Table 2.

Antioxidant metabolism and defense under various environmental stresses.

Plant Species	Stress Levels	Antioxidant Metabolism	Reference
Drought
Lolium perenne L.	Drought stress (withholding irrigation), 45 d	Significant improvement of APX, CAT, and SOD activity, but POD activity remained unchanged up to 15 d, whereas increased thereafter.	[171]
Vigna radiata L. cv. BARI Mung-2	Drought stress (5% PEG), 48 h	Decreased AsA and high DHA content with reduced AsA/DHA ratio.	[69]
		Downregulated GSH/GSSG ratio.
		Increased GR, APX, GPX, and GST activity with reduced CAT and MDHAR activity.
Lens culinaris L. Cultivars: drought tolerant (PDL-2) and sensitive (JL-3)	Drought stress (seedlings exposed to dry air for 4h), 3 d	Upregulation of SOD, APX, and GPX in both tolerant and sensitive cultivars (higher in PDL-2 by 32, 44, and 57% than in JL-3).	[77]
		CAT activity showed no significant difference.
Triticum aestivum L. cv. Jing 852	Drought stress (10% PEG), 6 h	CAT and SOD activities consistently increased.	[206]
		POD and APX activities were increased initially but declined later.
T. aestivum L.	Drought stress (70, 50, and 35% of soil water holding capacity)	Uplifting SOD and CAT activities in a dose-dependent manner compared to respective control.	[74]
Brassica napus L. cvs. Dunkeld and Cyclone	Water deficit (60% FC), 21 d	Slightly enhanced total phenolics in both canola cultivars.	[173]
		Increased activities of POD and CAT enzymes.
		Dunkeld performed better compared to Cyclone in POD activity, whereas, in the case of SOD activity, Cyclone was better.
Sorghum bicolor L. cvs. M-81E and Roma	Drought stress (sand water content 4.2%), 7 d	APX and SOD activities increased in both cultivars.	[105]
		M-81E had uplifted enzymatic antioxidant activities as well as stronger scavenging ability than Roma.
Oryza sativa L.	Drought stress (15 and 20% PEG), 7 d	Elevated antioxidant enzyme activities, including CAT, SOD, APX, GPX, and GR.	[71]
		Increased level of AsA and GSH.
Capsicum annuum L.	Drought stress (without watering), 7 d	Increased APX and CAT activities.	[231]
		No significant changes in SOD activity were observed.
T. aestivum L. cv. Sakha-94	Drought stress (stopped irrigation at 10 DAS), 11 d	Enhanced GPX but inhibited CAT activity.	[232]
Salinity
O. sativa L.	Salinity 150 and 300 mM NaCl, 48 h	In the BRRI dhan54, Pro, GB, and GSH contents increased.	[219]
		In BRRI dhan49, Pro and GB increased together with enhanced SOD activity.
V. radiata L.	Salinity 200 mM NaCl, 48 h	Exogenous application of PAs enhanced AsA content and AsA/DHA while restored CAT activity.	[233]
V. radiata L.	Salinity 50–200 mM NaCl, 2 d to 3 weeks	Transgenic plants overexpressing AtNHX1 from A. thaliana enhanced APX, SOD, GPX and GR.	[234]
High Temperature
Gossypium hirsutum (84-S and M-503)	30–45 °C, 7 d	Enhanced the activity of FeSOD and Cu/ZnSOD in M-503; also increased APX and GR activities.	[179]
Portulaca oleracea L.	42 °C, 7 d	Increased SOD and POD activities except for CAT.	[102]
T. aestivum L. cv. Gayetri, Gandhari, Kedar, PBW343	25, 30, 35, and 40 °C, 6 h	Elevated activity of CAT (1.02-fold), POD and APX.	[235]
		GSH content increased.
Low Temperature
Ipomoea batatas L.	4 and 13 °C, 8 weeks	Transgenic plants overexpressing AtP3B enhanced POD and CAT activities.	[236]
Lycopersicon esculentum	4 °C, 5 d	Transgenic plants overexpressed AtDREB1A enhanced SOD and CAT activities.	[237]
Camellia sinensis L.	−5 °C, 3, 6, and 12 h	High tea polyphenol to the amino acid ratio by 48, 83, and 86%, respectively.	[99]
Triticum spp.	Frost injury (−3, −5, and −7 °C), 24 h	Amplified transcript level of GST and APX enzymes in all wheat cultivars under frost injury.	[238]
Waterlogging/Flooding
G. max cv. Daewon	Waterlogging, 2 d	GSH activity was reduced in both shoot and root.	[239]
		GR activity was reduced in shoots but unaffected in the roots.
Prunuspersica L. Batsch	Waterlogging, 72 h	Activities of CAT, SOD, and POD increased up to 24 h but decreased at 48 and 72 h.	[181]
G. max L.	Waterlogging, 10 d	Up-stimulation of SOD, CAT, and APX activities.	[182]
P. mahaleb, P. pseudocerasus, P. cerasus × P. canescens	Waterlogging, 24 h	Higher the POD, CAT, and GR activities in all rootstock.	[183]
		AsA and DHA contents increased in P. cerasus × P. canescens and decreased in the other two species.
		GSH and GSSG contents decreased in Prunus mahaleb while increased significantly in the other two species.
G. max L. genotypes Grobogan, Willis and Detam-1	Inundation condition, 72 h	Activities of both SOD and POD enzymes were higher compared to control plants.	[240]
Zea mays L. cvs. Zhengdan-958 and Xing Ken-6	Waterlogging, 14 d	Higher activities of SOD, POD, CAT, APX and GR.	[119]
Metal/Metalloids Toxicity
Nicotiana tabacum and Petunia × atkinsiana	100 mM of CuSO4, ZnSO4, K2Cr2O7, or 500 mM MnSO4,10 d	Plants overexpressing RsMYB1 improved the activities of SOD, CAT, POX, and GST.	[241]
N. tabacum	100 μM CdCl2, 1 mM MnCl2, 500 μM ZnSO4, or 50 μM CuSO4, 72 h	Genotypes overexpressing LmSAP improved the activities of SOD, CAT, and POD.	[242]
O. sativa L.	CdCl2 (2.0 mM), 72 h	Decreased AsA and DHA contents with a sharp increase in both GSH and GSSG contents.	[177]
		Higher activity of APX, MDHAR, GR, SOD, GPX.
		Reduced the activity of DHAR (by 33%), CAT (by 35%), and GST.
Solanumlycopersicum cv. çiko F1	Cd, Cu, and Pb (50 ppm)	Decreased APX activity in leaves except for Cu-toxicity, which was increased.	[243]
		Increased in POD and SOD activities.
Withania somnifera L.	CdSO4 (5 μM, 10 μM, 20 μM, 50 μM, 100 μM, 150 μM, 200 μM and 300 μM)	Tocopherol content was the maximum at 10 μM, about 2.75-fold.	[176]
		GSH content increased by 2.02-fold.
		AsA and DHA content was enhanced by 4.46-, 2.16- and 38.75-fold, respectively.
		MDHAR, DHAR, GR, and GPX activity upregulated.
Cucumis sativus L. cv. Jingyan-4	80 mM Cu2+ was supplied as CuSO4, 14 d	Decreased SOD, POD, and APX activity in roots but increased in leaves.	[178]
		Increased SOD, POD, APX and GR activities in leaves.
		Increased GSH and GSSG and their ratio in both leaves and root tissue.
Morus alba L.	PbCl2 and CdCl2 at 100 and 200 μM, respectively	Lower activity of APX and SOD but slightly increased SOD activity was found only in the lower dose of Pb.	[14]
High Light
O. sativa L. cv. Liangyoupeijiu	1400–1600 µmol photons m−2 s−1, 1 h	CAT, DHAR, MDHAR, and POD activity were higher (0.147 to 0.534-fold) in leaf lamina, while SOD and APX were higher in midvein.	[188]
		The AsA and GSH contents increased, and DHA and GSSG decreased.
		AsA/DHA and GSH/GSSG ratios increased in midvein.
S.lycopersicum L.	500, 1000 µmol photons m−2 s−1, 5 d	SOD and POD activity down-regulated.	[189]
		APX gene expression was higher, and GR expression was lower.
Anacardium occidentale L.	850 µmol photons m−2 s−1, 5 d	CAT activity decreased while the activity of APX and SOD upregulated.	[124]
		AsA content decreased by 25%, and GSH content increased by 63%.
A. thaliana pgr5 and WT glabrous 1	1000 µmol photons m−2 s−1, 1 h	CAT activity increased in mutants than WT under control.	[244]
		DHAR activity increased in HL treated mutants. Expression of APX2, DHAR1, CDS1, CDS2, and FDS2 were down-regulated, and APX1, CAT2, and FDS1 were upregulated in the mutant.
UV-Radiation
T. aestivum L. cv. HP 1761	UV-B radiation (8.6 kJ m−2 d−1) at 12th and 14th day after emergence	Higher accumulation of AsA was recorded.	[129]
		Lower SOD and APX activities were observed, while CAT and GPX activities increased.
A. thaliana cvs. C24 and rsr4-1	UV-B radiation (3.9 kJ m−2) up to 4 h d–1, 4 d	Activity of SOD was not affected in C24 but drastically reduced in rsr4-1.	[245]
		In C24, the activity of POD, APX and GPX increased while remaining unchanged in rsr4-1.
Olea europaea L. cv. Galega Vulgar	UV-B radiation (6.5 kJ m−2 d−1, UV-B1) and 12.4 kJ m−2 d−1, UV-B2), 5 d	Reduced activities of GR (by 75%) and APX (by 36%) under UV-B1 treatment, while GR increased by 59% under UV-B2 treatment remaining APX unaffected.	[190]
		Activities of SOD, CAT, and GPX increased in a dose-dependent manner with the highest value of UV-B2 treatment.
G. max cv. Jin 36	UV-C radiation (0.284 mW cm−2) for 20 min per day, 50 d	Activities of SOD and POD increased by 30 and 28%, respectively.	[130]
Elevated Ozone
S. tuberosum L.	70 ppb O3, 3 months	POX and APX activity enhanced by 73 and 21%, respectively, under ambient CO2 and elevated O3.	[192]
		CAT, POX, GR, and SOD activities increased.
Malus crabapple	100 ± 10 nL L−1 O3, 3 h	Increased CAT, POD, and SOD by 85, 50, and 51%, respectively.	[246]
O. sativa	70–150 ppb O3, 10 d	Increased AsA level.	[194]
T. aestivum	59.6 ppb O3, 122 d	Increased CAT, GR, APX, and POD activities.	[195]
Acidity and Alkalinity
S. lycopersicum L. cv. Micro-Tom	Simulated acid rain stress (pH 2.5 and 5.6), 17 d	Enhanced activities of antioxidant enzymes (CAT, APX, SOD and POD), increased total phenolic, flavonoids, Pro and total antioxidant contents.	[197]
Medicago sativa L. cv. Gongnong No. 1	Alkaline stress (25 mM Na2CO3, pH 11.2), 48 h	Decreased oxidative stress-induced damages by upregulating the AsA content and POD and CAT activities.	[145]
B. oleracea L. cv. Bronco’	Alkaline stress (50 mM NaHCO3:Na2CO3) (pH 9), 25 d	Declined total GSH concentration, GR and POX activity.	[199]
		APX activity increased.
		Total AsA, reduced AsA and DHA diminished.
T.aestivum L. cv. BARI Gom-25	Extreme acidic (pH 4.0) and extreme alkaline (pH 8.5)-stress, 72 h	Extreme pH levels (4.0, 5.5, and 8.5) decreased AsA and GSH contents.	[146]
		Upregulated activities of CAT, APX, GPX, and GST.
		DHAR and SOD activity down-regulated under extreme pH stress, compared to control.
T.aestivum L. cvs. BARI Gom-21, 24–26 and 30	Different pH of growth medium, 6.5 (control), 5.5, 4.5 (acidic) and 3.5 (extreme acidic), 4 d	Decreased antioxidant enzyme activity with the gradual increase in the acidity severity in all the cultivars.	[144]
		Decreased GSH and GSSG ratio.
		Upregulated antioxidant enzymes’ activities, including APX, GPX, GR, MDHAR, DHAR and GST were observed in BARI Gom-26.
Herbicides Toxicity
Hordeum vulgare L.	Glyphosate (6 mM)	Increased the activity of CAT (80% in leaves and 46% in roots), APX (106% in leaves and 97% in roots), and GST (61% in leaves and 95% in roots)	[162]
Salvinia natans L.	Glyphosate (0.006, 0.03, 0.15, 0.3 and 0.45 mM)	Increased CAT, SOD, POD and APX activity.	[201]
B. napus L.	Paraquat (62.5, 125 and 250 mM)	Increased enzymatic antioxidant activities, and AsA and GSH content.	[164]
N. tabacum cv. oriental	Imazapic (0.030, 0.060 and 0.120 mM)	Improved GSH content.	[203]
		Increased CAT, APX, GST and GR activities.
Cucurbita spp.	Paraquat (0.05, 0.1, 0.2, 0.3, 0.5 and 1.0 mM)	Lower MDA content and cellular leakage in youngest leaves (4th leaf) than older leaves.	[202]
		Increased CAT, POX, and APX (2 times) activity in youngest leaves.
C. sativus L.	Paraquat (0.05, 0.1, 0.2, 0.3, 0.5 and 1.0 mM)	Lower LPO and higher antioxidant enzyme activity.	[247]