Independent Control of Fiber Development and Nitrate Reduction in Cultured Cotton Ovules

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Abstract
Several lines of evidence implicate ammonium as an important factor in the growth and development of cotton (Gossypium hirsutum L.) ovules cultured in vitro. For example, ovules cultured at 28.degree. C require IAA and either ammonium or GA3 in the medium for fiber development, whereas ovules cultured at 34.degree. C require only IAA. Because of this effect of ammonium supply, it seemed possible that hormones or increased temperature were also promoting the availability of reduced N by induction of increased nitrate reductase activity in the ovules. This possibility was tested. In vivo, where ovules received mostly reduced N and very little nitrate, they did not display appreciable nitrate reductase activity even when nitrate was forced into the ovary wall by transpiration. After initiation of culture, nitrate became freely available to ovules and their nitrate reductase activity increased rapidly. Treatment with ammonium, GA3, IAA, or increased temperature had no effect upon this induction. Possibly ammonium, hormone and temperature effects on fiber development are independent of the availability of reduced N as a general substrate for growth.