In plants with large genomes, each of the classes of the histones (H1, H2A, H2B, H3 and H4) are not unique polypeptides, but rather families of closely related proteins that are called histone variants. The small genome and preponderance of single-copy DNA in Arabidopsis thaliana has led us to ask if this plant has such families of histone variants. We have thus isolated histones from Arabidopsis and analyzed them on four polyacrylamide gel electrophoretic systems: an SDS system; an acetic acid-urea system; a Triton transverse gradient system; and a two-dimensional system combining SDS and Triton-acetic acid-urea systems. This approach has allowed us to identify all four of the nucleosomal core histones in Arabidopsis and to establish the existence of a set of H2A and H2B variants. Arabidopsis has at least four H2A variants and three H2B variants of distinct molecular weights as assessed by electrophoretic mobility on SDS-polyacrylamide gels. Thus, Arabidopsis displays a diversity in these histones similar to the diversity displayed by plants with larger genomes such as wheat.The high mobility group (HMG) non-histone chromatin proteins have attracted considerable attention because of the evidence implicating them as structural proteins of transcriptionally active chromatin. We have isolated a group of non-histone chromatin proteins from Arabidopsis that meet the operational criteria to be classed as HMG proteins and that cross-react with antisera to HMG proteins of wheat.
In Mesembryanthemum crystallinum, salt stress induces the accumulation of proline and a specific isoform of the enzyme phosphoenolpyruvate carboxylase (PEPCase) prior to the switch from C3 to Crassulacean acid metabolism (CAM). To determine whether plant growth regulators initiate or imitate these responses, we have compared the effects elicited by NaCI, abscisic acid (ABA), and cytokinins using PEPCase and proline levels as diagnostic tools.
We have isolated two cDNA clones from wheat (Triticum aestivum L. var Stephens), designated WHSP16.8 and WHSP16.9, that are highly similar in sequence to the low molecular weight heatshock protein genes previously isolated from soybean. RNA blot analysis confirms that these sequences are present in heat-shocked wheat seedlings, but not in control tissues. The WHSP16.8 and WHSP16.9 cDNAs were isolated by screening a lambda gt1l expression library with antibodies to HMGc (a chromosomal protein of wheat). Immunoblot analysis has demonstrated that the antibodies raised against HMGc also recognize a group of proteins that are induced by heat shock and have molecular weights (estimated by sodium dodecyl sulfate electrophoresis) consistent with the molecular weights of the proteins deduced from the sequences of the cDNAs.Heat-shock proteins are a set of proteins whose synthesis is induced upon heat stress. The induction of heat-shock proteins is a highly conserved response that has been observed in every species studied thus far. The heat-shock proteins are also induced by other environmental stresses, and in some organisms, certain heat-shock proteins are induced during the course of normal development. The function of the heat-shock proteins is as yet unknown. However, evidence suggests that these proteins may provide organisms with a mechanism for thermotolerance (10).The low mol wt heat-shock proteins are the predominant heat-shock-induced proteins in plants. These been documented (1,2,6,8,12,30), and the number of low mol wt heat-shock proteins induced in several monocot species has been determined (12). These studies reveal that in wheat, 11 low mol wt proteins are induced and 1 enhanced by heat shock. We have isolated two wheat (Triticum aestivum L. var Stephens) cDNA clones that are highly similar to the soybean 17-kD heat-shock protein genes described by Nagao et al. (17). The work presented in this article shows that these cDNA clones represent heat-shock-inducible transcripts in wheat. Because the wheat heat-shock cDNA clones were isolated through screening an expression library with the antibodies to the HMGc3 chromosomal protein of wheat (25), it seemed likely that the HMGc antibodies would cross-react with low mol wt heat-shock proteins of wheat. Immunoblot analysis of protein extracts from heat-stressed tissues has confirmed this conjecture. Use of the HMGc antibodies has revealed a set of immunologically related proteins that are induced upon heat shock in wheat and have mol wts consistent with those deduced from the cDNA sequences. MATERIALS AND METHODS Plant MaterialWheat (Triticum aestivum L. var. Stephens) seeds were surface sterilized with 0.5% sodium hypochlorite and allowed to imbibe for 3 h. Seedings were grown in the dark at 200C for 5 d and were then transferred to 400C for heat-shock treatments. The etiolated coleoptiles and first leaves were harvested into liquid nitrogen and stored frozen at -700C.Preparation and Screening of a Wheat cDNA Library Total RNA was isolated from the c...
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