Publikationen - Molekulare Signalverarbeitung

In the present paper we study the possible biological relevance of endogenous jasmonic acid (JA) and exogenous salicylic acid (SA) in a plant-microbial system maize-virus. The virus disease "Mal de Río Cuarto" is caused by the maize rough dwarf virus - Río Cuarto. The characteristic symptoms are the appearance of galls or "enations" in leaves, shortening of the stem internodes, poor radical system and general stunting. Changes in JA and protein pattern in maize control and infected plants of a virus-tolerant cultivar were investigated. Healthy and infected-leaf discs were collected for JA measurement at different post-infection times (20, 40, 60 and 68 days). JA was also measured in roots on day 60 after infection. For SDS-PAGE protein analysis, leaf discs were also harvested on day 60 after infection. Infected leaves showed higher levels of JA than healthy leaves, and the rise in endogenous JA coincided with the enation formation. The soluble protein amount did not show differences between infected and healthy leaves; moreover, no difference in the expression of soluble protein was revealed by SDS-PAGE. Our results show that the octadecanoid pathway was stimulated in leaves and roots of the tolerant maize cultivar when infected by this virus. This finding, together with fewer plants with the disease symptoms, suggest that higher foliar and roots JA content may be related to disease tolerance. SA exogenous treatment caused the reversion of the dwarfism symptom.

The accumulation of abundant proteins and their respective transcripts, induced by 10−4 M cisabscisic acid or 10−5 M jasmonic acid methyl ester, was studied in barley (Hordeum vulgare L.) leaf segments and compared to that resulting from osmotic stress caused by floating the segments on solutions of sorbitol, glucose, polyethyleneglycol (PEG)-6000 or NaCl. Osmotic stress or treatment with abscisic acid led to the synthesis of novel proteins which were identical to jasmonateinduced proteins (JIPs) with respect to immunological properties and molecular masses. The most prominent polypeptides were characterized by molecular masses of 66, 37 and 23 kDa and were newly synthesized. Whereas sorbitol, mannitol, sucrose, glucose and PEG provoked the synthesis of JIPs, 2deoxyglucose and NaCl did not. We provide evidence that the synthesis of JIPs induced by osmotic stress is directly correlated with a preceding rise in endogenous jasmonates. These jasmonates, quantified by an enzyme immunoassay specific for (−)jasmonic acid and its aminoacid conjugates, increased remarkably in leaf segments treated with sorbitol, glucose or other sugars. In contrast, no increase in jasmonates could be observed in tissues exposed to salts (NaCl). The results strengthen the hypothesis that the accumulation of jasmonates, probably by de-novo synthesis, is an intermediate and essential step in a signalling pathway between (osmotic) stress and activation of genes coding for polypeptides of high abundance.

BarJey leaf segments treated with jasmonate respond with the synthesis of specific proseins, referred to as jasmonate‐induced proteins (JIPs). Application of abscisic acid (ABAl also induced JIP synthesis (Weidhase et al. 1987). In this study the effects of inhibitors on sorbitol‐induced increases of endogenous jasmonates and ABA were investigated. The promotion of jasmonates by sorbitol was inhibited by the growth retardant tetcyclacis at concentrations as low as 1 ftM. In parallel with the decrease of jasmonates, JIP gene expression was reduced as reflected by a decline in the level of a 23‐kDa protein UIP‐23) and mRNAs of JIP‐6 and JIP‐23. 12‐Oxo‐phytodienoic acid, an inlermediale in the lipoxygenase (LOX) pathway leading to jasmonic acid was able to overcome the inhibition by tetcyclacis and increases both the endogenous jasmonate content and transcript accumulation. This suggests that tetcyclacis acts upstream of 12‐oxo‐phytodienoic acid and in keeping with this proposal, an increase in relative LOX activity was detected after tetcyclacis treatment. Although tetcyclacis was shown to inhibit the degradation of ABA to phaseic acid, its effect on jasmonate synthesis is much more pronounced.