INHIBITION OF MAIZE ENDOSPERM CELL-DIVISION AND ENDOREDUPLICATION BY EXOGENOUSLY APPLIED ABSCISIC-ACID

Abseisic acid (ABA) is thought to play a role in inhibiting or abortin g kernel growth during water deficit. To test the responsiveness of ea rly endosperm development to ABA concentrations. cylinders containing (+/-)ABA in a buffered agar medium were applied to the apical pericarp surface of kernels on intact, well-watered maize (Zea mays L. cv. Pio neer Brand 3925) plants from 5 to 11 days after pollination (DAP), End osperm nuclei were analyzed by Bow cytometry to assess effects on cell division and endoreduplication. ABA treatments of greater than or equ al to 100 mu M substantially decreased endosperm cell numbers and fres h weight accumulation, but did not affect average cell size. ABA at gr eater than or equal to 300 mu M decreased the proportion of nuclei in the size classes greater than or equal to 12C, indicating that the rat e of transition to endoreduplication status was inhibited, and decreas ed the progressive advance from 12C to 24C to 48C, indicating that the rate af S-phase cycling of endoreduplicating cells was inhibited. We conclude that cell division was more responsive to ABA concentrations than were endoreduplication or cell expansion growth.