Abstract
The glucosinolate-myrosinase system is a well-known plant chemical defence system. Two functional myrosinase-encoding genes, THIOGLUCOSIDASE 1 (TGG1) and THIOGLUCOSIDASE 2 (TGG2), express in aerial tissues of Arabidopsis. TGG1 expresses in guard cells (GCs) and is also a highly abundant protein in GCs. Recently, by studying wild type (WT), tgg 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, tgg1, tgg2 single, and tgg1 tgg2 double mutants. The tgg mutants showed distinctive features of GCs. The GCs of tgg1 and tgg1 tgg2 mutants showed vacuoles that had less electron-dense granular material. Both tgg single mutants had bigger stomata complexes. The WT and tgg 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 tgg1 single and tgg1 tgg2 double mutants. The data provides a basis to perform comprehensive further studies to find physiological and molecular mechanisms associated with ultrastructure differences in tgg 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.
Highlights
The glucosinolate-myrosinase system is a well-known plant defence strategy towards insect herbivores and pathogens [1,2,3,4,5,6]
Through the use of imaging techniques, we have found that the wild type (WT) and tgg1, tgg2 single, and double mutants show different and characteristic features for cell wall, chloroplasts, starch grains, stomatal ledges, and vacuolation in guard cells (GCs)
Through Abscisic acid (ABA) treatment, we found that the stomatal aperture was reduced in tgg1 single and tgg1 tgg2 double mutants
Summary
The glucosinolate-myrosinase system is a well-known plant defence strategy towards insect herbivores and pathogens [1,2,3,4,5,6]. The molecular mechanism causing the development of myrosin cells is mostly unknown, the basic helix-loop-helix (bHLH) transcription factor FAMA, whose transcript and protein are expressed in the stomatal lineage and acts as a master regulator of the terminal differentiation of GCs, is necessary for myrosin cell differentiation [2,9,24]. Through extensive metabolite and structural analysis of leaves of Arabidopsis thioglucosidase (tgg) mutants, we found a novel association between the glucosinolatemyrosinase defence system, a chemical barrier, and the cuticle, as a physical barrier [31] This achievement led us on to further investigations into the structural characteristics of GCs of wild type (WT) and tgg single and double mutants. Through ABA treatment, we found that the stomatal aperture was reduced in tgg single and tgg tgg double mutants
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