Rufty T W, Mackown C T, Volk R J
United States Department of Agriculture, Agricultural Research Service, North Carolina State University, Raleigh, North Carolina 27695.
Plant Physiol. 1989 Feb;89(2):457-63. doi: 10.1104/pp.89.2.457.
An experiment was conducted to investigate the relative changes in NO(3) (-) assimilatory processes which occurred in response to decreasing carbohydrate availability. Young tobacco plants (Nicotiana tabacum [L.], cv NC 2326) growing in solution culture were exposed to 1.0 millimolar (15)NO(3) (-) for 6 hour intervals during a normal 12 hour light period and a subsequent period of darkness lasting 42 hours. Uptake of (15)NO(3) (-) decreased to 71 to 83% of the uptake rate in the light during the initial 18 hours of darkness; uptake then decreased sharply over the next 12 hours of darkness to 11 to 17% of the light rate, coincident with depletion of tissue carbohydrate reserves and a marked decline in root respiration. Changes also occurred in endogenous (15)NO(3) (-) assimilation processes, which were distinctly different than those in (15)NO(3) (-) uptake. During the extended dark period, translocation of absorbed (15)N out of the root to the shoot varied rhythmically. The adjustments were independent of (15)NO(3) (-) uptake rate and carbohydrate status, but were reciprocally related to rhythmic adjustments in stomatal resistance and, presumably, water movement through the root system. Whole plant reduction of (15)NO(3) (-) always was limited more than uptake. The assimilation of (15)N into insoluble reduced-N in roots remained a constant proportion of uptake throughout, while assimilation in the shoot declined markedly in the first 18 hours of darkness before stabilizing at a low level. The plants clearly retained a capacity for (15)NO(3) (-) reduction and synthesis of insoluble reduced-(15)N even when (15)NO(3) (-) uptake was severely restricted and minimal carbohydrate reserves remained in the tissue.
进行了一项实验，以研究因碳水化合物可利用性降低而发生的硝酸盐（NO₃⁻）同化过程的相对变化。在溶液培养中生长的年轻烟草植株（烟草 [L.]，品种 NC 2326）在正常的 12 小时光照期和随后持续 42 小时的黑暗期内，每隔 6 小时暴露于 1.0 毫摩尔的¹⁵NO₃⁻中。在黑暗的最初 18 小时内，¹⁵NO₃⁻的吸收量降至光照期间吸收速率的 71%至 83%；在接下来的 12 小时黑暗期内，吸收量急剧下降至光照速率的 11%至 17%，这与组织碳水化合物储备的耗尽以及根系呼吸的显著下降同时发生。内源性¹⁵NO₃⁻同化过程也发生了变化，这些变化与¹⁵NO₃⁻吸收的变化明显不同。在延长的黑暗期内，吸收的¹⁵N 从根向地上部的转运有节律地变化。这些调节与¹⁵NO₃⁻吸收速率和碳水化合物状态无关，但与气孔阻力的节律性调节以及可能与通过根系的水分移动呈反比关系。整株植物对¹⁵NO₃⁻的还原始终比吸收受到的限制更大。¹⁵N 在根中同化为不溶性还原态氮的比例在整个过程中始终保持恒定，而在地上部的同化在黑暗的最初 18 小时内显著下降，然后稳定在低水平。即使¹⁵NO₃⁻吸收受到严重限制且组织中剩余的碳水化合物储备极少，植株显然仍保留了¹⁵NO₃⁻还原和合成不溶性还原态¹⁵N 的能力。
