巴西橡胶树树皮厚壁组织结构和发育研究

Development and Structure of Sclerenchyma in Bark of Rubber Tree

植物中的厚壁组织对植株起着重要的支持和保护作用,但目前对橡胶树树皮中该组织的研究较少。以无性系RY7-33-97不同发育阶段的萌条以及无性系PB86、PR107、RY8-79定植7年的树干树皮为材料,利用光学显微技术对树皮中厚壁组织的结构和发育进行较为系统的研究。结果表明,幼嫩萌条的树皮中仅有纤维组织,根据其所在位置可分为皮层纤维和初生韧皮纤维。皮层纤维数量较少,分散分布在皮层中;而初生韧皮纤维常由2~3层纤维细胞形成完整的纤维带围绕在初生韧皮部外侧。成龄大树树皮中仅观察到短石细胞,常成团分布,这些石细胞由薄壁细胞通过同心环的方式木质化加厚细胞壁发育形成。石细胞的内腔中常积累红褐色物质和结晶体,有的石细胞外包有晶鞘。在PB86、PR107、RY8-79三个无性系中,石细胞在树皮中的分布和石细胞壁的厚度具有明显的品系特征。最早出现的石细胞列到砂皮外层这一范围内,石细胞团排列最紧密的是PR107,面积比例为28.9%;其次是PB86,为27.4%;RY8-79中的石细胞团少而稀疏,仅12%,极显著低于PR107和PB86。在PR107中,石细胞壁的厚度最大,约为14μm;PB86和RY8-79则分别为9和7.8μm,可见,石细胞壁的厚度PR107极显著高于PB86和RY8-79。这些石细胞的特征可能与不同品系树皮的抗压、抗风能力、割胶难易程度相关,对橡胶树树皮厚壁组织尤其是石细胞的研究将为橡胶树选育种中副性状的选择提供依据。

The sclerenchyma in plants has supporting and protecting functions, it is, however, still not well known in the bark of rubber tree. In the present study, the structure and development of sclerenchyma in trunk bark of7-year-old rubber tree clone PB86, PR107 and RY8-79 as well as in the bark of epicormic shoots of rubber tree clone RY7-33-97 at the different developmental stages was observe by using optical microscopy. In the bark of epicormic shoots, only the fiber, a kind of sclerenchyma, was observed. It could be recognized as cortical fiber and primary phloem fiber according to its distribution. The cortical fiber sparsely dispersed in cortex, while primary phloem fiber located outside the primary phloem, in a ring form of 2-3 fiber layers. By contrast, only the brachysclereid was present in the trunk bark of 7-year-old rubber tree clones. The stone cells existed generally in a cluster form and developed from parenchyma cells after the cell wall of the parenchyma cells lignified and thickened in a manner of concentric ring. The stone cells usually contained bronzing materials or crystals in the cavity. Some of stone cells were enclosed with a crystal sheath. The distribution and cell wall thickness of stone cells were clone-specific. Within the area from the innermost stone cell line to the outer layer of the sandy skin,the ratio of stone cells to the area was 28.9% in PR107, 27.4% in PB86, 12% in RY8-79. The thickness of stone cell wall was about 14 μm in PR107, 9 μm in PB86 and 7.8 μm in RY8-79. The difference in the density and cell wall thickness of stone cells may be related to the difference in the capacity of anti-pressure and anti-wind and bark hardness among the three clones. Knowledge about the sclerenchyma, especially the stone cells in the trunk bark of rubber tree will contribute to the selection of related accessory characters in Hevea breeding.