Photoprotective Effects of D1 Protein Turnover and the Lutein Cycle on Three Ephemeral Plants under Heat Stress

To clarify the characteristics of photoinhibition and the primary defense mechanisms of ephemeral plant leaves against photodestruction under high temperature stress,inhibitors and the technology to determine chlorophyll fluorescence were used to explore the protective effects of D1 protein turnover and the lutein cycle in the high temperature stress of the leaves of three ephemeral plants.The results showed that the maximum light conversion efficiency(Fv/Fm)of the ephemeral plant leaves decreased,and the initial fluorescence(Fo)increased under 35℃±1℃ heat stress for 1-4 h or on sunny days in the summer.Both Fv/Fm and Fo could be recovered after 8 h of darkness or afternoon weakening of the external temperature.Streptomycin sulfate(SM)or dithiothreitol(DTT)accelerated the decrease of Fv/Fm and the photochemical quenching coefficient(qP)in the leaves of three ephemeral plants at high temperature,and the decrease was greater in the SM than in the DTT treatment.When the high temperature stress was prolonged,the Y(II)values of light energy distribution parameters of PSII decreased,and the Y(NPQ)and Y(NO)values increased gradually in all the treatment groups of the three ephemeral plants.The results showed that the leaves of the three ephemeral plants had their own highly advanced mechanisms to protect against photodamage,which inhibited the turnover of D1 protein and xanthophyll cycle.This can damage the PSII reaction center in the leaves of the three ephemeral plants under high temperature.The protective effect of D1 protein turnover on heat stress in Erodium oxyrrhynchum and Senecio subdentatus was greater than that of the lutein cycle,while the protective effect of lutein cycle was greater than that of D1 protein turnover in Heliotropium acutiflorum subjected to heat damage.

Study on the Response and Recovery Characteristics of Different Herbaceous Peony (<i>Paeonia lactiflora</i>Pall.) Varieties to Waterlogging Stress

The root of herbaceous peony (Paeonia lactiflora Pall.) is fleshy, and different varieties have different tolerance to waterlogging stress. In order to explore its response and recovery characteristics to waterlogging stress, six varieties of herbaceous peony with strong, medium and weak waterlogging tolerance and high ornamental value were selected as experimental materials. After the vegetative growth of each variety was completed, the field simulated waterlogging stress experiment was carried out by the semi-flooded (the water surface is half the height of the flowerpot) pot method. Changes in photosynthetic parameters, chlorophyll fluorescence parameters, relative water content (RWC), relative conductivity (REC), chlorophyll content, lutein cycle, and leaf microstructure were analyzed during recovery from waterlogging stress and stress relief. The results showed that the time of reaching the most significant difference between CK and tested varieties was different. From the beginning of stress to 60% of the leaves with symptoms, the varieties with strong and moderate waterlogging tolerance experienced longer time;the proportion of palisade tissue in leaves was larger;the maximum photochemical quantum yield (Fv/Fm) was reduced less;it could increase xanthophyll cycle and heat dissipation (NPQ) to consume excess light energy, and maintain a higher net photosynthetic rate (Pn) for normal growth of plants in a short period of time. The REC in leaves of varieties with weak waterlogging tolerance increased more, and the damage of cell membrane was more serious. After the stress was removed, all indexes recovered to different degrees. Based on our comprehensive analysis, the comprehensive waterlogging resistance of the experimental materials followed the pattern: “Lihong” > “Yangfeichuyu” > “Taohuafeixue” > “Dafugui” > “Qihualushuang” > “Hongxiuqiu”. It is suggested that the variety “Lihong” and “Yangfeichuyu”, with strong comprehensive waterlogging tolerance, can be selected for propagation and cultivation in areas prone to waterlogging. In the later stage, it is still necessary to further expand the number and scale of varieties, combined with the in-depth study of waterlogging-resistance genes, so as to provide a theoretical reference for the cultivation and production of new waterlogging-resistant varieties.