木薯块根蔗糖卸载及淀粉合成对摘叶减源的响应机制

Reducing the amount of crop source to get a reasonable ratio of source to sink is an important strategy for high-yielding cultivation. With indeterminate growth habit of cassava, and the leaf number has been increased up to 130~200 in the growth period. The upper leaves of plant are the main function leaves for cassava, while the lower leaves are easy to cause the shade and consume nutrients. Experimental results showed that when the leaves number of cassava retained less than 45, the growth. morphogenesis, material production, yield and starch accumulation of cassava were significantly effected by leaf-cutting. Therefore, photosynthetic production, starch synthesis, and allocation and unloading of sucrose of cassava have inevitable science relation with the retained leaf number, but the response mechanism has not been reported now. In this study, using different types of cassava varieties as experiment material, with no-leaf-cutting as control treatment, cutting a different number of leaf number to establish three mode of source deficit, source / sink coordination and adequate source, focuses on the analysis the effects of sucrose and starch content in different parts and different stages of cassava, and the activity difference of tuber sucrose unloading enzymes and starch synthase by leaf-cutting, and reveal difference of sucrose transporter gene expression in root tuber in different treatments of mode, so as to reveal the response mechanism of starch synthesis and sucrose unloading to leaf-cutting, provide a theoretical basis for the high-yielding cultivation of cassava.

适量减源可调控作物合理的源/库比，是高产栽培的重要策略。木薯具有无限生长习性，生育期内叶片数一直增加，可达130~200片。植株上部叶片是木薯的主要功能叶，而下部叶片既容易造成荫蔽，又容易消耗养分。试验研究表明，当木薯保留的叶片数低于45片时，摘叶对木薯生长发育、形态建成、物质生产、产量形成和淀粉累积均有显著影响。由此可见，木薯光合生产能力、淀粉合成以及蔗糖的分配和卸载与保留的叶片数有着必然的科学关系，而其响应机制尚未见报道。本研究以不同株型木薯品种为试验材料，以不摘叶为对照，通过采摘不同数量的叶片数，建立源亏缺型、源/库协调型和源充足型等三种源-库模式，重点研究摘叶对木薯不同生育时期不同部位蔗糖含量和淀粉含量、块根蔗糖卸载酶活性和淀粉合成酶活性的影响，并检测不同源-库模式块根蔗糖转运载体的基因表达差异，从而揭示蔗糖卸载及淀粉合成对摘叶减源的响应机制。

木薯具有无限生长习性，全生育期叶片一直不断生长，数量持续增加。叶片是木薯光合作用的主要器官，与物质生产、养分吸收和产量形成有密切关系。试验设计不同株型木薯品种和留叶数处理，分析了摘叶对生长发育、产量形成、养分特性和生理特征的影响，以期明确了块根蔗糖卸载、块根淀粉合成、养分积累分配和产量形成对摘叶的响应机制。随着留叶数增多，单株总摘叶数和摘叶的氮、磷、钾素积累量随之下降，单株鲜薯产量随之显著增加，成熟期全株和全生育期植株的氮、磷、钾素积累量随之呈显著增加或“单峰”或“双峰”趋势。紧凑型品种摘叶的氮素积累量较伞型品种降低了4.56%，而磷、钾素积累量较伞型品种分别提高了10.2%、10.0%。紧凑型品种成熟期全株的氮、磷、钾素积累量较伞型品种分别提高了31.0%、42.5%和50.9%。在成熟期，随着留叶数增多，在块根和叶片中的氮、磷、钾素分配率随之提高，而在茎秆中的氮、磷、钾素分配率随之下降，氮、磷、钾素收获指数随之呈增加或“单峰”趋势。随着留叶数增加，淀粉卸载基因SUC4和SUC4like相对表达量随之增加，SUC2like随之下降，SUC3随之先增后降；块根SSS活性随之增加，而SBE、SPS、CWI和SS活性随之下降；叶片可溶性总糖含量随之增加，蔗糖和总淀粉含量随之先增后降。紧凑型品种SUC2like和SUC3相对表达量、SSS、SPS、CWI和SS活性、Fm和Fv/Fm均高于伞型品种，而SUC4和SUC4like相对表达量、SBE活性和F0低于伞型品种。木薯留叶数越多，摘叶时期越晚，摘叶的数量和干物质量越少。随着留叶数增加，木薯产量随之增加，成熟期全株的养分积累量和块根、叶片的养分分配率随之提高。木薯摘叶后，叶片光合产物优先满足地上部生长。木薯块根膨大期适宜的留叶数为81~90片，有利于确保木薯产量和养分积累利用，同时为病虫害防控和旱情危害提出预警。