Editorial: Physiology and Cellular Mechanisms of Isothiocyanates and Other Glucosinolate Degradation Products in Plants

Isothiocyanates (ITCs), thiocyanates, and epithionitriles are produced enzymatically from sulfur-containing glucosinolates (GLS) by β-thioglucosidases (thioglucoside glucohydrolase EC 3.2.3.147) called myrosinases (Bones and Rossiter, 2006), whilst there is growing evidence that they have multiple roles in host plants. The role of ITCs in plant defense against pests and pathogens has been thoroughly described and multiple roles and functions for GLSs and their derived products suggested. These amongst others include a role as allelochemicals and in sulfur storage, water transport, heat tolerance, stomatal regulation, apoptosis, growth inhibition, and signaling. There are many thousands of papers on the cellular effects of ITCs when used in microbial and animal/human cell studies. Sulforaphane is one of the most studied ITCs and in the Thompson ISI gives approximately 6000 hits, which highlights the importance of this natural product. Included in this topic is a large body of data on the chemopreventive effects of ITCs in cancer models and on their cytotoxicity against bacteria, fungi, nematodes and insects. In comparison there are considerably fewer studies of the physiological and cellular activities of ITCs in plant models (Hara et al., 2010, 2013). The aim of this specialist research topic was to highlight the physiological role of ITCs and other GLS degradation products in plants and plant cells as well as pointing toward future research. Plants contain, or are able to synthesize on demand, a plethora of defense compounds, including GLSs, that provide a substantial and effective arsenal against pathogens and pests. A knowledge of the GLSs, their tissue and cellular localization and metabolism under various environmental conditions is important in the assessment of potential physiological effects. The response of four Arabidopsis thaliana accessions differing in GLS composition and formation of GLS degradation products were investigated by Witzel et al. (2015) following exposure to the hemi-biotrophic fungus Verticillium longisporum. The data showed that V. longisporum infections affected both GLS profiles and the composition of degradation products in accession-and organ-specific ways. The plant-pathogen interaction between A. thaliana and Alternaria brassicicola was studied by Calmes et al. (2015) and set out to explore the mechanism by which ITCs could promote cell death. A decline in oxygen consumption, accumulation of reactive oxygen species and depolarization of the mitochondrial membrane in A. brassicicola was observed following exposure to ITCs. Two potential major players in the A. brassicicola response to ITC were identified to be a MAP kinase (AbHog1) and a transcription factor (AbAP1). …