Effects Of Water Deficit On The Carbon Metabolism In Cotton Bolls And Their Subtending Leaves During Flowering And Fruiting And Its Relationship With Fiber Quality

Mid-summer drought during mid-July to mid-August is a main climatic disaster for cotton production in the Yangtse valley region.Soil water deficit usually leads to decreased fibre length and low fibre quality during flowering and boll-setting stage.Two upland cotton breeding lines A001 and A705,were used in a pot culture experiment in greenhouse with exposure to different of water regimes(normal irrigation and drought)throughout 2015 to 2016.The dynamic changes of non-structural carbohydrate(glucose,fructose,sucrose,starch),osmotic adjustment substances and carbon metabolism key enzymes(vacuolar acid invertase VIN,cell wall acid invertase CWIN,sucrose synthase SS,sucrose synthase SPS)in cotton bolls and subtending leaves during fiber elongation were investigated.The differences between treatements were analyzed.Antioxidant metabolism and photosynthetic characteristics in cotton boll subtending leaves response to water deficit were evaluated.The main findings are as follows:1.The soil drought stress led to decreased cotton fiber length and strength.The the two lines exhibited different sensibility to water stress with A001 being more sensitive genotype than A705.2.The soil drought stress led to a reduction in osmotic adjustment substances(glucose,fructose,fructose,malic acid and K+)and starch concentrations in cotton fibers during fiber elongation stage,and in turn the decreased osmotic potential and turgor pressure in fiber cells.This is the main reason for the decline in fiber length.Osmotic adjustment substances exhibited more strong fluctuations in A001 fibers than A705 fibers during fiber elongation phase.3.The effects of soil drought on the concentrations of non-structural carbohydrates(glucose,fructose,sucrose and starch)and the activities of carbon metabolism key enzymes(SS,SPS,VIN,CWIN)in cotton ovules were inconsistent among different yeares and sampling dates.No significant difference between treatments was observed on most of sampling dates.It was suggested that the soil drought had little influence on carbon metabolism in embryos.4.The soil drought stress resulted in an increase in non-structural carbohydrate(glucose,fructose,sucrose and starch)concentration in leaves subtending cotton boll during fiber elongation stage.The decreased photosynthesis in subtending leaves was due to the drought stress.The accumulation of carbohydrate in the subtending leaves under water stress should be ascrible to the limited carbon export to the boll sink,and then led to decreased carbohydrate levels relative to the control,which could be partly responsible for the reduction in fiber length and strength for water stressed fibers.Non-structural carbohydrates in subtending leaves exhibited greater fluctuation in A001 than A705 suggesting A705 having more tolerance to water stress than A001.Carbon metabolism key enzymes(SS,SPS,VIN,CWIN)in subtending leaves response to water stress was not observed over different years and sampling dates.5.The soil drought stress led to the increase of antioxidant metabolites(POD,MDA and proline)in cotton boll subtending leaves,and decreased the concentration of soluble protein during fiber elongation phrase.there was a significant difference in response to water stress between the different genotypes with A001 being greater than A705,which further indicated that A001 was sensitive to drought stress,and A705 was tolerant to drought stress.Drought stress also led to decreased net photosynthetic rate,transpiration rate and stomatal conductance of the main stem leaf of the cotton.There was a little difference in photosynthesis response to water deficit between the different genotypes.