杜仲根组织分化的观察与分析

An anatomical study on development of root of Eucommia ulmoides Oliv.

杜仲(Eucommia ulmoides Oliv.)的根为主根系。根尖顶端原始细胞分旱层为中柱原、皮层原和表皮-根冠原。整个根尖基本生长速率,自原始细胞向基端320μm前后最大,1200μm处下降到最小。原始细胞最初无分化,向基100μm处开始分化为初生分生组织,210μm处中柱鞘开始分化,500μm处出现最早筛管分子,620μm处出现最早导管分子,1300μm处表皮成熟形成根毛,2500μm处初生结构分化完成。内皮层凯氏带不明显,中柱鞘由一层细胞构成。木质部束多数为二原型,另外有三原、四原和五原型。韧皮部薄壁细胞形成许多橡胶丝。初生结构形成后,维管形成层即活动,产生次生维管组织,同时皮层第二层细胞分裂形成第一次的木栓形成层,产生周皮。次生韧皮部的轴向系统中也分化产生橡胶丝。侧根原基由木质部放射棱顶端中柱鞘细胞发生,根尖及成熟结构与主根相同。

This paper deals with a study on the development and differentiation of the root of Eucommia ulmoides, whose root is a tap-root system. The root-tip contains three groups of initials: epidermo-calyptrogen, cortical initials and plerome. There exists a gradient in the ground rate of growth from a maximum in the place of about 0.32 mm from initials to a minimum in the region of 1.2 mm. Initials have no differentiation while in the place about 0.1 mm they begin te differentiate into primary meristem. The earliest differentiation of pericycle is at a distance of about 0.27 mm from the apex. We also found the following places between the apical promeristem and the first mature vascular elements: protophloem sieve-tube elements, 0.50 mm; protoxylem vessel elements, 0.62 mm. Some epidermal cells mature into root hairs in a place of 1.3 mm and in 2.5 mm the differentiation of primary structure has done. The pericycle consists of a uniseriate cylinder of cells and the casparian strips of endodermis are not very apparent. Diarch roots are dominant but triarch, tetrarch and pentarch roots have been found. A lot of gutta laticiferous cells in the primary phloem are formed there. After maturation of primary structure, the activity of vascular cambium begins, producing the secondary vascular tissue as a result. About at the same time, the second layer cells of cortex begin cell division to form first cork cambium. In the longitudinal system of the secondary phloem there also differentiate into gutta laticifers. Lateral root primordia are initiated in the pericycle opposite the protoxylem groups. The development and mature structure of lateral root-tip are the same as main root.