Olmos Enrique, García De La Garma Jesús, Gomez-Jimenez Maria C, Fernandez-Garcia Nieves
Department of Abiotic Stress and Plant Pathology, Centro de Edafología y Biología Aplicada del Segura (CSIC)Murcia, Spain.
Department of Plant Physiology, Faculty of Science, University of ExtremaduraBadajoz, Spain.
Front Plant Sci. 2017 Jun 20;8:1092. doi: 10.3389/fpls.2017.01092. eCollection 2017.
Arabinogalactan proteins (AGPs) are a highly diverse family of glycoproteins that are commonly found in most plant species. However, little is known about the physiological and molecular mechanisms of their function. AGPs are involved in different biological processes such as cell differentiation, cell expansion, tissue development and somatic embryogenesis. AGPs are also involved in abiotic stress response such as salinity modulating cell wall expansion. In this study, we describe how salt-adaptation in tobacco BY-2 cell cultures induces important changes in arabinogalactan proteins distribution and contents. Using the immuno-dot blot technique with different anti-AGP antibodies (JIM13, JIM15, and others), we observed that AGPs were highly accumulated in the culture medium of salt-adapted tobacco cells, probably due to the action of phospholipases. We located these AGP epitopes using immunogold labeling in the cytoplasm associated to the endoplasmic reticulum, the golgi apparatus, and vesicles, plasma membrane and tonoplast. Our results show that salt-adaptation induced a significant reduction of the cytoplasm, plasma membrane and tonoplast content of these epitopes. Yariv reagent was added to the control and salt-adapted tobacco cell cultures, leading to cell death induction in control cells but not in salt-adapted cells. Ultrastructural and immunogold labeling revealed that cell death induced by Yariv reagent in control cells was due to the interaction of Yariv reagent with the AGPs linked to the plasma membranes. Finally, we propose a new function of AGPs as a possible sodium carrier through the mechanism of vesicle trafficking from the apoplast to the vacuoles in salt-adapted tobacco BY-2 cells. This mechanism may contribute to sodium homeostasis during salt-adaptation to high saline concentrations.
阿拉伯半乳聚糖蛋白（AGPs）是一类高度多样化的糖蛋白家族，常见于大多数植物物种中。然而，对于其功能的生理和分子机制却知之甚少。AGPs参与不同的生物学过程，如细胞分化、细胞扩张、组织发育和体细胞胚胎发生。AGPs还参与非生物胁迫响应，如盐度调节细胞壁扩张。在本研究中，我们描述了烟草BY-2细胞培养物中的盐适应性如何诱导阿拉伯半乳聚糖蛋白分布和含量的重要变化。使用不同的抗AGP抗体（JIM13、JIM15等）进行免疫斑点印迹技术，我们观察到AGPs在盐适应烟草细胞的培养基中高度积累，这可能是由于磷脂酶的作用。我们使用免疫金标记在内质网、高尔基体、囊泡、质膜和液泡相关的细胞质中定位这些AGP表位。我们的结果表明，盐适应导致这些表位在细胞质、质膜和液泡中的含量显著降低。将Yariv试剂添加到对照和盐适应的烟草细胞培养物中，导致对照细胞中的细胞死亡诱导，但盐适应细胞中没有。超微结构和免疫金标记显示，Yariv试剂在对照细胞中诱导的细胞死亡是由于Yariv试剂与连接到质膜的AGPs相互作用。最后，我们提出AGPs的一个新功能，即作为一种可能的钠载体，通过盐适应烟草BY-2细胞中从质外体到液泡的囊泡运输机制。这种机制可能有助于在盐适应高盐浓度期间维持钠稳态。
