SPECIAL ISSUE | FOREWORD https://doi.org/10.1071/FP22170 Polyamines and nitric oxide crosstalk in plant development and abiotic stress tolerance Durgesh K. Tripathi A, * , Javaid A. Bhat B , Parvaiz Ahmad C and Suleyman I. Allakhverdiev D, * For full list of author affiliations and declarations see end of paper *Correspondence to: Durgesh K. Tripathi Crop Nanobiology and Molecular Stress Physiology Lab, Amity Institute of Organic Agriculture (AIOA), Amity University, Noida, Uttar Pradesh, India Email: dktripathiau@gmail.com Suleyman I. Allakhverdiev K.A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Street 35, Moscow 127276, Russian Federation Email: suleyman.allakhverdiev@gmail.com Published: 3 February 2023 Cite this: Tripathi DK et al. (2023) Functional Plant Biology, 50(2), i–iv. doi:10.1071/FP22170 © 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing. ABSTRACT Polyamines (PAs) and nitric oxide (NO) are crucial signalling molecules that exhibit a promising role in improving stress tolerance in plants, maintaining their growth and development. They act as protecting agents for plants through activation of stress adaptation strategies such as membrane stabilisation, acid neutralisation and suppression of ROS generation. NO interacts with PAs during several developmental processes and stress responses. External supplementation of PAs to plants is also reported to cause an increase in NO content. However, it is unclear whether PAs promote synthesis of NO by either as substrates, cofactors, or signals. Impact of NO on synthesis of PAs has been also reported in some studies, yet the exact governing mechanisms of the interrelation between NO and PAs is currently obscure. Understanding the crosstalk between PAs and NO during growth and stress condition in plants can aid in providing better tolerance to plants against stressful environment. Keywords: abiotic, biotic, chlorophyll, hydrogen peroxide, lipid peroxidation, nitric oxide, oxidative stress, polyamines, ROS, spermidine, spermine. Polyamines and nitric oxide: signalling molecules for plant growth regulation and stress resistance Polyamines (PAs) are aliphatic amines found either in free, conjugated or bound forms in the plant cells and their contents vary on the basis of species and developmental stage of the plants (Mustafavi et al. 2018; Chen et al. 2019). PAs show direct protective effect in plant cells owing to their cationic nature that enables them to interact with macromolecules having negative charge for stabilising their structure during normal as well as stressful situations (Takahashi 2020). They also play the role of signalling molecules for regulation of several cellular processes in plants, especially during exposure to abiotic stresses (Pál et al. 2015; Paul et al. 2018; Allakhverdiev 2020). Nitric oxide (NO), a gaseous free radical, regulates plant growth and development and varies in concentration in different tissues depending on plant species and environmental conditions (Domingos et al. 2015; Kolbert et al. 2019). NO is a crucial signalling molecule in plants surviving under stressful conditions by interacting with other signalling molecules including phytohormones and reactive oxygen species (ROS) along with regulating the protein activity and expression of genes (Simontacchi et al. 2015; Sahay and Gupta 2017; Nabi et al. 2019). Collectively, PAs and NO are crucial signalling molecules acting as regulators of plant growth and development (Krasuska et al. 2017). Both interact with phytohormones to perform various biological functions under normal as well as stressful situations responses (Nahar et al. 2016). Scavenging of ROS through antioxidant activation, protecting biomolecules and bio-membranes are common mechanisms of action of PAs and NO (Choudhary et al. 2022). The biosynthesis pathways of PAs and NO overlap as PAs either induce generation of NO or directly convert to NO (Nahar et al. 2016). Inter-relation between PAs and NO can provide improved resistance to plants under challenging environment; however, the studies are limited in this context (Nahar et al. 2016; Choudhary et al. 2022). This special issue brings latest researches evaluating the