Tissue Preparation and Fine Structure of the Radicle Apex from Cotton Seeds

Abstract

A comparative methodological study was made of the fine structure of apical cortical cells in excised radicles from cotton (Gossypium hirsutum L. var M-8) seeds. Radicles from dry seed had 12% moisture content and were prepared for electron microscopy using several different techniques. These included different methods of chemical fixation or freeze-fracture and etching of unfixed tissue for transmission electron microscopy (TEM) and cryofracturing of fixed and dehydrated radicles for scanning electron microscopy (SEM). Cortical cells had a similar appearance regardless of the method used in tissue preparation. Cell walls had a pronounced waviness which was particularly evident in SEM images of cells lining the elongated intercellular air spaces. The plasma membrane (PM) delimited the cytoplasm of each cell as an intact unit membrane. Single layers of tightly-packed lipid bodies (LB) were apposed to the PM and protein bodies (PB). Distension of cells, membranous organelles and LB was observed in radicles fixed by immersion in aqueous solutions, suggesting that a certain amount of hydration occurred during fixation. This interpretation was supported by the compact appearance of cells and organelles in tissue prepared by freeze-etch or vapor fixation. We conclude that freeze-fracture and etching of unfixed tissue provided the best information for cell morphology and structure of membranes and organelles in dry tissue. Complementary data on the fine details of nuclei and cytoplasmic organelles were best observed with TEM of fixed tissue. These data when viewed collectively indicate the advantage of using several techniques to obtain analogous and complementary information essential for establishing a baseline level of information on the fine structure of cells in dry tissue.