Folic Acid Reinforces Maize Tolerance to Sodic-Alkaline Stress through Modulation of Growth, Biochemical and Molecular Mechanisms

Bandar S Aljuaid; Soumya Mukherjee; Amany N Sayed; Yasser Abd El-Gawad El-Gabry; Mohamed M A Omar; Samy F Mahmoud; Moodi Saham Alsubeie; Doaa Bahaa Eldin Darwish; Salem Mesfir Al-Qahtani; Nadi Awad Al-Harbi; Fahad Mohammed Alzuaibr; Mohammed A Basahi; Maha M A Hamada

doi:10.3390/life12091327

Folic Acid Reinforces Maize Tolerance to Sodic-Alkaline Stress through Modulation of Growth, Biochemical and Molecular Mechanisms

Life (Basel). 2022 Aug 27;12(9):1327. doi: 10.3390/life12091327.

Authors

Affiliations

¹ Department of Biotechnology, College of Science, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia.
² Department of Botany, Jangipur College, University of Kalyani, Kalyani 742213, India.
³ Department of Agronomy, Faculty of Agriculture, Ain Shams University, Cairo 11566, Egypt.
⁴ Department of Biochemistry, Faculty of Agriculture, Ain Shams University, Cairo 11566, Egypt.
⁵ Biology Department, College of Science, Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh 11623, Saudi Arabia.
⁶ Botany Department, Faculty of Science, Mansoura University, Mansoura 35511, Egypt.
⁷ Biology Department, Faculty of Science, Tabuk University, Tabuk 71491, Saudi Arabia.
⁸ Biology Department, University College of Tayma, University of Tabuk, P.O. Box 741, Tabuk 47512, Saudi Arabia.
⁹ Department of Biology, Faculty of Science, University of Tabuk, P.O. Box 741, Tabuk 71491, Saudi Arabia.
¹⁰ College of Science and Arts Sajir, Shaqra University, P.O. Box 33, Shaqra 11961, Saudi Arabia.

Abstract

The mechanism by which folic acid (FA) or its derivatives (folates) mediates plant tolerance to sodic-alkaline stress has not been clarified in previous literature. To apply sodic-alkaline stress, maize seedlings were irrigated with 50 mM of a combined solution (1:1) of sodic-alkaline salts (NaHCO₃ and Na₂CO₃; pH 9.7). Maize seedlings under stressed and non-stressed conditions were sprayed with folic acid (FA) at 0 (distilled water as control), 0.05, 0.1, and 0.2 mM. Under sodic-alkaline stress, FA applied at 0.2 mM significantly improved shoot fresh weight (95%), chlorophyll (Chl a (41%), Chl b (57%), and total Chl (42%)), and carotenoids (27%) compared to the untreated plants, while root fresh weight was not affected compared to the untreated plants. This improvement was associated with a significant enhancement in the cell-membrane stability index (CMSI), relative water content (RWC), free amino acids (FAA), proline, soluble sugars, K, and Ca. In contrast, Na, Na/K ratio, H₂O₂, malondialdehyde (MDA), and methylglycoxal (MG) were significantly decreased. Moreover, seedlings treated with FA demonstrated significantly higher activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), and ascorbate peroxidase (APX) compared to the untreated plants. The molecular studies using RT-qPCR demonstrated that FA treatments, specifically at 0.2 mM, enhanced the K⁺/Na⁺ selectivity and the performance of photosynthesis under alkaline-stress conditions. These responses were observed through up-regulation of the expression of the high-affinity potassium-transporter protein (ZmHKT1), the major core protein of photosystem II (D2-Protein), and the activity of the first enzyme of carbon fixation cycle in C4 plants (PEP-case) by 74, 248, and 225% over the untreated plants, respectively. Conversely, there was a significant down-regulation in the expression ZmSOS1 and ZmNHX1 by 48.2 and 27.8%, respectively, compared to the untreated plants.

Keywords: Zea maize; alkalinity; folates; ion homeostasis; leaf pigments and osmolytes; sodium efflux.

Grants and funding

This research was funded by Faculty of Agriculture, Ain Shams University, Cairo, Egypt.