Differences Of Carbon Metabolism And Starch Remobilization In Stems And Roots In Cotton With Different Growth Period

Cotton,is widely planted as an important fiber crop around the world.There are still some doubts over the occurrence of remobilization of carbonhydrate storage in roots and stems before anthesis.It remains unclear whether there is an association between carbon remobilization and cotton yield.Two Near Isogenic lines 4003-6 and 4003-10 share the same genetic background but have diverse growth period with 4003-6 being mid-season and 4003-10 being short season.They were employed to investigate the dynamics of phostosynthesis,biomass accumulation,carbohydrate content and carbon metabolism related enzyme activities in roots and stems.The photosynthesis parameters were measured and the whole plant was sampled over different growth l periods includings peak budding,early flowering,peak flowering,peak fruitingl andboll open.Dry samples of roots,stems(below cotyledons)and fruit branches were used to determine the concentration and content of non-structure carbohydrates(NSC including sucrose,hexose,starch).Fresh samples of roots and stems(below cotyledons)were used to determine the key enzymes of sucrose metabolism(sucrose synthase SS,sucrose phosphate synthase SPS,vacuole invertase VIN,cell wall invertase CWIN)and starch metabolism(α-amylase;β-amylase;starch synthase StS;adenosine diphosphate glucose pyrophosphatase AGPase).The main research results are as follows:1.In 2018 and 2019,the lint yield and seed cotton yield per hectare in 4003-6 were significantly higher than those in 4003-10,and the yield traits such assingle boll fiber weight,lint percentage,coat index,and seed index were all higher than thoset in 4003-10.Fiber qualitythe average length of the upper half of the fiber and micronaire value are higher in 4003-6 than 4003-10.2.The changes of dry matter accumulation in the root system,shoot,vegetative growth,and reproductive growth of the two lines were well fit into the Logistic growth curve.During the two years,the rapid accumulation duration and maximum accumulation rate of vegetative growth and reproductive growth in 4003-6 were all greater than those in4003-10.3.The concentrations of hexose,starch and non structural total carbon in root and lower part of main stem decreased from full bloom to full boll.The amount of starch transport was positive from the first flowering stage to the full boll stage,which indicated that starch decomposition occurred during this period.The concentration of starch,sucrose and non structural total carbon in root system of 4003-10 was higher than that of 4003-6,and the concentration of starch in the lower part of main stem of 4003-6 was higher than that of 4003-104.The activity of key enzymes of sucrose metabolism in roots and stems: 1)In roots,the activities of SPS,SS,and AI in 4003-10 were higher than those in 4003-6 before peak flowering.The SS and VIN activities of 4003-6 were higher from full blooming onwards..2)In the lower part of the main stem,the activities of sucrose synthesis and decomposition enzymes decreased during peak flowering to peak fluiting,and the activities of SPS and SS were much higher than that of AIe.5.Activities of key enzymes of starch metabolism inroots and stems: 1)In roots,4003-6 exhibited a higher α-amylase activity than 4003-10.;StS decreased sharply down to e peak flowering.The activity of AGPase decreased during the first flowering to full flowering.The starch concentration of 4003-10 was higher than that of 4003-6;2)In the lower part of the main stem,β-Amylase and α-Amylase decreased sharply down to peak flowering or boll open stage.StS had the highest activity in vegetative growth period,and the StS activity of 4003-6 was higher than that of 4003-10.The activity of AGPase in4003-6 was higher than that in 4003-10.The starch concentration in the lower part of the main stem of 4003-6 was higher than that of 4003-10.During the vigorous reproductive growth,cotton roots and stems expressed decreasing concentration and content of NSC.The result may be due to the decrease of NSC synthesis combined with the increase of NSC degradation during that period.The results unraveled the dynamics of NSC in roots and stems of cotton and genotypic difference between two lines differing in growth periodit,which can provide some theoretical basis for high-yield cultivation in cotton and enrich the biological content of cotton growth and development.