McLarnon Emma, McQueen-Mason Simon, Lenk Ingo, Hartley Susan E
Department of Biology, University of YorkYork, United Kingdom.
DLF Seeds Ltd.Hoejerupvej, Denmark.
Front Plant Sci. 2017 Jul 18;8:1199. doi: 10.3389/fpls.2017.01199. eCollection 2017.
Silicon (Si) is taken up from the soil as monosilicic acid by plant roots, transported to leaves and deposited as phytoliths, amorphous silica (SiO) bodies, which are a key component of anti-herbivore defense in grasses. Silicon transporters have been identified in many plant species, but the mechanisms underpinning Si transport remain poorly understood. Specifically, the extent to which Si uptake is a passive process, driven primarily by transpiration, or has both passive and active components remains disputed. Increases in foliar Si concentration following herbivory suggest plants may exercise some control over Si uptake and distribution. In order to investigate passive and active controls on Si accumulation, we examined both genetic and environmental influences on Si accumulation in the forage grass We studied three varieties that differ in the levels of Si they accumulate. Varieties not only differed in Si concentration, but also in increases in Si accumulation in response to leaf damage. The varietal differences in Si concentration generally reflected differences in stomatal density and stomatal conductance, suggesting passive, transpiration-mediated mechanisms underpin these differences. Bagging plants after damage was employed to minimize differences in stomatal conductance between varieties and in response to damage. This treatment eliminated constitutive differences in leaf Si levels, but did not impair the damage-induced increases in Si uptake: damaged, bagged plants still had more leaf Si than undamaged, bagged plants in all three varieties. Preliminary differential gene expression analysis revealed that the active Si transporter Lsi2 was highly expressed in damaged unbagged plants compared with undamaged unbagged plants, suggesting damage-induced Si defenses are regulated at gene level. Our findings suggest that although differences in transpiration may be partially responsible for varietal differences in Si uptake, they cannot explain damage-induced increases in Si uptake and deposition, suggesting that wounding causes changes in Si uptake, distribution and deposition that likely involve active processes and changes in gene expression.
硅（Si）以单硅酸的形式被植物根系从土壤中吸收，运输到叶片并沉积为植硅体，即无定形二氧化硅（SiO）体，这是禾本科植物抗食草动物防御的关键组成部分。许多植物物种中已鉴定出硅转运蛋白，但硅转运的潜在机制仍知之甚少。具体而言，硅吸收在多大程度上是一个主要由蒸腾作用驱动的被动过程，或者是同时具有被动和主动成分，这一点仍存在争议。食草后叶片硅浓度的增加表明植物可能对硅的吸收和分布有一定的控制能力。为了研究对硅积累的被动和主动控制，我们研究了遗传和环境对饲用禾本科植物硅积累的影响。我们研究了三个积累硅水平不同的品种。这些品种不仅在硅浓度上存在差异，而且在叶片受损后硅积累的增加量上也有所不同。硅浓度的品种差异通常反映了气孔密度和气孔导度的差异，这表明被动的、由蒸腾作用介导的机制是这些差异的基础。受损后对植株进行套袋处理，以尽量减少品种之间以及因损伤而导致的气孔导度差异。这种处理消除了叶片硅水平的组成性差异，但并未削弱损伤诱导的硅吸收增加：在所有三个品种中，受损且套袋的植株叶片中的硅含量仍高于未受损且套袋的植株。初步的差异基因表达分析表明，与未受损且未套袋的植株相比，受损且未套袋的植株中活性硅转运蛋白Lsi2高度表达，这表明损伤诱导的硅防御在基因水平上受到调控。我们的研究结果表明，虽然蒸腾作用的差异可能部分导致了品种间硅吸收的差异，但它们无法解释损伤诱导的硅吸收和沉积增加，这表明伤口会引起硅吸收、分布和沉积的变化，这可能涉及主动过程和基因表达的变化。
