甘薯耐低钾性形成的机制研究

Sweetpotato is a typical ‘potassium-preferred’crop, its growth and development, as well as the yield and quality formation processes, are closely related to the soil potassium supply. However,in China, potassium deficiency（namely low potassium）in soils exists commonly in sweetpotato-growing areas, especially in the middle and lower reaches of the Yangtze river,southern China and neighboring areas. Therefore, it is a key way to realize the good quality and high yield of sweetpotato by improving its tolerance to low potassium. At present, less attention have been paid to the mechanism of the low-potassium tolerance formation in sweetpotato. In view of the scientific problem, this study choose two representative sweetpotato cultivars with different capacity of low potassium deficiency tolerance, by combining the methods of nutrient solution culture and field experiment (long-term located fertilizer experiment). This research will focus its aim on the relationship between the physiological metabolism characteristics and the tolerance to low potassium in sweetpotato roots and leaves, by comparing the changes of different potassium treatment on antioxidant system functions, leaf photosynthesis, root-leaf morphology, plant hormone level and functional expression of related potassium channel gene in different sweetpotato genotypes. Meantime, this research will also investigate the effects of exogenous hormones on the low-potassium tolerance formation in sweetpotato and analyze their causing reasons. Thus, this research will elucidate systematically the physiological and molecular mechanisms on the low-potassium tolerance formation of sweetpotato, and the findings would be helpful for developing effective techniques to alleviate the lack of potassium resources and improving the yield and quality of sweetpotato in China.

甘薯是典型“喜钾”作物，其生长发育及产量品质形成等过程与土壤钾供应状况均存在密切联系。鉴于中国土壤钾缺乏（即低钾）现象十分普遍，采用科学手段提高甘薯自身耐低钾性是实现甘薯优质高产的关键途径。针对目前国内外关于甘薯耐低钾性形成的机制研究尚不明朗这一现状，本研究选择耐低钾性差异较大的2个关键甘薯品种(高耐低钾性徐薯32和低耐低钾性宁紫薯1)为材料，以根叶为切入点，以作物生理学、分子生物学等为手段，利用营养液培养和大田试验（长期定位试验田）相结合的方式，通过研究不同钾处理对不同基因型甘薯的抗氧化系统功能、光合性能、根叶形态结构、激素水平及相关钾离子通道蛋白基因表达等影响，明确甘薯生理代谢特征与耐低钾能力差异形成的关系；全面解析甘薯耐低钾性差异形成的生理及分子机制，研究低钾条件下外源激素调节甘薯耐低钾性形成的作用及其内在原因，从而为缓解我国钾素资源缺乏、提升甘薯产量与品质提供理论依据。

以徐薯32（高耐低钾）与宁紫薯1（低耐低钾）为材料，利用水培与大田试验（长期定位试验）相结合的方式开展相关研究，主要研究结论：1) 低钾下，徐薯32根系数目、根体系、长度及根系活力等显著高于宁紫薯1号，根系形态差异是甘薯耐低钾能力差异形成的重要原因；低钾处理28d后，宁紫薯1号叶绿素含量显著降低59.8%，Pn、Gs和Tr分别显著下降了59.7%、62.3%和66.0%，徐薯32的叶绿素含量仅降低27.4%，Pn、Gs和Tr的下降率均明显低于宁紫薯1号；宁紫薯1号根系MDA含量显著增加，诱导了SOD、POD和CAT等抗氧化酶活性的显著提高，而徐薯32的MDA水平和抗氧化酶活性显著低于宁紫薯1号，保持了相对稳定的生理功能。2) 低钾处理14天后甘薯苗叶面喷施外源IAA、ABA和GA3发现，IAA和ABA可有效提高叶片中抗氧化酶活性，以及叶绿素含量和净光合速率，降低脂质过氧化水平；IAA和ABA的施用增加了根系活力，减轻根尖细胞超微结构的损伤，显著增加干重、K+含量和K+积累量，表明外源IAA和ABA可作为提高甘薯耐低钾能力的潜在工具。3) 转录组测序共获得14-16Gb的clean bases；低钾处理前后，徐薯32差异表达基因为3259个，宁紫1号差异表达基因为3201个；徐薯32差异表达基因多集中在离子转运体、二级信号传导途径和钙离子传导途径相关基因中，宁紫1号差异基因多集中在非生物胁迫相关基因中。利用甘薯基因组信息，分离得到4个HKT基因家族成员，并对这些家族成员进行了基因结构、亚细胞定位、跨膜结构、系统进化树、表达模式分析，4个HKT蛋白都定位在质膜上，具有6-7个不等的跨膜区；IbHKT基因家族成员分布在甘薯的第3号染色体上；PCR分析表明IbHKT基因受低钾胁迫诱导表达，但诱导程度在不同耐低钾性的甘薯品种间存在差异。4) 克隆得到一个甘薯钾离子转运体IbHKT-like基因，其序列全长为1647bp，编码548个氨基酸，有两个TrkH保守结构域，10个跨膜片段；主要定位在细胞质膜，在叶绿体中存在少量分布；叶中表达量最高；其表达水平受到低温、干旱、高盐及过氧化氢诱导表达，说明IbHKT-like基因可能在甘薯抵御非生物胁迫中发挥着重要的作用。