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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

Contents of sodium (a, b) and cyclitols (c, d) in leaves and roots of wild-type (solid bars) and CAM-deficient mutant (open bars) 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. 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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fig5: Contents of sodium (a, b) and cyclitols (c, d) in leaves and roots of wild-type (solid bars) and CAM-deficient mutant (open bars) 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. 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: Roots and particularly shoots accumulated substantial amounts of Na over the 14 d salinity treatment (Fig. 5a, b). Wild-type leaves showed significantly higher Na contents than mutant leaves (P < 0.05), but Na contents of roots of the wild type and mutant were similar. Imposition of salinity resulted in comparable increases in cyclitols in the leaves of both the wild type and mutant (Fig. 5c), with a 5-fold increase in leaf cyclitol content noted over the 14 d treatment period. There was no significant day–night change in leaf cyclitol content (data not shown). The roots of well-watered mutants contained significantly higher concentrations of cyclitols compared with the wild type and, after 4 d of salinity, the cyclitol content of the mutant roots was 5-fold higher than that of wild-type roots (Fig. 5d). However, with increasing salinity stress, root cyclitol content declined in the mutant and, by day 14 of salinity, cyclitol contents were similar in the roots of the mutant and wild type.


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)

Contents of sodium (a, b) and cyclitols (c, d) in leaves and roots of wild-type (solid bars) and CAM-deficient mutant (open bars) 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. 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

fig5: Contents of sodium (a, b) and cyclitols (c, d) in leaves and roots of wild-type (solid bars) and CAM-deficient mutant (open bars) 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. 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: Roots and particularly shoots accumulated substantial amounts of Na over the 14 d salinity treatment (Fig. 5a, b). Wild-type leaves showed significantly higher Na contents than mutant leaves (P < 0.05), but Na contents of roots of the wild type and mutant were similar. Imposition of salinity resulted in comparable increases in cyclitols in the leaves of both the wild type and mutant (Fig. 5c), with a 5-fold increase in leaf cyclitol content noted over the 14 d treatment period. There was no significant day–night change in leaf cyclitol content (data not shown). The roots of well-watered mutants contained significantly higher concentrations of cyclitols compared with the wild type and, after 4 d of salinity, the cyclitol content of the mutant roots was 5-fold higher than that of wild-type roots (Fig. 5d). However, with increasing salinity stress, root cyclitol content declined in the mutant and, by day 14 of salinity, cyclitol contents were similar in the roots of the mutant and wild type.

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