Abstract:

The structure, distribution and the patterns of resin ducts in processes of its initiation and development were studied with the methods of thin section and ultrathin section. This paper emphasized the ultrastructual changes during canal development in Pinus massoniana. Our observations revealed that the resin ducts were relatively large intercellular spaces surrounded by a ring of the alive epithelial cells, and the epithelial cells were usually surrounded with one or two layered sheath cells, which were normal parenchyma cells in some primary resin ducts and became dead cells with thick walls in other primary and secondary resin ducts. The resin ducts were found to occur in almost all organs, except in cotyledon. The resin ducts were formed by Schizolysigeny according to characteristics of cell morphologic changes at the different stages of canal development and three developmental stages could be divided, namely initial stage, formative stage and mature stage, respectively. At the initial stage, the initials had dense cytoplasm and the abundant plastids in large size and elliptical shape, which contain one or two starch grains, without internal structure visible apart from a few short membranous profiles. A small number of osmiophilic droplets were present in the plastids. At the formative stage, the plastids, mitochondria and Golgi bodies in the cytoplasm increased in number. The plastids were commonly surrounded by an endoplasmic reticulum (ER) sheath. The larger osmiophilic droplets in cytoplasm and the smaller osmiophilic droplets on the plastids envelope, mitochondrion envelope and in Golgi vesicles obviously increased in number while canal developing. At the mature stage, the cytoplasm of epithelial cells became thin with a small nucleus. The number of mitochondria and Golgi body decreased, but numerous plastids still existed. Osmiophilic droplets were abundant in epithelial cells as previous status. The structures of plastids in epithelial cells gradually became welldeveloped so that the synthesis of resin remarkably enhanced during resin ducts formation and plastids would be main site for resin synthesis.

Key words: Pinus massoniana, resin duct, development, ultrastructure