Hughes Nicole M, Vogelmann Thomas C, Smith William K
Department of Biology, Wake Forest University, 136 Winston Hall, Winston-Salem, North Carolina 27106, USA.
J Exp Bot. 2008;59(12):3435-42. doi: 10.1093/jxb/ern193. Epub 2008 Jul 24.
A red/purple coloration of lower (abaxial) leaf surfaces is commonly observed in deeply-shaded understorey plants, especially in the tropics. However, the functional significance of red abaxial coloration, including its role in photosynthetic adaptation, remains unclear. The objective of this study was to test the back-scatter hypothesis for abaxial leaf coloration, which posits that red pigments internally reflect/scatter red light transmitted by the upper leaf surface back into the mesophyll, thereby enhancing photon capture in light-limited environments. Abaxially red/non-red variegated leaves of Begonia heracleifolia (Cham. & Schltdl.) were used to compare reflectance spectra and chlorophyll fluorescence profiles of abaxially anthocyanic (red) and acyanic (non-red) tissues under red light. Photosynthetic gas exchange in response to red light was also compared for abaxially red/non-red leaf sections. The results did not support a back-scattering function, as anthocyanic leaf surfaces were not more reflective of red light than acyanic surfaces. Anthocyanic tissues also did not exhibit any increases in the mesophyll absorbance of red light, or increased photosynthetic gas exchange under red light at any intensity, relative to acyanic tissues. These results suggest that abaxial anthocyanins do not significantly enhance the absorption of red light in the species tested, and alternative functions are discussed.
在深度遮荫的林下植物中，尤其是在热带地区，通常会观察到叶片下（背面）表面呈现红/紫色。然而，叶片背面红色的功能意义，包括其在光合适应中的作用，仍不清楚。本研究的目的是检验叶片背面颜色的后向散射假说，该假说认为红色色素将通过叶片上表面透射的红光在内部反射/散射回叶肉，从而在光照受限的环境中增强光子捕获。利用海棠（Cham. & Schltdl.）叶片背面红色/非红色的杂色叶片，比较了红色光下叶片背面含花青素（红色）和不含花青素（非红色）组织的反射光谱和叶绿素荧光曲线。还比较了叶片背面红色/非红色叶段对红光的光合气体交换。结果不支持后向散射功能，因为含花青素的叶片表面对红光的反射并不比不含花青素的表面更强。相对于不含花青素的组织，含花青素的组织在叶肉对红光的吸收上也没有任何增加，在任何强度的红光下光合气体交换也没有增加。这些结果表明，在所测试的物种中，叶片背面的花青素不会显著增强对红光的吸收，并对其他功能进行了讨论。
