Study On The Male And Female Differences In Photosynthesis And Antioxidant System Of Torreya Grandis Seedlings Under Drought Stress

Content:Due to different resource utilization modes of dioecious plants and competitive population relationships,different environmental adaptation mechanisms are differentiated between genders,and gender differences under stress are more pronounced,mainly in morphology,physiology and population structure.Drought is an important environmental factor for the yield limitation of dioecious plant Torreya grandis,and also affects the sex ratio of wild populations of torreya.Photosynthesis is the basis of plant survival and an important research means to reflect the status of plant organisms.At the same time,plants also respond to the damage of reactive oxygen species generated under stress through antioxidant enzyme systems.Therefore,it is of great significance to study the photosynthetic and physiological conditions of torreya seedlings between different sexes under drought conditions,and to grasp the possible gender bias direction of torreya seedlings under natural stress.Male and female torreya seedlings under drought stress for 20 days were used as experimental materials to study the drought response mechanism from the aspects of photosynthetic parameters and chlorophyll fluorescence antioxidant enzymes,the specific results are as follows:（1）Drought significantly reduced the RWC,Pn and Gs of male and female torreya seedlings,while the increase in Ci indicated that the decrease in Pn was caused by non-stomatal constraints.Compared with the male torreya seedlings,the female plants could maintain a high level of Pn and were less affected by drought than the male plants.（2）Drought had a significant effect on the photosynthetic electron transport process of male and female torreya seedlings.The exchange capacity between Q_A to Q_B became limited compared to the onset of drought.The oxygen-evolving complex（OEC）was also damaged,Vcmax and PI_ABS was significantly reduced by drought.Drought stress affects either the oxidation of plastocyanin（PC）and the PSI reaction center(P₇₀₀)or the re-reduction of PC⁺and P⁺₇₀₀ over time in response to drought stress.Compared with the female torreya seedlings,the oxidation of male plants was faster,and the negative impact of electron transport was greater,resulting in the decline of photosynthetic function.（3）Drought had significant effects on antioxidant enzyme activities of torreya seedlings.Short-term（0–10 days）drought increased SOD,POD and CAT in the leaves of torreya seedlings.Long-term（10–20 days）drought prevented the antioxidant system of torreya seedlings from eliminating excessive reactive oxygen species,and the seedlings were subjected to severe oxidative stress.Compared with female torreya seedlings,the decrease of antioxidant enzymes in male plants was significantly higher,the key enzymes in As A-GSH,APX and GR were significantly lower,and the accumulation of MDA was significantly higher than that in female plants,resulting in greater membrane damage.The results showed that the inhibitory effect of long-term drought stress on torreya seedlings significantly reduced the photochemical activities of PSⅡ and PSI,but PSⅡ was more sensitive than PSI.The gender differences of gas exchange in torreya seedlings under drought conditions were compared.In terms of fluorescence curve,the damage rate of PSⅡ and PSI in female plants and the transfer rate of photosynthetic electron chain were also slower than those in male plants under drought stress.In physiological and biochemical aspects,female plants had stronger antioxidant enzyme system,so that they were less damaged by reactive oxygen species than male plants.Therefore,female torreya may have better drought adaptability than male plants.