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 lines of cells that have highly lignified, interlocking walls and are differentiated from cells of the neighboring endocarp only by being somewhat smaller and slightly elongate in the radial plane. Apical dehiscence occurs at the site where transmitting tissue penetrates the ovary wall to enter the ovarian locule. In most fruits, cells delineating the line of apical dehiscence possess thin, primary walls that stain only diffusely for pectic materials. In rare cases, possibly when apical dehiscence fails, these cells become lignified. Measurements of seeds and inner dimensions of endocarps of mature fruits show that dehiscent endocarps differ from indehiscent endocarps by 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 dehiscence events occur: longitudinal shell spli...