Salicylic acid (SA) and jasmonic acid (JA) cross-communicate in the plant immune signaling network to finely regulate induced defenses. In Arabidopsis, SA antagonizes many JA-responsive genes, partly by targeting the ETHYLENE RESPONSE FACTOR (ERF)-type transcriptional activator ORA59. Members of the ERF transcription factor family typically bind to GCC-box motifs in the promoters of JA- and ethylene-responsive genes, thereby positively or negatively regulating their expression. The GCC-box motif is sufficient for SA-mediated suppression of JA-responsive gene expression. Here, we investigated whether SA-induced ERF-type transcriptional repressors, which may compete with JA-induced ERF-type activators for binding at the GCC-box, play a role in SA/JA antagonism. We selected ERFs that are transcriptionally induced by SA and/or possess an EAR transcriptional repressor motif. Several of the 16 ERFs tested suppressed JA-dependent gene expression, as revealed by enhanced JA-induced PDF1.2 or VSP2 expression levels in the corresponding erf mutants, while others were involved in activation of these genes. However, SA could antagonize JA-induced PDF1.2 or VSP2 in all erf mutants, suggesting that the tested ERF transcriptional repressors are not required for SA/JA cross-talk. Moreover, a mutant in the co-repressor TOPLESS, that showed reduction in repression of JA signaling, still displayed SA-mediated antagonism of PDF1.2 and VSP2. Collectively, these results suggest that SA-regulated ERF transcriptional repressors are not essential for antagonism of JA-responsive gene expression by SA. We further show that de novo SA-induced protein synthesis is required for suppression of JA-induced PDF1.2, pointing to SA-stimulated production of an as yet unknown protein that suppresses JA-induced transcription.

The distribution of octopamine in the metathoracic ganglion, brain and corpus cardiacum of Locusta migratoria and Schistocerca gregaria was investigated by means of immunocytochemistry with an antiserum against octopamine. The dorsal unpaired median (DUM) cells of the metathoracic ganglion were found to be strongly octopamine-immunoreactive. In the rostroventral part of the protocerebrum a group of seven immunopositive cells was demonstrated. Stained nerve fibres of these cells run into three directions: circumoesophageal connectives, midbrain, and optic lobes. As far as the protocerebrum is concerned, immunoreactive fibres were found in the central body, the protocerebral bridge, and in other neuropile areas. In the optic lobe a dense plexus of immunopositive fibres was found in the lobula and in the medulla. In the brain one other immunopositive cell was demonstrated, situated at the lateral border of the tritocerebrum. Octopamine could not be shown to occur either in the globuli cells of the mushroom bodies or in the dorsolateral part of the protocerebrum, where the perikarya of the secretomotor neurones are located that innervate the glandular cells of the corpus cardiacum. In the nervi corporis cardiaci II, which contain the axons of the neurones that extend into the glandular part of the corpus cardiacum, and in the corpus cardiacum proper no specific octopamine immunoreactivity could be found.

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The intracellular localization of calcium in the saccus vasculosus of the rainbow trout, Salmo gairdneri Richardson, was studied by means of ultracytochemical and X-ray microanalytical techniques. Using a variant of the glutaraldehyde/potassium pyroantimonate-osmium tetroxide method, Ca was detected in mitochondria, smooth endoplasmic reticulum and primary vesicles of coronet cells, and in mitochondria and smooth endoplasmic reticulum of tanycytes. Mitochondria and smooth endoplasmic reticulum in both cell types are considered as general Ca-stores. The primary vesicles in the ciliary globules of coronet cells are viewed as additional Ca-reservoirs. Possible roles of these Ca-stores in the regulation of transport activities of coronet cells in the homeostasis of the CSF are discussed.

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