Time Course of mRNA Induction Elicited by Salt Stress in the Common Ice Plant (Mesembryanthemum crystallinum)

Abstract

In the facultative halophyte Mesembryanthemum crystallinum (common ice plant), irrigation with solutions containing NaCI induces an altemate mode of carbon dioxide fixation, Crassulacean acid metabolism (CAM). The salt stress protocol which we have established facilitates the study of CAM induction and the correlation of changes in metabolism and gene expression. We have studied the time course of mRNA induction for phosphoenolpyruvate carboxylase (PEPCase) (gene: ppc) and several other enzymes of carbon metabolism during stress. While CAM is not fully established for at least 10 days after the start of stress, mRNA amounts for PEPCase and for other CAM enzymes, such as Pyruvate orthophosphate dikinase, increase between day 2 and 3 after stress induction. Increases continue for at least 5 days. Concomitant with the increase of CAM transcripts, fluctuations in the mRNA amounts for genes rbcS and cab were observed. Transcript levels for these proteins decreased severalfold during a 3 to 4 day period.Plants are subjected to a number of environmental stimuli, including stresses imposed either by lack of water or by increases in electrolyte concentration. Both drought and salt stress are probably perceived similarly. The effects of both stresses have been studied mainly at physiological levels and only in part biochemically. Genetic traits which contribute to salt tolerance are not yet sufficiently understood. As salt tolerance appears to be a multigenic trait only the simultaneous change of several or many characters would produce desired phenotypes. Up to now, however, it has been impossible to discern responses that are at the basis of the tolerance from the plethora of accompanying adaptations in metabolism. In our attempts to learn more about the basic regulatory mechanisms determining the phenotype 'salt tolerant,' we are studying characteristics which distinguish halophytic (i.e. salt tolerant) plants from glycophytic (salt sensitive) plants.

Induction of Crassulacean Acid Metabolism in the Facultative Halophyte Mesembryanthemum crystallinum by Abscisic Acid

“…Conceivably, the proteins induced by all treatments may represent enzymes involved in CAM and other common functions associated with water stress, whereas those induced more specifically by salt may be involved in the adaptation of the plant to a saline environment. These results are in agreement with recent molecular studies on the salt induction of PEPC and other photosynthetic enzymes or proteins in M. crystallinum (6,8,9). These investigators found that in salt-treated plants the increase of PEPC enzyme activity is the result of de novo protein synthesis, which is paralleled by an increase in PEPC mRNA.…”

Regulation of Phosphoenolpyruvate Carboxylase and Crassulacean Acid Metabolism Induction in Mesembryanthemum crystallinum L. by Cytokinin

“…Plant Mol Biol inexsd prehydrt evdleaveiscnistacelerithatnedg (Fig.7) rgRep 6: [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] The present evidence is consistent with a negative regula- …”

“…Diurnal fluctuations in PEPCase transcript abundance are, indeed, observed, but only in salt-stressed (10) and not in well-watered plants (R. Hofner, personal communication). Another puzzling observation is that in wilting, excised leaves PEPCase mRNA is induced within 2 h (23), about an order of magnitude faster than in intact plants under salt stress (18).…”

Posttranscriptional and Posttranslational Control of Enolase Expression in the Facultative Crassulacean Acid Metabolism Plant Mesembryanthemum crystallinum L

“…Salt-stress treatment results in increased transcription rate, mRNA, and enzyme accumulation of certain enzymes that are important to CAM such as PEPC (Cushman et al, 1989;Michalowski et al, 1989). For enolase, we observed increased transcription rates and mRNA accumulation in response to salt stress; however, we failed to detect any significant changes at the leve1 of protein accumulation.…”