Iron homeostasis regulates maturation of tomato (climacteric) and capsicum (non-climacteric) fruits
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Iron homeostasis regulates maturation of tomato (climacteric) and capsicum (non-climacteric) fruits Rashmi Shakya1 • Neha Singh2 • Satish C. Bhatla3 Received: 12 June 2020 / Accepted: 15 September 2020 Ó Society for Plant Biochemistry and Biotechnology 2020
Abstract Endogenous iron quickly interchanges its oxidation states (Fe III and Fe II), which modulate production of reactive oxygen species (ROS) and nitric oxide (NO), and also serve as co-factor for various enzymes. A sharp increase in Fe(III) content in mature fruits of tomato (climacteric) is a unique observation from the present work. Iron homeostasis in non-climacteric capsicum fruits, however, accompanies a balancing of Fe(III) and Fe(II) levels during turning and ripe stages. Heme oxygenase-1 (HO-1), which mobilizes toxic heme and produces Fe(II), apparently regulates iron homeostasis in tomato. Nearly static HO-1 activity in capsicum indicates that HO-1 probably does not have a major role in iron homeostasis in non-climacteric fruit maturation. Endogenous NO content is much higher during tomato fruit maturation than in capsicum. ROS production is highest in green (unripe) tomato and capsicum fruits and it sharply declines with fruit maturation. Tomato fruits exhibit very high b-cyanoalanine synthase (b-CAS) activity in turning stage and mature fruits, highlighting its crucial role in maintaining a static level of cyanide (CN) generated as a byproduct of ethylene biosynthesis during fruit maturation. In contrast, b-CAS activity is very low in maturing capsicum fruits. Thus, a coordination between iron signal and, NO and ROS accumulation in climacteric and non-climacteric fruits is apparently perceived by hormonal (ethylene) signals getting altered differentially during fruit ripening. Keywords Climacteric fruit Non-climacteric fruit Iron homeostasis Nitric oxide Reactive oxygen species Abbreviations b-CAS b-Cyanoalanine synthase HO-1 Heme oxygenase-1 H 2S Hydrogen sulphide NO Nitric oxide
Physiological and biochemical changes accompanying fruit ripening are governed by a set of genetically programmed processes (Gong et al. 2018; Ziogas et al. 2018). Noticeable differences in the antioxidant properties of capsicum and tomato have been reported at different developmental & Satish C. Bhatla [email protected] 1
Department of Botany, Miranda House, University of Delhi, Delhi, India
2
Department of Botany, Gargi College University of Delhi, Delhi, India
3
Laboratory of Plant Physiology and Biochemistry, Department of Botany, University of Delhi, Delhi 110007, India
stages (Shakya and Lal 2018). A number of signaling molecules, such as nitric oxide (NO), reactive nitrogen species (RNS), hydrogen sulphide (H2S) and melatonin also regulate fruit ripening (Palma et al. 2019). NO transcriptionally represses gene expression involved in ethylene biosynthesis and post-translationally modifies methionine adenosyl transferase (MAT) activity through S-nitrosylation. It also inhibits the autocatalytic ethylene biosynthesis by binding
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