The Imaging of Guard Cells of thioglucosidase (tgg) Mutants of Arabidopsis Further Links Plant Chemical Defence Systems with Physical Defence Barriers

Abstract

The glucosinolate-myrosinase system is a well-known plant chemical defence system. Two functional myrosinase-encoding genes, THIOGLUCOSIDASE 1 (<i>TGG1</i>) and THIOGLUCOSIDASE 2 (<i>TGG2</i>), express in aerial tissues of Arabidopsis. <i>TGG1</i> expresses in guard cells (GCs) and is also a highly abundant protein in GCs. Recently, by studying wild type (WT), <i>tgg</i> single, and double mutants, we showed a novel association between the glucosinolate-myrosinase system defence system, and a physical barrier, the cuticle. In the current study, using imaging techniques, we further analysed stomata and ultrastructure of GCs of WT, <i>tgg1</i>, <i>tgg2</i> single, and <i>tgg1 tgg2</i> double mutants. The <i>tgg</i> mutants showed distinctive features of GCs. The GCs of <i>tgg1</i> and <i>tgg1 tgg2</i> mutants showed vacuoles that had less electron-dense granular material. Both <i>tgg</i> single mutants had bigger stomata complexes. The WT and <i>tgg</i> mutants also showed variations for cell wall, chloroplasts, and starch grains of GCs. Abscisic acid (ABA)-treated stomata showed that the stomatal aperture was reduced in <i>tgg1</i> single and <i>tgg1 tgg2</i> double mutants. The data provides a basis to perform comprehensive further studies to find physiological and molecular mechanisms associated with ultrastructure differences in <i>tgg</i> mutants. We speculate that the absence of myrosinase alters the endogenous chemical composition, hence affecting the physical structure of plants and the plants' physical defence barriers.