Sugar saves the seed set
In the accompanying ContentSelect we noted that cells may lose water because of intercellular ice formation. However, cellular water deficit is more usually associated with a shortage of water under non-freezing conditions, particularly during drought. Many plants show some degree of tolerance to water deficit but that tolerance may vary according to the developmental stage of the individual plant. Thus, as pointed out by McLaughlin and Boyer at the University of Delaware (pp. 675–689), maize (Zea mays) is especially vulnerable around the time of pollination when water deficit leads to abortion of ovaries and thereby reducing seed set. This in turn has been ascribed to inhibition of photosynthesis by water shortage. In support of this, previous work by these and other authors suggests that feeding sucrose may reduce the extent of ovary abortion. The authors have now made a thorough study of some of the molecular mechanisms underlying this phenomenon. Here they focus especially on expression of genes encoding sucrose-metabolizing enzymes. The authors used the increasingly popular technique of real-time quantitative PCR to estimate mRNA populations, showing that under conditions of water deficit, the expression of these genes is strongly down-regulated (although that of an invertase inhibitor remains high). In addition, as the water deficit, imposed by withholding water, becomes more severe, two senescence-associated genes are up-regulated and the expression of these genes may be linked specifically with ovary abortion. However, if sucrose is supplied, the down-regulation of genes encoding cell wall invertases is reversed although those encoding other sucrose-metabolizing enzymes are unaffected by addition of sucrose. These data thus show a correlation during water deficit between the fate of the ovary and the expression of some of the genes encoding sucrose-metabolizing enzymes. Future challenges include understanding the roles of all the sucrose-metabolizing enzymes during normal pollination and development, and also determining the significance of the differential responses to sucrose.
Professor J. A. Bryant
BUniversity of Exeter, UK
j.a.bryant{at}exeter.ac.uk
