This study investigates the influence of ABA, Calcium, along with chloropromazine (CPZ, Calcium antagonist), Ethylene Glycol Tetraacetic Acid (EGTA, Calcium chelator), Fluridone (Inhibitor of ABA biosynthesis), and combination of ABA with calcium chloride and fluridone on growth related enzyme activities during fiber development at 15 and 35 Days After Anthesis (DAA). CaCl₂ and F enhance the esterase activity, and the inhibition by ABA was alleviated in the combination treatments with CaCl₂ and F. ABA treatment inhibited acid invertase activity at both the stages in G. arboreum, whereas Ca²⁺ proved to be stimulatory, thus indicating that ABA and Calcium act independently of each other in the regulation of acid invertase activity. The role of stimulation of this enzyme was supported by the observations that EGTA and CPZ markedly decreased acid invertase activity. ABA, CPZ, and EGTA inhibited a-galactosidase activity at 15 and 35 DAA, whereas CaCl₂, F and the combination treatments enhanced the a-galactosidase activity. ABA inhibited both Mg²⁺ and Ca²⁺-ATPases, in contrast the calcium treatments markedly enhanced both the enzyme activities, the enhancement being more in the Ca²⁺-ATPases. It may be inferred that Ca²⁺ may be regulating a preferential activity of ATPases to the cell wall, its activation or synthesis during fiber elongation. Exogenous application of EGTA and CPZ appreciably enhanced the activities at both the stages, thus supporting the non-involvement of Calcium Calmodulin in their regulation.

Cotton fibers are single elongated cells which develop from certain epidermal cells of ovules. Epidermal cells differentiate into fiber cells between two and three days of pre-anthesis (Stewart, 1975). Fiber initiation starts a day before and up to a day or two after anthesis and then fiber initials enter into elongation. Secondary wall deposition in fibers begins before cessation of elongation and at a time related closely to the formation of final fiber (Ruan et al., 1997). Developing cotton fibers provide a good model system for investigating basic questions in plant cell biology. In fact, several aspects of cell growth and differentiation are programmed during fiber development, thus, making cotton hair a model system to investigate processes such as elongation, wall synthesis, and organization.

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