A CYTOCHEMICAL STUDY ON THE ROLE OF ATPASES DURING POLLEN GERMINATION IN AGAPANTHUS-UMBELATUS LHER

Cytochemical detection of ATPase activity in the pollen grain (PG) and pollen tube (PT) of Agapanthus umbelatus showed that the enzymes concerned presented specific patterns of membrane distribution according to their ionic dependencies and to the time-course of germination and tube growth. In the pollen tubes Ca2+-ATPases were mainly localized in mitochondria and ER membranes, while Mg2+-ATPases were found especially in the tonoplast and in the membrane of the P-particles. K+-ATPases showed a high activity at the plasma membrane. In the pollen grain similar patterns of ATPase activity were observed. The highest activity of all three types was observed at the plasma membrane of the grain and at the intine and inner exine layers of the cell wall. The activity observed in the pollen grain cell wall decreased with germination time. In vivo germination studies in the presence of specific inhibitors of the ATPases showed patterns of inhibition that could be correlated with the corresponding ATPase putative role. The results are discussed in terms of the ultrastructural organization of the PG and PT, especially those correlated with (1) formation and maintenance of ionic gradients throughout the PT, (2) polarized growth and (3) hydrodynamics of PT elongation.