Photosynthetic Acclimated Mechanism Of Leaf In Cotton Under Drought Stress

Drought acclimation is a protective mechanism of plants to reduce the damage in waterstress condition. Because different plants have different sensitivity to kinds of stress, theyformed various acclimation mechanisms during the process of drought stress. As adrought-tolerance plant, it is of great significance to study the photosynthetic acclimatedmechanisms of cotton under drought. This study used the xinluzao45as the materials anddesigned three drought treatments, i.e. control (well-watered), acclimated drought andnon-acclimated drought. In order to study various physiological mechanisms of acclimateddrought undergoing water stress, we measured the carbon assimilation characteristics,photosynthetic pigment content, carbon and nitrogen ratio, fluorescence characteristic,anatomical structure, stoma and the antioxidase system in leave. This research may help toreveal the physiological process of cotton forming phenotypic drought acclimation.Additionally, the results obtained can provide theoretical basis for technology of regulateddeficit irrigation and drought-tolerance cotton breeding. Below are the main results in thisthesis:1The differences between the acclimated cotton and non-acclimated cotton in gasexchange and chlorophyll fluorescence parameters were studied to reveal photosyntheticacclimated mechanism during the drought. The topmost full-expanded leaf on the main stemwas chosen and gas-exchange, photosynthetic pigment content, and fluorescencecharacteristic were measured. The result showed that the photosynthetic characteristic ofleaves had changed significantly in the acclimated cotton. Comparing with non-acclimatedcotton, higher stomatal conductance (Gs) and chlorophyll contents in acclimated cotton maylead to higher net photosynthetic rate. The fluorescent parameters result showed that higherelectron transport rate (ETR), actual photochemical efficiency (Yield) and photochemicalquenching (qp) were observed in acclimated cotton than in non-acclimated cotton. Thesemaybe the most important reasons to improve the net photosynthetic rate (Pn). Higher cyclicelectron flow around PSI (CEF) in acclimated cotton than in non-acclimated cotton was notonly beneficial to the synthesis of ATP to increase the photosynthetic capacity but also canmaintain higher trans-membrane pH (ΔpH) to enhance the energy dissipation.2The specific leaf weight, carbon nitrogen ratio and activity of antioxidase system ofleave in different treatment cotton were explored to reveal the acclimated mechanism ofnutrients and antioxidase system. The result showed that drought was lower the content ofcarbon and nitrogen, reduced the activity of antioxidase system and increased the content ofMDA, consequently lipid peroxidation of membrane. Compared with non-acclimated cotton,the specific leaf weight in acclimated cotton was higher. The activity of SOD and CAT washigher in acclimated cotton than in non-acclimated cotton. Higher activity of SOD and CATcould strengthened the scavenging of active oxygen and reduced the content of MDA andmembrane lipid peroxidation.3When the plants were subjected to drought stress, the leaf anatomical structure was themost sensitive response. we found that drought reduced the leaf thickness and had smaller epidermis cell; spongy parenchyma and palisade parenchyma was compact arrangement,especially spongy parenchyma. These increased the density of leave to enhance the resistanceof light propagation and diffusion in mesophyll to strengthen the resistance of high light indrought non-acclimated cotton. The leaf thickness increased and the palisade parenchyma andspongy parenchyma arrangement were loose. Meanwhile the size of epithelial cell increasedin acclimated cotton. These were beneficial to capture low light to enhance the utilization oflight. Larger stomata size and smaller stomata density could increase the stomatalconductance to enhance the photosynthetic rate.