Published by Oxford University Press [2008] on behalf of the Society for Experimental Biology
Preface
Many endogenous signals are known to regulate plant growth and development. These include the classical plant growth regulators (PGRs) auxin, cytokinins, ethylene, gibberellins, and abscisic acid (ABA), plus newly discovered signals such as mRNAs, sugars, amino acids, and proteins. Often these signals are synthesized distant from their site of action and must be transported within the plant. Some travel only short distances between cells and are termed local signals. Others must travel longer distances between tissues and organs to exert their effects and are termed systemic signals. This Special Issue of the Journal of Experimental Botany (JXB) contains 11 invited papers from a session on ‘The Transport of Plant Growth Regulators’ held at the Society for Experimental Biology (SEB) Annual Meeting at The Scottish Exhibition and Conference Centre, Glasgow, in April 2007. These papers review our current knowledge of the identity and action of endogenous signals regulating plant growth and development, and focus specifically on recent insights to their movement within the plant.Local signals control cell or tissue responses to their immediate environment. Of the classical PGRs, both gibberellins and ethylene appear to act over short distances stimulating cell growth and root hair development, respectively. This Special Issue begins with a paper by Jasper Dugardeyn and colleagues describing the interactions between these two important PGRs in the root elongation zone and their impact on root morphology. The growth-promoting brassino steroids are also thought to act over relatively short distances. Greg Symons and colleagues have reviewed the distribution, transport, and actions of these chemicals, with particular reference to their sites of synthesis and perception within the plant cell. Another gaseous chemical that acts over short distances is nitric oxide (NO). The evolution and perception of NO is reviewed here by Steven Neill and colleagues, who speculate whether NO might be the local product of a systemic signal.
Many classical PGRs are transported through tissues and between organs and are responsible for systemic signals. Fan Jiang and Wolfram Hartung describe the movement of ABA within plants and discuss how this signal affects plant responses to stress. Auxin impacts almost every aspect of plant development. For this Special Issue, Eric Kramer has reviewed the development and use of computer models that depict auxin transport within and between cells and tissues, Mikael Lucas and colleagues report how auxin fluxes in the root apex regulate root gravitropism and lateral root initiation, and Veronica Ongaro and Ottoline Leyser describe how the interactions of auxin with other PGRs controls shoot branching. Like auxin, cytokinins have been implicated in many diverse roles, including stimulating cell division and shoot morphogenesis and development. Genes encoding cytokinin transporters have recently been cloned and the corresponding proteins characterized. A paper by Naoya Hirose and colleagues describes the biosynthesis, transport, and action of cytokinins in plants, with particular emphasis on their role in co-ordinating plant responses to mineral deficiencies. Following this theme, Julia Kehr and Anja Buhtz describe the long-distance transport of RNA in the phloem and its possible physiological consequences, including the regulation of plant responses to phosphorus (P) starvation. John Hammond and Philip White present recent evidence that sucrose transport in the phloem behaves as a systemic signal for integrating root responses to P starvation and, finally, Anthony Miller and colleagues review the hypothesis that endogenous and exogenous amino acids are important signals for the regulation of nitrogen acquisition.
We thank the SEB, the SEB-Plant Transport Group and JXB for their financial support, and the JXB staff, especially Mary Traynor, Diana Hudspith, and Raquel Gonzalez-Cuesta, for helping us solicit and edit these papers.
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