Effects Of Combined Elevated Temperature And Soil Waterlogging During Flowering And Boll Formation Stage On Physiological And Molecular Mechanisms Of Cotton Fiber Development

Driven largely by anthropogenic greenhouse gas emissions,average air temperature increases of 2-4? are expected in the coming decades.With the intensification of the warming effect,the probability of the regional extreme precipitation increases,and the flood disaster is becoming more and more frequent all over the world.Summer high temperature is often accompanied by waterlogging events in the Yangtze River valley,which usually occurres during the cotton flowering and boll formation period.While this period is the most critical for cotton production and fiber qualities formation,cotton is more sensitive to external adversity.In this paper,the co-effects of elevated temperature and waterlogging on the yield and fiber quality of cotton were studied.The experiment was carried out at the Pailou Experimental Station(118 ° 50'E,32 ° 02'N)of Nanjing Agricultural University from 2013 to 2015.Experimental treatments during flowering and boll development stages were:(a)ambient temperature(A=31.6/26.5?)with a well-watered control(AC);(b)3 and 6 day soil waterlogging treatments under 31.6/26.5?(AW3,AW6);(c)elevated temperature(E=34.1/29.0?)plus a well-watered control(EC)and(d)3 and 6 days soil waterlogging treatments under 34.1/29.0?(EW3 and EW6).The current study mainly focued on the co-effects of waterlogging and elevated temperature on cotton yield and fiber qualities,which revealed the physiological and molecular mechanisms of how the combined two stresses affect fiber elongation and fiber secondary cell thickening from the aspects of fiber related substances,related enzyme activities,key gene expression and proteomics based on the fiber developmental features.The main results are as follows:1.Co-effects of elevated temperature and soil waterlogging on the cotton yield and cotton fiber quality formationThe results showed that:(1)under elevated temperature treatment,the cotton boll weight and the lint percentage were significantly decreased,and there were inter-annual differences in the number of bolls and seed cotton yield;The cotton bolls numbers and seed-cotton yield in 2013 were significantly lower for EC compared with control,while number of cotton bolls was higher than those in the control in 2014 and 2015,which led to higher seed-cotton yield relative to control.Waterlogging treatment significantly reduced cotton boll numbers,bolls weight,lint percentage and seed cotton yield among the three experimental years.(2)Among the three production factors,the number of bolls is the most sensitive to combined elevated temperature and waterlogging,which is the main factor causing the differences on seed-cotton yield.There was a significant coupling effect between elevated temperature and waterlogging on the number of bolls,boll weight and seed-cotton yield,while the coupling effect was not significant on lint percentage.In the year with high temperature(2013),there elevated temperature exacerbated the negative impact of waterlogging on cotton boll numbers,which resulted in lower yield of seed-cotton yield under combined two stresses than under either single stress.In low temperature years(2014,2015),the elevated temperature can increase the number of bolls to alleviate the reduction of seed-cotton yield under 3 days of soil waterlogging(3)The cotton fiber length under elevated temperature was decreased about 0.7%-5.6%,but the fiber strength and the micronaire value was increased,while the fiber length,strength were decreased and micronaire value was increased under waterlogging.There was a significant or very significant coupling effect on the fiber length and strength in the upper and middle branches of cotton,and the coupling effect on micronaire was not significant in neither branches.2.Co-effects of elevated temperature and soil waterlogging on the cotton fiber length formation.In the current study,the co-effect of elevated temperature(ET)and soil waterlogging(SW)more negatively decreased final fiber length(reduced by 5.4%-11.3%)than either stress alone by altering the composition of osmotically active solutes(sucrose,malate,and K+),where SW had the most pronounced effect.High temperature accelerated early fiber development,but limited the duration of elongation,thereby limiting final fiber length.Treatment of ET alone altered fiber sucrose content mainly through decreased source strength and the expression of the sucrose transporter gene GhSUT-1,making sucrose availability the primary determinant of final fiber length under ET.Waterlogging stress alone decreased source strength,down-regulated GhSUT-1 expression and enhanced SuSy catalytic activity for sucrose reduction.Waterlogging treatment alone also limited fiber malate production by down-regulating GhPEPC-1&-2.However,combined elevated temperature and waterlogging limited primary cell wall synthesis by affecting GhCESAs genes and showed a negative impact on all three major osmotic solutes through the regulation of GhSUT-1,GhPEPC-1&-2 and GhKT-1 expression and altered SuSy activity,which functioned together to produce a shorter fiber length.3.Co-effects of elevated temperature and soil waterlogging on the cotton fiber cellulose synthesis.Soil waterlogging events and elevated temperature conditions occured frequently in the Yangtze River Valley,yet the effects of these co-occurring stresses on fiber development have received little attention.In this study,combined elevated temperature(34.1/29.0?)and soil waterlogging(3,6 days)on fiber cellulose synthesis was investigated during flowering and boll development.The coupling of elevated temperature(ET)and soil waterlogging(SW)more negatively impacted final cellulose content(reduced by 9.5%-27.5%)than either stress individually,and the effect of SW alone was greater than ET alone(34.1/29.0?).Treatment of ET alone mainly limited cellulose synthesis by decreasing activities of sucrose degrading enzymes,especially sucrose synthase.The combination of ET and SW disrupted deposition of sucrose and cellulose but increased the callose content of developing fibers.Increased sucrose synthase(SuSy)activity was the dominant factor influencing sucrose degradation in the fiber under the combination of ET and SW.Both sucrose phosphate synthase(SPS)and acid/alkaline Invertase activities were decreased under combined stresses of ET and SW and SPS was the most sensitive to the aforementioned stresses.GhSuSy-A and GhSPS-1 were the key gene isoforms closely associated with fiber sucrose metabolism under combined stresses.Co-occurring elevated temperature and waterlogging stresses highly up-regulated GhCalS-5 and ?-1,3-glucanase expression levels,which led to increased fiber callose content.Thus,we concluded that concomitant exposure to elevated temperature and waterlogging limited cellulose synthesis not only by lowering sucrose metabolism enzyme activities but also by favoring the conversion of UDPG to callose rather than cellulose.4.Co-effects of elevated temperature and soil waterlogging on the cotton fiber proteomics research.In this study,we used the iTRAQ technique to study the expression profiles of protein in cotton fiber under elevated temperature,waterlogging and the combined teo stresses,which showed that 113,263 and 290 differential proteins related to fiber development were identified respectively.Among them,there were 59 up-regulated proteins and 54 down-regulated proteins under the elevated temperature treatment.There were 127 up-regulated proteins and 136 down-regulated proteins under waterlogging treatment.Total of 137 up-regulated proteins and 153 down-regulated treatments protein were identified in the study.The proteins can be classified as:carbohydrate and energy metabolism(22.4%),protein metabolism(16.1%),amino acid metabolism(12.2%),intracellular structural components(9.6%),transport(7.2%),oxidation-reduction process(7.2%),signal transduction(6.0%),lipid metabolism(5.1%),stress response(5.1%),nucleic acid metabolism(4.5%),organic acid metabolism(3.0%),other(1.8%).Proteins participated in carbohydrate/energy metabolism,such as sucrose synthase and other significant up regulated proteins involved in the regulation of substances such as PEPCase metabolism of down-regulated expression,which are not conducive to the development of cotton fiber elongation.We concluded that the fiber cell elongation and secondary wall thickening were inhibited mainly due to the compressed accumulation of osmolytes substances,the blocked secondary wall substance synthesis and transport and the disordered cytoskeleton protein system.