| In the production process of facility horticulture,the methods of manual control are commonly used to change the environmental conditions of crop growth.In recent years,there have been many reports on improving the light environment of crop growth in the greenhouse through artificial supplemental lighting.However,it is still unclear how to supplemental lighting can induce plant stress resistance.Therefore,we applied foliar light supplement to tomato seedlings under sub-low temperature stress.In this experiment,white:blue 2:1 composite light was used to supplement the tomato seedlings under 15/8℃(day/night).A total of five treatments were set,which were normal temperature without light treatment(set to CK),normal temperature supplemental upward lighting from underneath(set to CK+USL),sub-low temperature stress(set to LT),sub-low temperature stress supplemental upward lighting from underneath(set to LT+USL)and under the low temperature stress supplemental lighting from the frontal of the leaves(set to LT+TSL).Firstly,by analyzing the differences in plant height,stem thickness and biomass,the effect of supplemental upward lighting from underneath on the growth and development of the plant was studied,in addition,supplemental upward lighting from underneath of the leaf was studied on tomato seedlings under sub-low temperature stress.The effects of photosynthesis and photosynthesis system were analyzed,and the changes of the microstructure and submicrostructure of tomato seedling leaf tissue were analyzed,in order to find out the inner rules of leaf supplemental light on the growth and light energy utilization of tomato seedlings under mild hypothermia.Finally,we also studied the effects of back light supplementation on membrane lipid peroxidation,cell damage,and reactive oxygen metabolism of tomato seedlings under sub-low temperature stress,in order to explore the stress resistance of leaf backside supplementation on tomato seedlings under sub-low temperature stress and changes in carbohydrate distribution.The above researches are aim to improve plant growth under low temperature stress,enhance seedling quality,assist production practices,and create higher economic benefits under sub-low temperature stress.The main findings are as follows:(1)To supplemental upward lighting from underneath of leaves promoted the growth of tomato seedlings under sub-low temperature stress.Compared with the LT+TSL treatment on the front surface of sub-temperature leaves,the dry fresh weight and total dry weight of the light-filling leaves on the back surface of the low-temperature leaves increased significantly by 6.39%,12.58%and 4.12%,7.35%,respectively,The total volume and the number of root tips increased significantly by 11.85%,9.99%,7.41%and 9.92%,respectively.(2)Supplemental upward lighting from underneath under sub-low temperature leaves improves the activity of the photochemical reaction center,so that more photosynthetic energy and electrons are distributed to the photochemical reaction direction,and the photochemical reaction is promoted.The maximum photochemical efficiency Fv/Fm of the low-temperature leaf backfill is increased by 13%compared with that of the low-temperature leaf frontfill,PSII quantum yield Y(Ⅱ),PSII electron transfer rate ETR(Ⅱ),PSI quantum yield Y(Ⅰ)and PSI electron transfer rate ETR(Ⅰ)increased by 26%,26%,18%and 24%respectively,P700+dark reduction initial rate increased by 11%,ETR(Ⅱ)max,curve slope α and half-saturated light intensity Ek increased photosynthetic%,24%and 5%of tomato seedlings,PQ pool increased by 12%,leaf performance index PI(abs)and original maximum photochemical efficiency φPo increased significantly by 91%and 9%.(3)Supplemental upward lighting from underneath under sub-low temperature leaves improved the light and performance of tomato seedlings.Compared with mild hypothermia treatment,supplemental upward lighting from underneath under sub-low temperature of leaves significantly increased the content of chlorophyll a,total chlorophyll and chlorophyll a/b in the leaves of tomato seedlings,respectively increased by 9.39%,5.25%and 29.26%,net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)increased by 85.77%,19.09%and 44.59%,respectively,while the intercellular carbon dioxide concentration(Ci)decreased by 15.60%;the apparent quantum efficiency was significantly increased,light saturation point LCP,carboxylation efficiency and CO2 saturation point CCP,respectively increased by 20.50%,6.30%,15.06%and 4.06%.(4)Supplemental upward lighting from underneath under sub-low temperature leaf promotes the opening of the stomata,improves the leaf tissue structure and sub-microstructure,and makes the leaf have better carbon assimilation.Compared with the treatment of mild hypothermia,the stomatal area and stomatal number of leaves were significantly increased by 128.36%and 40.51%respectively;the thickness of palisade tissue and sponge tissue increased,the arrangement was closer,and the cell gap decreased;The degree of deformation is reduced,the stacking is tight,the gap between the sheets is small,the deformation of the matrix cystic body is relieved,the mitochondria are oblong,the structure is complete and the internal crest is clear.(5)Compared with the sub-low temperature leaf front light supplement,supplemental upward lighting from underneath enhances the leaf antioxidant enzyme activity and osmotic adjustment ability,while reducing the degree of cell membrane lipid peroxidation,thereby improving the resistance of tomato seedlings Damage to plants caused by sub-low temperature stress.Among them,relative conductivity,cell damage rate and malondialdehyde content were significantly reduced by 12.85%,11.42%and 20.25%respectively;soluble protein content and superoxide dismutase(SOD)activity were significantly increased by 9.75%and 18.76%Soluble sugar content in leaves,stems and roots were significantly reduced by 6.92%,18.42%and 11.05%,respectively.In summary,supplemental upward lighting from underneath of the leaf under sub-low temperature effectively relieved the stress of the seedlings;weakened the degree of light inhibition of the light system,improved the photochemical reaction and photosynthetic performance of tomato leaves;and improved the leaf tissue structure and ultrastructure,Thereby promoting the growth of tomato plants and enhancing their stress resistance.This study will further study the internal rules of foliar supplementary light on tomato seedling growth or light energy utilization under low temperature stress,and explore effective measures to improve low temperature and low light stress,thus providing more theoretical support for future production. |
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