Relevance of a decrease in the amount of magnesium in the guard cells for light-induced stomatal opening and guard cell photosynthesis in field bean (Vicia faba L.)

植物营养镁（Mg 2+）具有多种功能。例如，它与光合电子传递、通过促进质膜（PM）H+-易位ATP酶的活性而挤出质子（H+）或糖分配有关。在Mg ~（2+）缺乏的情况下，叶肉细胞的光系统（PS）II的运转效率降低，并积累光合源中的糖。有大量的信息证明Mg 2+与叶肉组织中这些过程的相关性。然而，目前的研究还没有达到澄清是否同样的过程中受到影响的警卫细胞（GC），如果这些细胞含有不够的Mg 2+。毕竟，迫切需要澄清这一点，因为越来越多的证据表明这些依赖于Mg 2+的过程，即GC-光合作用、GC-糖分配和GC-H+-挤出对于调节气孔孔径至关重要。在GCs中，PM-H+-ATPase在光照下通过水解ATP酸化质外体来激活气孔开放，而GC光合作用是这种ATP的来源。扰动糖分配改变GC中的渗透势，暗示GC溶胀。迫切的问题是：是否有一个在GC中的Mg 2+的量和光诱导的气孔开放之间的联系？本研究旨在阐明，如果减少量的Mg 2+在蚕豆（蚕豆）GCs阻碍光诱导的气孔开放。一旦GC中没有足够的Mg 2+，则推测光诱导的气孔开放被延迟，因为GC PS II操作效率降低（即ATP产生减少）和PM-H+-ATP酶介导的H+挤出减少。此外，预计糖分配在GC内受到干扰，其特征在于Mg 2的量减少，这可能改变GC溶质浓度，影响GC溶胀。GC PM-H+-ATP酶对光的敏感性依赖于GC Mg 2+含量，使用基于显微镜的比率pH定量对完整GC进行测试。GC PS II操作效率是使用显微镜脉冲幅度调制叶绿素荧光计在分离的完整GC上测定的。为了判断GC-内部碳水化合物分配，GC和GC叶绿体都将进行GC-EI/TOF-MS或UPLC-MS/MS，以定量卡尔文循环衍生的糖和酶。两个级分之间的比较（GC与GC叶绿体）将揭示碳水化合物分配是否在不含足够Mg 2+的GC中受到影响。这项研究计划的成果是GC-内部Mg 2+的GC光合作用和气孔开放的相关性的一个先进的理解。

The plant nutrient magnesium (Mg2+) has many functions. For instance, it is relevant for photosynthetic electron transport, for extrusion of protons (H+) by contributing to the activity of the plasma membrane (PM) H+-translocating ATPase, or for sugar partitioning. Under Mg2+-deficiency, mesophyll cells show a reduced operating efficiency of the photosystem (PS) II and accumulate sugars in photosynthetic sources. There is a wealth of information witnessing the relevance of Mg2+ for these processes in the mesophyll tissue. However, current research has not yet achieved to clarify whether the same processes are affected within guard cells (GCs), should these cells contain not enough Mg2+. After all, there is a pressing need to clarify this because evidence is increasing that these Mg2+-dependent processes, i.e. GC-photosynthesis, GC-sugar partitioning, and GC-H+-extrusion are pivotal for regulating stomatal pore size. In GCs at post-dawn, the PM-H+-ATPase energizes stomatal opening upon illumination via hydrolysing ATP for acidifying the apoplast, while GC photosynthesis is a source of this ATP. Disturbed sugar partitioning changes osmotic potential in the GCs with implication on GC swelling. The pressing question is: Is there a link between the amount of Mg2+ in the GCs and light-induced stomatal opening? This research program seeks elucidation if a reduced amount of Mg2+ in GCs of field bean (Vicia faba) obstructs light-induced stomatal opening. As soon as there is not enough Mg2+ in the GCs, it is hypothesized that light-induced stomatal opening is delayed because of a reduced GC PS II operating efficiency (i.e. reduced production of ATP) and a reduced PM-H+-ATPase–mediated extrusion of H+. Moreover, it is anticipated that sugar partitioning is disturbed within GCs that are characterized by a reduced amount of Mg2, which may change GC solute concentration, influencing GC swelling. The sensitivity of the GC PM-H+-ATPase to light, in dependency of the GC Mg2+ content, is tested using microscopy-based ratiometric pH quantification on intact GCs. GC PS II operating efficiency is determined on isolated intact GCs using a microscopy–pulse amplitude modulation chlorophyll fluorometer. For judging on GC-internal carbohydrate partitioning, both GCs and GC chloroplasts will be subjected to GC-EI/TOF-MS or UPLC-MS/MS for the quantification of Calvin cycle-derived sugars and enzymes. A comparison between both fractions (GC v. GC chloroplast) will reveal if carbohydrate partitioning is affected in GCs that contain not enough Mg2+. The outcome of this research programme is an advanced understanding of the relevance of GC-internal Mg2+ for GC photosynthesis and stomatal opening.