Table 2 Effect of different concentrations of Put, CQDs and Put-CQD NPs on photosynthetic pigments and SPAD index of Vitis vinifera cv. ‘Sultana’ under salinity stress (CQDs, carbon quantum dots; Put, putrescine, Put-CQD NPs, carbon quantum dots functionalized by putrescine nanoparticles). Different letters indicate significant differences based on Duncan’s post-hoc analysis at P ≤ 0.05

NaCl (0 mM) + No Treatment

2.039 ± 0.05^ef

0.579 ± 0.002^cd

0.521 ± 0.003^e

26.86 ± 0.73^c

NaCl (0 mM) + Put 5 mg L^− 1

2.228 ± 0.02^c

0.657 ± 0.008^b

0.633 ± 0.012^bc

29.38 ± 0.83^ab

NaCl (0 mM) + Put 10 mg L^− 1

2.317 ± 0.12^bc

0.682 ± 0.011^ab

0.662 ± 0.009^b

29.91 ± 0.54^ab

NaCl (0 mM) + CQDs 5 mg L^− 1

1.797 ± 0.09^fg

0.538 ± 0.009^d

0.584 ± 0.011^cd

28.13 ± 0.91^b

NaCl (0 mM) + CQDs 10 mg L^− 1

1.983 ± 0.01^ef

0.582 ± 0.023^cd

0.604 ± 0.013^c

25.83 ± 0.95^cd

NaCl (0 mM) + Put-CQD NPs 5 mg L^− 1

2.324 ± 0.08^b

0.697 ± 0.016^b

0.649 ± 0.008^bc

29.26 ± 0.38^ab

NaCl (0 mM) + Put-CQD NPs 10 mg L^− 1

2.426 ± 0.05^a

0.723 ± 0.008^a

0.721 ± 0.009^a

31.82 ± 0.77^a

NaCl (100 mM) + No Treatment

1.482 ± 0.12^h

0.357 ± 0.014^f

0.358 ± 0.007^f

19.63 ± 0.14^g

NaCl (100 mM) + Put 5 mg L^− 1

1.718 ± 0.07^fg

0.477 ± 0.021^e

0.597 ± 0.012^cd

21.7 ± 0.54^ef

NaCl (100 mM) + Put 10 mg L^− 1

1.891 ± 0.11^f

0.534 ± 0.016^d

0.612 ± 0.018^c

22.7 ± 1.12^e

NaCl (100 mM) + CQDs 5 mg L^− 1

1.686 ± 0.09^g

0.456 ± 0.009^e

0.523 ± 0.014^de

20.13 ± 0.82^fg

NaCl (100 mM) + CQDs 10 mg L^− 1

1.751 ± 0.08^fg

0.461 ± 0.015^e

0.542 ± 0.009^d

21.4 ± 0.61^f

NaCl (100 mM) + Put-CQD NPs 5 mg L^− 1

2.052 ± 0.01^e

0.596 ± 0.022^c

0.648 ± 0.019^bc

22.23 ± 1.24^ef

NaCl (100 mM) + Put-CQD NPs 10 mg L^− 1

2.141 ± 0.08^d

0.586 ± 0.008^cd

0.663 ± 0.008^b

24.2 ± 0.43^d