ABSTRACT
The aim of this study is to describe the ultrastructural changes of the egg apparatus associated with fertilisation of the natural tetraploid Trifolium pratense. The pollen tube enters one of the synergids through the filliform apparatus from the micropyle. Before the entry of the pollen tube into the embryo sac, one of the synergids begins to degenerate, as indicated by increased electron density and a loss of volume. This cell serves as the site of entry for the pollen tube. Following fertilization, the vacuolar organisation in the zygote changes; in addition to the large micropylar vacuole, there are several small vacuoles of varying size. Ribosomal concentration increases significantly after fertilisation. In T. pratense, ultrastructural changes between the egg cell and zygote stages are noticeable. Several marked changes occur in the egg cell because of fertilisation. The zygote cell contains ribosomes has many mitochondria, plastids, lipids, vacuoles. After fertilization, most of the food reserves are located in the integument in the form of starch. The zygote shows ultrastructural changes when compared to the egg cell and appears to be metabolically active.
Subject(s)
Ovum/ultrastructure , Pollen/physiology , Trifolium/physiology , Fertilization/physiology , Microscopy, Electron , Trifolium/embryology , Trifolium/ultrastructureABSTRACT
The regeneration of natural tetraploid T. pratense, originated from Erzurum-Turkey, is reported in this study. This plant has low seed setting and hard seed problems due to polyploidy. Hypocotyl, cotyledon, apical meristems, epicotyl and young primary leaves were inoculated on MS and PC-L2 media containing different concentrations of BAP and NAA as growth regulators. The best shoot formation has been observed on explants initiated from apical meristem placed on PC-L2 medium that includes 2 mg dm-3 BAP and 1 mg dm-3 NAA. 94.4 percent of the shoots originated from calli were rooted on PC-L2 medium with 1 mg dm-3 NAA. In vitro organogénesis has been accomplished in the natural tetraploid T. pratense regenerated plants successively transferred to the field.