[Effects of wounding on jasmonic acid distribution in vicia faba leaves].

Higher plants have to cope with environmental stimulus such as wounding. Jasmonic acid (JA) is an essential long-distance signaling compound. There is rare information about JA cellular and subcellular localization by now. In this work, using the immuno-fluorescence and immuno-gold electron microscopy, distributions of JA were determined in different cells of Vicia faba leaf. It showed that JA existed in the epidermal cells, mesophyll cells and guard cells, mainly localized in the cytosol and chloroplast of mesophyll cells, cell wall of epidermal cells, and cytosol, cell wall, chloroplast and nucleus of guard cells. Wounding increased JA accumulation in the apoplast and guard cells. Our results suggest that JA plays an important role as a signal in the defense response and involves in regulation of the stomatal movement in response to wounding stress.

[Calcium involved in the signaling pathway of jasmonic acid induced stomatal closure of Vicia faba L].

Ca2+, an ubiquitous second messenger in the signal transudation pathway, is required for various physiological and developmental processes in plant. Jasmonic acid (JA) has been known to induce the stomatal closure. By monitoring the changes of [Ca2+]cyt with fluorescent probe Fluo-3 AM under the confocal microscopy, we observed that exogenous JA increased [Ca2+]cyt in guard cells of Vicia faba L. while the control and linolenic acid (LA), which is a precursor of JA, could hardly affect the change of [Ca2+]cyt. EGTA, a chelator of Ca2+ completely blocked JA-induced stomatal closure. After epidermis pretreated with EGTA, JA failed to result in [Ca2+]cyt increasing. Ruthenium red that blocked Ca2+ released from intracellular Ca2+ store could not significantly change JA-induced stomatal closure, while JA still increased [Ca2+]cyt. Furthermore, Ca2+ channel inhibitor of nifedipine (NIF) reduced the effectiveness of JA-induced stomatal closure and JA-induced increasing fluorescent intensity in guard cells. The results demonstrated that Ca2+ is involved in the signal transduction of JA induced stomatal closure, and the source of [Ca2+]cyt increasing in guard cells induced by JA might derive mainly from the external stores.

[Redistribution of cell contents between declining old and growing young leaves in spring onion].

During storage of a spring onion (Allium fistulosa var. dacong), the plant is unable to assimilate 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 measure 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 withdrawal 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 protoplasmic 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.