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A CAM- and starch-deficient mutant of the facultative CAM species Mesembryanthemum crystallinum reconciles sink demands by repartitioning carbon during acclimation to salinity.

Haider MS, Barnes JD, Cushman JC, Borland AM - J. Exp. Bot. (2012)

Bottom Line: Under salinity, CAM deficiency reduced 24 h photosynthetic carbon gain by >50%.Dark respiration of leaves and roots was a stronger sink for carbohydrate in the mutant compared with the wild type and implied higher maintenance costs for the metabolic processes underpinning acclimation to salinity when CAM was curtailed.The data suggest a key role for the vacuole in regulating the supply and demand for carbohydrate over the day/night cycle in the starch-/CAM-deficient mutant.

View Article: PubMed Central - PubMed

Affiliation: Newcastle Institute for Research on Sustainability, Newcastle University, Newcastle upon Tyne, UK.

ABSTRACT
In the halophytic species Mesembryanthemum crystallinum, the induction of crassulacean acid metabolism (CAM) by salinity requires a substantial investment of resources in storage carbohydrates to provide substrate for nocturnal CO(2) uptake. Acclimation to salinity also requires the synthesis and accumulation of cyclitols as compatible solutes, maintenance of root respiration, and nitrate assimilation. This study assessed the hierarchy and coordination of sinks for carbohydrate in leaves and roots during acclimation to salinity in M. crystallinum. By comparing wild type and a CAM-/starch-deficient mutant of this species, it was sought to determine if other metabolic sinks could compensate for a curtailment in CAM and enable acclimation to salinity. Under salinity, CAM deficiency reduced 24 h photosynthetic carbon gain by >50%. Cyclitols were accumulated to comparable levels in leaves and roots of both the wild type and mutant, but represented only 5% of 24 h carbon balance. Dark respiration of leaves and roots was a stronger sink for carbohydrate in the mutant compared with the wild type and implied higher maintenance costs for the metabolic processes underpinning acclimation to salinity when CAM was curtailed. CAM required the nocturnal mobilization of >70% of primary carbohydrate in the wild type and >85% of carbohydrate in the mutant. The substantial allocation of carbohydrate to CAM limited the export of sugars to roots, and the root:shoot ratio declined under salinity. The data suggest a key role for the vacuole in regulating the supply and demand for carbohydrate over the day/night cycle in the starch-/CAM-deficient mutant.

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Related in: MedlinePlus

Sucrose (a, b), fructose (c, d), and glucose (e, f) contents in leaves of wild-type and CAM-deficient mutant plants of Mesembryanthemum crystallinum under control conditions (day 0/C and day 14/C) and following the imposition of 300 mM NaCl for 4, 8, and 14 d. Measurements were made at the start (dawn) and end (dusk) of the photoperiod, and each bar is the mean of four replicates ±SE. Asterisks indicate statistical differences at P < 0.05 between the wild type and mutant at comparable stages of salinity treatment as determined by t-tests.
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fig3: Sucrose (a, b), fructose (c, d), and glucose (e, f) contents in leaves of wild-type and CAM-deficient mutant plants of Mesembryanthemum crystallinum under control conditions (day 0/C and day 14/C) and following the imposition of 300 mM NaCl for 4, 8, and 14 d. Measurements were made at the start (dawn) and end (dusk) of the photoperiod, and each bar is the mean of four replicates ±SE. Asterisks indicate statistical differences at P < 0.05 between the wild type and mutant at comparable stages of salinity treatment as determined by t-tests.

Mentions: Leaves of the mutant contained significantly higher concentrations of soluble sugars compared with the wild type, particularly glucose and fructose (Fig. 3). Concentrations of glucose, fructose, and sucrose increased over the course of the day in the mutant at all stages of salinity, indicating that in the absence of starch, the mutant made use of soluble sugars to maintain 24 h net carbon balance. In the roots, the mutant showed higher concentrations of glucose and fructose compared with the wild type at day 0 and after 4 d of salinity (Fig. 4). At other stages of salinity, concentrations of root soluble sugars were similar in the wild type and mutant, and overall concentrations of all soluble sugars declined over the duration of the salinity treatment in both the wild type and mutant (Fig. 4).


A CAM- and starch-deficient mutant of the facultative CAM species Mesembryanthemum crystallinum reconciles sink demands by repartitioning carbon during acclimation to salinity.

Haider MS, Barnes JD, Cushman JC, Borland AM - J. Exp. Bot. (2012)

Sucrose (a, b), fructose (c, d), and glucose (e, f) contents in leaves of wild-type and CAM-deficient mutant plants of Mesembryanthemum crystallinum under control conditions (day 0/C and day 14/C) and following the imposition of 300 mM NaCl for 4, 8, and 14 d. Measurements were made at the start (dawn) and end (dusk) of the photoperiod, and each bar is the mean of four replicates ±SE. Asterisks indicate statistical differences at P < 0.05 between the wild type and mutant at comparable stages of salinity treatment as determined by t-tests.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3295396&req=5

fig3: Sucrose (a, b), fructose (c, d), and glucose (e, f) contents in leaves of wild-type and CAM-deficient mutant plants of Mesembryanthemum crystallinum under control conditions (day 0/C and day 14/C) and following the imposition of 300 mM NaCl for 4, 8, and 14 d. Measurements were made at the start (dawn) and end (dusk) of the photoperiod, and each bar is the mean of four replicates ±SE. Asterisks indicate statistical differences at P < 0.05 between the wild type and mutant at comparable stages of salinity treatment as determined by t-tests.
Mentions: Leaves of the mutant contained significantly higher concentrations of soluble sugars compared with the wild type, particularly glucose and fructose (Fig. 3). Concentrations of glucose, fructose, and sucrose increased over the course of the day in the mutant at all stages of salinity, indicating that in the absence of starch, the mutant made use of soluble sugars to maintain 24 h net carbon balance. In the roots, the mutant showed higher concentrations of glucose and fructose compared with the wild type at day 0 and after 4 d of salinity (Fig. 4). At other stages of salinity, concentrations of root soluble sugars were similar in the wild type and mutant, and overall concentrations of all soluble sugars declined over the duration of the salinity treatment in both the wild type and mutant (Fig. 4).

Bottom Line: Under salinity, CAM deficiency reduced 24 h photosynthetic carbon gain by >50%.Dark respiration of leaves and roots was a stronger sink for carbohydrate in the mutant compared with the wild type and implied higher maintenance costs for the metabolic processes underpinning acclimation to salinity when CAM was curtailed.The data suggest a key role for the vacuole in regulating the supply and demand for carbohydrate over the day/night cycle in the starch-/CAM-deficient mutant.

View Article: PubMed Central - PubMed

Affiliation: Newcastle Institute for Research on Sustainability, Newcastle University, Newcastle upon Tyne, UK.

ABSTRACT
In the halophytic species Mesembryanthemum crystallinum, the induction of crassulacean acid metabolism (CAM) by salinity requires a substantial investment of resources in storage carbohydrates to provide substrate for nocturnal CO(2) uptake. Acclimation to salinity also requires the synthesis and accumulation of cyclitols as compatible solutes, maintenance of root respiration, and nitrate assimilation. This study assessed the hierarchy and coordination of sinks for carbohydrate in leaves and roots during acclimation to salinity in M. crystallinum. By comparing wild type and a CAM-/starch-deficient mutant of this species, it was sought to determine if other metabolic sinks could compensate for a curtailment in CAM and enable acclimation to salinity. Under salinity, CAM deficiency reduced 24 h photosynthetic carbon gain by >50%. Cyclitols were accumulated to comparable levels in leaves and roots of both the wild type and mutant, but represented only 5% of 24 h carbon balance. Dark respiration of leaves and roots was a stronger sink for carbohydrate in the mutant compared with the wild type and implied higher maintenance costs for the metabolic processes underpinning acclimation to salinity when CAM was curtailed. CAM required the nocturnal mobilization of >70% of primary carbohydrate in the wild type and >85% of carbohydrate in the mutant. The substantial allocation of carbohydrate to CAM limited the export of sugars to roots, and the root:shoot ratio declined under salinity. The data suggest a key role for the vacuole in regulating the supply and demand for carbohydrate over the day/night cycle in the starch-/CAM-deficient mutant.

Show MeSH
Related in: MedlinePlus