Role of Asymmetric Cell Division in Pteridophyte Differentiation. II. Effect of CA 2+ on Asymmetric Cell Division, Rhizoid Elongation, and Antheridium Differentiation in Vittaria Gemmae

Abstract

Gametophytes of Vittaria graminifolia reproduce vegetatively by means of gemmae. Each gemma consists of a linear array of six cells: four body cells and a knob-shaped terminal cell at each end. When gemmae are shed from the gametophyte onto Knop's mineral medium, the two terminal cells do not divide, but elongate to form primary rhizoids. The body cells undergo asymmetric cell division, and the smaller daughter cells differentiate into either secondary rhizoids or prothalli. When gibberellic acid is included in the medium, antheridia are formed as a result of asymmetric cell division instead of vegetative structures. We studied the effect of Ca2+ on asymmetric cell division, rhizoid elongation, and antheridium formation in gemmae cultured on Knop's mineral medium and variations of Knop's medium. Ca2+ inhibited the onset of cell division and rhizoid elongation, but was required for differentiation of antheridia. Treatments which lowered the Ca2+ content of gemmae (EGTA and dilute HCl extraction, culture on verapamil-containing and Ca2+-deficient medium) caused an early onset of cell division and rhizoid elongation. The stimulation of growth was most pronounced when gemmae were deprived of Ca2+ during the first 24 hr of culture. The proportion of cell divisions which differentiated into antheridia in response to GA was greatly reduced when the Ca2+ status of gemmae was lowered with verapamil and Ca2+-EGTA buffers.

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