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Gabaculine is a potent inhibitor of glutamate-1-semialdehyde aminotransferase [EC 5.4.3.8] involved in the synthesis of chlorophyll in plants.
 Recently it has been shown that the synthesis of chlorophyll via 5-aminolevulinate in higher plants, involves the enzymes glutamyl-tRNA synthetase, glutamyl-tRNA reductase, and glutamate-1-semialdehyde aminotransferase, and does not involve a glutamate-1-phosphate intermediate as originally proposed. It has been suggested that the two genes encoding glutamyl-tRNA reductase in cucumber may have different functions ... hemA1 may be involved in chlorophyll biosynthesis and hemA2 in the synthesis of porphyrins other than chlorophylls (Tanaka et al, 1996). Tobacco plants expressing glutamate-1-semialdehyde aminotransferase (GSA-AT) antisense RNA exhibit marked reduction in chlorophyll synthesis. Decreased GSA-AT expression does not seem to suppress other enzymic steps in the chlorophyll synthesis pathway (Hartel et al, 1997). Calcium and calmodulin are involved in the blue light induction of the gsa gene (encoding glutamate-1-semialdehyde aminotransferase (GSA-AT)) in Chlamydomonas reinhardtii (Im et al, 1996). For reviews of chlorophyll biosynthesis see von Wettstein et al (1995), and Reinbothe and Reinbothe (1996).
Avissar YJ, Beale SI 1989 Biosynthesis of tetrapyrrole pigment precursors. Plant Physiol. 89: 852-859. Gardener G, Gorton HL 1985 Inhibition of phytochrome synthesis by gabaculine. Plant Physiol. 77: 540-543. Hartel H, Kruse E, Grimm B 1997 Restriction of chlorophyll synthesis due to expression of glutamate 1-semialdehyde aminotransferase antisense RNA does not reduce the light-harvesting antenna size in tobacco. Plant Physiol. 113: 1113-1124. Im C, Matters GL, Beale SI 1996 Calcium and calmodulin are involved in blue light induction of the gsa gene for an early chlorophyll biosynthetic step in Chlamydomonas. Plant Cell 8: 2245-2253. Kannangara CG, Gough SP 1978 Biosynthesis of delta-aminolevulinate in greening barley leaves: glutamate-1-semialdehyde aminotransferase. Carlsberg Res. Commun. 43: 185-194. Reinbothe S, Reinbothe C 1996 Regulation of chlorophyll biosynthesis in angiosperms. Plant Physiol. 111: 1-7. Tanaka R, Yoshida K, Nakayashiki T, Masuda T, Tsuji H, Inokuchi H, Tanaka A 1996 Differential expression of two hemA mRNAs encoding glutamyl-tRNA reductase proteins in greening cucumber seedlings. Plant Physiol. 110: 1223-1230. von Wettstein D, Gough S, Kannangara CG 1995 Chlorophyll biosynthesis. Plant Cell 7: 1039-1057.
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