A Homoeotic Mutant of Arabidopsis thaliana with Leafy Cotyledons

Cotyledons are specialized leaves produced during plant embryogenesis. Cotyledons and leaves typically differ in morphology, ultrastructure, and patterns of gene expression. The leafy cotyledon (Iec) mutant of Arabidopsis thaliana fails to maintain this distinction between embryonic and vegetative patterns of plant development. Mutant embryos are phenotypically abnormal, occasionally viviparous, and intolerant of desiccation. Mutant cotyledons produce trichomes characteristic of leaves, lack embryo-specific protein bodies, and exhibit a vascular pattern intermediate between that of leaves and cotyledons. These results suggest that lec cotyledons are partially transformed into leaves and that the wild-type gene (LEC) functions to activate a wide range of embryo-specific pathways in higher plants.     

An optimal transition path for controlling greenhouse gases

Designing efficient policies to slow global warming requires an approach that combines economic tools with relations from the natural sciences. The dynamic integrated climate-economy (DICE) model presented here, an intertemporal general-equilibrium model of economic growth and climate change, can be used to investigate alternative approaches to slowing climate change. Evaluation of five policies suggests that a modest carbon tax would be an efficient approach to slow global warming, whereas rigid emissions- or climate-stabilization approaches would impose significant net economic costs.