Ultrastructure study of Vanda Kasem's Delight orchid's protocorm-like body

Estudo da ultra-estrutura do protocormio da orquídea Vanda Kasem's Delight

ABSTRACT

Growing orchids has been classified as an international business since it covers 8% of the world floriculture trade. Thus, large-scale micropropagation of orchid using tissue culture techniques and improvement of some essential traits, such as resistances to various diseases and pests, and tolerances to environmental stresses, such as low temperatures and low light intensities, via genetic engineering acknowledged the orchids as one of the top ten cut flowers. Protocorm-like bodies (PLBs) are excellent explants for clonal propagation, artificial seeds development and genetic engineering since they are organized and easily regenerable somatic embryos that propagate rapidly. Vanda Kasem's Delight hybrid orchid's PLBs derived from shoot tip culture were examined in order to understand the fundamental ultrastructure of PLB. Examination of the cross sections of PLB revealed that PLB is made of a discrete bipolar structure that contains anterior and posterior meristems. Actively dividing meristem cells and outer layer lined by several rows of small and isodiametric cells with a dense cytoplasm and a prominent nucleus were also observed via cytological studies. Scanning Electron Microscope investigations revealed that the surface of PLBs is occupied by vertically positioned branched trichome appendages and regularly spaced stomatal openings with two guard cells. Organelles such as mitochondria of various sizes, shapes and biconvex chloroplast in the cytoplasm were revealed by Transmission Electron Microscope analysis. Hence, inheriting actively dividing cells, and bestowed with elements related to transpiration, photosynthesis and energy synthesizing power house makes PLB a suitable explant for micropropagation and genetic engineering studies.

Keywords:
Vanda Kasem's Delight; morphology; scanning electron microscope; transmission electron microscope.