尼泊尔马桑放线菌共生固氮根瘤的感染和发育

INFECTION AND DEVELOPMENT OF SYMBIOTIC NITROGENFIXING ACTINORHIZA OF CORIARIA NEPALENSIS WALL.

弗兰克氏放线菌通过感染尼泊尔马桑的根毛侵入根的皮层细胞。由于内生菌侵入的刺激,部分皮层细胞分裂和增大,产生前根瘤原基。根瘤原基分裂、分化,形成初生根瘤瘤片。瘤片顶端分生组织不断双叉分枝,发育,并伴随着内生菌感染的寄主细胞,产生多次双叉分枝的珊瑚状根瘤。观察瘤片的横切面,含菌组织是一个马蹄形的致密整体,不完全地包围着稍偏的中柱。观察瘤片的纵切面,可将其划分为6个区域,即顶端分生组织,未感染皮层细胞组织、新感染含菌组织、成熟含菌组织、衰老含菌组织和中柱及其外围数层富含淀粉粒的皮层细胞。

Frankia hyphae penetrate root ha rs and invade root cortical cells of Coriaria nepalensis Wall., leading to nodulation. Owing to the stimulation caused by infection, a part of the cortical cells in the infected root divide and hypertrophy, resulting in the formation of a prenodulein which the nodule primordium develops. The primordium divides and differentiates, forming a primary nodule lobe. The apical meristem of a lobe hranchs dichotomously and the branchings develop with the infection of new host cells by the endophytes, giving rise to a coralloid root nodule consisting of many dichotomic branchings. In cross section, the endophyte-infected tissue zone in a lobe is a horse-shoeshaped compactmass, incompletely surrounding the acentral stele. In longitudinal section, the apical part of a mature lobe is the meristem, followed successively by the non-infected tissue, the newly infected tissue, the mature infected tissue and the senescent infected tissue. The lobal stele is surrounded by several layers of cortical cells containing starch granules.