Plants have evolved both passive and active defence mechanisms to withstand insect herbivory. Passive defences include physical barriers and toxic substances on the plant's surface, while active defences are triggered by herbivore-associated signals. Recent studies have shown that defence mechanisms, including volatile emission, molecular pattern recognition, changes in Ca2+ levels, shifts in plasma membrane potential, NADPH oxidase mobilization and oxygen radical formation, are triggered by interplant and intraplant signalling. Plants detect specific elicitors produced by insects during infestation, enabling them to recognize and respond to herbivory. Infested plants emit chemical signals that lead to the production of volatile terpenoids, attracting host-seeking insects. Plants deploy a wide array of defensive compounds, including cyanogenic glucosides, glucosinolates (GSLs), phenolics, alkaloids, proteinase inhibitors (PIs) and saponins, which deter feeding and impair insect digestion. Morphological features such as trichomes and thorns provide additional protection. Plant hormones such as ethylene (ET), jasmonic acid (JA) and salicylic acid (SA) mediate plant immunity. Calcium (Ca2+) is crucial for regulating cellular processes and plant defence. Oxygen radical, especially hydrogen peroxide (H2O2), are critical for disease resistance. Nitric oxide (NO) influences H2O2 production, modulates the redox status and activates defence genes, thereby enhancing plant resilience against herbivory through various signalling pathways. By detailing the roles of various signalling molecules, hormones and defence compounds, the article aims to enhance understanding of plant defence strategies and the intricate signalling networks that underpin these responses.
Yash et al. (Wed,) studied this question.
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