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Acid Invertase Activity in Kernels of Normal and Opaque-2 Corn at Different Growth Stages through Maturity¹

Acid invertase activity in the placento-chalazal tissue of developing corn (Zea mays L.) kernels was measured from 23 to 49 days after pollination. Because sucrose, the transported saccharide in corn, is thought to be converted by acid invertase to glucose and fructose before passing into the developing endosperm, acid invertase activity of the placento-chalazal tissue during kernel-fill period may be a useful index of maturity and potential productivity, as well as an indicator of yield difference among genotypes.

Ten single cross corn hybrids were grown in the field near Middletown, Del., in 1973, including five normal endosperm hybrids of varying relative maturity and their sister hybrids with opaque-2 (o-2) genotype. Daily high and low temperatures and rainfall were recorded for the growing period. At 23 to 49 days post-pollination, kernel samples were harvested, lyophilized, and acid invertase activity of the placento-chalazal tissue determined.

Pioneer Brand hybrids 3570, 3516, and 3387 had significantly higher levels of acid invertase activity than did Pioneer Brand hybrids 3369 A and 3306, but no differences in acid invertase activity were found between normal and o-2 hybrids. During the period from 23 to 37 days post-pollination, acid invertase activity decreased, then the activity increased sharply from 37 to 39 days and decreased but more slowly during the 39 to 49 day period. The o-2 hybrids had lower yields than did the normal genotype hybrids, even though the acid invertase activity was very similar in the paired comparisons. Acid invertase activity in the placental-chalazal tissues did not appear to be limiting yield of these hybrids.

Key Words: Reducing sugar • Sucrose • High-lysine • Growing degree units • Grain yield

² Assistant manager, Middletown Corn Research Station, Pioneer Hi-Bred International, Inc., Middletown, DE 19709, and assistant professor, Plant Science Dep., Univ. of Delaware, Newark, DE 19711. (Presently associate professor, South Central Research Station, Univ. of Nebraska, Box 66, Clay Center, NE 68933.)

Received for publication September 3, 1975.