DEHISCENCE OF FRUIT IN OILSEED RAPE (BRASSICA-NAPUS L) .1. ANATOMY OF POD DEHISCENCE

The development sequence of anatomical changes taking place within the pericarp tissues of Brassica napus siliquae have been studied at a fine- and ultra-structural level. Tissue differentiation occurred during the initial 20 d after anthesis (DAA) and allowed the identification of dehiscence zone cells. This descrete tissue was subsequently further delineated by extensive lignification of adjacent valve edge and replar vascular cells. Concomitant with the onset of pericarp lignification, cytoplasmic contents of the thin-walled dehiscence zone cells exhibited progressive senescence and degradation. Wall breakdown, initially evident in pods by 60 DAA, exclusively affected cells within the dehiscence zone, and eventually extended throughout this tissue from the epidermal suture to the locule, thus precipitating valve detachment. Ultrastructural examination confirmed that this loss of cellular cohesion was primarily attributable to middle lamella degradation and, furthermore, the dissolution of wall material was apparently dependent on rupture of the dehiscence zone protoplast. The significance of dehiscence zone cell modifications in relation to autolytic cell wall breakdown, together with possible implications for the regulation of pod shatter, are discussed. © 1990 Oxford University Press.