Table 1.

Summarises the growth‐related effects of different NPs on several plant species

NPs	Effective concentration	Plant/plant part applied with	Effects observed	Probable mechanism	Reference (s)
AuNPs	10 ppm	B. juncea seedlings	(i) increased number of leaves, plant length, stem thickness, number of branches per plant; (ii) increased chlorophyll content by 29%; and (iii) accelerated rate of seed germination	(i) antagonistic effect on ethylene; increased effect of gibberellic acid; (ii) increased water and molecular oxygen uptake by seed capsule	Arora et al. [20]
MWCNTs	2 g/l	rye grass tomato whole plant barley, soybean, corn seeds tobacco cell culture	enhanced seedling root growth greater plant biomass, more flowers and fruits	increased Ca and Fe nutrient uptake altered gene expression, enhanced water absorption by aquaporins. Genes such as NNtPIP1 (aquaporin) responsible for water transport, CycB responsible for cell division, NtLRX1 responsible for cell wall formation are upregulated	Villagarcia et al. [21]; Tiwari 2014 [22]; Lin and Xing [23]; Khodakovskaya et al. [24]; Lahiani et al. [25]
citric acid‐coated CNTs	6 g/l	C. arietinum	increased water uptake and growth	nanotubes form an ‘aligned network’ inside vascular tissue	Tripathi et al. [26]
wsCNTs	6 µg/ml	C. arietinum	enhanced root and shoot length, increased branching	better water retention and absorption	Tripathy 2011 [26]
TiO2 NPs	—	spinach seeds, leaves	increased and accelerated growth	increases the activity of several enzymes and promotes the adsorption of nitrate	Zheng et al. 2005 [27]; Hong et al. [28]; Yang et al. [29]; Gao et al. [30]
TiO2	0.5 g/l	L. minor	plant elongation, increased fresh weight.	increased photosynthesis, enzyme activity, increased chemical fixation of atmospheric oxygen	Yang et al. [29]; Gao et al. [30]; Su et al. [31]; Song et al. [32]
TiO2	20 g/l	T. aestivum; foliar application	stem elongation, increased yield, flowering, biomass, ear mass, seed number, improved starch and gluten content	modified activities of different nitrogen metabolising enzymes, namely nitrate reductase, glutamate dehydrogenase, glutamine synthase and glutamic‐pyruvic transaminase	Jaberzadeh et al. [33]; Yang et al. [34]; Mishra 2014 [35]
CuO NP	1 mg/l	Elodea densa plant	photosynthesis rate increased to 130–140% of control	increased lipid peroxidation, increased catalase and SOD activities	Nekrasov et al. [36]
ZnNP	10 mg/l	P. americanum, mixed with soil	increased accumulation of soluble leaf proteins (19.9%); chlorophyll (18.4%); enhanced root area (18.4%); shoot length (10.8%); increased grain yield (29.5%); and dry biomass (12.0%)	enhanced activity of different enzymes, namely phytase, alkaline phosphatase, acid phosphatase, dehydrogenase	Tarafdar et al. [37]