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Pakistan Journal of Biological Sciences
Year: 2002  |  Volume: 5  |  Issue: 5  |  Page No.: 523 - 528

Effect of Elevated CO2 and Drought on Proline Metabolism and Growth of Saf-flower (Carthamus mareoticus L.) Seedlings Without Improving Water Status

Laila, E. Abdel-Nasser and Adel E. Abdel-Aal    

Abstract: Plants subjected to ambient (350μmol mol–1) and elevated (700μmol mol–1) CO2 were either well-watered or droughted. It was found that well-watered plants grown either in ambient or elevated CO2 had the same water potential (Ψw), whereas the drought reduced (Ψw) especially in elevated CO2. Leaves of elevated-CO2 and well-watered grown plants contained more total soluble sugars, and starch contents than those of the ambient CO2 , whereas sucrose levels were similar for the well-watered plants of both elevated and ambient CO2 treatments. In contrast, drought reduced the leaf starch and increased the total soluble sugars and sucrose contents in both CO2 treatments. The activity of leaf sucrose phosphate synthase (SPS, EC: 2.4.1.14) of well-watered plants was not affected by high CO2 , whereas that of ambient-CO2-grown plants was reduced 42 % by drought. Most of the amino acids showed an increase with the induction of drought and elevated CO2 , but proline only increased more markedly than did other amino acids, amounting to 37 folds compared to about 2 fold in ambient-CO2-well watered grown plants. The activities of three enzymes, Δ1-pyrroline-5-carboxylase reductase (P5CR, EC: 1.5.1.2) and ornithine aminotransferase (OAT, EC: 2.6.1.1.3) and proline dehydrogenase (PDH, EC: 1.5.1.2) were measured. The activity of P5CR and OAT was found to increase 6 and 3 folds respectively in high-CO2 droughted plants. On the other hand, the activity of PDH was reduced by 40%. Accordingly, we concluded that proline accumulation in Carthamus mareoticus is caused by both the activation of its biosynthesis and inhibition of its degradation.

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