The Key Laboratory of Oasis Eco-agriculture, Xinjiang Production and Construction Group, Shihezi University, Shihezi, P.R. China.
Research Group in Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears-Instituto de Agroecología y Economía del Agua (INAGEA), Palma, Illes Balears, Spain.
J Exp Bot. 2018 Nov 26;69(22):5433-5443. doi: 10.1093/jxb/ery296.
Mesophyll conductance (gm) has been shown to affect photosynthetic capacity and thus the estimates of terrestrial carbon balance. While there have been some attempts to model gm at the leaf and larger scales, the potential contribution of gm to the photosynthesis of non-leaf green organs has not been studied. Here, we investigated the influence of gm on photosynthesis of cotton bracts and how it in turn is influenced by anatomical structures, by comparing leaf palisade and spongy mesophyll with bract tissue. Our results showed that photosynthetic capacity in bracts is much lower than in leaves, and that gm is a limiting factor for bract photosynthesis to a similar extent to stomatal conductance. Bract and the spongy tissue of leaves have lower mesophyll conductance than leaf palisade tissue due to the greater volume fraction of intercellular air spaces, smaller chloroplasts, lower surface area of mesophyll cells and chloroplasts exposed to leaf intercellular air spaces and, perhaps, lower membrane permeability. Comparing bracts with leaf spongy tissue, although bracts have a larger cell wall thickness, they have a similar gm estimated from anatomical characteristics, likely due to the cumulative compensatory effects of subtle differences in each subcellular component, especially chloroplast traits. These results provide the first evidence for anatomical constraints on gm and photosynthesis in non-leaf green organs.
叶肉导度（gm）已被证明会影响光合作用能力，从而影响陆地碳平衡的估算。虽然已经有一些尝试在叶片和更大的尺度上模拟 gm，但 gm 对非叶绿色器官光合作用的潜在贡献尚未得到研究。在这里，我们研究了 gm 对棉苞光合作用的影响，以及 gm 如何通过解剖结构受到影响，方法是将叶片栅状组织和海绵组织与苞叶组织进行比较。我们的结果表明，苞叶的光合能力远低于叶片，gm 对苞叶光合作用的限制程度与气孔导度相当。由于细胞间空气空间的体积分数较大、叶绿体较小、暴露于叶片细胞间空气空间的叶肉细胞和叶绿体的表面积较小，以及膜通透性可能较低，因此苞叶和叶片海绵组织的 gm 低于叶片栅状组织。与叶片海绵组织相比，尽管苞叶具有更大的细胞壁厚度，但根据解剖学特征估计的 gm 相似，这可能是由于每个亚细胞成分的细微差异（尤其是叶绿体特征）的累积补偿效应所致。这些结果为非叶绿色器官 gm 和光合作用的解剖限制提供了第一个证据。
