Melatonin Improves Drought Stress Tolerance of Tomato by Modulating Plant Growth, Root Architecture, Photosynthesis, and Antioxidant Defense System

Muhammad Ahsan Altaf; Rabia Shahid; Ming-Xun Ren; Safina Naz; Muhammad Mohsin Altaf; Latif Ullah Khan; Rahul Kumar Tiwari; Milan Kumar Lal; Muhammad Adnan Shahid; Ravinder Kumar; Muhammad Azher Nawaz; Mohammad Shah Jahan; Basit Latief Jan; Parvaiz Ahmad

doi:10.3390/antiox11020309

Melatonin Improves Drought Stress Tolerance of Tomato by Modulating Plant Growth, Root Architecture, Photosynthesis, and Antioxidant Defense System

Antioxidants (Basel). 2022 Feb 3;11(2):309. doi: 10.3390/antiox11020309.

Authors

Muhammad Ahsan Altaf¹, Rabia Shahid², Ming-Xun Ren^{3

4}, Safina Naz⁵, Muhammad Mohsin Altaf⁴, Latif Ullah Khan⁶, Rahul Kumar Tiwari^{7

8}, Milan Kumar Lal^{7

8}, Muhammad Adnan Shahid⁹, Ravinder Kumar^{7

8}, Muhammad Azher Nawaz¹⁰, Mohammad Shah Jahan¹¹, Basit Latief Jan¹², Parvaiz Ahmad¹³

Affiliations

¹ School of Horticulture, Hainan University, Haikou 570228, China.
² School of Management, Hainan University, Haikou 570228, China.
³ Center for Terrestrial Biodiversity of the South China Sea, Hainan University, Haikou 570228, China.
⁴ College of Ecology and Environment, Hainan University, Haikou 570228, China.
⁵ Department of Horticulture, Bahauddin Zakariya University, Multan 60800, Pakistan.
⁶ College of Tropical Crop, Hainan University, Haikou 570228, China.
⁷ ICAR-Indian Agricultural Research Institute, New Delhi 110012, India.
⁸ ICAR-Central Potato Research Institute, Shimla 171001, India.
⁹ Department of Agriculture, University of New Hampshire, Durham, NC 03824, USA.
¹⁰ Department of Horticulture, College of Agriculture, University of Sargodha, Sargodha 171001, Pakistan.
¹¹ Department of Horticulture, Faculty of Agriculture, Sher-e-Bangla Agricultural University, Dhaka 1207, Bangladesh.
¹² Department of Clinical Pharmacy, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia.
¹³ Botany and Microbiology Department, King Saud University, Riyadh 11451, Saudi Arabia.

Abstract

Tomato is an important vegetable that is highly sensitive to drought (DR) stress which impairs the development of tomato seedlings. Recently, melatonin (ME) has emerged as a nontoxic, regulatory biomolecule that regulates plant growth and enhances the DR tolerance mechanism in plants. The present study was conducted to examine the defensive role of ME in photosynthesis, root architecture, and the antioxidant enzymes' activities of tomato seedlings subjected to DR stress. Our results indicated that DR stress strongly suppressed growth and biomass production, inhibited photosynthesis, negatively affected root morphology, and reduced photosynthetic pigments in tomato seedlings. Per contra, soluble sugars, proline, and ROS (reactive oxygen species) were suggested to be improved in seedlings under DR stress. Conversely, ME (100 µM) pretreatment improved the detrimental-effect of DR by restoring chlorophyll content, root architecture, gas exchange parameters and plant growth attributes compared with DR-group only. Moreover, ME supplementation also mitigated the antioxidant enzymes [APX (ascorbate peroxidase), CAT (catalase), DHAR (dehydroascorbate reductase), GST (glutathione S-transferase), GR (glutathione reductase), MDHAR (monodehydroascorbate reductase), POD (peroxidase), and SOD (superoxide dismutase)], non-enzymatic antioxidant [AsA (ascorbate), DHA (dehydroascorbic acid), GSH (glutathione), and GSSG, (oxidized glutathione)] activities, reduced oxidative damage [EL (electrolyte leakage), H₂O₂ (hydrogen peroxide), MDA (malondialdehyde), and O₂^•- (superoxide ion)] and osmoregulation (soluble sugars and proline) of tomato seedlings, by regulating gene expression for SOD, CAT, APX, GR, POD, GST, DHAR, and MDHAR. These findings determine that ME pretreatment could efficiently improve the seedlings growth, root characteristics, leaf photosynthesis and antioxidant machinery under DR stress and thereby increasing the seedlings' adaptability to DR stress.

Keywords: drought; gene expression; melatonin; oxidative damage; photosynthesis; root growth; tomato.