Harley P. C., Litvak M. E., Sharkey T. D., Monson R. K.
Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder, Colorado 80309-0334 (P.C.H., M.E.L., R.K.M.).
Plant Physiol. 1994 May;105(1):279-285. doi: 10.1104/pp.105.1.279.
Although isoprene synthesis is closely coupled to photosynthesis, both via ATP requirements and carbon substrate availability, control of isoprene emission is not always closely linked to photosynthetic processes. In this study we grew velvet bean (Mucuna sp.) under different levels of photon flux density (PFD) and nitrogen availability in an effort to understand better the degree to which these two processes are linked. As has been observed in past studies, we found that during early leaf ontogeny the onset of positive rates of net photosynthesis precedes that of isoprene emission by 3 to 4 d. Other studies have shown that this lag is correlated with the induction of isoprene synthase activity, indicating that overall control of the process is under control of that enzyme. During leaf senescence, photosynthesis rate and isoprene emission rate declined in parallel, suggesting similar controls over the two processes. This coordinated decline was accelerated when plants were grown with high PFD and high nitrogen availability. The latter effect included declines in the photon yield of photosynthesis, suggesting that an unexplained stress arose during growth under these conditions, triggering a premature decline in photosynthesis and isoprene emission rate. In mature leaves, growth PFD and nitrogen nutrition affected photosynthesis and isoprene emission in qualitatively similar, but quantitatively different, ways. This resulted in a significant shift in the percentage of fixed carbon that was re-emitted as isoprene. In the case of increasing growth PFD, isoprene emission rate was more strongly affected than photosynthesis rate, and more carbon was lost as isoprene. In the case of increasing nitrogen, photosynthesis rate increased more than isoprene emission rate, and leaves containing high amounts of nitrogen lost a lower percentage of their assimilated carbon as isoprene. Taken together, our results demonstrate that, although the general correlation between isoprene emission rate and photosynthesis rate is consistently expressed, there is evidence that both processes are capable of independent responses to plant growth environment.
尽管异戊二烯的合成通过对ATP的需求和碳底物的可用性与光合作用紧密相关，但异戊二烯排放的控制并不总是与光合过程紧密相连。在本研究中，我们在不同光子通量密度（PFD）和氮素供应水平下种植黎豆（黎豆属），以便更好地了解这两个过程的关联程度。正如过去研究中所观察到的，我们发现，在叶片发育早期，净光合速率开始呈正值比异戊二烯排放早3至4天。其他研究表明，这种滞后与异戊二烯合酶活性的诱导相关，这表明该过程的总体控制受该酶的调控。在叶片衰老期间，光合速率和异戊二烯排放速率平行下降，这表明对这两个过程有相似的控制。当植株在高PFD和高氮供应条件下生长时，这种协同下降加速。后一种效应包括光合光子产量下降，这表明在这些条件下生长期间出现了一种无法解释的胁迫，引发了光合作用和异戊二烯排放速率的过早下降。在成熟叶片中，生长PFD和氮素营养对光合作用和异戊二烯排放的影响在性质上相似，但在数量上不同。这导致作为异戊二烯重新排放的固定碳百分比发生了显著变化。在生长PFD增加的情况下，异戊二烯排放速率比光合速率受到的影响更大，更多的碳以异戊二烯的形式损失。在氮素增加的情况下，光合速率的增加超过了异戊二烯排放速率，并且含氮量高的叶片以异戊二烯形式损失的同化碳百分比更低。综上所述，我们的结果表明，尽管异戊二烯排放速率与光合速率之间的一般相关性始终存在，但有证据表明这两个过程都能够对植物生长环境做出独立反应。
