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    Plant growth coordination during stress conditions: Role of phytohormones
    (Elsevier B.V., 2024) Gupta, Shreya; Devi, Loitongbam Lorinda; Singh, Amar Pal
    Plants encounter multiple stresses which are associated with compromised plant growth and yield across the globe. Several studies have been done in the past few years to understand plant acclimatization under numerous stresses like nutrient deficiency, drought, salinity, temperature, and pathogen attack. The shoot and root system architecture in plants seems a promising approach as it is highly sensitive to edaphic and internal signals and plants adapt by modulating them to these stresses. Intrinsic factors such as growth hormones are the key components of the plant whose levels and signaling determine the extent of plant growth and performance. The major phytohormones that are involved in monitoring plant development for optimized plant growth during environmental stresses are auxin, brassinosteroids, cytokinin, abscisic acid, jasmonic acid, gibberellins, and ethylene. In recent years, detailed genetic and biochemical analysis of the signaling and biosynthesis genes and transcription factors of these hormones have been studied from the model plant Arabidopsis to different crops. Genetic studies have shown that these hormones regulate several biological processes of root and shoot growth including cell elongation, division and differentiation, root hair and lateral root formation, and floral and leaf morphology in response to altered environmental conditions. In this chapter, the current understanding of both above- and below-ground plant organs and their developmental plasticity during stress conditions along with the interplay of growth hormones has been summarized and discussed.
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    Regulatory role of phytohormones in the interaction of plants with insect herbivores
    (Elsevier B.V., 2023) Kundu, Pritha; Bera, Paramita; Mishra, Shruti; Vadassery, Jyothilakshmi
    Insect herbivores affect crop growth worldwide, causing significant yield losses annually. Phytohormones are prime signaling molecules that coordinate many physiological phenomena, besides triggering stress-responsive regulatory genes involved in plant defense. Here, we present a holistic picture of the central role of various phytohormones—jasmonic acid, salicylic acid, ethylene, abscisic acid, auxin, cytokinin, gibberellins, and brassinosteroids in regulating the diverse molecular interactions between plants and insect herbivores. With an initial overview of the early signaling response, the chapter majorly focuses on the role of different key phytohormones in defending plants against herbivory and their cross talk. We also describe the phytohormone-mediated production of secondary metabolites and other defense toxins to counteract harmful herbivores. With the well-established myriad of information in selected plant–herbivore model systems, it is now critical to translate this knowledge to less explored crop plants for sustainable development in agriculture.
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    Regulation of plants nutrient deficiency responses by phytohormones
    (Elsevier B.V., 2023) Deepika, Deepika; Sonkar, Kamankshi; Singh, Amarjeet
    Living organisms have the ability to acquire nutrients from their physical environment and subsequently convert them into an energy source for survival and growth. In plants, nutrients are involved in metabolism and physiology either as constituents of metabolites or enzymes for macromolecule biosynthesis. Based on their concentration in plant dry matter, the 14 essential inorganic elements are categorized into macronutrients and micronutrients. Macronutrients include six elements, nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), and magnesium (Mg), whereas the micronutrients comprised eight elements, chlorine (Cl), iron (Fe), boron (B), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), and nickel (Ni) (de Bang et al., 2020; Sustr et al., 2019). Nutrients are distributed in a patchy manner in soil due to their variable interactions with spatially and temporally dispersed charged soil particles (Hodge, 2006). This, along with many other factors, leads to either low nutrient concentration in soil or low accessibility for plants. Low availability of a nutrient causes specific deficiency symptoms. But plants usually face multiple nutrient deficiencies simultaneously leading to a complex response and symptoms. Moreover, various biotic and abiotic stress factors, such as pests, pathogens, water deficit, salinity, and light, also interact to cause atypical nutrient deficiency symptoms (Amtmann et al., 2008; Troufflard et al., 2010; Atkinsonand Urwin., 2012). Globally, nutrient deficiencies are major threats to crop production, causing reduced yields and poor food and feed quality. The world food security challenge is being met by the use of chemical fertilizers (natural and anthropogenic).
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    Jasmonic acid biosynthesis pathway and its functional role in plants
    (Elsevier B.V., 2023) Ankit, Ankit; Kamali, Saravanappriyan; Singh, Amarjeet
    Plants encounter various abiotic and biotic stresses including drought, heat, cold, salinity, osmotic stress, fungal infection, herbivore attacks in their natural habitat. In these unavoidable circumstances various phytohormones play crucial roles in regulating plant growth and development (Khan et al., 2019, 2020a, 2020b; Nazir et al., 2019, 2021, 2022; Poo´r et al., 2021). Jasmonic acid (JA) is a lipid-derived phytohormone which acts as a signal as well as regulator in various physiological processes and stress conditions. Methyl ester of JA (MeJA) is the first active jasmonate which was detected and isolated as an odorant from Jasminium grandiflorum flowers (Demole et al., 1962). Among the conjugates of JA, JA-Ile is the most biologically active form (Fonseca et al., 2009). Recently, cis-(1)-12- oxophytodienoic acid (OPDA) an intermediate in the lipoxygenases (LOX) pathway for JA biosynthesis has been shown to be functional signaling molecule instead of JA in lower plants, such as Marchantia polymorpha (liverworts), Physcomitrella patens (moss) and Selaginella martensii (spikemoss) (Ogorodnikova et al., 2015; Stumpe et al., 2010; Yamamoto et al., 2015). Apart from bryophytes, fungus species such as Fusarium oxysporum have JA and/or JA-Ile conjugate (Miersch et al., 1999). Although, JA and its derivatives are distributed among bryophytes and fungi, most of the homologs of JA biosynthesis enzymes are present in major lineages of land plants (Han, 2017). In last decade, studies have been performed in both monocotyledons as well as dicotyledons plants to better understand the JA biosynthesis mechanism. In Arabidopsis, JA biosynthesis mainly occurs in chloroplast, peroxisome and cytoplasm (Ruan et al., 2019). In chloroplast, OPDA is synthesized from unsaturated fatty acid α-linolenic acid (α-LeA) derived from the chloroplast membrane, followed by its conversion into JA in peroxisome. The conversion of JA into different functional and structural metabolites takes place in the cytoplasm. JA and its other derivatives like MeJA and JA-Ile are collectively known as jasmonates.