Makino A., Nakano H., Mae T.
Department of Applied Biological Chemistry, Faculty of Agriculture, Tohoku University, Tsutsumidori-Amamiyamachi, Sendai 981, Japan.
Plant Physiol. 1994 May;105(1):173-179. doi: 10.1104/pp.105.1.173.
The photosynthetic gas-exchange rates and various biochemical components of photosynthesis, including ribulose-1,5-bisphosphate carboxylase (Rubisco) content, cytochrome (Cyt) f content, and the activities of two sucrose synthesis enzymes, were examined in young, fully expanded leaves of rice (Oryza sativa L.) grown hydroponically in different nitrogen concentrations. The light-saturated rate of photosynthesis at an intercellular CO2 pressure of 20 Pa (CO2-limited photosynthesis) was linearly dependent on leaf nitrogen content, but curvilinearly correlated with Rubisco content. This difference was due to a greater than proportional increase in Rubisco content relative to leaf nitrogen content and the presence of a CO2 transfer resistance between the intercellular air spaces and the carboxylation sites. CO2-limited photosynthesis was proportional to Cyt f content, one of the key components of electron transport, but was not proportional to the activities of cytosolic fructose-1,6-bisphosphatase and sucrose phosphate synthase, the two regulatory enzymes of sucrose synthesis. Light-saturated photosynthesis above an intercellular CO2 pressure of 60 Pa (CO2-saturated photosynthesis) was curvilinearly dependent on leaf nitrogen content. This CO2-saturated photosynthesis was proportional to Cyt f content in the low- and normal-nitrogen leaves, and correlated better with the activities of cytosolic fructose-1,6-bisphosphatase and sucrose phosphate synthase in the high-nitrogen leaves. The increase in the activities of these two enzymes with increasing leaf nitrogen was not as great as the increase in Cyt f content. Thus, as leaf nitrogen increased, the limitation caused by the activities of sucrose synthesis enzymes came into play, which resulted in the curvilinear relationship. However, this limitation by sucrose synthesis enzymes did not affect photosynthesis under normal ambient air.
在不同氮浓度水培条件下生长的水稻（Oryza sativa L.）幼嫩、完全展开的叶片中，检测了光合气体交换速率以及光合作用的各种生化成分，包括1,5-二磷酸核酮糖羧化酶（Rubisco）含量、细胞色素（Cyt）f含量以及两种蔗糖合成酶的活性。在细胞间CO2压力为20 Pa时的光饱和光合速率（CO2限制的光合作用）与叶片氮含量呈线性相关，但与Rubisco含量呈曲线相关。这种差异是由于Rubisco含量相对于叶片氮含量的增加幅度大于比例关系，以及细胞间气隙与羧化位点之间存在CO2转移阻力。CO2限制的光合作用与电子传递的关键成分之一Cyt f含量成正比，但与蔗糖合成的两种调节酶——胞质果糖-1,6-二磷酸酶和蔗糖磷酸合酶的活性不成正比。在细胞间CO2压力高于60 Pa时的光饱和光合作用（CO2饱和的光合作用）与叶片氮含量呈曲线相关。这种CO2饱和的光合作用在低氮和正常氮叶片中与Cyt f含量成正比，在高氮叶片中与胞质果糖-1,6-二磷酸酶和蔗糖磷酸合酶的活性相关性更好。随着叶片氮含量的增加，这两种酶活性增加的幅度不如Cyt f含量增加的幅度大。因此，随着叶片氮含量的增加，蔗糖合成酶活性造成的限制开始起作用，导致了曲线关系。然而，这种由蔗糖合成酶造成的限制在正常环境空气中并不影响光合作用。
