Abstract

The fine structure of the secretory papillae of the extrafloral nectaries of cotton (Gossypium hirsutum) is described. The cells contain a dense cytoplasm with the rough endoplasmic reticulum being particularly prominent. The cuticle covering the papillae has a typical two-layered appearance and is detached from the wall in secretory cells. With maturity, the lateral walls of the stalk cell at the base of each papilla become impregnated with cuticle-like electron-opaque material. The frequency and distribution of plasmodesmata have been estimated in all walls of the papillae. The periclinal walls are traversed by numerous plasmodesmata (about 16 per μ m2 in the distal wall of the stalk cell) which, in general, change from a simple to a more complicated structure during nectary development. The results are discussed in relation to the role of the ER in nectar secretion and are considered to support the view that pre-nectar follows a symplastic pathway from the phloem to the secretory cells.

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