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Degradation of ribulose-l,5-bisphosphate carboxylase and chlorophyll in senescing barley leaf segments triggered by jasmonic acid methyiester, and counteraction by cytokinin, -Physiol, Plantarum 69: 161-166, Barley (Hordeum vulgare L, cv, Saiome) primary leaf segments responded to the application of a putative plant growth regulator, + jasmonic acid methyiester (JA-Me), with accelerated senescence, as indicated by the loss of chlorophyll and the rapid decrease in activity and immunoreactive protein content of ribulose-l,5-bisphosphate carboxylase/oxygenase (RuBP carboxylase, EC 4.1,1,39), The senescence-promoting action of JA-Me differed in light and in darkness; e,g, the initial rates of chlorophyll and RuBP carboxylase breakdown were markedly higher in light than in darkness in the presence of 4-10 ' M JA-Me. Cytokinin (benzyladenine, 4-10' Af) stopped the loss of chlorophyll and RuBP carboxylase during senescence; however, the rapid drop induced by JA-Me in the early phase of leaf segment senescence could not be prevented by concomitant or previous addition of BA, On the other hand, BA added 24 h after JA-Me application resulted in a recovery of chlorophyll and RuBP carboxylase at the later stages, indicating a possible rapid inactivation of JA-Me in the tissues. The activities of a number of other chloroplastic and cytosoiic enzymes were not significantly altered in JA-Me-treated leaf segments compared with controls floated on water. Time-dependent chlorophyll decrease in isoiated chloroplasts did not change upon JA-Me addition to the isolated organeUes, It is suggested that JA-Me acts on chloroplast senescence by promoting cytoplasmic events which eventually bring about the degradation of chloroplast constituents.Additional key words -Avena sativa, benzyladenine, chloroplasts, jasmonates, leaf senescence, phytohormones, R. A. Weidhase (reprint requests) et al.,

(-)-Jasmonic acid was identified as a plant growth inhibitor of the pericarp of Vicia faba by means of gas-liquid chromatography, high resolution mass spectrometry, (1)H-nuclear magnetic resonance ((1)H-NMR), and (13)C-NMR. Additionally, the pericarp contains very small amounts of abscisic acid (ABA) and 4'-dihydrophaseic acid. The highest level of jasmonic acid was reached prior to full pericarp length. This amount (3 μg g(-1) fresh weight) is similar to the maximal ABA content in the developing seed. Jasmonic acid is a plant growth inhibitor possessing a relative activity in the wheat seedling bioassay of 1-2.5%, compared to ABA. Contrary to ABA, jasmonic acid does not cause retardation of leaf emergence. The possible physiological role of jasmonic acid in the pericarp is discussed and compared with the assumed function of ABA in developing seeds.