Jasonc acid (JA) and its methyl ester, methyl jasmonate (MeJA), are plant lipid derivatives that resemble mammalian eicosanoids in structure and biosynthesis. These compounds are proposed to play a role in plant wound and pathogen responses. Here we report the quantitative determination ofJA/MeJA in panta by a procedure based

Changes in chromatin composition are often a prerequisite for gene induction. Nonallelic histone variants have recently emerged as key players in transcriptional control and chromatin modulation. While the changes in chromatin accessibility and histone posttranslational modification (PTM) distribution that accompany gene induction are well documented, the dynamics of histone variant exchange that parallel these events are still poorly defined. In this study, we have examined the changes in histone variant distribution that accompany activation of the inducible CD69 and heparanase genes in T cells. We demonstrate that the chromatin accessibility increases that accompany the induction of both of these genes are not associated with nucleosome loss but instead are paralleled by changes in histone variant distribution. Specifically, induction of these genes was paralleled by depletion of the H2A.Z histone variant and concomitant deposition of H3.3. Furthermore, H3.3 deposition was accompanied by changes in PTM patterns consistent with H3.3 enriching or depleting different PTMs upon incorporation into chromatin. Nevertheless, we present evidence that these H3.3-borne PTMs can be negated by recruited enzymatic activities. From these observations, we propose that H3.3 deposition may both facilitate chromatin accessibility increases by destabilizing nucleosomes and compete with recruited histone modifiers to alter PTM patterns upon gene induction.

The tightly regulated expression patterns of structural cell wall proteins in several plant species indicate that they play a crucial role in determining the extracellular matrix structure for specific cell types. We demonstrate that AtPRP3, a proline-rich cell wall protein in Arabidopsis, is expressed in root-hair-bearing epidermal cells at the root/shoot junction and within the root differentiation zone of light-grown seedlings. Several lines of evidence support a direct relationship between AtPRP3 expression and root hair development. AtPRP3/␤-glucuronidase (GUS) expression increased in roots of transgenic seedlings treated with either 1-aminocyclopropane-1-carboxylic acid (ACC) or ␣-naphthaleneacetic acid (␣-NAA), compounds known to promote root hair formation. In the presence of 1-␣-(2-aminoethoxyvinyl)glycine (AVG), an inhibitor of ethylene biosynthesis, AtPRP3/GUS expression was strongly reduced, but could be rescued by co-addition of ACC or ␣-NAA to the growth medium. In addition, AtPRP3/GUS activity was enhanced in ttg and gl2 mutant backgrounds that exhibit ectopic root hairs, but was reduced in rhd6 and 35S-R root-hair-less mutant seedlings. These results indicate that AtPRP3 is regulated by developmental pathways involved in root hair formation, and are consistent with AtPRP3's contributing to cell wall structure in Arabidopsis root hairs.

High conductance ␥-aminobutyric acid type A (GABA A ) channels (>40 picosiemens (pS)) have been reported in some studies on GABA A channels in situ but not in others, whereas recombinant GABA A channels do not appear to display conductances above 40 pS. Furthermore, the conductance of some native GABA A channels can be increased by diazepam or pentobarbital, which are effects not reported for expressed GABA A channels. GABARAP, a protein associated with native GABA A channels, has been reported to cause clustering of GABA A receptors and changes in channel kinetics. We have recorded single channel currents activated by GABA in L929 cells expressing ␣ 1 , ␤ 1 , and ␥ 2S subunits of human GABA A receptors. Channel conductance was never higher than 40 pS and was not significantly increased by diazepam or pentobarbital, although open probability was increased. In contrast, in cells expressing the same three subunits together with GABARAP, channel conductance could be significantly higher than 40 pS, and channel conductance was increased by diazepam and pentobarbital. GABARAP caused clustering of receptors in L929 cells, and we suggest that there may be interactions between subunits of clustered GABA A receptors that make them open co-operatively to give high conductance "channels." Recombinant channels may require the influence of GABARAP and perhaps other intracellular proteins to adopt a fuller repertoire of properties of native channels.

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We have characterized the molecular organization and expression of four proline-rich protein genes from Arabidopsis (AtPRPs). These genes predict two classes of cell wall proteins based on DNA sequence identity, repetitive motifs, and domain organization. AtPRP1 and AtPRP3 encode proteins containing an N-terminal PRPlike domain followed by a C-terminal domain that is biased toward P, T, Y, and K. AtPRP2 and AtPRP4 represent a second, novel group of PRP genes that encode two-domain proteins containing a nonrepetitive N-terminal domain followed by a PRP-like region rich in P, V, K, and C. Northern hybridization analysis indicated that AtPRP1 and AtPRP3 are exclusively expressed in roots, while transcripts encoding AtPRP2 and AtPRP4 were most abundant in aerial organs of the plant. Histochemical analyses of promoter/␤-glucuronidase fusions localized AtPRP3 expression to regions of the root containing root hairs. AtPRP2 and AtPRP4 expression was detected in expanding leaves, stems, flowers, and siliques. In addition, AtPRP4 expression was detected in stipules and during the early stages of lateral root formation. These studies support a model for involvement of PRPs in specifying cell-type-specific wall structures, and provide the basis for a genetic approach to dissect the function of PRPs during growth and development.

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