THE VACUOLAR-TUBULAR CONTINUUM IN LIVING TRICHOMES OF CHICKPEA (CICER-ARIETINUM) PROVIDES A RAPID MEANS OF SOLUTE DELIVERY FROM BASE TO TIP

A vacuolar continuum exists from base to tip in the secretory trichome s of chickpea (Cicer arietinum). This continuum is seen in living tric homes which have been labeled with Lucifer yellow CH and examined with confocal microscopy. It encompasses the large vacuole of the lower st alk cell, the vacuoles and tubules of the central stalk cell, the thin tubules of the upper stalk cell, and the tubules and vacuoles of the secretory head cells. The vacuolar-tubular system is structurally dist inct within each cell, forming a gradient of large vacuoles in the low er stalk cell, thick tubules in the central stalk cell, and thin anast amozing tubules in the upper stalk cell. This membrane system appears to be continuous between trichome cells, as thin tubules emanate from plasmodesmata between stalk cells and between the upper stalk and lowe r head cell. In the upper stalk cell, the thin rubules of this continu um are streaming up and down the long axis of the cell at 0.67 mu m/s. The larger vacuolar-tubular system in the central and lower stalk cel ls is also slowly moving, with apparent peristalsis occurring in the c entral cell. The vacuolar-tubular system of the secretory head cells i s completely labeled with Lucifer yellow when the dye has only partly diffused up the long walls of the trichome, indicating that the stream ing tubular system delivers solute through the stalk cells to the secr etory head cells faster than diffusion through the trichome walls. In the lower head cells, tubules emanate from the plasmodesmata connectin g to the upper stalk cell, and these tubules are continuous with the h ead cell vacuoles. In addition, another layer of thin tubules forms al ong the edges of the secretory head cells, at the site of exocytotic s ecretion. We propose that the continuous vacuolar-tubular system in th ese trichomes functions to rapidly deliver solute from the base of the trichome to the secretory head cells. This system provides a pathway for the transport of secretory material.