Yemm E W, Bidwell R G
Department of Biology, Case Western Reserve University, Cleveland, Ohio 44106.
Plant Physiol. 1969 Sep;44(9):1328-34. doi: 10.1104/pp.44.9.1328.
In order to measure CO(2) exchange reactions by leaves using isotopes of CO(2), it is necessary to know precisely the discrimination against (14)CO(2) by leaves. Earlier determinations of discrimination are at variance, and may be inaccurate because of assumptions made about the rate of photorespiration. Maize leaves evolve little or no CO(2) in light, and so provide suitable material for this measurement. Discrimination against (14)CO(2) in photosynthesis by maize leaves is almost precisely the same as in CO(2) absorption by NaOH solution, amounting to 2.1 and 2.0% respectively. The agreement between these values and their close approximation to the relative rates of diffusion of (12)CO(2) and (14)CO(2), calculated from Graham's law, shows that diffusion into the leaf is primarily responsible for discrimination against (14)CO(2) in photosynthesis.
为了利用二氧化碳同位素测量叶片的二氧化碳交换反应,有必要精确了解叶片对¹⁴CO₂的歧视情况。早期对歧视的测定存在差异,并且由于对光呼吸速率所做的假设,可能并不准确。玉米叶片在光照下释放很少或不释放二氧化碳,因此为这种测量提供了合适的材料。玉米叶片在光合作用中对¹⁴CO₂的歧视与氢氧化钠溶液吸收二氧化碳时的情况几乎完全相同,分别为2.1%和2.0%。这些值之间的一致性以及它们与根据格雷厄姆定律计算出的¹²CO₂和¹⁴CO₂相对扩散速率的紧密近似,表明扩散进入叶片是光合作用中对¹⁴CO₂产生歧视的主要原因。