Dark Metabolism of CO2during Fibre Elongation of Two Cottons Differing in Fibre Lengths

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Abstract
A study has been made of the dark metabolism of CO2 by elongating fibres of Gossypium arboreum L. cv. LD 133 (a short staple type) and Gossypium hirsutum L. cv. LH 372 (a long staple type) at different fibre ages. In both cultivars, phosphoenolpyruvate carboxylasc, glutamate-oxalacetate transaminase and malate dehydrogenase show elevated activities during the period of rapid fibre growth and lowered activity with ageing. Malic enzyme activity increases as extension growth levels off. Levels of K+ and malate rise during rapid extension growth and fall as the rate of elongation decreases. The results indicate that malate may act as an osmoticum and a counterion for K+ accumulation during rapid expansion of the fibres. Amounts of enzymes, K+ and malate are higher in the fibres of the long staple cultivar than the short staple. During the period of active elongation, K+/malate ratio is higher in the short staple cultivar.