Pectin secretion and distribution in the anther during pollen development in Lilium

Using the monoclonal antibodies JIM 5 and 7, pectin was immunolocalized and quantitatively assayed in three anther compartments of Lilium hybrida duri ng pollen development. Pectin levels in both the anther wall and the loculu s increased following meiosis, were maximal during the early microspore sta ges and declined during the remainder of pollen ontogenesis. In the microsp ores/pollen grains, pectin was detectable at low levels during the microspo re stages but accumulated significantly during pollen maturation. During ea rly microspore vacuolation, esterified pectin epitopes were detected both i n the tapetum cytoplasm and vacuoles. In the anther loculus, the same epito pes were located simultaneously in undulations of the plasma membrane and i n the locular fluid. At the end of microspore vacuolation, esterified pecti n epitopes were present within the lipids of the pollenkitt, and released i n the loculus at pollen mitosis. Unesterified pectin epitopes were hardly d etectable in the cytoplasm of the young microspore but were as abundant in the primexine matrix as in the loculus. During pollen maturation, both unes terified and esterified pectin labelling accumulated in the cytoplasm of th e vegetative cell, concurrently with starch degradation. In the mature poll en grain, unesterified pectin epitopes were located in the proximal intine whereas esterified pectin epitopes were deposited in the distal intine. The se data suggest that during early microspore development, the tapetum secre tes pectin, which is transferred to the primexine matrix via the locular fl uid. Further, pectin is demonstrated to constitute a significant component of the pollen carbohydrate reserves in the mature grain of Lilium.