quality, and improves the Y(NPQ), Y(ND) and cyclic electron transfer Y(CEF); In addition B, P treatment reduced the thylakoid membrane integrity, the activity of ATP enzyme, proton motive force(pmf) and transmembrane potential(Δψ); During the light, Fv/Fm and Pm of tomato seedling under monochromatic lighting are significantly lower than combination lighting, and compared with W, B and P treatment reached extremely significant level, Pm value changes consistent between different processing when low temperature, drought stress happens, but Fv/Fm of seedlings under W, RB and R falling rapidly, On the contrary, B and P treatment reduced slowly. In conclusion, the influence of different light quality on tomato seedling photochemical reaction difference is very big, blue and purple light significantly reduces the operating efficiency of photochemical reaction through lowering photosynthetic electron transport activity, and the experiment of drought and low temperature stress shows that blue and purple light irradiation have the role of strengthening tomato seedling resistance.(2) Use two indicators of Fv/Fm and Pm screening the concentration of melatonin application, identified 1000μmol is optimal concentration for leaf spraying and root application; Further studied the effects of melatonin priming on photoinhibition of tomato seedling under low temperature, drought stress through using 1000umol melatonin spraying on the leaf (L100) and root application (R100), respectively, the results show that L100 and R100 processing improved leaf net photosynthetic rate Pn, transpiration rate E, stomatal conductance GH2O, intercellular CO2 concentration Ci, decreased stomatal limitation Ls of tomato under low temperature and drought stress, and leaf gas exchange parameters under L100 is superior to the influence of the R100; Fast Light response curves show that melatonin priming improved Fv’/Fm’and qP of tomato seedling under low temperature, drought stress, improved the ETR (Ⅱ) and ETR (Ⅰ), Y(Ⅱ) and Y (Ⅰ) also improved, indicate that melatonin priming is conducive to the direction of light energy to PSI and PSII photochemical reaction distribution, the influence of L100 treatment on photochemical activity of PSI and PSII is better than R100 processing; P515 rapid induction kinetics curve shows that melatonin priming protected the thylakoid membrane from the damage of low temperature, drought stress and strengthen the ATPase activity. In conclusion,100 umol melatonin priming alleviate the occurrence of photoinhibition of tomato seedlings under low temperature and drought stress, strengthened the photochemical reaction process of tomato leaf, and leaf spraying treatment were better than root processing, is a simple and effective adjustment measures in application.