ONTOGÊNESE E FORMAÇÃO DO NÚCLEO EM CÉLULAS DO TAPETE DE Passiflora L.

Abstract

The analysis of the ontogenetics characteristics of androceu during the pollen grain development in Passiflora species have involved anatomic studies of the tapetum. The tapetum is the main tissue involved in the pollen grain formation, it is widely preserved, has a short life period and nuclei formed for mitotic irregularities. The development of your cells is closely related with the microsporogenesis and microgametogenesis. Researches removing cells from the tapetum of different species shows the critical and specific role that it plays, leading to the pollen grain collapse when these cells are removed. There is still no available information regarding the cytogenetic development of the Passiflora tapetum relating it with the organelles that are present in the cells during different stages, only occurrence description of acytokinetic mitoses and endomitoses in the cells. The objective of this research was to describe the ontogenesis and the dynamic of the tapetum nuclei in species of the Passiflora L. genus, subgenus Passiflora. The analyzed material comes from collections of Passiflora actinia in Paraná and of Passiflora elegans in Rio Grande do Sul. The currently research was conducted through technics of anatomy and cytochemistry, transmission electronic microscopy, flow cytometry, conventional and molecular cytogenetics. The tapetum regulates the development of the pollen grain during microsporogenesis divided into pre-meiosis and meiosis and during microgametogenesis that occurs pos- meiosis and formation of the pollen. The tapetum cells of P. actinia shows great nuclear variation. After meiosis and posmeiosis events, cells vary from uninucleate to quadrinucleate with different sizes and variation in ploidy degrees between 2n and 32n. The formation of these nuclei takes place through acytokinetic mitosis, endomitosis, nuclear fusions and restitution mitosis. In P. actinia and P. elegans the binucleated cells have nuclei joined by a rough endoplasmic reticulum and the nuclei that are fusing have an invagination filled by the rough endoplasmic reticulum, were also found nucleoplasmic reticulum that can participate both in the regulation of nuclear mitosis and in the programmed cellular death of tapetum. The cells have a high quantity of cortical endoplasmic reticulum related to the cell sustain, secretion of substances, elaioplasts and tapetosomes characteristic of tapetum related with the disposition of the tryphine and pollenkitt. During the meiosis and pos-meiosis the cells have a high quantity of endoplasmic reticulum, mitochondria and dictyosomes that are related to the functions of the tapetum such as: the deposition of calase in the tetrad, formation and deposition of the elaioplasts, tapetosomes and sporopollenin in the pollen. The ploidy increase as a result of the mitotic irregularities can be related to the quantity increase of necessary genes for specific functions that the tapetum performs during his short life period in the pollen grain formation.