Willms JR, Salon C, Layzell DB
Department of Biology, Queen's University at Kingston, Kingston, Ontario, Canada K7L 3N6.
Plant Physiol. 1999 Aug;120(4):1117-28. doi: 10.1104/pp.120.4.1117.
In leaves, the light reactions of photosynthesis support fatty acid synthesis but disagreement exists as to whether this occurs in green oilseeds. To address this question, simultaneous measurements of the rates of CO(2) and O(2) exchange (CER and OER, respectively) were made in soybean (Glycine max L.) fruits. The imbalance between CER and OER was used to estimate the diverted reductant utilization rate (DRUR) in the equation: DRUR = 4 x (OER + CER). This yielded a quantitative measure of the rate of synthesis of biomass that is more reduced per unit carbon than glucose (in photosynthesizing tissues) or than the substrates of metabolism (in respiring tissues). The DRUR increased by about 2.2-fold when fruits were illuminated due to a greater increase in OER than decrease in CER. This characteristic was shown to be a property of the seed (not the pod wall), to be present in fruits at all developmental stages, and to reach a maximal response at relatively low light. When seeds were provided with (13)CO(2), light reduced (12)CO(2) production but had little effect on (13)CO(2) fixation. When they were provided with (18)O(2), light stimulated (16)O(2) production but had no effect on (18)O(2) uptake. Together, these findings indicate that light stimulates fatty acid synthesis in photosynthetic oilseeds, probably by providing both ATP and carbon skeletons.
在叶片中，光合作用的光反应为脂肪酸合成提供支持，但绿色油料种子中是否如此尚存在争议。为解决这一问题，对大豆（Glycine max L.）果实中的二氧化碳和氧气交换速率（分别为CER和OER）进行了同步测量。CER和OER之间的不平衡用于估算方程中的还原物转移利用率（DRUR）：DRUR = 4×(OER + CER)。这得出了一种生物量合成速率的定量测量方法，该生物量比葡萄糖（在光合组织中）或代谢底物（在呼吸组织中）的单位碳还原程度更高。当果实受光照时，DRUR增加了约2.2倍，这是由于OER的增加幅度大于CER的降低幅度。结果表明，这一特性是种子（而非豆荚壁）所具有的，在果实的所有发育阶段均存在，并且在相对较低的光照下达到最大响应。当为种子提供¹³CO₂时，光照减少了¹²CO₂的产生，但对¹³CO₂的固定影响不大。当为种子提供¹⁸O₂时，光照刺激了¹⁶O₂的产生，但对¹⁸O₂的吸收没有影响。这些发现共同表明，光照可能通过提供ATP和碳骨架来刺激光合油料种子中的脂肪酸合成。
