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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

Day/night profiles of net CO2 exchange for leaves of wild-type (solid line) and CAM-deficient mutant (dashed line) plants of Mesembryanthemum crystallinum grown under control conditions (day 0) and after 4, 6, 8, 10, and 14 d of treatment with 300 mM NaCl in hydroponics. The solid bars on the x-axes represent the periods of darkness and each gas exchange profile is for a representative leaf from three replicate determinations.
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fig1: Day/night profiles of net CO2 exchange for leaves of wild-type (solid line) and CAM-deficient mutant (dashed line) plants of Mesembryanthemum crystallinum grown under control conditions (day 0) and after 4, 6, 8, 10, and 14 d of treatment with 300 mM NaCl in hydroponics. The solid bars on the x-axes represent the periods of darkness and each gas exchange profile is for a representative leaf from three replicate determinations.

Mentions: In wild-type plants, net dark CO2 uptake was apparent after 6 d of salinity, and nocturnal net CO2 uptake increased further over the time period of the salinity treatment (i.e. 14 d; Fig. 1). In contrast, the mutant showed no net uptake of CO2 at night over the entire 14 d of salinity, indicating CAM deficiency. The wild-type plants showed higher rates of net CO2 uptake during the day (on average 20% higher) compared with the mutant at comparable stages of salinity. After 14 d of exposure to salinity, 24 h net CO2 uptake in the wild-type plants was reduced to 36% of that of well-watered controls, but in the mutant was reduced to only 10% of that of well-watered controls.


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)

Day/night profiles of net CO2 exchange for leaves of wild-type (solid line) and CAM-deficient mutant (dashed line) plants of Mesembryanthemum crystallinum grown under control conditions (day 0) and after 4, 6, 8, 10, and 14 d of treatment with 300 mM NaCl in hydroponics. The solid bars on the x-axes represent the periods of darkness and each gas exchange profile is for a representative leaf from three replicate determinations.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig1: Day/night profiles of net CO2 exchange for leaves of wild-type (solid line) and CAM-deficient mutant (dashed line) plants of Mesembryanthemum crystallinum grown under control conditions (day 0) and after 4, 6, 8, 10, and 14 d of treatment with 300 mM NaCl in hydroponics. The solid bars on the x-axes represent the periods of darkness and each gas exchange profile is for a representative leaf from three replicate determinations.
Mentions: In wild-type plants, net dark CO2 uptake was apparent after 6 d of salinity, and nocturnal net CO2 uptake increased further over the time period of the salinity treatment (i.e. 14 d; Fig. 1). In contrast, the mutant showed no net uptake of CO2 at night over the entire 14 d of salinity, indicating CAM deficiency. The wild-type plants showed higher rates of net CO2 uptake during the day (on average 20% higher) compared with the mutant at comparable stages of salinity. After 14 d of exposure to salinity, 24 h net CO2 uptake in the wild-type plants was reduced to 36% of that of well-watered controls, but in the mutant was reduced to only 10% of that of well-watered controls.

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