Endocarp dehiscence in pistachio (Pistacia vera L.)

Two sites exist for endocarp dehiscence (shell split) in the pistachio nut (Pistacia vera L., Anacardiaceae). Longitudinal dehiscence occurs along lin es of cells that have highly lignified, interlocking walls and are differen tiated from cells of the neighboring endocarp only by being somewhat smalle r and slightly elongate in the radial plane. Apical dehiscence occurs at th e site where transmitting tissue penetrates the ovary wall to enter the ova rian locule. In most fruits, cells delineating the line of apical dehiscenc e possess thin, primary walls that stain only diffusely for pectic material s. In rare cases, possibly when apical dehiscence fails, these cells become lignified. Measurements of seeds and inner dimensions of endocarps of matu re fruits show that dehiscent endocarps differ from indehiscent endocarps b y having more massive seeds and seeds that are larger relative to the size of the endocarp. These results and observations indicate to us that two deh iscence events occur: longitudinal shell split, which is driven by physical forces exerted on the endocarp by the seed, and apical dehiscence, which o ccurs at the site of intrusion of the transmitting tissue tract into the ov ary and varies according to the extent of transmitting tissue present at an thesis as well as the degree of cytodifferentiation that may occur in these cells.