TABLE 2.
Use of different stress alleviators and their interactions with endogenous H2S for higher metal tolerance in plants.
| Stress alleviator | Exogenous H2S | Plant species | Experiment | Duration/growth stage | Heavy metal/source | Exposure level | Endogenous H2S | Stress alleviating symptoms | References |
| Silicon (Na2SiO3) 2.0 mM | NO | Pepper (Capsicum annuum L.) | Potted soil | 35 days/young seedlings | Cadmium: CdCl2 | 0.1 mM | Upregulated ∼10 μmol g–1 fresh weight | Reduced leaf Cd content and oxidative stress Improved K and Ca uptake | Kaya et al., 2020 |
| Nitric oxide (NO) 50 μM | NO | Tomato (Solanum lycopersicum L.) | Pot filled with vermiculite-perlite | 21 days/young seedlings | Chromium: K2Cr2O7 | 100 μM Cr (VI) | Upregulated ∼98 nmol g–1 fresh weight | Increased S assimilation and kinked enzyme metabolism averted DNA and oxidative damages. | Alamri et al., 2020 |
| Thiamine (THI) 50 mgL–1 | 0.2 mM sodium hydrosulfide (NaHS) | Strawberry (Fragaria × ananassa Duch) | Hydroponic culture | 28 days | Cadmium: CdCl2 | 0.1 mM | Upregulated ∼15 μmol g–1 fresh weight | Upregulated endogenous NO and hydrogen sulfide (H2S); Enhanced Ca and K uptake | Kaya and Aslan, 2020 |
| 0.5 mM salicylic acid (SA) | 0.2 mM sodium hydrosulfide (NaHS) | Pepper (Capsicum annuum L.) | Perlite pot | 28 days/young seedlings | Lead; PbCl2 | 0.1 mM | Upregulated ∼23 μmol g–1 fresh weight | Pb induced phytotoxicity was alleviated by SA + NaHS related upregulation in ascorbate–glutathione cycle | Kaya, 2020 |
| Calcium (CaCl2) 15 mM | 100 μM sodium hydrosulfide (NaHS) | Zucchini (Cucurbita pepo L.) | Hydroponic culture | 14 days/young seedlings | Nickel: Ni (NO3)2 | 50 mg L–1 | Upregulated ∼323 nmol g–1 fresh weight | Both extracellular (Ca2+) and intracellular (CaM) complex activated crosstalk of Ca2+ and H2S to revert plant oxidative damages | Valivand et al., 2019 |
| 0.5 mM salicylic acid (SA) | 0.5 mM sodium hydrosulfide (NaHS | Maize (Zea mays L.) | Potted sand–perlite | 9 days/young seedlings | Lead: Pb (NO3)2 | 2.5 mM | Not detected | Regulated metal toxicity by increasing glycine betaine and NO at the expense of S-amino acids metabolism, i.e., arginine, methionine | Zanganeh et al., 2018 |
| 0.5 mM salicylic acid (SA) | NO | Maize (Zea mays L.) | Potted sand–perlite | 9 days/young seedlings | Lead: Pb (NO3)2 | 2.5 mM | Upregulated ∼3.5 μmol g–1 fresh weight | Minimized chlorophyll related damages, built-up ascorbic acid glutathione and upregulation of antioxidant enzyme activity | Zanganeh et al., 2019 |
| 1 μM methyl jasmonate (MeJA) | 50 μM sodium hydrosulfide (NaHS) | Foxtail millet (Setaria italica L.) | Hydroponic culture | 14 days/young seedlings | Cadmium chloride (CdCl2) | 200 μM | Upregulated 75–120 nm g–1 fresh weight | Alleviated growth retardations by decreasing H2O2 and malondialdehyde content, also repressed Cd accumulation in seedlings | Tian et al., 2017 |