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- Hurry, Vaughan, 1960-, et al.
(författare)
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Cold-hardening results in increased activity of enzymes involved in carbon metabolism in leaves of winter rye (Secale-Cereale L)
- 1995
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Ingår i: Planta. - 0032-0935 .- 1432-2048. ; 195:4, s. 554-562
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Tidskriftsartikel (refereegranskat)abstract
- Light- and CO2-saturated photosynthesis of nonhardened rye (Secale cereale L. cv. Musketeer) was reduced from 18.10 to 7.17 mu mol O-2.m(-2).s(-1) when leaves were transferred from 20 to 5 degrees C for 30 min. Following cold-hardening at 5 degrees C for ten weeks, photosynthesis recovered to 15.05 mu mol O-2.m(-2).s(-1), comparable to the non-hardened rate at 20 degrees C. Recovery of photosynthesis was associated with increases in the total activity and activation of enzymes of the photosynthetic carbon-reduction cycle and of sucrose synthesis. The total hexose-phosphate pool increase by 30% and 120% for nonhardened and cold-hardened leaves respectively when measured at 5 degrees C. The large increase in esterified phosphate in cold-hardened leaves occurred without a limitation in inorganic phosphate supply. In contrast, the much smaller increase in esterified phosphate in nonhardened leaves was associated with an inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase and sucrose-phosphate synthase activation. It is suggested that the large increases in hexose phosphates in cold-hardened leaves compensates for the higher substrate threshold concentrations needed for enzyme activation at low temperatures. High substrate concentrations could also compensate for the kinetic limitations imposed by product inhibition from the accumulation of sucrose at 5 degrees C. Nonhardened leaves appear to be unable to compensate in this fashion due to an inadequate supply of inorganic phosphate.
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| 2. |
- Hurry, Vaughan, 1960-, et al.
(författare)
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Effect of cold hardening on the components of respiratory decarboxylation in the light and in the dark in leaves of winter rye
- 1996
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Ingår i: Plant Physiology. - 0032-0889 .- 1532-2548. ; 111:3, s. 713-719
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Tidskriftsartikel (refereegranskat)abstract
- In the dark, all decarboxylation reactions are associated with the oxidase reactions of mitochondrial electron transport. In the light, photorespiration is also active in photosynthetic cells. In winter rye (Secale cereale L.), cold hardening resulted in a P-fold increase in the rate of dark respiratory CO2 release from leaves compared with nonhardened (NH) controls. However, in the light, NH and cold-hardened (CH) leaves had comparable rates of oxidase decarboxylation and total intracellular decarboxylation, Furthermore, whereas CH leaves showed similar rates of total oxidase decarboxylation in the dark and light, NH leaves showed a 2-fold increase in total oxidase activity in the light compared with the dark. Light suppressed oxidase decarboxylation of end products of photosynthesis 2-fold in NH leaves and 3-fold in CH leaves in air. However, in high-CO2, light did not suppress the oxidase decarboxylation of end products. Thus, the decrease in oxidase decarboxylation of end products observed in the light and in air reflected glycolate-cycle-related inhibition of tricarboxylic acid cycle activity. We also showed that the glycolate cycle was involved in the decarboxylation of the end products of photosynthesis in both NH and CH leaves, suggesting a flow of fixed carbon out of the starch pool in the light.
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