The Floral Nectaries of Hibiscus rosa-sinensis: 1. Development of the Secretory Hairs

Abstract

Floral nectaries of Hibiscus rosa-sinensis occur on the lower inner side of the fused sepals and each one consists of numerous (50000–55000) secretory hairs, occupying a cylinder-like zone completely lining the inner side of the sepals. Each hair originates from a single protodermal mother cell and, at maturity, it is built up of a basal cell, a stalk, 35–40 intermediate cells and a tip secretory cell. Development of protodermal cells into secretory hairs is asynchronous, the first cells to initiate development being those situated in the lowermost part of the cylindrical zone, and development progressing upwards.

Volume increase of protodermal mother cells initiating development is accompanied by cell polarization manifested by organelle displacement towards the apical region. Secretory hairs are formed through a sequence of transverse and, later on, anticlinal divisions. Divisions of apical cells are preceded by well defined pre-prophase microtubule bands, which foreshadow the plane of the forthcoming division and predict with accuracy the sites of parental walls where the new cell plate fuses at cytokinesis.

Stalks consist of either one or two cells. Two-celled stalks occur in 40 per cent of secretory hairs and derive from a transverse division of one stalk cell; the wall formed is always deposited parallel to the proximal and distal walls, but never to the lateral ones. The significance of this mode of division is discussed in relation to the fact that lateral walls are entirely impregnated with a cutin-like material that blocks apoplastic movement of solutes.

Hibiscus rosa-sinensis, nectaries, development, preprophase microtuble bands, stalk cells