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. 1966 Mar;41(3):500–505. doi: 10.1104/pp.41.3.500

CO2 Fixation in Opuntia Roots 1

Irwin P Ting 1,2, W M Dugger Jr 1
PMCID: PMC1086371  PMID: 16656280

Abstract

Nonautotrophic CO2 metabolism in Opuntia echinocarpa roots was studied with techniques of manometry and radiometry. The roots were grown in a one-quarter strength nutrient solution for several days; the distal 2 cm was used for physiological studies. The roots assimilated significant quantities of 14CO2 and appeared to show a crassulacean-type acid metabolism with respect to quality and quantity. Most of the 14C activity was associated with the distal portion of the elongating root indicating correlation with metabolic activity. The 14CO2 assimilation was comparable to a crassulacean leaf succulent, but 3 times greater than that found for stem tissue of the same Opuntia species.

The rates of O2 and CO2 exchange and estimated CO2 fixation were 180, 123, and 57 μl/g per hour. A respiratory quotient of 0.66 was found.

The products of 14CO2 fixation were similar in most respects to reported experiments with leaf succulents. Equilibration of the predominant malic acid with isocitric, succinic, and fumaric acids was not evident. The latter observation was interpreted as metabolic isolation of the fixation products rather than poor citric acid cycle activity.

A rapid turnover of the fixed 14CO2 was measured by following decarboxlyation kinetics and by product analysis after a postincubation period. The first order rate constant for the steady state release was 4.4 × 10−3 min−1 with a half-time of 157.5 minutes. Amino acids decayed at a more rapid rate than organic acids.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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