C4 PHOTOSYNTHESIS - THE CO2-CONCENTRATING MECHANISM AND PHOTORESPIRATION
C4 PHOTOSYNTHESIS - THE CO2-CONCENTRATING MECHANISM AND PHOTORESPIRATION
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DOI：
10.1104/pp.103.1.83
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发表时间：
1993-09-01
期刊：
影响因子：
7.4
通讯作者：
EDWARDS, GE
中科院分区：
文献类型：
--
作者：
DAI, ZY;KU, MSB;EDWARDS, GE
尽管之前根据在不同[CO 2 ]下2％O 2 和21％O 2 下的气体交换测量结果表明C4植物中没有明显的光呼吸作用，但玉米(Zea mays)的光合作用显示出对变化[O 2 ]的双重响应。玉米光合作用的最大速率取决于 02（大约 10%）。这种 O2 依赖性与气孔导度无关，因为测量是在恒定的细胞间 CO2 浓度 (C(i)) 下进行的；它可能与呼吸或伪循环电子流有关。在给定的 C(i) 下，将 [02] 增加到 10% 以上会抑制强光下测量的光合作用速率和限制光 (PHI(CO2)) 下测量的最大量子产率。如果仅在 2% 和 21% O2 下进行测量，则 02 的双重效应会被掩盖。随着 C(i) 的降低，02（在 10% O2 以上测量）对光合作用和 PHI(CO2) 的抑制以非常相似的方式增加，典型地是由于光呼吸引起的 02 抑制。当C(i)降低到CO 2 以下50 mubar 时，O 2 抑制急剧增加。此外，在限制 CO2 和 40% O2 的情况下，升高温度有利于光呼吸，会导致 PHI(CO2) 降低。通过比较不同 C(i) 下玉米和 C3 种小麦 (Triticum aestivum) 光合作用的抑制程度，评估了 C4 光合作用在叶片中浓缩 CO2 的有效性。在高光、30℃和大气CO2浓度（340mubar）下，02对玉米光合作用几乎没有抑制，束鞘室中核酮糖-1，5-二磷酸羧化酶/加氧酶（Rubisco）周围的CO2估计水平为900mubar，比小麦叶肉细胞中Rubisco周围的值高约3倍。玉米的束鞘室中维持高 [CO2]，直到 C(i) 降至约 100 mubar 以下。这些气体交换测量的结果表明，玉米中发生光呼吸，但光呼吸速率很低，除非细胞间[CO2]受到胁迫的严重限制。
Despite previous reports of no apparent photorespiration in C4 plants based on measurements of gas exchange under 2 versus 21% 02 at varying [CO2], photosynthesis in maize (Zea mays) shows a dual response to varying [O2]. The maximum rate of photosynthesis in maize is dependent on 02 (approximately 10%). This 02 dependence is not related to stomatal conductance, because measurements were made at constant intercellular CO2 concentration (C(i)); it may be linked to respiration or pseudocyclic electron flow. At a given C(i), increasing [02] above 10% inhibits both the rate of photosynthesis, measured under high light, and the maximum quantum yield, measured under limiting light (PHI(CO2)). The dual effect of 02 is masked if measurements are made under only 2 versus 21% 02. The inhibition of both photosynthesis and PHI(CO2), by 02 (measured above 10% O2) with decreasing C(i) increases in a very similar manner, characteristically Of 02 inhibition due to photorespiration. There is a sharp increase in 02 inhibition when the C(i) decreases below 50 mubar of CO2. Also, increasing temperature, which favors photorespiration, causes a decrease in PHI(CO2) under limiting CO2 and 40% O2. By comparing the degree of inhibition of photosynthesis in maize with that in the C3 species wheat (Triticum aestivum) at varying C(i), the effectiveness of C4 photosynthesis in concentrating CO2 in the leaf was evaluated. Under high light, 30-degrees-C, and atmospheric levels of CO2 (340 mubar), where there is little inhibition of photosynthesis in maize by 02, the estimated level of CO2 around ribulose-l,5-bisphosphate carboxylase/oxygenase (Rubisco) in the bundle sheath compartment was 900 mubar, which is about 3 times higher than the value around Rubisco in mesophyll cells of wheat. A high [CO2] is Maintained in the bundle sheath compartment in maize until C(i) decreases below approximately 100 mubar. The results from these gas exchange measurements indicate that photorespiration occurs in maize but that the rate is low unless the intercellular [CO2] is severely limited by stress.