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Photosynthetic Carbon Assimilation in a Shootless Orchid, Chiloschista usneoides (DON) LDL

A Variant on Crassulacean Acid Metabolism

Department of Botany, University of Leicester, Leicester LE1 7RH United Kingdom, Department of Botany, National University of Singapore, Kent Ridge, Singapore, 0511

Photosynthetic carbon assimilation in the roots of a shootless orchid Chiloschista usneoides (DON) LDL involves the synthesis and accumulation of malic acid from CO₂ in darkness. Malic acid is consumed in the light.

The roots do not possess stomata or any means of diurnally regulating the diffusive conductance of the pathway between the internal gas phase of the plant and the atmosphere. Regulation of internal CO₂ concentration near to atmospheric levels avoids a large net loss of CO₂ to the atmosphere during malic acid consumption in the light.

The water-absorbing function of the velamen conflicts with the photosynthetic function of the roots. Plants with water-saturated velamina do not acquire CO₂ from the atmosphere at night.

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