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Some Factors Limiting Nitrate Reduction in Developing Ovules of Cotton¹

Ovules of developing cotton (Gossypium hirsutum L.) bolls had significant nitrate reductase activity, although considerably less than in leaves. The capability of the ovules to reduce nitrate (total nitrate reductase activity) increased during development, whereas the absolute rate of nitrate assimilation in situ reached a maximum at about 16 days after anthesis and then declined. Nitrate was present only in extremely small quantities in ovules, severely limiting their rate of nitrate reduction in situ. Transpiration from bolls was extremely slow, suggesting that ovules lack a mechanism for rapid replenishment of consumed nitrate. Estimated rates of ovular nitrate reduction could account for < 5% of the accumulation of reduced nitrogen.

Key Words: Gossypium L. • Nitrate reductase • In vivo assay • Transpiration

² Plant physiologist and physical sciences technician, respectively, ARS, USDA Western Cotton Res. Lab., 4135 E. Broadway Rd., Phoenix, AZ 85040.

Received for publication February 18, 1975.