Carbon Monoxide Alleviates Salt-Induced Oxidative Damage in Sorghum bicolor by Inducing the Expression of Proline Biosynthesis and Antioxidant Genes

Vivian Chigozie Ikebudu; Mulisa Nkuna; Nzumbululo Ndou; Rachel Fanelwa Ajayi; Stephen Chivasa; Katrina Cornish; Takalani Mulaudzi

doi:10.3390/plants13060782

Carbon Monoxide Alleviates Salt-Induced Oxidative Damage in Sorghum bicolor by Inducing the Expression of Proline Biosynthesis and Antioxidant Genes

Plants (Basel). 2024 Mar 10;13(6):782. doi: 10.3390/plants13060782.

Authors

Vivian Chigozie Ikebudu¹, Mulisa Nkuna¹, Nzumbululo Ndou^{1

2}, Rachel Fanelwa Ajayi², Stephen Chivasa³, Katrina Cornish^{4

5}, Takalani Mulaudzi¹

Affiliations

¹ Life Sciences Building, Department of Biotechnology, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa.
² SensorLab, Department of Chemical Sciences, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa.
³ Biosciences Department, Durham University, Durham DH1 3LE, UK.
⁴ Department of Horticulture and Crop Science, Ohio Agricultural Research and Development Center, The Ohio State University, 1680 Madison Avenue, Wooster, OH 44691-4096, USA.
⁵ Department of Food, Agriculture and Biological Engineering, Ohio Agricultural Research and Development Center, The Ohio State University, 1680 Madison Avenue, Wooster, OH 44691-4096, USA.

Abstract

Crop growth and yield are affected by salinity, which causes oxidative damage to plant cells. Plants respond to salinity by maintaining cellular osmotic balance, regulating ion transport, and enhancing the expression of stress-responsive genes, thereby inducing tolerance. As a byproduct of heme oxygenase (HO)-mediated degradation of heme, carbon monoxide (CO) regulates plant responses to salinity. This study investigated a CO-mediated salt stress tolerance mechanism in sorghum seedlings during germination. Sorghum seeds were germinated in the presence of 250 mM NaCl only, or in combination with a CO donor (1 and 1.5 μM hematin), HO inhibitor (5 and 10 μM zinc protoporphyrin IX; ZnPPIX), and hemoglobin (0.1 g/L Hb). Salt stress decreased the germination index (47.73%) and root length (74.31%), while hydrogen peroxide (H₂O₂) (193.5%), and proline (475%) contents increased. This increase correlated with induced HO (137.68%) activity and transcripts of ion-exchanger and antioxidant genes. Salt stress modified vascular bundle structure, increased metaxylem pit size (42.2%) and the Na⁺/K⁺ ratio (2.06) and altered primary and secondary metabolites. However, exogenous CO (1 μM hematin) increased the germination index (63.01%) and root length (150.59%), while H₂O₂ (21.94%) content decreased under salt stress. Carbon monoxide further increased proline (147.62%), restored the vascular bundle structure, decreased the metaxylem pit size (31.2%) and Na⁺/K⁺ ratio (1.46), and attenuated changes observed on primary and secondary metabolites under salt stress. Carbon monoxide increased HO activity (30.49%), protein content, and antioxidant gene transcripts. The alleviatory role of CO was abolished by Hb, whereas HO activity was slightly inhibited by ZnPPIX under salt stress. These results suggest that CO elicited salt stress tolerance by reducing oxidative damage through osmotic adjustment and by regulating the expression of HO₁ and the ion exchanger and antioxidant transcripts.

Keywords: ROS; antioxidant; carbon monoxide; epidermis; hematin; heme oxygenase; oxidative stress; salinity; vascular bundles.

Grants and funding

121939; 112201/National Research Foundation