Genotypic Differences In Seeds And Fibers Carbon Metabolism Of Cotton Differring In Lint Percentage

Cotton is grown commercially in the Yellow River basin,the Yangtze River and the Inland Northwest,China.Recently,the cotton planting area of the Yellow River and the Yangtze River Basin have been reduced greatly.On the premise of limited cultivated land,increasing the yield and quality of cotton continues to be the focus of cotton production and research.Lint percentage is an important cotton lint yield component.Mordern cotton cultivars are characterized by high lint percentage,which depends on the carbohydrates partitioning between fibers and seeds.Therefore,it is of great significance to investigate the development and establishment of seed sink and fiber sink and their interaction,which will shed light on breeding of cotton varieties with high lint percentage,and reveal the regulation mechanism responsible for carbon allocation between the fiber and seed sinks,and provide deep insights on cotton developmental biology.Two high quality upland cotton lines A201 and A705 differing in lint percentage were employed in this research,which have been bred by ourselves and selfed for a couple of generations prior to their usage.The two lines were planted in the experimental station of Jiangxi Agricultural University(JXAU)across 2015 to 2017.On the commence of peak flowering white flowers from the proximal positions on middle fruiting branches were labeled.Samples(bolls and their subtending sympodial leaves)were taken periodically during a period of 5days post anthesis(DPA)to 45 DPA.The following physiological and biochemical variables were assayed including nonstructural carbohydrates(glucose,fructose,sucrose,starch,etc.),biopolymers(cellulose,fat,etc.),key carbon metabolism enzymes activity(invertase,sucrose synthetase,sucrose phosphate synthetase),etc.The objectives of this research were to i)investigate the expression profile of carbon metabolism enzymes effects on the development and establishment of the seed and fiber sink and its relationship of lint percentage development;ii)disclose the interaction mechanism between the seed and fiber sinks and the synergistic regulation mechanism of carbon metabolism enzymes.The main results are as follows:1.A201 had higher boll weight,seed mass per boll and seed index than A705,but lower lint mass per boll,lint index and lint percentage than A705,indicating a larger seed sink strength with the former and a smaller fiber sink strength with the latter.There was a greater fiber initial densitity at 1 DPA in the ovule epidermis of A705 than in those of A201 indicating a larger fiber sink volume with the former.A201 embryos accumulated more oil than A705 embryos at mature.Moreover,A201 exhibited a higher cotyledon thickness than A705 at 20 DPA and 25 DPA indicating a greater seed sink volume with the former.A201 expressed more superior fiber quality than A705 but not statistically significant.2.During the period of fiber growth A705 had lower and higher hexose concentrations infibers than A201 at early stage(? 24 DPA days post anthesis)and mid-late stage(?31DPA),respectively.Sucrose concentration in fibers was higher in A705 than in A201,but the opposition was observed for starch concentration.A705 fibers expressed lower vacuolar invertase(VIN)and cell wall invertase(CWIN)activities at early-mid stage(?31 DPA)relative to A201 fibers,but no difference at late stage(?38DPA).There was a greater sucrose synthase(SS)activity in A705 fibers than in A201 fibers.Sucrose phosphate sucrose(SPS)activity was higher at early-mid stage and lower at late stage in A705 fibers compared to A201 fibers,respectively.The above results indicated that A705 fibers exhibited greater sucrose and hexose concentrations and SS activity,and then led to higher sink activity in cellulose accumulation at mid-late stage in comparison with A201.3.During the period of ovule development A201 ovules had lower hexose concentration at early stage(?17 DPA),but higher at mid-late stage(?31DPA)compared to A705 ovules.There was a consistent higher sucrose concentration in the ovule at early stage and the embryo at mid-late stage with A201 relative to A705.The ovule starch concentration was higher at early stage(?17 DPA)in A201 than in 705,but lower at embryo maturity(45DPA).Higher sucrose concentration in seed coats at mid-late stage was documented in A201 compared with A705,but the reverse was true of starch concentration.A201 expressed lower VIN and CWIN activities in ovules at early-mid stage(?24 DPA)than A705,but no difference at late stage.A201 exhibited a higher SS activity in ovules at early stage(?17 DPA)and in embryos at mid-late stage than A705,respectively.Lower VIN,CWIN and SPS activities and higher SS activity in seed coats were found in A201 relative to A705 at mid-late stage,respectively.The above results indicated that A201 ovules exhibited greater sucrose and hexose concentrations and SS activity,and then led to higher sink activity in fat(main component in embryos)accumulation at mid-late stage in comparison with A705.In conclusion,higher lint percentage in A705 could be attributed to the larger fiber sink strength in collaboration with the smaller seed sink strength relative to A201.