[目的]探索两种不同耐寒红树植物对低温胁迫的生理响应机制,为红树林抗寒性研究提供重要理论依据.[方法]以秋茄、红榄李幼苗为试验材料,设置25℃(昼)/20℃(夜)、24 h 7℃(昼)/4℃(夜)、48 h 7℃(昼)/4℃(夜)3个处理,分别比较分析了两种红树植物幼苗叶片的光合参数、荧光特征、抗氧化能力、叶绿体超微结构等生理过程对低温响应的差异.[结果]低温胁迫抑制红榄李幼苗生长和光合作用,而对秋茄的影响却较小.在低温胁迫处理48h后,红榄李幼苗叶片超氧歧化酶(SOD)、过氧化物酶(POD)活性显著降低,而超氧阴离子(O2·-)、过氧化氢(H2O2)含量、丙二醛(MDA)含量增加,同时气孔关闭,光合色素合成受阻,叶绿体超微结构受损,最终导致叶片净光合速率(Pn)、气孔导度(Gs)、最大光化学效率(Fv/Fm)、实际光化学效率(ΦPSⅡ)、光化学猝灭系数(qP)以及非光化学猝灭系数(NPQ)等降低.相同低温胁迫下秋茄幼苗叶片Pn也受到抑制,但其Pn下降幅度约为红榄李的79%.[结论]秋茄耐寒能力较强于红榄李,这可能是因为秋茄在低温胁迫下不仅能够保持较高的气孔开张度、光合色素含量以及POD活性,维持较好的叶绿体超微结构,而且还会通过调控能量耗散减轻PSⅡ光抑制,降低低温胁迫带来的膜脂过氧化伤害,最终维持自身较强的光合能力.
Effects of Low Temperature Stress on Leaf Photosynthetic Physiology and Antioxidant Characteristics in Mangrove Plants Seedlings with Different Cold Tolerance
[Objective]This study investigates the physiological response of two different cold-tolerant man-grove plant species to low temperature stress,which provides a theoretical basis for studying on cold res-istance of mangrove.[Method]Based on the cold-tolerant variety Kandelia obovata and the non-cold-tol-erant variety Lumnitzera littore,three temperature treatments were set for treatment,including 25℃/20℃(day/night),24 hours at 7℃/4℃(day/night),and 48 hours at 7℃/4℃(day/night).The differences in the of photosynthetic parameters and fluorescence characteristic,antioxidant capacity,chloroplast ultrastruc-ture of two mangrove seedlings were compared and analyzed.[Result]Low-temperature stress inhibited the growth and photosynthesis of L.littore seedlings but had less effect on K.obovate.After 48 hours of low-temperature stress treatment,the activities of superoxide dismutase(SOD)and peroxidase(POD)in the leaves of L.littore seedlings were reduced,but the content of superoxide anion(O2·-),malondialde-hyde(MDA)and hydrogen peroxide(H2O2)in L.littore seedlings were increased.It was also observed that the leaf stomata were closed,and the contents of photosynthetic pigments were decreased.Additionally,the ultrastructure of the chloroplast was damaged,which eventually led to a decrease in the net photosyn-thetic rate(Pn),stomatal conductance(Gs),maximum photochemical efficiency(Fv/Fm),actual photochem-ical efficiency(ΦPSⅡ),photochemical quenching coefficient(qP),and non-photochemical quenching coeffi-cient(NPQ)of the leaves.Under the same low-temperature stress,the photosynthesis of K.obovata seed-lings'leaves was also inhibited,but the decrease in leaf Pn was approximately 79%of that observed in L.littore.[Conclusion]K.obovata exhibits stronger cold tolerance than L.littore,possibly because K.obovata can not only maintain higher stomatal opening,photosynthetic pigment content,and POD activity,redu-cing the damage to chloroplast ultrastructure,but also regulate energy dissipation to alleviate PSⅡ photoin-hibition,thereby reducing the damage caused by low-temperature stress to membrane lipid peroxidation.Consequently,K.obovata maintains its robust photosynthetic capacity.
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