心材化过程中木质部薄壁细胞代谢活性与心材成分生成机制

In order to reveal the changes of metabolic activity of xylem parenchyma cells, generating and transporting mechanism of heartwood extractives during the process of heartwood formation, the changes of the cell morphology and structure, cellular respiration and enzymatic activity of xylem parenchyma cells in the sapwood-transition zone-heartwood was focused firstly, and the relationship between parenchyma cells metabolic activity and live environment water and oxygen was also considered, so that the process and reason of metabolic activity decrease, even death of parenchyma cells was clarified during the transformation of sapwood into heartwood.Secondly, the structure of polyphenol compositions or their precursor of generating polyphenol substances, and the chemical reaction pathways of biosynthetic course of different phenolic compounds or precursors which generate different polyphenol constituents will be analyzed through the generation process of polyphenol compositions or the precursor of generating polyphenols in the parenchyma cells of sapwood-transition zone-heartwood. Thirdly, transport pathway of heartwood extractives generated from parenchyma cells exuded into adjacent wood tissues, heartwood especially away from transition zone will be investigated, based on the type and accumulation state of parenchyma cells among parenchyma cells, vessels and wood fiber of sapwood- transition zone-heartwood. The “metabolic activity of xylem parenchyma cells and the mechanism of heartwood extractives generating during heartwood formation” as advanced subject will be answered in this project, as well providing basis science reference for regulating and controlling heartwood formation by different ways, for example the artificial cultivation of “Hongmu” tree.

为了揭示心材形成过程中木质部薄壁细胞的代谢活性变化及心材成分生成和迁移机制，本研究首先聚焦边材-过渡区-心材木质部薄壁细胞形态、结构以及细胞呼吸作用、酶活性等变化，并结合薄壁细胞代谢活性与其生活环境水分、氧气等关系，明确边材转化为心材过程中薄壁细胞代谢活性减少直至死亡过程及原因。其次，透过边材-过渡区-心材薄壁细胞多酚类成分或生成多酚类物质的前驱体生成过程，分析多酚类成分或生成多酚类物质前驱体的结构，以及多酚类不同物质合成过程或其前驱体合成不同多酚物质的化学反应路径。最后，透过边材-过渡区-心材薄壁细胞与导管、木纤维心材成分的类型和蓄积状态，分析薄壁细胞生成心材成分向周围其它组织，特别是向远离心材成分生成区域的迁移规律。项目致力解答“心材化过程中木质部薄壁细胞代谢活性和心材成分生成机制”前沿课题，为多渠道调控心材形成、例如红木树种的人工培育提供基础科学依据。

木材心材具有耐腐、色深、纹理美观等优点，但关于心材形成机理知之甚少。为了揭示心材形成过程中木质部薄壁细胞的代谢活性变化及心材成分生成机制，重点选取南方珍贵树种降香黄檀作全面研究，同时，选择火力楠、大花序桉、白木香等乡土树种和引种速生树种作为对比，采用快速冷冻、木材超微解剖、组织化学、化学成分分析、飞行时间二次离子质谱法、代谢组学、基因组学等方法研究了其心材化过程中薄壁细胞代谢功能变化与心材成分生成机制。主要研究结果如下：.（1）生理性心材：.①发现生理性心材形成于心边材过渡区狭窄范围，由薄壁细胞快速生成并向内层迁移及逐步积累。心材化过程中，边材薄壁细胞活力旺盛，酶活性较高；过渡区淀粉粒和大多数细胞器消失，糖类等营养物质分解转化心材成分，细胞核消失；由边渡材到心材抽提物含量陡然增加。.②降香黄檀心材形成于过渡材~1mm区域，发现主要黄酮类成分的生成首先是由莽草酸途径产生的苯丙氨酸在苯丙氨酸解氨酶等酶的催化下产生类黄酮前体物质对香豆酰辅酶A,之后经查尔酮合成酶、异构酶等酶的催化下生成甘草素后在细胞色素P450和氧甲基转移酶等酶修饰下生成类型多样的黄酮成分，其中DodPAL, DodCHS, DodCYP81E，DodCoMT是关键结构基因，转录因子DodMYB89是关键的调控因子。.③大花序桉心边材中有88个差异代谢物，心材相较于边材发生上调表达的有69种代谢物，心材代谢物主要为黄酮类和脂肪酸类，心材鞣花酸是边材的近5倍，心材黄酮类上调差异倍数最大的代谢物是美迪紫檀素，是木材显色的关键性成分。.（2）病理性心材：.病理性心材在胁迫条件下产生防御反应而生成，心材与胁迫位置有关，形状多样，新使用Gongronella butleri、Saitozyma podzolica、Cladorrhinum bulbillosum、Humicola grisea和Tetracladium marchalianum等5种真菌诱导沉香树木结香，效果好，6个月即满足《中国药典》标准，其生物活性与野生沉香高度相似。.项目发现了心材形成关键区域、生成心材成分的薄壁细胞生理功能变化、代谢过程与心材成分生成的路径及关键调控基因等重要树木心材化规律，为多渠道调控心材形成提供科学指导。