REDISTRIBUTION OF CELL CONTENTS BETWEEN DECLINING OLD AND GROWING YOUNG LEAVES IN SPRING ONION
SUN Zhao Yu ZHANG Shu Qiu LOU Cheng Hou (Slute Key Laboratory of Plant Physiology and Biochemistry, College of Brologrcal Sciences, China Agricultural Unrversity Beijing 100094)
During storage of a spring onion (Allium fistulosa var. dacong), the plant is unable to assimi late external resource, nutrient requirement of the new bud is entirely drawn from the withering leaf where both food reserves and protoplasmic constituents (i. e. organic complexes containing the essential mineral elements) are to be mobilized. Evidences were given to show that the withdrawal process of cell contents from the old part for establishing the new growth should be considered as an alternative mode or a supplementary mea sure of normal phloem transport of leaf photosynthates. Removal of cell contents from the declining old part to the developing new growth is of frequent occurrence in higher plants. In the present case, it followed the process of programmed cell death (PCD), That was examined and shown by electron microscopy and biochemical analysis. There appeared shrinkage of cell volume, dissolution of cell constitution and degradation of DNA. The present investigation has also shown that the with drawal of cell contents from the declining leaf sheath of spring onion can be wholly exhaustive. It may be carried out by active movement of the partially degraded protoplastllic constituents in forms of fragments and vesicles across the tissue, until hardly anything in the cellulose framework of the dry papery sheath, except a few crystals of Ca2+ . Presence of high ATPase and APase activities along the transport path also supports this view.