Publikationen - Molekulare Signalverarbeitung

A particular isoform of lipoxygenase (LOX) localized on lipid bodies was shown by earlier investigations to play a role in initiating the mobilization of triacylglycerols during seed germination. Here, further physiological functions of LOXs within whole cotyledons of cucumber (Cucumis sativus L.) were analyzed by measuring the endogenous amounts of LOX-derived products. The lipid-body LOX-derived esterified (13S)-hydroperoxy linoleic acid was the dominant metabolite of the LOX pathway in this tissue. It accumulated to about 14 µmol/g fresh weight, which represented about 6% of the total amount of linoleic acid in cotyledons. This LOX product was not only reduced to its hydroxy derivative, leading to degradation by β-oxidation, but alternatively it was metabolized by fatty acid hydroperoxide lyase leading to formation of hexanal as well. Furthermore, the activities of LOX forms metabolizing linolenic acid were detected by measuring the accumulation of volatile aldehydes and the allene oxide synthase-derived metabolite jasmonic acid. The first evidence is presented for an involvement of a lipid-body LOX form in the production of volatile aldehydes.

Plants are sessile organisms. Consequently they have to adapt constantly to fluctuations in the environment. Some of these changes involve essential factors such as nutrients, light, and water. Plants have evolved independent systems to sense nutrients such as phosphate and nitrogen. However, many of the environmental factors may reach levels which represent stress for the plant. The fluctuations can range between moderate and unfavorable, and the factors can be of biotic or abiotic origin. Among the biotic factors influencing plant life are pathogens and herbivores. In case of bacteria and fungi, symbiotic interactions such as nitrogen-fixating nodules and mycorrhiza, respectively, may be established. In case of insects, a tritrophic interaction of herbivores, carnivores, and plants may occur mutualistically or parasitically. Among the numerous abiotic factors are low temperature, frost, heat, high light conditions, ultraviolet light, darkness, oxidation stress, hypoxia, wind, touch, nutrient imbalance, salt stress, osmotic adjustment, water deficit, and desiccation.In the last decade jasmonates were recognized as being signals in plant responses to most of these biotic and abiotic factors. Signaling via jasmonates was found to occur intracellularly, and systemically as well as interorganismically. Jasmonates are a group of ubiquitously occurring plant growth regulators originally found as the major constituents in the etheric oil of jasmine, and were first suggested to play a role in senescence due to a strong senescence-promoting effect. Subsequently, numerous developmental processes were described in which jasmonates exhibited hormone-like properties. Recent knowledge is reviewed here on jasmonates and their precursors, the octadecanoids. After discussing occurrence and biosynthesis, emphasis is placed upon the signal transduction pathways in plant stress responses in which jasmonates act a signal. Finally, examples are described on the role of jasmonates in developmental processes.