Plant Secondary Metabolites for Insect Resistance: Seed–Pest Interaction: An Overview

Food safety and security are major concerns in the present world. Over the last decades, most of the food grain production has increased in many countries. Food grains must be preserved and stored safely to ensure their timely delivery to consumers. Various herbivores and microorganisms consumed the nutritional reserves of seeds during storage. Therefore, to protect their nutritional reserves from pests, seeds had physical, chemical, and biological defense mechanisms. Based on “seed defense theory,” to deflect lethal infection of seeds by pathogens, four mechanisms can be used: (i) Physical barriers provide protection to seeds from pathogens; (ii) endogenous chemical defenses of seeds; (iii) induced chemical defenses by beneficial association’s seed-microbial; and (iv) rapid seed germination. In fact, the concentrations and diversity of secondary compounds varied among plant parts. Indeed, the seeds required significant protection, for that, they had higher concentrations of secondary metabolites. However, rarely researchers have evaluated the seeds’ chemical defenses against different predators and pathogens. Indeed, chemical defenses regularly were assigned primarily to seed coats instead of embryo or endosperm tissue. Furthermore, the seeds induce defense enzymes such as polyphenol oxidase. Polyphenol oxidases (PPOs), peroxidases, and oxalate oxidases were linked to enzyme-based biochemical defenses. Isoforms of PPOs, peroxidases, and oxalate oxidases were found on the exterior of seeds and associated in metabolism of oxygen and reactive oxygen species. Furthermore, they conducted the synthesis of low-molecular weight defense compounds. The aim of this chapter was to review recent advances in plant secondary metabolites for insect resistance, focusing primarily on research published in the last 15 years on seed defense theory. The chapter will focus on the seeds’ physical, chemical, and biological defense mechanisms.