Graine et procaulôme d'Orobanche crenata Forsk: étude histocytologique et cytochimique

Abstract

A study of Orobanche crenata Forsk. seeds and their germination was carried out using scanning and transmission electron microscopy. The minute seeds possess a brownish testa, representing vestiges of the cell wall of a superficial layer. The embryo is slightly differentiated with small cells in the micropylar zone and vacuolated ones in the chalazal region. In response to a host root stimulus, germination of the seeds occurs, giving rise to a very delicate organ, the "procaulôme," whose tip is composed of approximately 10 meristematic cells. These cells are rich in dictyosomes emitting numerous vesicles whose polysaccharide contents react strongly to PATAg. The other part of the "procaulôme" is entirely parenchymatous and has no conducting elements. Both the nature and function of this organ formed during germination are discussed on the basis of the new histological and ultrastructural data. The terms root, radicule, and germ tubelike organ should be replaced by "procaulôme," which is more appropriate for describing its special character.