Starch and the Control of Kernel Number in Maize at Low Water Potentials

Abstract

After reproduction is initiated in plants, subsequent reproductive development is sometimes interrupted, which decreases the final number of seeds and fruits. We subjected maize (Zea mays L.) to low water potentials ( w ) that frequently cause this kind of failure. We observed metabolite pools and enzyme activities in the developing ovaries while we manipulated the sugar stream by feeding sucrose (Suc) to the stems. Low w imposed for 5 d around pollination allowed embryos to form, but abortion occurred and kernel number decreased markedly. The ovary contained starch that nearly disappeared during this abortion. Analyses showed that all of the intermediates in starch synthesis were depleted. However, when labeled Suc was fed to the stems, label arrived at the ovaries. Solute accumulated and caused osmotic adjustment. Suc accumulated, but other intermediates did not, showing that a partial block in starch synthesis occurred at the first step in Suc utilization. This step was mediated by invertase, which had low activity. Because of the block, Suc feeding only partially prevented starch disappearance and abortion. These results indicate that young embryos abort when the sugar stream is interrupted sufficiently to deplete starch during early ovary development, and this abortion results in a loss of mature seeds and fruits. At low w , maintaining the sugar stream partially prevented the abortion, but invertase regulated the synthesis of ovary starch and partially prevented full recovery.

An Invertase Inhibitor from Maize Localizes to the Embryo Surrounding Region during Early Kernel Development

“…Mutations in this gene result in miniature kernels (the mn1 mutation) and have a severely reduced endosperm (Cheng et al, 1996;Vilhar et al, 2002). Recently, the association of a IVR2, a soluble invertase expressed during early kernel development, with seed yield under conditions of limiting photosynthesis suggests that soluble invertases also play a significant role in providing hexose sugars to support cell division during the prestorage phase (Andersen et al, 2002), as has been previously suggested (Zinselmeier et al, 1999).…”

“…Mutations in this gene result in miniature kernels (the mn1 mutation) and have a severely reduced endosperm (Cheng et al, 1996;Vilhar et al, 2002). Recently, the association of a IVR2, a soluble invertase expressed during early kernel development, with seed yield under conditions of limiting photosynthesis suggests that soluble invertases also play a significant role in providing hexose sugars to support cell division during the prestorage phase (Andersen et al, 2002), as has been previously suggested (Zinselmeier et al, 1999).Invertases exhibit complex regulation at the transcriptional and posttranscriptional levels in response to developmental, environmental, and carbohydrate signals (Sturm, 1999). In addition, small (Ͻ20-kD) inhibitor proteins (INVINH) have been associated with invertase preparations in a number of dicot plant species (Pressey, 1994;Weil et al, 1994;Krausgrill et al, 1996Krausgrill et al, , 1998Greiner et al, 1998Greiner et al, , 2000 since their first biochemical characterization (Pressey, 1966;Jaynes and Nelson, 1971).…”

Yield stability for cereals in a changing climate

“…Drought-stressed ovules show decreased vacuolar and cell wall invertase activity, starch depletion and inhibited photosynthesis (Zinselmeier et al 1999). The maize nucellus is supported by the pedicel and cell wall invertase is expressed in the placento-chalaza cell layer which separates the nucellus from the pedicel (Miller and Chourey 1992).…”

Differential response of wild and cultivated wheats to water deficits during grain development: changes in soluble carbohydrates and invertases

“…The sensitivity of wheat crop to soil drought is particularly important during reproductive and grain-filling period (Zrenner et al 1995;Zinselmeier et al 1999). Water deficit stress during reproductive development restricts the supply of sucrose to floral organs (anthers and young ovaries) and often leads to floral abortion, significantly affecting grain number.…”