Velikova V, Loreto F, Brilli F, Stefanov D, Yordanov I
Institute of Plant Physiology, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Bl. 21, 1113 Sofia, Bulgaria.
Plant Biol (Stuttg). 2008 Jan;10(1):55-64. doi: 10.1055/s-2007-964964.
Heteroblastic Eucalyptus (Eucalyptus globulus L.) leaves were characterized for their functional diversity examining photosynthesis and photosynthesis limitations, transpiration, and the emission of isoprene and monoterpenes. In vivo and combined analyses of gas-exchange, chlorophyll fluorescence, and light absorbance at 830 nm were made on the adaxial and abaxial sides of juvenile and adult leaves. When adult leaves were reversed to illuminate the abaxial side, photosynthesis and isoprene emission were significantly lower than when the adaxial side was illuminated. Monoterpene emission, however, was independent on the side illuminated and similarly partitioned between the two leaf sides. The abaxial side of adult leaves showed less diffusive resistance to CO(2) acquisition by chloroplasts, but also lower ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity, than the adaxial leaf side. In juvenile leaves, photosynthesis, isoprene, and monoterpene emissions were similar when the adaxial or abaxial side was directly illuminated. In the abaxial side of juvenile leaves, photosynthesis did not match the rates attained by the other leaf types when exposed to elevated CO(2), which suggests the occurrence of a limitation of photosynthesis by ribulose bisphosphate (RuBP) regeneration. Accordingly, a reduced efficiency of both photosystems and a high non-radiative dissipation of energy was observed in the abaxial side of juvenile leaves. During light induction, the adaxial side of juvenile leaves also showed a reduced efficiency of photosystem II and a large non-radiative energy dissipation. Our report reveals distinct functional properties in Eucalyptus leaves. Juvenile leaves invest more carbon in isoprene, but not in monoterpenes, and have a lower water use efficiency than adult leaves. Under steady-state conditions, in adult leaves the isobilateral anatomy does not correspond to an equal functionality of the two sides, while in juvenile leaves the dorsiventral anatomy does not result in functional differences in primary or secondary metabolism in the two sides. However, photochemical limitations may reduce the efficiency of carbon fixation in the light, especially in the abaxial side of juvenile leaves.
对异态叶桉（Eucalyptus globulus L.）叶片的功能多样性进行了表征，研究了光合作用及其限制因素、蒸腾作用以及异戊二烯和单萜的排放。对幼叶和成熟叶的正面和背面进行了气体交换、叶绿素荧光和830nm光吸收的活体及综合分析。当成熟叶翻转使背面受光时，光合作用和异戊二烯排放显著低于正面受光时。然而，单萜排放与受光面无关，且在叶片两侧的分布相似。成熟叶的背面显示出对叶绿体获取CO₂的扩散阻力较小，但核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）活性也低于正面。在幼叶中，正面或背面直接受光时，光合作用、异戊二烯和单萜排放相似。在幼叶的背面，当暴露于高浓度CO₂时，光合作用速率无法达到其他叶型的水平，这表明存在由核酮糖二磷酸（RuBP）再生限制光合作用的情况。相应地，在幼叶的背面观察到两个光系统的效率降低以及能量的高非辐射耗散。在光诱导过程中，幼叶的正面也显示出光系统II的效率降低和大量非辐射能量耗散。我们的报告揭示了桉树叶的不同功能特性。幼叶在异戊二烯而非单萜上投入更多碳，且水分利用效率低于成熟叶。在稳态条件下，成熟叶的等面叶结构并不对应于两侧的同等功能，而幼叶的背腹叶结构并未导致两侧在初级或次级代谢上的功能差异。然而，光化学限制可能会降低光照下碳固定的效率，尤其是在幼叶的背面。
