|Passioura, John - CSIRO, CANBERRA, AS|
|Munns, Rana - CSIRO, CANBERRA, AS|
Submitted to: International Plant Growth Substance Association
Publication Type: Abstract Only
Publication Acceptance Date: July 12, 1994
Publication Date: N/A
Technical Abstract: Chemical signals from roots, such as ABA, might affect seed set on wheat plants growing in dry soil during floral development. To test this possibility, we grew uni-culm plants in a controlled environment and withheld water from pollen mother cell meiosis to late boot stage--a period of high sensitivity to drought and exogenous ABA. The water potential of glumes decreased in concert with leaf water potential, but ovary and anther water potential were buffered from changes in leaf water potential. Free ABA content of flag leaves increased approximately 20-fold as turgor declined. ABA content in floral tissues increased approximately 10-fold, compared to controls, even though turgor remained at or above control levels in all floral tissues examined. The drought treatment decreased seed set approximately 17%. In half the droughted plants, we pressurized the roots and soil as the soil dried to maintain leaf water potential at control levels. Seed set on (droughted) pressurized plants was not different from that on well-watered unpressurized plants even though soil moisture in droughted and (droughted) pressurized treatments decreased to a similar extent. ABA content of leaves and floral tissues of (droughted) pressurized plants increased 2- to 3-fold over control levels. These results indicate that a favorable shoot water status is critical for high seed set in wheat. ABA (or a precursor of ABA) produced by roots in dry soil may ultimately accumulate in floral tissues. However, this chemical signal apparently has little effect on seed set.