排序方式: 共有1条查询结果,搜索用时 0 毫秒
1
1.
Acclimation of NO3 transport fluxes (influx, efflux)in roots of oilseed rape (Brassica napus L. cv. Bien venu) andtheir sensitivity to growth at low root temperature was studiedin relation to external NO3 supply, defined by constantconcentrations ranging from sub- to supra-optimal with respectto plant growth rate. Plants were grown from seed in flowingnutrient solutions containing 250 mmol m3 NO3at 17°C for 20d, and solution temperature in half the cultureunits was then lowered decrementally over 3 d to 7°C. Threedays later plants were supplied with NO3 at 1, 10, 100or 1000 mmol m3 maintained for 18 d. Dry matter productionwas decreased more by low root zone temperature than low [NO3]e. Root specific growth rates were inversely related to [NO3]eand shoot:root ratios increased with time at [NO3]e between101000 mmol m3. Net uptake of NO3 at 17°Cwas twice that at 7°C, and at both temperatures it doubledwith increasing [NO3]e between 110 mmol m3with further small increases at higher [NO3]e. Mean unitabsorption rates of NO3 between 06 d and 614d were linearly related (r2 of 0.790.99) to log10[NO].Steady-state Q10 (717°C) for uptake between 06d were 0.91, 1.62, 1.27, and 1.10, respectively, at [NO3]eof 1, 10, 100, and 1000 mmol m3, compared with correspondingvalues of 0.98, 1.38, 1.68, and 1.89 between 614 d. Thedata indicated that net uptake rates at 7 and 17°C divergedover time at high [NO3]e. Short-term uptake rates from1 mol m3 NO3 measured at 17°C were higherin plants grown with roots at 7°C than at 17°C; for7°C plants there was a strong inverse linear relationship(r2=0.94) between uptake rate and treatment log10 [NO3]ewhilst rates in 17°C plants were independent of prior [NO3]e. Rates of NO3 influx and efflux under different steady-stateconditions of NO3 supply and root temperature were calculatedfrom dilution of 15N added to culture solutions. Efflux wassubstantial relative to net uptake in all treatments, and wasinversely related to [NO3]e at 17°C but not at 7°C.Ratios of influx: efflux ranged from 1.62.9 at 17°Cand 1.31.8 at 7°C, indicating the proportionatelygreater impact of efflux at low root temperature. Ratios ofefflux: net uptake were 0.531.56 at 17°C and 1.213.58at 7°C. The apparent sensitivities of influx and effluxto steady-state root temperature varied with [NO3]e.Both fluxes were higher at 17°C than 7°C in the presenceof 1001000 mmol m3 NO3 but the trend wasreversed at 110 mmol m3 NO. Concentrations oftotal N measured in xylem exudate were at least 2-fold higherat 7°C compared with 17°C, attributable mainly to higherconcentrations of NO3 glutamine and proline. The resultsare discussed in terms of acclimatory and other responses shownby the NO3 transport system under conditions of limitingNO3 supply and low root temperature. Key words: Brassica napus, nitrate supply, efflux, influx, root temperature, xylem exudate 相似文献
1