Elrifi I R, Turpin D H
Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6.
Plant Physiol. 1986 May;81(1):273-9. doi: 10.1104/pp.81.1.273.
Nitrate-limited chemostat cultures of Selenastrum minutum Naeg. Collins (Chlorophyta) were used to determine the effects of nitrogen addition on photosynthesis, dark respiration, and dark carbon fixation. Addition of NO(3) (-) or NH(4) (+) induced a transient suppression of photosynthetic carbon fixation (70 and 40% respectively). Intracellular ribulose bisphosphate levels decreased during suppression and recovered in parallel with photosynthesis. Photosynthetic oxygen evolution was decreased by N-pulsing under saturating light (650 microeinsteins per square meter per second). Under subsaturating light intensities (<165 microeinsteins per square meter per second) NH(4) (+) addition resulted in O(2) consumption in the light which was alleviated by the presence of the tricarboxylic acid cycle inhibitor fluoroacetate. Addition of NO(3) (-) or NH(4) (+) resulted in a large stimulation of dark respiration (67 and 129%, respectively) and dark carbon fixation (360 and 2080%, respectively). The duration of N-induced perturbations was dependent on the concentration of added N. Inhibition of glutamine 2-oxoglutarate aminotransferase by azaserine alleviated all these effects. It is proposed that suppression of photosynthetic carbon fixation in response to N pulsing was the result of a competition for metabolites between the Calvin cycle and nitrogen assimilation. Carbon skeletons required for nitrogen assimilation would be derived from tricarboxylic acid cycle intermediates. To maintain tricarboxylic acid cycle activity triose phosphates would be exported from the chloroplast. This would decrease the rate of ribulose bisphosphate regeneration and consequently decrease net photosynthetic carbon accumulation. Stoichiometric calculations indicate that the Calvin cycle is one source of triose phosphates for N assimilation; however, during transient N resupply the major demand for triose phosphates must be met by starch or sucrose breakdown. The effects of N-pulsing on O(2) evolution, dark respiration, and dark C-fixation are shown to be consistent with this model.
利用新月菱形藻（Nitrate-limited chemostat cultures of Selenastrum minutum Naeg. Collins，绿藻门）的硝酸盐限制恒化器培养物来确定添加氮对光合作用、暗呼吸和暗碳固定的影响。添加硝酸根离子（NO₃⁻）或铵离子（NH₄⁺）会引起光合碳固定的短暂抑制（分别为70%和40%）。抑制期间细胞内二磷酸核酮糖水平下降，并与光合作用同步恢复。在饱和光强（每秒每平方米650微爱因斯坦）下，氮脉冲会降低光合放氧量。在亚饱和光强（<每秒每平方米165微爱因斯坦）下，添加铵离子（NH₄⁺）会导致光下耗氧，而三羧酸循环抑制剂氟乙酸的存在可缓解这种情况。添加硝酸根离子（NO₃⁻）或铵离子（NH₄⁺）会导致暗呼吸大幅增加（分别为67%和129%）以及暗碳固定大幅增加（分别为360%和2080%）。氮诱导扰动的持续时间取决于添加氮的浓度。重氮丝氨酸对谷氨酰胺2-酮戊二酸转氨酶的抑制减轻了所有这些影响。有人提出，响应氮脉冲对光合碳固定的抑制是卡尔文循环与氮同化之间对代谢物竞争的结果。氮同化所需的碳骨架将来自三羧酸循环中间体。为维持三羧酸循环活性，磷酸丙糖将从叶绿体输出。这将降低二磷酸核酮糖再生速率，从而减少光合碳的净积累。化学计量计算表明，卡尔文循环是用于氮同化的磷酸丙糖的一个来源；然而，在短暂的氮再供应期间，对磷酸丙糖的主要需求必须通过淀粉或蔗糖分解来满足。氮脉冲对氧气释放、暗呼吸和暗碳固定的影响与该模型一致。
