ABSTRACT
As sessile organisms, environmental conditions have far-reaching and critical effects on plants. Any conditions adversely influencing a plant’s growth and development is generally considered to be stress. Plant stresses are placed in three basic categories based on their duration (short- and long-term), intensity (high- and low-intensity), and type (biotic and abiotic stresses). Biotic and abiotic stresses are two common groups which have been widely studied. Drought (water deficit), salinity/sodicity, nutrient-deficiency, light, water (logging/flooding), temperature (cold, frost, and heat) stresses can be representative examples of abiotic stresses. Apart from abiotic stress-induced damages, plants may encounter tensions caused by biotic stresses, which can be instigated by living organisms, including pathogens (bacteria, viruses, fungi, and nematodes), plants (weeds), and pests. Facing environmental stresses can trigger some reactions in plants, i.e., signaling mechanisms, in which various components like plant hormones play leading roles (Pandey et al. 2016). Along with the major classes of hormones, i.e., auxins, ethylene (ET), cytokinins (CKs), gibberellins (GAs), abscisic acid (ABA), and brassinosteroids, some signaling molecules should also be pointed out, e.g., jasmonic acid, salicylic acid, and karrikins (Ren and Dai 2012; Munné-Bosch and Müller 2013). As a result of a decade’s research, nowadays a new signaling molecule is universally recognized which is called strigolactone (SL). SL is a carotenoid derivative serving a dual function, as both an endogenous and exogenous signaling molecule (Foo et al. 2013; Pandey et al. 2016). Due to possessing the essential properties of phytohormones, i.e., acting in low concentration, having importance in plant growth and development, local or distal site of action, and crosstalk, SL is classified as a phytohormone (Gray 2004; Pandey et al. 2016). In this chapter, the hormone, its function, biosynthesis, and transduction, are briefly explained. Then, SL roles in plant responses to stresses are indicated to provide an integrated view of the newly discovered multifaceted phytohormone. Thus far, a limited number of research studying in-depth the roles of SL in stressful conditions is available which implies the absolute necessity of further research on this aspect of strigolactones.
