Table 3.

Effects of nZnO on plants under drought conditions.

Stress Conditions	nZnO Concentrations; Primary (PS) or Hydrodynamic Size (HS)	Plant Species	Application Method	Ameliorative Effects	Ref.
30% of total moisture for 3 days.	Not stated	Triticum aestivum L.	Seed priming for 4 h	Increased leaf RWC, chlorophyll and carotenoids levels, and antioxidant enzyme activities (SOD and CAT). Decreased lipid peroxidation	[91]
40% field capacity	1, 3 and 5 mg L−1; PS 18 nm	Sorghum bicolor	Soil amended	Increased grain yield	[37]
40% field capacity for 210 days	2.17 mg kg−1; not stated	Triticum aestivum L.	Soil amended	Increased chlorophyll content and grain nutrient	[92]
6 days at 45% (soil water content).	100 mg L−1; PS 20 nm	Zea mays L.	Seed priming	Increased root and shoot height, fresh and dry weight, as well as sugars, protein, amino acids (tryptophane) and proline. Improvement of antioxidant enzyme activities and gene relative expression (SOD, POD, APX and CAT). Decreased H2O2 production	[93]
12 days	25 and 100 mg L−1; PS 50 nm	Cucumis sativus L.	Foliar application 3 time a week, for two weeks	Increased shoot fresh and dry weight, root dry weight and length, leaf RWC, chlorophylls, carotenoids, protein content, net CO2 assimilation rate, stomatal conductance, transpiration rate, intercellular CO2 concentration, Fv/Fm, qP and ΦPSII. Accumulation of proline, glycine betaine, free amino acids, and sugars. Improvement of antioxidant enzyme activities (SOD, POD, APX, CAT, GR, DHAR and MDHAR) and PAL activity. Increased total phenols, flavonoids, ascorbate (AsA) and glutathione. Decreased O2−• and H2O2 production, lipid peroxidation, electrolyte leakage and NPQ	[80]
60% of crop evapotranspiration (ETc) for 5 months.	50 and 100 mg L−1; not stated	Solanum melongena L.	Foliar application 2 times	Increased leaf RWC and Fv/Fm. Improved membrane stability	[90]