Cell differentiation in microsporangia of Pinus sylvestris. II. Early pachytene

Abstract

Tapetal cells of Pinus sylvesiris L. underwent one hypersecretory cycle during early pachytene and entered a second cycle by the time of mid pachytene in microspore mother cells. Initially in each cycle tapetal cells became papillaform then dome‐shaped and thereafter, in conjunction with radial narrowing of the cells, dilation of the ER system was intensive throughout the cytoplasm. Recovery from hyperactivity culminated with the presence of plasmodesma‐like connections between tapetal cells and a period of mitosis in tapetal cells. The differentiation of tapetal cells occurred asynchronously within a microsporangium and their dedifferentiation began nonuni‐formly, becoming synchronous coincidental with the presence of “plasmodesmata”. Microsporangia increased in size and tapetal cells were laterally wide before “plasmodesmata” receded and tapetal cells again differentiated asynchronously.