Roles of carbohydrate supply and ethylene, polyamines in maize kernel set.

Glucose appears to have an antagonistic relationship with ethylene and ethylene and polyamines appear to play antagonistic roles in the abortion of seeds and fruits. Moreover, ethylene, spermidine, and spermine share a common biosynthetic precursor. The synchronous changes of them and the relationships with kernel set are currently unclear. Here, we stimulated maize (Zea mays L.) apical kernel set and studied their changes at 4, 8, 12, and 16 d after pollination (DAP). The status of the apical kernels changed from abortion to set, showing a pattern similar to that of the middle kernels, with slow decrease in glucose and rapid decline in ethylene production, and a sharp increase in spermidine and spermine after four DAP. Synchronous changes in ethylene and spermidine were also observed. However, the ethylene production decreased slowly in the aborted apical kernels, the glucose and polyamines concentrations were lower. Ethephon application did not block the change from abortion to set for the setting apical kernels. These data indicate that the developmental change may be accompanied by an inhibition of adequate glucose to ethylene synthesis and subsequent promotion of spermidine and spermine synthesis, and adequate carbohydrate supply may play a key role in the developmental process.