杨梅根瘤的显微和亚显微结构及固氮活性

Observation on the Structure and Ultrastructure of Root Nodule and Nitrogenase Activity in Myrica rubra

杨梅根瘤的横切面是圆形、对称的,含菌组织位于皮层的中部。未成熟根瘤的感染细胞充满内生菌丝。内生菌丝是分枝。具隔膜的Frankia菌。成熟根瘤中,内生菌丝顶端膨大形成无隔膜、表面光滑、球形的泡囊,直径比菌丝直径大,内含有某种内含物。泡囊的大量出现可能是固氮活力提高的标志,成熟壮瘤的固氮活性比幼瘤和衰老瘤的高。

The structure of root nodule of Myrica rubra Sieb. et Zucc. was observed under light microscope, and was investigated by electron microscope, In the meantime, the nitrogenase activity of nodules at different stages of development were determined separately. The tip of root nodule of M. rubra has a nodule root which is negatively geotropic. The transverse section of root nodule is round and symmetric. There is tissue of containing endophyte in the middle cortex (Fig. 1). In young nodules, infected cell becomes filled withthe endophyte which has a branched, septate and fillamentous hypha (Fig. 3). The endophyte hypha has, a single layer of electrondense cell wall and a diameter about 0.5～0.7 μm. No cell nucleus can be seen. The endophyte is a actinomycete. In mature nodules, the terminal of endophyte hypha swells to form vesicle formation. These vesicles are non-septate, smooth and spherical, about 1.5～4.0μm in diameter (Fig.4). There may be certain material inside these vesicles (Fig. 6,7). The structure of a mature vesicle differs from that of one in development. In nitrogen fixation, vesicles play an important role. Vesicles forming may be taken as an indication of maturation of the root nodule. Root nodules of M. rubra have a high nitrogen fixing activity. In different periods of development, the root nodule changes not only in structure, but also in colour. The young nodules are milkly white, the mature nodules yellow-brown, and the senescent nodules dark brown. The nitrogenase activity of root nodules is related to its development. In mature nodules, the nitrogenase activity is higher than that in both young nodules and in senescent nodules (Table 1).