...response: Nitrate and root branching

Abstract

`Why do plants bother to proliferate lateral roots into NO3−rich patches of soil?' was a question recently posed by David Robinson[ 1 Robinson D. Resource capture by localized root proliferation: why do plants bother?. Ann. Bot. 1996; 77: 179-185 Crossref Scopus (144) Google Scholar ]. He argued that although this localized proliferation of laterals should help a plant to capture ions that have very limited mobility in the soil (such as NH4+ and inorganic phosphate), it should have little or no beneficial effect on the exploitation of a highly mobile ion like NO3−. A similar point is made by Ottoline Leyser and Alastair Fitter in their article[ 2 Leyser O. Fitter A. Roots are branching out in patches. Trends Plant Sci. 1998; 3: 203-204 Abstract Full Text Full Text PDF Google Scholar ]. Our results suggest that Arabidopsis, with blatant disregard for the theory, has evolved a specific mechanism for sensing NO3− and for the proliferation of its lateral roots in response to localized supplies[ 3 Zhang H. Forde B.G. An Arabidopsis MADS box gene that controls nutrient-induced changes in root architecture. Science. 1998; 279: 407-409 Crossref PubMed Scopus (962) Google Scholar ]. To compound the paradox, we have evidence that Arabidopsis (unlike barley[ 4 Hobbie L. Estelle M. The axr4 auxin-resistant mutants of Arabidopsis thaliana define a gene important for root gravitropism and lateral root initiation. Plant J. 1995; 7: 211-220 Crossref PubMed Scopus (235) Google Scholar ]) does not respond to locally supplied NH4+ (H. Zhang and B. Forde, unpublished).