The Response Of Physiological Charcteristic To Nitrogen During Cotton (Gossypium Hirsutum L.) Fiber Thickening And Its Relaship With Fiber Formation

Fiber strength is an important criterion of cotton(Gossypium hirsutum L.) quality.The secondary wall thickening stage is a key period to cotton fiber strength formation.The biological synthesis and deposition patterns of cellulose synthesis within secondary wall thickening have a significant influence on fiber strength formation.As the genetic background is competently good,the environment ecological conditions show more important for fiber strength formation.Nitrogen is a limiting factor to produce high quality cotton fiber.The study on physiological mechanism of cellulose synthesis in cotton fiber to N rates has obvious implication for improving physiological ways to adjust fiber quality.In 2005 and 2006,field experiments were carried out in Nanjing(118°50′E,32°02′N,middle lower reaches of Yangtze River Valley) and three N rates 0 kgN·hm^-2,240 kgN·hm^-2,480 kgN·hm^-2,standing for low,optimum and high nitrogen application level respectively were applied,used two cultivars(AC-33B,average fiber strength is 32 cN·tex^-1;Kemian 1, average fiber strength is 35 cN·tex^-1.) as materials.The study focused on:(1) The responses of the related matters involved in cotton fiber thickening development and its relationship to fiber strength formation.(2) The responses of the related enzymes involved in cotton fiber thickening development and its relationship to fiber strength formation.(3) The responses of the gene expression of key enzymes involved in cotton fiber thickening development and its relationship to fiber strength formation.The main results were as follows:1.The response of related matters(sucrose andβ-1,3-glucan) involved in cotton fiber thickening development to nitrogen and its relationship with fiber strength formationThe dynamic changes of related matters involved in cotton fiber thickening development and its relationship with cellulose accumulation and fiber strength formation were studied.The results showed that compared with 0 kgN·hm^-2 and 480 kgN·hm^-2,under 240 kgN·hm^-2,the sucrose contents was much higher at 5^th day of boll age and much lower before boll opening,which resulted in higher sucrose transformed rates during whole boll age.During the period from 24^th day to 31^th day sucrose content increment much higher was found under 240 kgN·hm^-2.At the same time,it had a remarkable higher peak value inβ-1,3-glucan content at the beginning of secondary wall thickening and followed by a sharp drop.The total transformed rate ofβ-1,3-glucan in cotton fibers was the highest during whole boll age.The dynamic characteristics of sucrose andβ-1,3-glucan content in 240 kgN·hm^-2 level caused the cellulose accumulation to an optimized process:a longer period taking for cellulose speedy accumulation and a tempered rate in cellulose deposition.These were benefit to high strength fiber formation.The fiber strength had a period of quick increase from 17^th day to 31^th day and a stable increase from 31^th day to boll opening day.Finally the fiber strength was much higher.2.The response of related enzymes(sucrase,sucrose synthetase,sucrose phosphate synthetase andβ-1,3-glueanase) involved in cotton fiber thickening development to nitrogen and its relationship with fiber strength formationThe dynamic changes of related enzymes involved in cotton fiber thickening development and its relationship with cellulose accumulation and fiber strength formation were studied.The results showed that compared with 0 kgN·hm^-2 and 480 kgN·hm^-2,under 240 kgN·hm^-2,the sucrase activity was the highest,which bring abundant energy for cellulose accumulation in a long time.The Sucrose synthetase and sucrose phosphate synthetase presented the highest activities,which could produce more UDPG for cellulose accumulation in a slow speed and a long time.Theβ-1,3-glucanase activity was highest, which madeβ-1,3-glucan transformation rate high.These could optimize cellulose accumulation speed and make it more temper.So under 240 kgN·hm^-2,the changes of which talked above could result in a longer period and more tempered cellulose accumulation process,which was benefit to higher strength fiber formation.The fiber strength had a period of quick increase from 17^th day to 31^th day and a stable increase from 31^th day to boll opening day.Finally the fiber strength was much higher.3.The response of gene expression of key enzymes(sucrose synthetase andβ-1, 3-glueanase) involved in cotton fiber thickening development to nitrogen and its relationship with fiber strength formationThe dynamic changes of related matters involved in cotton fiber thickening development and its relationship with cellulose accumulation and fiber strength formation were studied.The results showed that compared with 0 kgN·hm^-2,under 240 kgN·hm^-2 the expression dynamic of sucrose synthetase gene was very high.It could laste a long time and stable.These benefited to produce more UDPG and to keep on a stabilization produce speed.Theβ-1,3-glucanase gene expression was highest after the 15^th DPA(day post anthesis).This could translate non-cellulose matters to UDPG and temper the speed of cellulose accumulation.The expression of Expansin was high and stable,which benefited to fiber thickening development.Under 240 kgN·hm^-2 the characteristics of sucrose synthase,β-1,3-glucanase and Expansin,which play very important roles in developing cotton fiber,were benefit to a longer time of cellulose accumulation and a gentler speed cellulose accumulation.The fiber strength had a period of quick increase from 17^th day to 31^th day and a stable increase from 31^th day to boll opening day.Finally the cotton fiber strength formation was much higher.