Salt stress leads to differential expression of two isogenes of phosphoenolpyruvate carboxylase during Crassulacean acid metabolism induction in the common ice plant.

Mesembryanthemum crystallinum L. plants shift the mode of carbon assimilation from C3 to Crassulacean acid metabolism when stressed by high salinity. A prerequisite for Crassulacean acid metabolism induction is the synthesis of phosphoenolpyruvate carboxylase (PEPCase). A moderate increase in the abundance of PEPCase transcripts and activity is observed in 7-weekold, well-watered plants. This increase in PEPCase coincides in time with a decrease in the growth rate of the shoots. The steadystate level of PEPCase activity is uniform along the leaves of well-watered plants, as can be shown by comparing leaves of different age from individual 7-week-old plants. In contrast, the rate of induction in response to salt stress varies with the age of plants and to a lesser extent with the age of the leaves. Twoweek-old seedlings induce PEPCase slowly under a moderate salt stress regimen, whereas older plants induce faster. When individual leaves from a seven-week-old plant are compared with respect to induction velocity, no clear-cut correlation with leaf age is apparent. The highest induction rate is observed in leaves from node five that are about 2 weeks old at the beginning of the experiment. PEPCase transcripts are readily down-regulated to minute levels when detached leaves are hydrated. The levels reached after 8 hours of rehydration are very similar, regardless of whether the leaves were cut from young or old plants or whether the plants were previously salt-stressed or well-watered. It is concluded that environmental rather than developmental factors are predominant in determining abundance of PEPCase activity and transcripts in leaves of mature M. crystallinum plants.

Section: Probesmentioning

confidence: 99%

“…During induction, a CAM-specific This (8) is synthesized de novo (9). Translation is directed by mRNA newly transcribed from one of two PEPCase isogenes (3). Rehydration of stressed plants (17) or detached leaves (14) leads to a rapid decrease in PEPCase mRNA abundance with a half-life in the range of hours.…”

mentioning

confidence: 99%

Environmental Control of Phosphoenolpyruvate Carboxylase Induction in Mature Mesembryanthemum crystallinum L.

Piepenbrock

Schmitt²

1991

“…In the CAM mode of photosynthesis, several carbon-metabolizing enzymes are increased in extractable activity (7). The induction of one of these enzymes, PEPCase2, has been studied in some detail (2,6,10,11). Under salt stress, transcription from a stress-specific isogene is increased, leading to accumulation ofCAM-specific mRNA (2) and enzyme protein (5).…”

mentioning

confidence: 99%

“…The induction of one of these enzymes, PEPCase2, has been studied in some detail (2,6,10,11). Under salt stress, transcription from a stress-specific isogene is increased, leading to accumulation ofCAM-specific mRNA (2) and enzyme protein (5). The CAM-specific PEPCase enzyme can be distinguished from its C3 counterpart by mobility on SDS gels and peptide mapping (5).…”

mentioning

confidence: 99%

Induction of mRNA for Phosphoenolpyruvate Carboxylase Is Correlated with a Decrease in Shoot Water Content in Well-Irrigated Mesembryanthemum crystallinum

Schmitt

Piepenbrock²

1992

The abundance of mRNA specific for phosphoenolpyruvate carboxylase (PEPCase) was measured in leaves from wellwatered plants of Mesembryanthemum crystallinum. Plants grown side by side in pots of four different volumes (0.16, 0.74, 2.6, 6.5 liters) were compared. The time of increase in the steady-state level of PEPCase mRNA in well-watered plants was dependent on soil volume. The larger the pot, the later PEPCase transcripts were increased. PEPCase mRNA induction started when shoot water content decreased to well below 4000% of dry weight. No positive correlation with the developmental status of the plants could be found. The data indicate that PEPCase mRNA induction in well-watered plants up to 10 weeks of age is controlled environmentally rather than developmentally.

“…Both (4,17). Inducers such as light and osmotic stress may recruit the plant growth regulator ABA to instigate and/or moderate these changes in gene expression (10,14).…”

mentioning

confidence: 99%

Light Moderates the Induction of Phosphoenolpyruvate Carboxylase by NaCl and Abscisic Acid in Mesembryanthemum crystallinum

McElwain

Bohnert²,

Thomas³

1992