荔枝白坚木皮醇的分布与运输特点、生物学性质及代谢机制探索

Litchi is a Sapindaceae subtropical fruit crop which native to southern China. China has the highest litchi planting area and production in the world. However, the photosynthetic products and carobohydrate transportation form in litchi are poorly documented. Our research group identified abundant quebrachitol in leave and phloem of litchi. Higher quebrachitol than sucrose was detected in leave and phloem of litchi, and the concentrations of quebrachitol increased with leaf development and maturation. These results suggested that in addition to sucrose quebrachitol might be one of the photopsynthetic products which was transported in phloem of litchi. In the present subject, litchi will be used as material. Radiocarbon feeding and carborhydrate component analysis of phloem sap will be employed to clearify whether quebrachitol is one of the main photosynthetic products and is transported in the phloem of litchi. And subsequantly the metabolism of quebrachitol will be investigated through physiological, biochemical and molecular biological methods combining with manipulation treatments. And furthermore the effect of environment factors and management practices on quebrachitol metabolism and the physiological response of quebrachitol synthesis maniputation will also be investigated. Hopefully, the research results will establish solid basis for the forms of photosynthetic products and the mechansim of phloem carbohydrate transportation for litchi even for other Sapindaceae plants, and also provide important evidence for the metabolism pathway of quebrachitol in plants.

荔枝是原产我国的无患子科亚热带常绿果树，种植面积和产量居世界首位。然而，至今为止尚无关于荔枝光合作用产物和产物韧皮部运输形态的报道。项目组在荔枝的叶片和韧皮部中检测到含量甚至高于蔗糖的白坚木皮醇，而且含量随着叶片的发育成熟逐渐增加，这结果说明在荔枝中除蔗糖以外，白坚木皮醇可能也作为光合产物之一，参与了产物的韧皮部运输。本项目以荔枝为试材，利用C同位素饲喂和韧皮部汁液碳水化合物组分测定等实验，在确定白坚木皮醇作为荔枝光合主要产物之一参与韧皮部碳水化合物运输的的基础上，运用生理生化和分子生物学等研究手段结合外源的调控措施，深入探讨荔枝白坚木皮醇生物合成和转化的生理机制，同时探索环境因素和栽培措施对白坚木皮醇代谢的影响,了解白坚木皮醇代谢异常的生物学效应，研究结果将为深入揭示荔枝乃至无患子科植物光合产物和产物韧皮部运输形态奠定扎实的基础，为白坚木皮醇在植物体内的代谢途径的阐明提供重要的参考。

荔枝是原产我国的无患子科亚热带常绿果树,本项目组针对前期在荔枝的叶片和韧皮部中检测到丰富白坚木皮醇的特点，运用高效液相色谱、气质连用、核磁共振、同位素示踪以及分子生物研究等技术和方法进行分析，发现白坚木皮醇是荔枝光合主要产物和韧皮部碳水化合物运输的主要形式，合成相对惰性的可溶性碳水化合物—白坚木皮醇是大型木本荔枝低耗、节能和高抗生物胁迫的碳素代谢策略；白坚木皮醇的生物合成涉及了由LcIMT1催化肌醇的甲基化形成肌醇甲醚中间体Bornesitol。研究首次揭示了荔枝特异合成白坚木皮醇的生物学意义和生物合成途径，并探讨了荔枝白坚木皮醇进一步代谢的途径，获得了荔枝特异合成白坚木皮醇可能与其丰富的酚类物质存在内在联系的创新性结果，该研究为多元醇在植物的代谢和转运机制提供重要的理论依据，充实了果树碳素营养分子生理知识。