Publications - Cell and Metabolic Biology

Barley leaves respond to application of (−)‐jasmonic acid (JA), or its methylester (JM) with the synthesis of abundant proteins, so‐called jasmonate induced proteins (JIPs). Here Western blot analysis is used to show a remarkable increase upon JM treatment of a 100 kDa lipoxygenase (LOX), and the appearance of two new LOX forms of 98 and 92 kDa. The temporal increase of LOX‐100 protein upon JM treatment was clearly distinguishable from the additionally detectable LOX forms. JM‐induced LOX forms in barley leaves were compared with those of Arabidopsis and soybean leaves. Both dicot species showed a similar increase of one LOX upon JM induction, whereas, leaves from soybean responded with additional synthesis of a newly formed LOX of 94 kDa.Using immunofluorescence analysis and isolation of intact chloroplasts, it is demonstrated that JM‐induced LOX forms of barley leaves are exclusively located in the chloroplasts of all chloroplast‐containing cells. Analogous experiments carried out with Arabidopsis and soybean revealed a similar plastidic location of JM‐induced LOX forms in Arabidopsis but a different situation for soybean. In untreated soybean leaves the LOX protein was mainly restricted to vacuoles of paraveinal mesophyll cells. Additionally, LOX forms could be detected in cytoplasm and nuclei of bundle sheath cells. Upon JM treatment cytosolic LOX was detectable in spongy mesophyll cells, too. The intracellular location of JM‐induced LOX is discussed in terms of stress‐related phenomena mediated by JM.