Table 2.

Genetic manipulation of GABA receptors modifies the abiotic stress phenotype.

Plant Species	Mutant or Transgenic Line	Abiotic Stress	Biochemical, Molecular and Physiological Responses	References
Arabidopsis (Arabidopsis thaliana (L.) Heyhn.)	almt4	Drought for 2 wk	↑ whole-plant wilting AtALMT4 Ox complements atalmt4 phenotype	[123]
	gork1	Waterlogging for up to 3 wk	↑ shoot FM, Chl; completes life cycle ↑ K+, Ca2+ retention in epidermal cells of mature and elongation zones of root ↓ K+ efflux rate	[117]
	almt9	Drought for up to 7 d	GABA impairs dark-induced stomatal closure gad2/almt9 retains low GABA of gad2 and restores stomatal conductance GAD∆C Ox does not alter stomatal conductance of almt9 stomatal conductance of ALMT9F243C/Y245C Ox similar to gad2 and greater than almt9	[40]
	ZmALMT2 Ox	10 μM Al3+ (pH 4.5) for 1 d	↑ length, constitutive and Al3+-activated Mal efflux (roots) reverses the Al3+-sensitive phenotype of almt1/mate	[125]
	BoALMT Ox	0.4 mM Al3+ (pH 4.5) for 2 d	↑ length, Al3+-activated Mal and H+ efflux (roots)	[126]
Arabidopsis and soybean (hairy roots) (Glycine max (L.) Merr.)	GmALMT1 Ox	0.4 mM Al3+ (pH 4.5) for 2 d	↑ seedling growth, Mal efflux in root ↓ Al3+ content	[127]
Tobacco (Nicotiana tabaccum L.)	MsALMT1 Ox	30 μM Al3+ (pH 4.2) for 1 d	↑ root growth ↓ Al3+ content	[128]
Barley (Hordeum vulgare L.)	TaALMT1 Ox	0.1 mM Al3+ (pH 4.5) for 22 h	↑ root growth in Al3+-sensitive line restores Al3+-activated, GABA-regulated Mal efflux in root	[101]

Symbols: ↑, increases; ↓, decreases. Abbreviations: Al³⁺, aluminum; ALMT, Al³⁺-activated malate transporter; Chl, chlorophyll; FM, fresh mass; GABA, γ-aminobutyrate; GAD, glutamate decarboxylase; Mal, malate; Ox, overexpression. Species abbreviations: Ms, Medicago sativa L. (alfalfa); Bo, Brassica oleracea var. capitata L. (cabbage); Zm, Zea mays L. (corn); Ta, Triticum aestivum L. (wheat).