Structural and photosynthetic re-acclimation to low light in C4 maize leaves that developed under high light.
Structural and photosynthetic re-acclimation to low light in C4 maize leaves that developed under high light.
复制标题
在高光下发育的 C4 玉米叶片对低光的结构和光合作用重新适应。
作者：
T. Yabiku;O. Ueno
背景和目标
C4 植物比 C3 植物具有更高的光合作用能力，但这种优势是以能量成本为代价的，这在弱光条件下会产生问题。在作物冠层中，下部叶片首先在强光下发育，但随后由于相互遮荫而经历弱光。为了探索 C4 叶子对弱光的重新适应，我们研究了在遮荫盆中生长的玉米植物叶子的结构和生理变化。
方法
首先将植物在强光下生长，然后将其中一些植物遮荫（20％的阳光）三周。检查了四种类型的叶子：在遮光期间在弱光下发育的新叶（L）、在高光下发育的新叶（H）、在遮光前在高光下发育然后接受弱光的成熟叶（H-L）以及始终经历强光的成熟叶（H-H）。
主要结果
H-L叶的单位面积叶质量、单位叶面积氮含量和叶绿素含量、叶绿素a/b比值以及C3和C4光合酶活性均低于H-H叶，L低于H叶。与L叶不同，H-L叶保持了H叶的Kranz解剖结构的厚度和框架，但H-L叶中的叶绿体含量减少了。叶绿体含量的减少主要是通过减小叶绿体的尺寸来实现的。虽然L叶的叶肉叶绿体基粒比H叶更发达，但H-L叶和H-H叶之间没有差异。 H-L和L叶的光合作用光变曲线非常相似，表现出遮荫叶的特征。
结论
在高光下发育的成熟玉米叶子通过调整其生化特性和叶绿体含量来重新适应弱光环境，以类似于遮荫叶，但保持阳光叶的解剖结构。
BACKGROUND AND AIMS
C4 plants have higher photosynthetic capacity than C3 plants, but this advantage comes at an energetic cost that is problematic at low light. In the crop canopy, lower leaves first develop under high light but later experience low light because of mutual shading. To explore the re-acclimation of C4 leaves to low light, we investigated the structural and physiological changes of the leaves of maize plants grown in shaded pots.
METHODS
Plants were first grown under high light, and then some of them shaded (20% of sunlight) for three weeks. Four types of leaves were examined: new leaves that developed under low light during shading (L), new leaves that developed under high light (H), mature leaves that developed under high light before shading and were then subjected to low light (H-L), and mature leaves that always experienced high light (H-H).
KEY RESULTS
The leaf mass per area, nitrogen and chlorophyll contents per unit leaf area, chlorophyll a/b ratio, and activities of C3 and C4 photosynthetic enzymes were lower in H-L than in H-H leaves and in L than H leaves. Unlike L leaves, H-L leaves maintained the thickness and framework of the Kranz anatomy of H leaves, but chloroplast contents in H-L leaves were reduced. This reduction of chloroplast contents was achieved mainly by reducing the size of chloroplasts. Although grana of mesophyll chloroplasts were more developed in L leaves than in H leaves, there were no differences between H-L and H-H leaves. The light curves of photosynthesis in H-L and L leaves were very similar and showed traits of shade leaves.
CONCLUSIONS
Mature maize leaves that developed under high light re-acclimate to low-light environments by adjusting their biochemical traits and chloroplast contents to resemble shade leaves but maintain the anatomical framework of sun leaves.