Abstract
The naturally occurring plant growth regulator (-)-jasmonic acid methyl ester (JaMe) induces the formation of novel abundant proteins in excised barley leaf segments. Concomitantly, this substance depresses the translation of most preexisting ("control") leaf mRNAs, including those for nuclear-encoded chloroplast proteins such as the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (SSU, rbcS gene product) and several light harvesting chlorophyll protein complex apoproteins (LHCPs, cab gene products). The changes in protein synthesis observed for SSU and LHCPs did not correspond to equivalent alterations in the rbcS and cab transcript levels. Analysis of polysome-associated in vitro translatable and hybridizable mRNAs, however, demonstrated a restriction of rbcS and cab transcripts to smaller polysomes in JaMe-exposed leaf tissues, in comparison to water-treated tissues. Since treatment of JaMe-incubated leaf segments with cycloheximide prior to harvest led to a shift of both transcripts toward larger polysomes, a hormone-induced impairment of chain initiation is assumed to lower translation of SSU and LHCP in situ. In contrast, the mRNA for plastid leucyl-tRNA synthetase (LRS1, lrs1 gene product) neither changed its abundance nor its association with polysomes in JaMe-treated leaves and was translated into the corresponding polypeptide. Together, our results highlight a remarkable variability of nuclear gene expression in response to plant growth regulators of the methyl jasmonate type.
Highlights
From the $Instituteof Plant Biochemistry, Weinberg 3, 0-0-4050 HallelSaale, Federal Republic of Germany, the §Department of Genetics, Institute for Plant Sciences, ETH Zentrum, Universitatsstrasse 2, CH-8092 Zurich, Switzerland, and the
The changes in protein synthesis observed for small subunits (SSU) and LHCPs didnot correspond to equivalent alterations in the rbcS and cab transcript levels
The abbreviations used are: JaMe, jasmonic acid methyl ester;jasmonateinduced proteins (JIPs)(s),jasmonate-induced proteins(s); LHC(P), light harvesting chlorophyll protein complex; LRS1, plastid leucyl-tRNA synthetase; P/T ratio, defines the proportion of polysomes to thesum of polysomes, ribosomal subunits, and monosomes; LSU, large subunits; SSU, small subunits; rbcL, gene for the large subunits of ribulose-1,5-bisphosphatecarboxylase/oxygenase
Summary
Plant Material-Seeds of barley (Hordeum uulgare L. cv. Salome) were germinated on vermiculite at 25 “Cunder continuous illumination for 7 days (modifiedafter Weidhase et al, 1987a, 1987h).Primary leaves were cut from the seedlings and placed onto eitherwater or on an aqueous solution of JaMe (45FM, Firmenich, Geneva, Switzerland) for the various periods of time indicated in the text. 1,the patternsof Coomassie-stained proteins from JaMaen-d water-treated leaf segments (Fig. 1,A versus C ) differ with respect to the disappearanceof several control protein(sopen circles i n Fig. I A ) andtheappearanceofthepreviously identified JIPs of 66, 37, 30, 23, and 12 k D a (arrowheads, see Muller-Uri et al, 1988; Reinbothe et al, 1992a). These cDNA clones are specific for the rbcS (pHuF08) and Distinct patterns of pulse-labeled proteins couldbe found for JaMe- and water-exposed leaf tissues (Fig. 1, D versus B ). After integration of the areas below the curves, the plast protein formation We have studied this phenomenon further by analyzing the protein patternosf isolated plastids from JaMe-and water-treated leaf segments.
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