Rudimento seminal y ginosporogénesis de Cucurbitella duriaei y Cayaponia citrullifolia (Cucurbitaceae)

POZNER, R.

KURTZIANA

Instituto Multidisciplianrio de Biología Vegetal

Lugar: Córdoba; Año: 1994 p. 55 - 72

0075-7314

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:595.3pt 841.9pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> This paper deals with he ovular structure and development, gynosporogensis and the selection mechanism of the functioinal gynospore in Cucurbitella duriaei and Cayaponia citrullifolia. Both species have 3-zonate ovule primordia, with epidermis, a subepidermal layer and an inner cellular group. The ovule is anatropous, bitegmic and crassinucellate. The outer integument is vascularized and several layers thick. The 3 primordial zones form the outer integument. The inner integument has only 2 epidermal layers and limits the micropyle. The nucellus is bottle shaped due to the development of its micropilar portion in a nucellar beak. The nucellar beak of Cucurbitella duriaei shows 2 or 3 median rows of cells with thick middle lamella. The nucellar beak of Cayaponia citrullifolia exhibits an increasing gradient of starch from the micropilar end up to the gynophyte. The chalazal portion of the nucellus derives from the inner zone of the ovular primordium. The micropilar portion of the nucellus develops from  a group of subdermal cells: the archesporium. Such archesporial cells behave as initial cells. They divide periclinally 2 or 3 times and one, rarely 2 or 3, of their derivatives differentiates as gynospore mother cells (GMC). The remainding ones form the nucellar beak and the nucellar cells that surrounds the gynophyte. The GMC forms a linear tetrad in Cucurbitella duriaei and a triad in Cayaponia citrullifolia. At first, 2 or more gynospores begin to grow, but finally the chalazal one forms the gynophyte. There is a lack of callose during meiosis of the GMC. Only few tetrads of Cucurbitella duriaei have callose on their transversal walls. The ovular structure of Cucurbitellla duriaei and Cayaponia citrullifolia corresponds to the general structure of the Cucurbitaceae ovules (Singh & Dathan, 1990). For this reason the ovular ontogeny of these two species could express the ordinary ovular development of this family. The micropilar strucutre and histological characters of the nucellar beak are the most variable aspects of the ovular structure, and they could be related to the fertilization. The nucellar ontogeny from the archesporium is a complex process, and agrees with the nucellar development in Potentilla (Hunziker, 1954) and the Rosaceae (Schnarf, 1929). Callose is not nvolved in the selection of the functional gynospore. This selection is based on the competence among the growing gynospores, and such interpretation could apply to other species of Cucurbitaceae.