role for shoot protein in shoot-root dry matter allocation in higher plants

• Published in: Annals of botany Vol. 97; no. 1; pp. 3 - 10
• Main Authors: Andrews, M, Raven, J.A, Lea, P. J, Sprent, J. I
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.01.2006; Oxford Publishing Limited (England)
• Subjects: Dry matter partitioning; Irradiance; leaves; Nicotiana - chemistry; Nicotiana - growth & development; Nicotiana - metabolism; Nicotiana tabacum; nitrate signalling; Nitrates; Nitrates - metabolism; Nitrogen; Nitrogen - metabolism; Nutritional deficiencies; Peas; Physiological assimilation; Plant Leaves - growth & development; Plant Leaves - metabolism; Plant Proteins - analysis; Plant Proteins - physiology; Plant roots; Plant Roots - growth & development; Plant Roots - metabolism; Plant Shoots - growth & development; Plant Shoots - metabolism; Plants; protein; protein content; protein transport; Root growth; roots; shoot : root ratio; shoots; signal transduction; tobacco; VIEWPOINT
• ISSN: 0305-7364; 1095-8290
• DOI: 10.1093/aob/mcj009

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.