TOTAL EPIDERMAL-CELL WALLS OF PEA STEMS RESPOND DIFFERENTLY TO AUXIN THAN DOES THE OUTER EPIDERMAL WALL ALONE

The effect of auxin on cell wall mass in the epidermis of third intern odes of Pisum sativum L. cv. Alaska grown in dim red light was investi gated using epidermal peels, to determine whether epidermal peels refl ect the behavior of the outer epidermal cell wall. In contrast to the outer epidermal wall itself, where auxin caused thinning in proportion to growth (M.S. Bret-Harte et al., 1991, Planta 185, 462-471), auxin promoted an increase in wall mass in epidermal peels from treated inte rnode segments in the absence of exogenously supplied sugar. The perce ntage gain in mass was smaller than the percentage elongation, however , so mass per unit length decreased in peels from auxin-treated segmen ts. Epidermal peels from auxin-treated segments gained more wall mass than control peels even when adhering internal tissue at the basal end of the peel was removed. Epidermal peels also had a gross composition different from that of the outer wall alone (M.S. Bret-Harte and L.D. Talbott, 1993, Planta 190, 369-378). These discrepancies can be expla ined by the observation that the outer wall makes up only 30% of the m ass of the epidermal peel. It appears that the inner walls of the epid ermis, and walls of the outer layer of cortical cells that remain atta ched to the epidermis during peeling, nearly maintain their thickness by biosynthesis while the outer wall loses mass as previously describe d (Bret-Harte et al. 1991). These results indicate that epidermal peel s may not be a good system for examining the biochemical and physiolog ical properties of the outer epidermal cell wall.