‘Stress’ protein synthesis in pea root meristem cells?

A novel stress-inducible metallothionein-like gene from rice

A novel rice genomic sequence encoding coding segments homologous to other metallothionein-like genes was isolated from Oryza sativa genomic library. This sequence, hereby designated as rgMT (rice genomic metallothionein-like gene), consists of two exons and one intron. From the coding sequence, it is predicted that rgMT encodes one protein of 74 amino acids. Differential expression of rgMT in rice plants was observed as mature transcripts were more abundant in roots than in leaves and sheaths. Under different stress conditions, such as excess heavy metals and heat shock, expression of rgMT was significantly elevated. This was especially noticeable with 250 microM CuCl2 for 16 h, 40 degrees C heat for 2 h and 0.06% DMSO for 1 h. Under sucrose starvation, rgMT transcripts also increased with time up to 72 h. During recovery from sucrose starvation, the transcripts declined slightly within 12 h of recovery. rgMT transcripts were also seen to have increased expression in senescent leaves. These results support the notion that rgMT is a stress-inducible gene in rice heretofore unreported.

Synthesis of characteristic proteins in nutrient-depleted cell suspension cultures of parsley

Cell suspension cultures of parsley (Petroselinum crispum) exhibited an altered pattern of protein synthesis after transfer from complete growth medium to water or medium containing no macronutrients. Similar changes occurred when cultures were grown in the original medium until the nutrients were depleted. The effect was reversible upon transfer to fresh medium and was not observed during regular subculturing of the cells. While total protein synthesis decreased sharply after nutrient depletion, the synthesis of a few characteristic proteins (starvation-related proteins, STPs) increased strongly. The protein labeled at highest rates with [(35)S]methionine in vivo (STP 62) had an apparent molecular weight of about 62000 and a pI of about 6.3. Although its increased rate of synthesis was therefore easily detected by labeling in vivo, translation of mRNA in vitro did not give comparable results. Thus, regulatory control may be exerted mainly at the level of translation. Synthesis of STP ceased rapidly when heat shock (37° C) was applied under conditions of nutrient depletion, whereas heat-shock proteins were strongly induced.

A study of the heat-shock response in Neurospora crassa

1. Neurospora crassa was grown at 28 degrees C for 12 hr and transferred to higher temperatures for 2 hr. 2. Cultures labelled with [35S]methionine showed the synthesis of several new proteins in response to heat-shock at 46 to 48 degrees C. 3. Major polypeptides of approximate Mr 105,000, 99,000, 78,000, 43,000 and 23,000 were detectable in one-dimensional SDS-polyacrylamide slab gel electropherograms. 4. 2-D analysis using isoelectric-focussing in the first dimension and electrophoresis in SDS-polyacrylamide gels in the second led to the resolution of some of the heat-induced polypeptide into multiple spots differing in pI values. 5. mRNA from heat-shocked cells was translated poorly in Wheat Germ extract and rabbit reticulocyte lysate in vitro translation systems.

Influence of the excision shock on the protein metabolism ofVicia faba L. meristematic root cells

UsingVicia faba root meristems we have shown that protein synthesis was dramatically changed after excision. The amino-acid incorporation dropped to 13% of the level in the unexcised control. This downshift was a direct consequence of the breakdown of polysomes which are converted into monosomes. In order to perform an analysis of the protein pattern by two-dimensional gel electrophoresis, endogenous proteolytic activity, which is high in broad bean root, had to be inhibited. Therefore, several protease inhibitors were tested and a very efficient inhibitor pool was obtained which could be used during the preparation of meristematic cell extracts. Protein-pattern analysis showed important differences between the unexcised control and excised apices. The number of proteins synthesized after excision droped from 250 in the control to 80, as a consequence of polysome breakdown. Futhermore, we present evidence that new and apparently specific proteins are synthesized in response to this excision shock.