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 sene scence. However, mechanisms by which plant senescence promotes remobilizati on of assimilates are rather obscure. This study examined the relationship between the senescence induced by water deficits and C remobilization durin g grain fill. Two semi-winter wheat cultivars (Triticum aestivum L.),Yangma i 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 w ater deficit, and severe water deficit). Results showed that water deficits enhanced the senescence by accelerating loss of leaf nitrogen and chloroph yll and increasing lipid peroxidation. At maturity, 75 to 92% of pre-anthes is C-14 stored in the straw was reallocated to grains in water-deficit trea tments, 50 to 80% higher than the amount in well-watered treatments, indica ting that water deficits promoted remobilization. The peak values of abscis ic acid (ABA) in both leaves and grains under water-deficit treatments were 63 to 144% higher than those under well-watered treatments. The elevated A BA level correlated with the degree of earlier leaf senescence, the C-14 pa rtitioning into grains, and the carbon remobilization. The activites of bot h acid invertase (INV) and sucrose synthase (SS) in grains were also enhanc ed by water deficits at the midstage of grain fill. Our results suggest tha t the senescence and remobilization promoted by water deficits during grain fill are coupled processes in wheat, and elevated ABA concentration may pl ay a regulative role.