Ovary development in cotton: (Gossypium hirsutum L.)

Abstract

A histological study of developing cotton ovary has been carried out, examining differentiation in the major tissues in successive stages before and after fertilization. Histochemistry, immunocytochemistry and in situ hybridization have been used for localization of cell wall components and enzymes. The results show that the young ovary produces four regions of meristematic tissue, which enclose the locular areas and give rise to the ovules. The ovules form on the placentae as rounded masses of meristematic cells from which develop the outer and inner integuments and the nucellus. In early stages the outer integument develops more rapidly than the inner integument and nucellus. Cotton fibres develop from the outer epidermis of outer integument. The lint fibres appear on the surface of the ovule on the day of anthesis, and fuzz fibres appear from seven days after fertilization. The fuzz fibres cells are more vacuolate than lint fibres in their initial stages. At maturity the lint fibres become like twisted ribbon but fuzz fibres did not become twisted. From the early zygote stage distinctive patterns of cell divisions were found in embryo and indicate that changes in group of cells undergoing mitosis are of fundamental importance in the development of form in the embryo. Dehiscence of the boll in essential for the exposure of the cotton fibre crop. Results indicate that the lignification of endocarp of fruit wall and septum, the development of sclerenchyma fibre in the mesocarp, and the formation of thick-walled valves all play active roles in boll dehiscence. Histochemical analysis has been used to examine patterns of cellular differentiation within the tissue of the developing fruit. Esterase activity is associated with cell expansion prior to; or in the absence of, subsequent signification’s group of monoclonal antibodies have been used for localization of arbinogalactans (AGPs), glycoproteins and pectins in the cell wall. Of those tested several showed uniform binding to most cell types, however JIM14 preferentially stained arbinogalactan (AGP) on the cell wall of the septum of just-fertilized ovary. Cellulase has been implicated in dehiscence mechanisms. Using in situ hybridization, a high level of gene expression for cellulase mRNA is seen in inner epidermis of the outer integument, and the outer epidermis of the inner integument of the ovule before fertilization, and after fertilization. By 15 days after fertilization cellulase mRNA was associated with vascular bundles of fruit wall and fibres. The levels of cellulose mRNA had declined at fruit maturity.