Responses Of Photosynthetic Characteristics And Photoprotection Mechanisms In Psii To Soil Water In Cotton Bracts

Although leaf was considered as the main photosynthetic organ, many parts of crop suchas non-foliar organs which contain chlorophyll can also performance photosynthesis,contributing to carbon acquisition and yield. This research was conducted from threeperspectives:1) changes in photosynthetic capacity of bracts in cotton and relativecontribution to yield during growth stages;2) differences in photorespiration charactertics ofbracts in cotton and3) the photoprotection of green bracts in cotton respond to water stress.On the basis of the three points above, photosynthetic charactertics, relative contribution to itsyield and adaptation respond to water stress of bracts in cotton were studied to elucidate a) thechanges in photosynthetic rate of green organs in cotton during growth stages and theimportant photosynthetic contribution of bracts to yield formation especially at later growthstage, b) differences in photosynthesis charactertic and photoprotection mechanism of bracts.Below are the main results in this thesis:1. ΦPSIIdecreased in bracts and leaves of cotton after anthesis under water-saving ofdrip irrigation condition,but the decrease of in bracts was lower than that in leaves.The resultexhibited that the photoinhibition of cotton bracts was lower than that in leaves of cotton. Pn，ΦPSII， photochemical quenching (qP),and non-photochemical quenching (NPQ)decreased inleaves of cotton after anthesis under saving drip irrigation condition,but no significantdifference was observed in bracts of cotton. The results of chlorophyll fluorescenceparameters showed quantum yield of regulated energy dissipation(Y(NPQ))of cotton bractswas higher than that in leaves under high irradiance and high temperature conditions,and thethermal dissipation of cotton bracts was no sensitive to water deficit and could protect thephotosynthetic apparatus against photodamage.2. We demonstrate that drought tolerance of the bracts is explained by its higher watercontent under saving drip irrigation. The ratio of photosynthetic electron partitioning (Jc/Jo)and Prwere calculated by combining measurements of gas exchange and chlorophyllfluorescence. Prdecreased, and Prsustained at a high level under water stress in the bracts.With the decrease of water supply, the Pr/Pnof cotton bracts was much higher than that inleaves of cotton and water deficit was no significant difference in bracts. This suggests thatphotorespiration of cotton bracts alleviate photoinhibition and play important roles inprotecting PSII.3. Compared with leaves, bracts showed greater RuBP regeneration/RuBP carboxylationcapacity ratio (Jmax/Vcmax) and lower stomatal conductance under high irradiance and temperature conditions. Photosynthetic area of per plant, chlorophyll content, water content,Pn, the actual photochemical efficiency of PSII (ΦPSII), and Rubisco content were lower inbracts than in leaves, but the decline of those parameters showed a significantly faster inleaves than in bracts at the late growth stage. Photosynthetic area of per plant, chlorophyllcontent, water content, Pn, ΦPSII, and Rubisco content decreased in the leaves of cotton plantsunder water-saving drip irrigation, but no significant difference was observed in the bracts.The photosynthetic activity of leaves decreased rapidly, but no significant difference wasobserved in the bracts at the late growth stage. The bracts contributed approximate9.93-10.44%of the carbon necessary at the late growth stage under normal drip irrigation, and12.91-15.47%under water-saving drip irrigation. We conclude that bracts are recognized asimportant carbon sources at the late growth stage.