Nitrogen management and senescence in two maize hybrids differing in the persistence of leaf greenness: agronomic, physiological and molecular aspects.

Here, nitrogen management within the plant was compared in an early-senescing maize hybrid and in a late-senescing maize hybrid, both grown under field conditions with a high fertilisation input involving large quantities of fertiliser. We monitored, in representative leaf stages, the changes in metabolite content, enzyme activities and steady-state levels of transcripts for marker genes of N primary assimilation, N recycling and leaf senescence. The hybrids differed in terms of persistence of leaf greenness, the expression of marker genes and the concentration of enzymes used to describe the transition from N assimilation to N recycling. The transcription of leaf-senescence marker genes did not differ. Agronomic studies confirmed the ability of the late-senescing hybrid to absorb and store more N in shoots. Despite the differences in the mode of N management adopted by the two hybrids, we conclude that leaf senescence occurs independently of the source-to-sink transition at the high level of fertilisation used involving large quantities of fertiliser. The possibility of improving N metabolic efficiency in the latest maize hybrids is discussed. Copyright New Phytologist (2005).