James S A, Smith W K, Vogelmann T C
Department of Botany, University of Wyoming, Laramie, Wyoming 82071-3165; and.
Am J Bot. 1999 Feb;86(2):198-207.
Mesophyll structure has been associated with the photosynthetic performance of leaves via the regulation of internal light and CO(2) profiles. Differences in mesophyll structure and chlorophyll distribution within three ontogenetically different leaf types of Eucalyptus globulus ssp. globulus were investigated. Juvenile leaves are blue-grey in color, dorsiventral (adaxial palisade layer only), hypostomatous, and approximately horizontal in orientation. In contrast, adult leaves are dark green in color, isobilateral (adaxial and abaxial palisade), amphistomatous, and nearly vertical in orientation. The transitional leaf type has structural features that appear intermediate between the juvenile and adult leaves. The ratio of mesophyll cell surface area per unit leaf surface area (A(mes)/A) of juvenile leaves was maximum at the base of a single, adaxial palisade layer and declined through the spongy mesophyll. Chlorophyll a + b content showed a coincident pattern, while the chlorophyll a:b ratio declined linearly from the adaxial to abaxial epidermis. In comparison, the mesophyll of adult leaves had a bimodal distribution of A(mes)/A, with maxima occurring beneath both the adaxial and abaxial surfaces within the first layer of multiple palisade layers. The distribution of chlorophyll a + b content had a similar pattern, although the maximum ratio of chlorophyll a:b occurred immediately beneath the adaxial and abaxial epidermis. The matching distributions of A(mes)/A and chlorophyll provide further evidence that mesophyll structure may act to influence photosynthetic performance. These changes in internal leaf structure at different life stages of E. globulus may be an adaptation for increased xeromorphy under increasing light exposure experienced from the seedling to adult tree, similar to the characteristics reported for different species according to sunlight exposure and water availability within their native habitats.
叶肉结构通过调节内部光照和二氧化碳分布与叶片的光合性能相关。对蓝桉原亚种三种发育阶段不同的叶片类型的叶肉结构和叶绿素分布差异进行了研究。幼叶呈蓝灰色，背腹型（仅具近轴栅栏层），具下气孔，且方向大致水平。相比之下，成熟叶呈深绿色，等面型（近轴和远轴均有栅栏层），具双面气孔，且方向近乎垂直。过渡叶型具有介于幼叶和成熟叶之间的结构特征。幼叶单位叶表面积中叶肉细胞表面积的比例（A(mes)/A）在单一近轴栅栏层基部最大，并在海绵状叶肉中逐渐降低。叶绿素a + b含量呈现出一致的模式，而叶绿素a:b比值从近轴表皮到远轴表皮呈线性下降。相比之下，成熟叶的叶肉A(mes)/A呈双峰分布，在多个栅栏层的第一层中近轴和远轴表面下方均出现最大值。叶绿素a + b含量的分布模式类似，尽管叶绿素a:b的最大比值出现在近轴和远轴表皮正下方。A(mes)/A和叶绿素的匹配分布进一步证明叶肉结构可能影响光合性能。蓝桉在不同生命阶段叶片内部结构的这些变化可能是一种适应，以在从幼苗到成年树过程中光照增加的情况下增强旱生形态，类似于根据其原生栖息地的阳光照射和水分可利用性报道的不同物种的特征。
