Titanium dioxide nanoparticles require K+ and hydrogen sulfide to regulate nitrogen and carbohydrate metabolism during adaptive response to drought and nickel stress in cucumber
M. Nasir Khan, Manzer H. Siddiqui, Khalaf Alhussaen, Alaa R. El-Alosey, Meshari Atallah M. AlOmrani, Hazem M. Kalaji
Abstract
Crop plants face severe yield losses worldwide owing to their exposure to multiple abiotic stresses . The study described here, was conducted to comprehend the response of cucumber seedlings to drought (induced by 15% w/v polyethylene glycol 8000; PEG) and nickel (Ni) stress in presence or absence of titanium dioxide nanoparticle (nTiO 2 ). In addition, it was also investigated how nitrogen (N) and carbohydrate metabolism , as well as the defense system, are affected by endogenous potassium (K + ) and hydrogen sulfide (H 2 S). Cucumber seedlings were subjected to Ni stress and drought, which led to oxidative stress and triggered the defense system. Under the stress, N and carbohydrate metabolism were differentially affected. Supplementation of the stressed seedlings with nTiO 2 (15 mg L −1 ) enhanced the activity of antioxidant enzymes , ascorbate-glutathione (AsA-GSH) system and elevated N and carbohydrates metabolism. Application of nTiO 2 also enhanced the accumulation of phytochelatins and activity of the enzymes of glyoxalase system that provided additional protection against the metal and toxic methylglyoxal . Osmotic stress brought on by PEG and Ni, was countered by the increase of proline and carbohydrates levels, which helped the seedlings keep their optimal level of hydration. Application nTiO 2 improved the biosynthesis of H 2 S and K + retention through regulating Cys biosynthesis and H + -ATPase activity, respectively. Observed outcomes lead to the conclusion that nTiO 2 maintains redox homeostasis , and normal functioning of N and carbohydrates metabolism that resulted in the protection of cucumber seedlings against drought and Ni stress. Use of 20 mM tetraethylammonium chloride (K + - channel blocker), 500 μM sodium orthovanadate (PM H + -ATPase inhibitor), and 1 mM hypotaurine (H 2 S scavenger) demonstrate that endogenous K + and H 2 S were crucial for the nTiO 2 -induced modulation of plants' adaptive responses to the imposed stress.