Harvard University, Harvard Forest, Petersham, Massachusetts 01366.
Plant Physiol. 1990 Feb;92(2):480-6. doi: 10.1104/pp.92.2.480.
Nitrogenase activity in root nodules of four species of actinorhizal plants showed varying declines in response to exposure to acetylene (10% v/v). Gymnostoma papuanum (S. Moore) L. Johnson. and Casuarina equisetifolia L. nodules showed a small decline (5-15%) with little or no recovery over 15 minutes. Myrica gale L. nodules showed a sharp decline followed by a rapid return to peak activity. Alnus incana ssp. rugosa (Du Roi) Clausen. nodules usually showed varying degrees of decline followed by a slower return to peak or near-peak activity. We call these effects acetylene-induced transients. Rapid increases in oxygen tension also caused dramatic transient decreases in nitrogenase activity in all species. The magnitude of the transient decrease was related to the size of the O(2) partial pressure (pO(2)) rise, to the proximity of the starting and ending oxygen tensions to the pO(2) optimum, and to the time for which the plant was exposed to the lower pO(2). Oxygen-induced transients, induced both by step jumps in pO(2) and by O(2) pulses, were also observed in cultures of Frankia. The effects seen in nodules are purely a response by the bacterium and not a nodule effect per se. Oxygen-induced nitrogenase transients in actinorhizal nodules from the plant genera tested here do not appear to be a result of changes in nodule diffusion resistance.
四种放线菌植物根瘤的固氮酶活性对乙炔（10%v/v）暴露的反应表现出不同程度的下降。Gymnostoma papuanum（S. Moore）L. Johnson. 和 Casuarina equisetifolia L. 根瘤的活性下降幅度较小（5-15%），在 15 分钟内几乎没有或没有恢复。Myrica gale L. 根瘤的活性急剧下降，随后迅速恢复到峰值。Alnus incana ssp. rugosa（Du Roi）Clausen. 根瘤通常表现出不同程度的下降，然后活性缓慢恢复到峰值或接近峰值。我们称这些效应为乙炔诱导的瞬变。所有物种的氧张力快速增加也会导致固氮酶活性的剧烈瞬变下降。瞬变下降的幅度与 O(2)分压（pO(2))上升的大小、起始和结束氧张力与 pO(2)最适值的接近程度以及植物暴露于较低 pO(2)的时间有关。通过 pO(2)阶跃和 O(2)脉冲引起的氧诱导瞬变也在 Frankia 的培养物中观察到。在根瘤中观察到的效应纯粹是细菌的反应，而不是根瘤本身的效应。在本研究中测试的植物属的放线菌根瘤中的氧诱导固氮酶瞬变似乎不是根瘤扩散阻力变化的结果。
