Submitted to: Australian Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/1996
Publication Date: N/A
Interpretive Summary: Drought during flower development causes large yield losses in wheat. Under droughty conditions, pollen in wheat flowers becomes sterile so that fertilization does not occur. The cause of pollen sterility is not known, but it is thought to result from a large concentration of the plant hormone abscisic acid (ABA for short) in flowers of droughted plants. To test this possibility, we measured the stress level and ABA content of flower parts, including those that contain the pollen, in wheat plants severely droughted during the early stages of flower development. We discovered that the flower parts containing the pollen are far less stressed by lack of water than are leaves and remain turgid even when leaves are wilted. By keeping the leaves turgid as the soil dried, we learned that leaves, rather than roots or floral tissues, are the likely source of ABA that accumulates in the flowers during drought. Even so, yield loss in droughted plants was not directly related to ABA content of pollen-containing floral tissues. These results suggest a factor other than ABA causes pollen sterility in drought-stressed wheat.
Technical Abstract: Chemical signals from roots growing in dry soil have been shown to moderate shoot response to drought. To test whether a root-derived signal, such as abscisic acid (ABA), produced during floral development might affect seed set in wheat (Triticum aestivum L.), we grew uni-culm plants in a controlled environment and withheld water from pollen mother cell meiosis to late boot stage--a period very sensitive to drought and exogenous ABA. In half the droughted plants, we pressurized the roots and soil as the soil dried to maintain leaf water potential at control levels. In the florets of droughted plants, glume water potential (w) decreased in parallel with leaf water potential but ovary and anther water potential were buffered from changes in leaf water potential. Turgor remained at or above control levels in all floral tissues examined. Free ABA content of leaves increased approximately equal to 20-fold as leaf turgor declined, while ABA in floral tissues increased approximately equal to 10-fold, compared to controls. The drought treatment decreased seed set approximately equal to 17%. Percent seed set on (droughted) pressurized plants was not different from that on well-watered plants even though soil moisture in droughted and pressurized treatments decreased to a similar extent and ABA content of leaves and floral tissues of 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 ultimately accumulated in floral tissues. But, this chemical signal apparently had little effect on seed set.