Five ways to stay green

The relationship between carbon income and expenditure over the life of a leaf is described and related to the productivity benefits of altering the timing of senescence initiation. In genetic variants with delayed leaf senescence ('stay-greens') deconstruction of the photosynthetic apparatus during leaf senescence is partially or completely prevented. Although the stay-green phenotype is superficially similar in all species and genotypes, the genetic and physiological routes to the trait are diverse. In one type of stay-green, chlorophyll catabolism is disabled. Legumes and monocots with pigment breakdown lesions are discussed. Sorghum is presented as an example of another kind of stay-green in which perennial tendencies have been bred into a monocarpic annual crop species. Transgenic approaches are briefly discussed (enhanced endogenous cytokinins, reduced ethylene production or perception). An alternative route towards making a stay-green phenotype is through quantitative trait mapping and marker-assisted selection. Loci for greenness in pearl millet have been identified, some of which are associated with drought responses or flowering time. Finally the question of the limits on stay-green as a productivity-enhancing character is addressed.