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Published online by Cambridge University Press: 05 December 2011
The actions of endogenous plant hormones are invoked to explain several morphological adaptations to poor aeration. These include changes to the growth and internal morphology of inundated roots, the promotion of extension growth by stems or leaves of aquatic and semi-aquatic species by submergence, and morphological changes in shoots where only the roots and lower shoot are inundated. This article considers ethylene-promoted aerenchyma formation in maize (Zea mays) and compares the promoting action of ethylene, low oxygen partial pressures and carbon dioxide on shoot extension in rice (Oryza sativa), a rice mimic Echinochloa oryzoides and a submersed aquatic monocot Potamogeton pecrinatus. Different kinds of hormonal messages (positive, negative, accumulative and debit) passing between roots and shoots co-ordinate shoot development with the roots and their environment. Recent progress in quantifying the delivery of abscisic acid (ABA) or the ethylene precursor 1-aminocyclopropane-1-car-boxylic acid (ACC) from roots to shoots in the transpiration stream is summarised in relation to control of stomatal closure and leaf epinastic curvature in flooded plants.