Ultrastructural localization of calcium in the organic acid secreting trichomes of chickpea (Cicer arietinum)

LAZZARO, M. D., and THOMSON, W. M. 1992. Ultrastructural localization of calcium in the organic acid secreting trichomes of chickpea (Cicer arietinurn). Can. J . Bot. 70: 2319-2325. In the organic acid secreting trichomes of chickpea (Cicer arietinutn L.), calcium is localized in the stalk and head cells using pyroantimonate and X-ray microanalysis. Light calcium deposits are present in the endoplasmic reticulum, mitochondria, and cytoplasm of the stalk and head cells and in the cell walls of the stalk cells. Dense calcium deposits are present in the vacuoles of stalk and head cells and within the plasmodesmata between stalk cells. In the head cells, heavy calcium deposits are present in small, secretory vesicles that fuse with the plasma membrane. In addition, calcium deposits are localized in the cell wall space around the head cells, in the secretion chamber, and in collected secretions. These observations suggest that secretion from the head cells occurs predominantly through an exocytotic, vesicular pathway. We conclude that once secreted, calcium diffuses through the walls to the collecting chamber and subsequently through the cuticular pores into the secretion droplet.