The Extrafloral Nectaries of Cotton

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Abstract
Localization of ATPase activity in the extrafloral nectaries of cotton (Gossypium hirsutum) shows most pronounced granular staining at the plasmalemma of the sieve tube companion cells below the nectaries and at the plasmalemma of cells in the secretory papillae, particularly in the apical cell. Staining was much more intense in mature, secreting nectaries than in young, non-secreting ones. When CaCl2 is included in the fixation and washing solutions with the aim of localizing calcium binding sites, prominent amorphous electron dense globules are seen at the plasmalemma of the cells in the papillae, but also associated with other membranes. Both granular and amorphous deposits are seen when staining for Ca2+-ATPase activity. Selective osmium impregnation shows pronounced staining of the ER and nuclear envelope in secreting nectaries but not in young non-secreting ones.