What are the key defense mechanisms of plants?
Some key defense mechanisms include a direct response to specific antimicrobial activities, metabolite biosynthesis, callose deposition, transcription of response genes, stomatal closure and programmed plant cell death signaling. Previous workers have elucidated the roles of phytochemicals (chiefly secondary plant metabolites) in protecting plants against pathogens and pests. In the case of brassica crops, they either produce phytochemicals as a component of their growth and development (i.e., inbuilt chemical barriers; structural barriers such as lignin, and pre-formed phytoanticipins such as GSLs) or de novo synthesis in response to pathogen attack or stress (phytoalexins).
Over the years, many studies have elucidated the GSL-triggered mechanisms by which plant immune systems respond upon attack by various pathogens. Also, the indole glucosinolate biosynthesis pathway has been successfully bioengineered in Nicotiana benthamiana, a non-brassica plant and molecular techniques have also shown in detail how specific glucosinolates like glucoraphanin (4-methyl sulfinyl butyl GLS; 4-MSB) inhibit tumor cell growth in tobacco. However, limited information on the effects of specific pathogens on specific brassica plants is available. This review presents a comprehensive investigation of some of the most important pathogens, which cause considerable damage to brassica plants. This report will also highlight studies that successfully demonstrated the mechanisms by which GSLs mitigate pathogen effects on specific brassica species. Some insights into future considerations for potential application in experiment and field studies will also be provided in this work.