Dark Metabolism of CO2 during Fibre Elongation of Two Cottons Differing in Fibre Lengths

A study has been made of the dark metabolism of CO₂ by elongatingfibres of Gossypium arboreum L. cv. LD 133 (a short staple type)and Gossypium hirsutum L. cv. LH 372 (a long staple type) atdifferent fibre ages. In both cultivars, phosphoenolpyruvatecarboxylasc, glutamate-oxalacetate transaminase and malate dehydrogenaseshow elevated activities during the period of rapid fibre growthand lowered activity with ageing. Malic enzyme activity increasesas extension growth levels off. Levels of K⁺ and malate riseduring rapid extension growth and fall as the rate of elongationdecreases. The results indicate that malate may act as an osmoticumand a counterion for K⁺ accumulation during rapid expansionof the fibres. Amounts of enzymes, K⁺ and malate are higherin the fibres of the long staple cultivar than the short staple.During the period of active elongation, K⁺/malate ratio is higherin the short staple cultivar. Key words: Gossypium hirsutum, CO₂ metabolism, Fibre extension