Arbuscular mycorrhiza improved drought tolerance of maize seedlings by altering photosystem II efficiency and the levels of key metabolites

Chemical and Biological Technologies in Agriculture

Table 6 Metabolic levels of free amino acids and polyamines in roots of maize plants under drought and arbuscular mycorrhizal fungal inoculation (mean ± SD, n = 5)

Treatment	AAs (μmol·g⁻¹)	Urea-N (mg·g⁻¹)	Ornithine cycle (ng·mg⁻¹)				Polyamines (ng·mg⁻¹)			GABA (ng·mg⁻¹)	DAO (U·g⁻¹)	GAD (U·g⁻¹)
Treatment	AAs (μmol·g⁻¹)	Urea-N (mg·g⁻¹)	Arg	Orn	Cit	Asp	Put	Spd	Spm	GABA (ng·mg⁻¹)	DAO (U·g⁻¹)
W
NM	18.70 ± 2.80c	0.08 ± 0.01b	8.69 ± 1.81c	0.90 ± 0.15c	1.06 ± 0.08c	18.57 ± 5.57c	2.74 ± 0.88b	0.0036 ± 0.002a	0.016 ± 0.005a	12.31 ± 1.40b	0.12 ± 0.02b	3.84 ± 0.77a
AM	51.84 ± 4.73b	0.07 ± 0.01b	16.41 ± 2.93a	2.91 ± 0.72a	2.47 ± 0.20a	28.52 ± 4.45b	6.00 ± 1.02a	0.0043 ± 0.001a	0.016 ± 0.005a	9.28 ± 2.20c	0.13 ± 0.02ab	3.19 ± 0.18ab
D
NM	12.86 ± 1.76d	0.11 ± 0.02a	8.49 ± 1.90c	1.24 ± 0.13c	1.02 ± 0.11c	26.85 ± 13.28b	1.47 ± 0.54c	0.0037 ± 0.002a	0.014 ± 0.002a	20.96 ± 1.94a	0.11 ± 0.02b	4.08 ± 0.83a
AM	69.53 ± 7.11a	0.09 ± 0.01b	11.44 ± 1.77b	2.11 ± 0.23b	2.02 ± 0.09b	53.10 ± 1.91a	1.41 ± 0.38c	0.0031 ± 0.001a	0.020 ± 0.010a	19.35 ± 3.21a	0.15 ± 0.03a	3.91 ± 1.25a
Two-way ANOVA
D	ns¹	**	ns	ns	*	*¹	**	ns	ns	**¹	ns	ns
I	*¹	*	**	**	**	*¹	*	ns	ns	ns¹	**	ns
D × I	–	ns	*	**	ns	–	**	ns	ns	–	*	ns

Different lowercase letters in the same column indicate statistically significant differences between treatments at P < 0.05 by Duncan’s test
D drought stress, I inoculation treatment, W well-watered, AM arbuscular mycorrhizal fungal inoculation, NM non-mycorrhizal fungal inoculation, AAs free amino acids, Arg arginine, Asp aspartic acid, Cit citrulline, DAO diamine oxidase, GABA γ-aminobutyric acid, GAD glutamic acid decarboxylase, Orn ornithine, Put putrescine, Spd spermidine, Spm spermine, ns not significant
*P < 0.05, **P < 0.01
¹ANOVA outputs by nonparametric statistical test