Details

Autor(en) / Beteiligte

• Macuff, J.H.
• Jarvis, S.C.
• Cockburn, J.E.

Titel

Acclimation of NO−3 fluxes to low root temperature by Brassica napus in relation to NO−3 supply

Ist Teil von

• Journal of experimental botany, 1994-08, Vol.45 (8), p.1045-1056

Ort / Verlag

Oxford University Press

Erscheinungsjahr

1994

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Acclimation of NO−3 transport fluxes (influx, efflux) in roots of oilseed rape (Brassica napus L. cv. Bien venu) and their sensitivity to growth at low root temperature was studied in relation to external NO−3 supply, defined by constant concentrations ranging from sub- to supra-optimal with respect to plant growth rate. Plants were grown from seed in flowing nutrient solutions containing 250 mmol m−3 NO−3 at 17°C for 20d, and solution temperature in half the culture units was then lowered decrementally over 3 d to 7°C. Three days later plants were supplied with NO−3 at 1, 10, 100 or 1000 mmol m−3 maintained for 18 d. Dry matter production was decreased more by low root zone temperature than low [NO−3]e. Root specific growth rates were inversely related to [NO−3]e and shoot:root ratios increased with time at [NO−3]e between 10–1000 mmol m−3. Net uptake of NO−3 at 17°C was twice that at 7°C, and at both temperatures it doubled with increasing [NO−3]e between 1–10 mmol m−3 with further small increases at higher [NO−3]e. Mean unit absorption rates of NO−3 between 0–6 d and 6–14 d were linearly related (r2 of 0.79–0.99) to log10[NO]. Steady-state Q10 (7–17°C) for uptake between 0–6 d were 0.91, 1.62, 1.27, and 1.10, respectively, at [NO−3]e of 1, 10, 100, and 1000 mmol m−3, compared with corresponding values of 0.98, 1.38, 1.68, and 1.89 between 6–14 d. The data indicated that net uptake rates at 7 and 17°C diverged over time at high [NO−3]e. Short-term uptake rates from 1 mol m−3 NO−3 measured at 17°C were higher in plants grown with roots at 7°C than at 17°C; for 7°C plants there was a strong inverse linear relationship (r2=0.94) between uptake rate and treatment log10 [NO−3]e whilst rates in 17°C plants were independent of prior [NO−3]e. Rates of NO−3 influx and efflux under different steady-state conditions of NO−3 supply and root temperature were calculated from dilution of 15N added to culture solutions. Efflux was substantial relative to net uptake in all treatments, and was inversely related to [NO−3]e at 17°C but not at 7°C. Ratios of influx: efflux ranged from 1.6–2.9 at 17°C and 1.3–1.8 at 7°C, indicating the proportionately greater impact of efflux at low root temperature. Ratios of efflux: net uptake were 0.53–1.56 at 17°C and 1.21–3.58 at 7°C. The apparent sensitivities of influx and efflux to steady-state root temperature varied with [NO−3]e. Both fluxes were higher at 17°C than 7°C in the presence of 100–1000 mmol m−3 NO−3 but the trend was reversed at 1–10 mmol m−3 NO. Concentrations of total N measured in xylem exudate were at least 2-fold higher at 7°C compared with 17°C, attributable mainly to higher concentrations of NO−3 glutamine and proline. The results are discussed in terms of acclimatory and other responses shown by the NO−3 transport system under conditions of limiting NO−3 supply and low root temperature.