Water deficit-induced senescence and its relationship to the remobilization of pre-stored carbon in wheat during grain filling

Remobilization and transfer of the pre-stored food in vegetative tissues to the grains in monocarpic plants require the initiation of whole plant senescence. However, mechanisms by which plant senescence promotes remobilization of assimilates are rather obscure. This study examined the relationship between the senescence induced by water deficits and C remobilization during grain fill. Two semi-winter wheat cultivars (Triticum aestivum L.),Yangmai 158 and Yangmai 931, were treated with two levels of nitrogen (normal [NN] or high [HN]) and three levels of soil moisture (well-watered, moderate water deficit, and severe water deficit). Results showed that water deficits enhanced the senescence by accelerating loss of leaf nitrogen and chlorophyll and increasing lipid peroxidation. At maturity, 75 to 92% of pre-anthesis C-14 stored in the straw was reallocated to grains in water-deficit treatments, 50 to 80% higher than the amount in well-watered treatments, indicating that water deficits promoted remobilization. The peak values of abscisic acid (ABA) in both leaves and grains under water-deficit treatments were 63 to 144% higher than those under well-watered treatments. The elevated ABA level correlated with the degree of earlier leaf senescence, the C-14 partitioning into grains, and the carbon remobilization. The activites of both acid invertase (INV) and sucrose synthase (SS) in grains were also enhanced by water deficits at the midstage of grain fill. Our results suggest that the senescence and remobilization promoted by water deficits during grain fill are coupled processes in wheat, and elevated ABA concentration may play a regulative role.