GERMINATION OF MONOCOLPATE ANGIOSPERM POLLEN - EFFECTS OF INHIBITORY FACTORS AND THE CA2+-CHANNEL BLOCKER, NIFEDIPINE

Hydration of pollen of Narcissus pseudonarcissus was retarded and germination blocked in media with supra-optimal concentrations of osmoticum. Activation of the grains, expressed in circulatory movement in the vegetative cell, was not blocked. Wall development was disrupted, and pectic material and callose were deposited throughout. In the absence of calcium many grains burst on hydration. The survivors showed evidence of activation, but few tubes were formed. In medium with supra-optimal Ca2+, activation proceeded, but where tube tips were produced they became occluded with callose, which eventually formed a general lining to the intine. Nifedipine, a Ca2+-blocker, did not prevent activation at I O'4 M, but reduced callose deposition and inhibited polarized movement in the vegetative cell. Prominences formed at the germination sites were mostly low and rounded. During recovery in normal medium, tube tipis with normal callose linings were formed. Colchicine, a microtubule inhibitor, had no effect on activation or germination. Cytochalasin D, an actin inhibitor, prevented activation of the vegetative cell, but did not arrest all wall deposition. Movement began soon after transfer to normal medium, and some grains produced adventitious tube tips. While Ca2+appears not to be essential for activation, these results may be interpreted as indicating links in the normal course of germination between the initial Ca2+influx at the potential germination sites and: (a) polarization of movement in the vegetative cell, probably related to re-orientation of the actin cytoskeleton; and (b) patterned deposition of callose, which appears to have an important morphogenetic role. © 1992 Annals of Botany Company.