Effects Of Elevated Temperature During Flowering And Boll Formation Stage On Physiological Mechanisms Of Cotton Leaves And Fiber

A global air temperature increase of 1.8-4.0℃ is predicted for 2100 as a result of climate change.Cotton(Gossypium hirsutum L.),one of the most important fiber crop across the world,was originated in the tropics,but it’s not necessary to be in a good quality and yield when grown under elevated temperature regime.To understand the implications of high temperature caused by global warming on cotton production,field experiments with ambient temperature regime and elevated temperature regime(ambient temperature plus 2-3 ℃ in 24h during flowering and boll formation stages)were carried out by using two cotton cultivars(Simian 3,conventional and non-hybrid cotton;Siza 3,hybrid Cotton)during 2010-2012 in Nanjing(118°50′E,32°02′N),China.The main results were as follows:1.Effect of elevated temperature on plant source-sink metabolism and yield in cotton during flowering and boll formation stage(1)Elevated temperature significantly decreased net photosynthetic rate(Pn)in leaf subtending to cotton boll(LSCB),but the decrease of Pn in the youngest fully expanded main-stem leaf(MSL)was not significant.Under elevated temperature,soluble sugar content and amino content in MSL were significant lower than those under ambient temperature during 10-17 DAT,but differences were insignificant during 24-31 DAT.Elevated temperature also decreased soluble sugar content and amino content in LSCB and the effects didn’t weaken with DAT.Shedding rates of squares and bolls were higher,number of bolls per plant were lower than those under ambient temperature before 17 DAT,but the trendy were opposite after 24 DAT.Elevated temperature decreased boll weight,lint percentage and seed index as a result of Pn inhibition of LSCB.Simultaneously,elevated temperature was advantageous to fiber strength,but disadvantageous to fiber length and micronaire.The results also showed that elevated temperature increased lint yield per plant in 2011 and 2012,but decreased it in 2010,indicating that elevated temperature based on higher temperature level was unfavorable for cotton yield.(2)Under elevated temperature regime,the yield distribution rate and boll number of fruiting position 3 and above 3 increased,but the photosynthesis of the leaf subtending to cotton boll on fruiting position 3 was inhibited by elevated temperature,which led to decreased boll weight.Besides,more carbon source produced by the leaf subtending to cotton boll on fruiting position 3 was used to supply for seed and shell development,thus lint percentage of fruiting position 3 was lower than those of fruiting position 1,and elevated temperature had a negative effect of lint percentage.The effect of elevated temperature on cotton fiber of fruiting position 3 was different from that on fruiting position 1.Under elevated temperature,sucrose content and callose content in cotton fiber on fruiting position 3 were lower than under ambient temperature,but cellulose content was higher.In addition,fiber length of fruiting position 3 under elevated temperature was slight higher than under ambient temperature.Elevated temperature during flowering and boll formation was beneficial fiber strength and micronaire of fruiting position 3.2.Elevated temperature effects on sucrose metabolism in the youngest fully expanded main-stem leaf and leaf subtending to cotton boll during flowering and boll formation stageEffects of elevated temperature on MSL depended on days after treatment(DAT).Under elevated temperature,specific leaf weight and starch content in MSL were significant higher and sucrose content was significant lower than under ambient temperature during 10-17 DAT,but those differences were insignificant during 24-31 DAT.Activities of sucrose phosphate synthase(SPS)displayed contrary tendency under elevated temperature during 10-17 DAT and 24-31 DAT,indicating that changes of photosynthate distribution in MSL were due to SPS activity.MSL collected during 24-31 DAT had adapted to elevated temperature,but LSCB collected during 24-31 DAT were sensitive to elevated temperature.Elevated temperature limited activities of Rubisco,cy-FBPase,sucrose synthase and SPS in LSCB.Elevated temperature decreased sucrose content but increased starch content in LSCB.cy-FBPase was the key enzyme contributing to changes of photosynthate distribution in LSCB.These results suggested that temperatures elevated were unfriendly to photosynthate distribution and sucrose metabolism in LSCB.3.Effects of elevated temperature during flowing and boll formation stage on cotton fiber elongationThe sensitivity of fiber elongation responding to elevated temperature decreased with days post anthesis(DPA).During 5-10 DPA,the activities of H+-ATPase(V-ATPase)and phosphoenolpyruvate carboxylase(PEPC)and the expression levels of GhXTH1 and GhXTH2 under elevated temperature were higher than those under ambient temperature,which led to a faster rate of fiber elongation and a longer fiber length during 5-15 DPA.However,the reduced activities of V-ATPase,PEPC,sucrose synthase and vacuolar invertase and down-regulated expression of V-ATPase,Expansin,GhPEPCs,GhVINVs,GhXTHs,SusA and SusD under elevated temperature after 15 DPA played negative roles in maintaining certain fiber rapid-elongation duration(FRED)and fiber elongation duration(FED),which resulted in a shorter fiber length after 17 DPA under elevated temperature compared with those grown under ambient temperature,and the shortened FRED and FED were main reasons for shorter fiber at boll opening.Besides,FRED and FED had significant negative correlations with mean nighttime air temperature(Tnight)and the hours of temperature>32℃ per day,which indicates that,with global warming in the future,high Tnight and prolonged high daytime temperature(>32°)were unfavorable factors for fiber elongation and fiber length.4.Effect of elevated temperature on sucrose metabolism and cellulose synthesis in cotton fiber during secondary wall developmentCompared with that under 30.1/25.8℃,cotton fiber callose content under 32.6/28.6℃increased,and the value-added of callose content was gradually smaller with days post anthesis(DPA).Sucrose content and cellulose content under 32.6/28.6℃ were lower than those under 30.1/25.8℃,and the reductions of sucrose content and cellulose content were greater at 17 DPA than those during 24 DPA to boll opening.This indicated that the effects of elevated temperature on both sucrose metabolism and cellulose synthesis were gradually smaller with DPA.Besides,under 32.6/28.6℃,measurable activities of sucrose synthase and acid/alkaline invertase in sucrose catabolism decreased,but sucrose phosphate synthase activity in fiber sucrose synthesis increased.It suggested that the restrained sucrose metabolism and cellulose synthesis under 32.6/28.6℃ were mainly attributed to the changed activities of sucrose synthase and invertase.