Abstract
Galactinol synthase (GolS) is a key enzyme in the synthesis of raffinose family oligosaccharides (RFOs). Recently, we have reported that the transcription of GolS1 and GolS2 is induced by treatment with H2O2, as is the transcription of HsfA2 (Plant J., 2006). Here we investigated the physiological roles of galactinol and/or RFOs as novel intracellular antioxidants. In leaves of the HsfA2-overexpressing transgenic Arabidopsis plants, the transcript levels of GolS1, 2 and 4 and raffinose synthase (RS) 2 were highly induced and thus levels of galactinol and raffinose increased. In the wild-type plants, the transcript levels of GolS1-4 and 8 and RS2 were induced and the levels of galactinol and raffinose were increased in response to oxidative stress. Galactinol and RFOs effectively protected salicylate from attack by hydroxyl radicals in vitro. Furthermore, GolS-overexpressing plants had increased levels of galactinol and raffinose in the leaves and showed increased tolerance to oxidative stress.
