Carbon dioxide fixation in orchid aerial roots |
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Authors: | C S Hew Y W Ng S C Wong H H Yeoh K K Ho |
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Institution: | Dept of Botany;National Univ. of Singapore, Lower Kent Ridge Road, Republic of Singapore 0511;Dept of Environmental Biology, Australian National Univ., Canberra, ACT, Australia 2601. |
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Abstract: | Acidity fluctuation, CO2 gas exchange, δ13C value, PEP carboxylase and RuBP carboxylase activities in aerial roots of selected thick-leaved orchid hybrids ( Arachnis and Aranthera ) were studied. Both aerial roots and leaves showed acidity fluctuation over a 24 h period. Dark acidification in aerial roots was enhanced at low temperature (15°C). Aerial roots had δ13C values close to those of leaves which have been previously demonstrated to possess crassulacean acid metabolism. Variation in δ13C values along the length of the roots was observed; the root tip having a less negative δ13C value (—13.34%‰) than the older portions of the roots (—14.55%‰). There was no net CO2 fixation by aerial root, although 1432CO2 fixation was observed in light and in darkness. The pattern of fluctuation in activities of PEP carboxylase and RuBP carboxylase in aerial roots was similar to that obtained for the leaves. In both aerial roots and leaves, PEP carboxylase activity was several times higher than that of RuBP carboxylase. |
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Keywords: | Arachnis Aranthera PEP carboxylase RuBP carboxylase δ13C values |
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