Study On Anatomy Of Secretory Structure In Gossypium Hirsutum L.

There are three types of secretory tissues in Gossypium hirsutum L.,which are nectaries,glandular trichomes and secretory cavities.The ontogenesis and deveopment of secretoy tissues were studyed by light micrographs and eletron micrographs,and the relationship between lysis of secretoy cells and the programmed cell death was studyed by TUNEL assay,4,6-Diamidino-2-phenylindole(DAPI)staining and DNA ladder detection.There are two types of nectaries in Gossypium hirsutum L.,which are floral nectaries and extrafloral nectaries.The floral nectaries occurred at the base of fused sepals,occupying a cylinder-like zone completely lining the inner side of the sepals. Extrafloral nectaries occurred at the base of nervation and inside and outside the base of calycles.Nectaries and extrafloral nectaries are composed of a lot of external multicellular nectary hair and subglandular tissue that located between the base of nectary hair and the vascular tissue of the sepales.Nectary hair is composed of secretory cell,stalk cell and foot cell.Each nectary hair originated from a single mother cell of protoderm,and subglandular tissue originated from some cells of ground meristem.The leaves of Gossypium hirsutum L.beared two types of glandular hairs,peltate and capitate,which comprised one basal cell,two stalk cells and some head cells.Glandular hair originated from a single mother cell of protoderm.The mother cell of protoderm divided periclinally several tomes and then created basal cell and stalk cells.The secretory cavites distributed in the ground tissues of all organs except root in Gossypium hirsutum L..Original cells of secretory in stem originated from some cells in ground meristem, while original cells in leaves come of some cells in plate meristem.Whether original cells in stems or in leaves will create original cell groups of secretory cavities first by periclinal division and then by periclinal and anticlinal division.The secretory cavities first appeared at intercellular gap between central cells,then increased along the intercellular.During cavity formation,cell lysis occurs from the cell boundary, meanwhile,the central cells have integral nuclear;then nuclei dissolve and lysis proceed successively until degrade the whole cell.At last,all the central cells dissolve. The mature secretory cavity is made up of three parts,a big central cavity is filled with secretions,remnant cells which are one or two layers and still send secretion to central cavity,and sheath cells including one or two layer of cells which compose to the boundary of pigment gland.During cavity formation,the first event is that cytoplasm becomes vacuolate,then the chloroplasts degrade and plasma membrane collapse.Autophagosomes play a key role to degrade cytoplasm.The cleavage of genomic DNA was detected and the process of degradation of secretory cells were identified as programmed cell death by in situ terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling(TUNEL)assay,gel electrophoresis and 4,6-Diamidino-2-phenylindole(DAPI)stain.