Byrd G T, Brown R H, Bouton J H, Bassett C L, Black C C
Department of Agronomy, University of Georgia, Athens, Georgia 30602.
Plant Physiol. 1992 Oct;100(2):939-46. doi: 10.1104/pp.100.2.939.
The degree of C(4) photosynthesis was assessed in four hybrids among C(4), C(4)-like, and C(3)-C(4) species in the genus Flaveria using (14)C labeling, CO(2) exchange, (13)C discrimination, and C(4) enzyme activities. The hybrids incorporated from 57 to 88% of the (14)C assimilated in a 10-s exposure into C(4) acids compared with 26% for the C(3)-C(4) species Flaveria linearis, 91% for the C(4) species Flaveria trinervia, and 87% for the C(4)-like Flaveria brownii. Those plants with high percentages of (14)C initially fixed into C(4) acids also metabolized the C(4) acids quickly, and the percentage of (14)C in 3-phosphoglyceric acid plus sugar phosphates increased for at least a 30-s exposure to (12)CO(2). This indicated a high degree of coordination between the carbon accumulation and reduction phases of the C(4) and C(3) cycles. Synthesis and metabolism of C(4) acids by the species and their hybrids were highly and linearly correlated with discrimination against (13)C. The relationship of (13)C discrimination or (14)C metabolism to O(2) inhibition of photosynthesis was curvilinear, changing more rapidly at C(4)-like values of (14)C metabolism and (13)C discrimination. Incorporation of initial (14)C into C(4) acids showed a biphasic increase with increased activities of phosphoenolpyruvate carboxylase and NADP-malic enzyme (steep at low activities), but turnover of C(4) acids was linearly related to NADP-malic enzyme activity. Several other traits were closely related to the in vitro activity of NADP-malic enzyme but not phosphoenolpyruvate carboxylase. The data indicate that the hybrids have variable degrees of C(4) photosynthesis but that the carbon accumulation and reduction portions of the C(4) and C(3) cycles are well coordinated.
利用¹⁴C标记、CO₂交换、¹³C同位素分馏以及C₄酶活性，对黄顶菊属中C₄、类C₄和C₃ - C₄物种间的四个杂交种的C₄光合作用程度进行了评估。与C₃ - C₄物种线叶黄顶菊（Flaveria linearis）的26%、C₄物种三脉黄顶菊（Flaveria trinervia）的91%以及类C₄物种布朗氏黄顶菊（Flaveria brownii）的87%相比，这些杂交种在10秒光照下吸收的¹⁴C中有57%至88%被整合到C₄酸中。那些最初固定到C₄酸中的¹⁴C比例较高的植株，其C₄酸代谢也很快，并且在暴露于¹²CO₂至少30秒后，3 - 磷酸甘油酸和糖磷酸中的¹⁴C比例增加。这表明C₄和C₃循环的碳积累和还原阶段之间具有高度协调性。这些物种及其杂交种的C₄酸合成与代谢与¹³C同位素分馏高度线性相关。¹³C同位素分馏或¹⁴C代谢与O₂对光合作用的抑制之间的关系呈曲线状，在类C₄的¹⁴C代谢和¹³C同位素分馏值时变化更快。最初的¹⁴C掺入C₄酸中随着磷酸烯醇式丙酮酸羧化酶和NADP - 苹果酸酶活性的增加呈双相增加（在低活性时陡峭），但C₄酸的周转与NADP - 苹果酸酶活性呈线性相关。其他几个性状与NADP - 苹果酸酶的体外活性密切相关，而与磷酸烯醇式丙酮酸羧化酶无关。数据表明，这些杂交种具有不同程度的C₄光合作用，但C₄和C₃循环的碳积累和还原部分协调良好。
