Sugar-responsive gene expression, invertase activity, and senescence in aborting maize ovaries at low water potentials

Background and Aims Ovary abortion can occur in maize (Zea mays) if water deficits lower the water potential (psi(w)) sufficiently to inhibit photosynthesis around the time of pollination. The abortion decreases kernel number. The present work explored the activity of ovary acid invertases and their genes, together with other genes for sucrose-processing enzymes, when this kind of abortion occurred. Cytological evidence suggested that senescence may have been initiated after 2 or 3 d of low psi(w), and the expression of some likely senescence genes was also determined. Methods Ovary abortion was assessed at kernel maturity. Acid invertase activities were localized in vivo and in situ. Time Courses for mRNA abundance were measured with real time PCR. Sucrose was fed to the stems to vary the sugar flux. Key Results Many kernels developed in controls but most aborted when yw became low. Ovary invertase was active in controls but severely inhibited at low psi(w) for cell wall-bound forms in vivo and soluble forms in situ. All ovary genes for sucrose processing enzymes were rapidly down-regulated at low psi(w) except for a gene for invertase inhibitor peptide that appeared to be constitutively expressed. Some ovary genes for senescence were subsequently up-regulated (RIP2 and PLD1). In some genes, these regulatory changes were reversed by feeding sucrose to the stems Abortion was partially prevented by feeding sucrose. Conclusions A general response to low psi(w) in maize ovaries was an early down-regulation of genes for sucrose processing enzymes followed by up-regulation of some genes involved in senescence. Because some of these genes were sucrose responsive, the partial prevention of abortion with sucrose feeding may have been caused in part by the differential sugar-responsiveness of these genes. The late up-regulation of senescence genes may have caused the irreversibility of abortion. (C) 2004 Annals of Botany Company.