【作者】 许桂苹；

【导师】 邓超冰；

【作者基本信息】 广西大学 ， 制糖工程， 2019， 博士

【摘要】 糖料甘蔗制糖业是广西支柱产业,广西糖料甘蔗种植面积和产量位居全国首位,而重金属污染是广西突出的环境问题之一,重金属在甘蔗体的吸收累积直接影响甘蔗品质,甘蔗制糖食品的安全引起高度关注。本研究以广西主栽的糖料甘蔗“台优”为试验材料,采用土培盆栽试验,研究不同浓度Pb胁迫下,甘蔗对Pb吸收累积特性及Pb对甘蔗生长的影响,并从光合荧光特性、抗氧化系统方面探明甘蔗对Pb生理响应机制,从细胞水平和分子水平揭示甘蔗对Pb耐性和解毒机理,为培育高耐性低累积的甘蔗品种提供理论基础,对于指导甘蔗在重金属污染农用地安全生产具有重要意义。取得的主要研究结果如下(1)甘蔗属于Pb高耐受性植物,在各Pb胁迫浓度下能正常生长且未见明显表观毒害症状。甘蔗体内的Pb富集量为:根>叶>茎,甘蔗根系对Pb的累积显著高于其地上部分,Pb从甘蔗根系向茎和叶的转移能力较弱,甘蔗可食部分茎中Pb富集量最少。Pb对甘蔗生长有“低促高抑”作用,Pb胁迫浓度为250.0 mg/kg时可以促进甘蔗的生长,而Pb胁迫浓度为1250.0 mg/kg及以上时则显著限制了甘蔗的生长。甘蔗根系对Pb的固定和截留,限制Pb向地上部分转移,减轻Pb对甘蔗的毒害,是甘蔗对Pb的耐性机制之一。(2)低浓度Pb胁迫促进光合作用,有利于甘蔗生长,高浓度Pb阻碍光合作用,抑制甘蔗生长。甘蔗光合速率的下降,主要受气孔开度的影响。在高浓度Pb的胁迫下,气孔关闭可能是甘蔗减少Pb进入体内的一种保护机制。甘蔗受到一定浓度Pb胁迫时,增加了非光化学猝灭,甘蔗通过增加热耗散来减轻Pb胁迫,使得Pb对其光合细胞的毒害减弱;但当Pb胁迫浓度大于1250.0 mg/kg时,抑制了光系统Ⅱ(PSⅡ)反应中心的潜在活性及PSⅡ和PSⅠ间的电子传递,导致电子传递过程受到阻碍,影响光合作用,抑制甘蔗生长。(3)甘蔗通过调节超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)的活性来提高其对Pb的防御性能。随着Pb胁迫浓度的升高,甘蔗根和叶中的SOD、CAT和POD活性先升高后降低。在Pb胁迫浓度为1250.0 mg/kg及以下时,甘蔗中的SOD、CAT和POD活性显著升高,有效消除Pb胁迫时产生的大量活性氧和H2O2,减少Pb对甘蔗抗氧化系统的伤害;而在Pb胁迫浓度为2500.0 mg/kg时,甘蔗中的SOD和CAT活性显著下降,不能消除逆境胁迫时产生的大量活性氧和H2O2,甘蔗明显受到氧化胁迫的毒害。(4)低浓度Pb胁迫促进甘蔗对K、Ca和Mg等大量元素和Cu、Fe、Zn和Mn等微量元素的吸收,而高浓度的Pb胁迫则抑制了甘蔗对这些矿物质的吸收。甘蔗在低浓度Pb胁迫时,可能通过提高细胞内DK、Ca等矿物质元素阳离子浓度,缓解Pb对甘蔗的毒害,而在高浓度Pb胁迫时,Pb破坏甘蔗体内矿物质养分的动态平衡,引起甘蔗对矿物质养分吸收不足或不平衡,抑制甘蔗的生长。(5)Pb在甘蔗根和叶中的亚细胞分布为:细胞壁>细胞器>胞液,大部分Pb沉积在甘蔗根和叶的细胞壁中,甘蔗根和叶中的Pb化学提取形态主要以醋酸提取态和盐酸提取态为主。甘蔗通过Pb与细胞壁的结合以及将部分可溶态Pb转换成活性低的磷酸盐或草酸盐来减少Pb对自身的伤害,这是甘蔗主要的解毒和耐受机制之一。(6)甘蔗根中共有32238条差异表达基因,其中10544条差异基因表达上调,21694条差异基因表达下调;甘蔗叶片中共有6263条差异表达基因,其中2774条差异基因表达上调,3489条差异基因表达下调。通过对Pb胁迫下的甘蔗差异表达基因进行分析,发现甘蔗中有11种转运蛋白基因、17种硫代谢相关的基因及15种抗氧化酶基因过量表达,表明甘蔗在Pb胁迫下主要通过激活转运蛋白基因、抗氧化酶基因及硫代谢相关基因来进行防御和解毒。更多还原

【Abstract】 Sugarcane industry is a pillar industry in Guangxi.The planting area and yield of sugarcane rank first in China.However,heavy metal pollution is one of the prominent environmental problems in Guangxi.The absorption and accumulation of heavy metals in sugarcane directly affect the quality of sugarcane,so the safety of sugarcane food has aroused great concern.In this research,the sugarcane "taiyou" was used as the experimental material,and the pot experiment was adopted to study the Pb absorption and accumulation characteristics of sugarcane and the influence of Pb on the growth of sugarcane under the different concentrations of Pb.The physiological response mechanism of sugarcane on Pb was explored from photosynthetic fluorescence characteristics and antioxidant system,and the tolerance and detoxification mechanism of sugarcane on Pb was revealed at the cellular and molecular level.The research provides a theoretical basis for the cultivation of sugarcane varieties with high tolerance and low accumulation,and it is of great significance to guide the safe production of sugarcane in heavy metal contaminated agricultural land.The main research results are as follows:(1)As high Pb tolerance plant,sugarcane is observed grown normally without obvious toxic symptoms under all Pb stress condition.Within the body of sugarcane,the accumulation of Pb is shown as:root>leaves>stems.The accumulation in sugarcane root system is apparently higher than its above-ground parts.The mobilities of Pb from root to stem and leaves are identified relatively weak,and Pb concentration in edible sugarcane stems is the lowest.The phenomenon of "low to promote,high to inhibit" of Pb on sugarcane is identified:below the stress level of 250.0 mg/kg,Pb promotes the growth of sugarcane;on the level of 1250 mg/kg and above,the grow-th of sugarcane is inhibited.Pb is fixed and remained in sugarcane roots and the transferring to above-ground organs is restricted,so the toxic effect of Pb to sugarcane is reduced and it is believed one of its tolerance mechanisms.(2)Low concentrations of Pb enhance the effects of photosynthesis and thus strengthen the growth of sugarcane.High levels of Pb inhibit the effects of photosynthesis.Rates of photosynthesis decline as the opening of stoma is reduced.With high level Pb stressed,the closing of stoma could be a protective mechanism of sugarcane to reduce Pb entering the body.When sugarcane is under Pb stress,its non-photochemical quenching is increased.Sugarcane increases the thermal dissipation to weaken Pb stress,which reduces the toxic effects of Pb on photosynthesis in cells;When the stress level of Pb is over 1250.0 mg/kg,the potential activities of PS Ⅱ reaction centre and the transport of electrons between PS Ⅱ and PSI are inhibited.As a result,the electron transport process is hindered,which affects photosynthesis and inhibits the growth of sugarcane.(3)Sugarcane can improve its defensive performance against Pb by regulating the activities of superoxide dismutase(SOD)、catalase(CAT)and peroxidase(POD).The activities of SOD、CAT and POD in root and leaves of sugarcane increase first and then decrease as Pb stress level increase.When the stress level of Pb is lower than 1250.0 mg/kg,SOD、CAT and POD activities in sugarcane increase obviously,which can effectively eliminated large amount of active oxygen and H2O2 caused by Pb stress,and reduce Pb damage to antioxidant system of sugarcane;However,when Pb stress concentration is 2500.0 mg/kg,SOD and CAT activities in sugarcane decrease significantly,which can not eliminate a large amount of reactive oxygen and H2O2,and sugarcane is obviously poisoned by oxidative stress.(4)Low levels of Pb enhance the assimilations of macro-elements such as K,Ca and Mg and also micro-elements such as Cu,Fe,Zn and Mn by sugarcane,while high concentrations of Pb inhibit the assimilation of these minerals by sugarcane.When sugarcane is stressed by low Pb concentration,the toxicity of Pb to sugarcane may be alleviated by increasing the concentration of cationic ions such as K and Ca in cells.However,under high Pb stress,Pb destroys the dynamic balance of mineral nutrients in sugarcane,causing insufficient or unbalanced absorption of mineral nutrients in sugarcane and inhibiting the growth of sugarcane.(5)The subcellular distribution of Pb in the root and leaves of sugarcane is as follows:cell wall>organelle>soluble.Most of Pb is deposited in the cell walls of sugarcane roots and leaves,and the chemical extraction forms of Pb in sugarcane roots and leaves are dominated by acetic acid extraction and hydrochloric acid extraction.The sugarcane reduces Pb damage to itself by binding Pb to cell wall and converting partially soluble Pb into low activity phosphate or oxalate,which is one of the main detoxification and tolerance mechanisms of sugarcane.(6)There are 32238 differential genes in sugarcane root,of which 10544 are up-regulated and 21694 are down-regulated.In mesophyll cells,there are 6263 differential genes,of which 2774 are up-regulated,3498 are down-regulated.Through the analysis of differential genes in sugarcane under Pb stress,it is found that 11 transport proteins,17 genes related to sulfur metabolism and 15 antioxidant enzyme genes are excessive expressions in sugarcane.The results show that sugarcane mainly detoxified and defended against Pb stress by activating transporter gene,antioxidant enzyme gene and sulfur metabolism related gene.更多还原