MORPHOLOGICAL AND HISTOCHEMICAL-DIFFERENTIATION OF THE POLLEN WALL OFBETULA-PENDULA ROTH DURING DORMANCY UP TO ANTHESIS

Anthers of Betula pendula were collected at regular intervals during t he dormancy period until anthesis. Ultrathin sections of maturing poll en grains were especially stained for polysaccharides and proteins and examined with TEM to determine whether structural or/and chemical cha nges in the pollen wall occur during the dormancy period of the plant life cycle. At the beginning of the dormancy period, the microspore wa ll consists of a well developed tectum, columellae and a foot layer. S pinules and supratectal elements are prominent. Microchannels are pres ent in the tectum but not obvious in the foot layer. Some of the colum ellae are not clearly connected with the foot layer, but some connecti ons are evident. Pores are filled with a thick fibrillar network ''flo cculent material''. The cytoplasm is packed with starch grains and lip id globules, The stainability for acidic and neutral polysaccharides a nd protein was tested, and variations in the pollen wall are illustrat ed. As temperature increased towards the end of dormancy and before an thesis there is obvious differentiation in the morphology of the polle n wall. The granular fibrillar layer beneath the pore and the Zwischen korper are the most variable part of the wall. Different histochemical reactions observed in different layers at the aperture sites indicate different functions of these layers.