AOBPreview published online on November 18, 2005
Annals of Botany, doi:10.1093/aob/mcj009
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1 School of Sciences, University of Sunderland, Sunderland SR1 3SD, UK
* To whom correspondence should be addressed.
• Background and Aims It is stated in many recent publications that nitrate (NO3-) acts as a signal to regulate dry matter partitioning between the shoot and root of higher plants. Here we challenge this hypothesis and present evidence for the viewpoint that NO3- and other environmental effects on the shoot : root dry weight ratio (S:R) of higher plants are often related mechanistically to changes in shoot protein concentration. • Methods The literature on environmental effects on S:R is reviewed, focusing on relationships between S:R, growth and leaf NO3- and protein concentrations. A series of experiments carried out to test the proposal that S:R is dependent on shoot protein concentration is highlighted and new data are presented for tobacco (Nicotiana tabacum). • Key Results/Evidence Results from the literature and new data for tobacco show that S:R and leaf NO3- concentration are not significantly correlated over a range of environmental conditions. A mechanism involving the relative availability of C and N substrates for growth in shoots can explain how shoot protein concentration can influence shoot growth and hence root growth and S:R. Generally, results in the literature are compatible with the hypothesis that macronutrients, water, irradiance and CO2 affect S:R through changes in shoot protein concentration. In detailed studies on several species, including tobacco, a linear regression model incorporating leaf soluble protein concentration and plant dry weight could explain the greater proportion of the variation in S:R within and between treatments over a wide range of conditions. • Conclusions It is concluded that if NO3- can influence the S:R of higher plants, it does so only over a narrow range of conditions. Evidence is strong that environmental effects on S:R are often related mechanistically to their effects on shoot protein concentration.
Received July 2, 2005
Revised August 1, 2005
Accepted September 29, 2005
Viewpoint
A Role for Shoot Protein in Shoot-Root Dry Matter Allocation in Higher Plants
M. ANDREWS 1 *,
J. A. RAVEN 2,
P. J. LEA 3,
and
J. I. SPRENT 4
2 University of Dundee at SCRI, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK
3 Department of Biological Sciences, Lancaster University, Lancaster LA1 4YQ, UK
4 Division of Environmental and Applied Biology, University of Dundee, Dundee DD1 4HN, UK
M. ANDREWS, E-mail: mitchell.andrews{at}sunderland.ac.uk
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