Physiologically, abscisic acid (ABA) is believed to be a general inhibitor of plant growth, including during the crucial early development of seedlings. However, this view contradicts many reports of stimulatory effects of ABA that, so far, have not been considered in the debate concerning ABA's function in plant development. To address this apparent contradiction, we propose a hypothetical mechanism to explain how ABA might contribute to the promotion of cell expansion. We wish to overturn conventional views on ABA's role during juvenile plant development and put forward the idea that, as for other phytohormones, the role of ABA is determined by dose and sensitivity and ranges from stimulatory to inhibitory effects.

Department of Biology University of Washington Seattle WA USA

Department of Molecular Biology Centre of the Region Haná for Biotechnological and Agricultural Research Palacký University Olomouc Šlechtitelů 27 783 71 Olomouc Czech Republic; These authors contributed equally to the work

Laboratory of Growth Regulators Centre of the Region Haná for Biotechnological and Agricultural Research Institute of Experimental Botany Czech Academy of Sciences and Palacký University Olomouc Šlechtitelů 27 783 71 Olomouc Czech Republic; Department of Chemical Biology and Genetics Centre of the Region Haná for Biotechnological and Agricultural Research Palacký University Olomouc Šlechtitelů 27 783 71 Olomouc Czech Republic; These authors contributed equally to the work

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Transcriptional changes during crown-root development and emergence in barley (Hordeum vulgare L.)