© New Phytologist (2001) 151: 607– 612 www.newphytologist.com 607 Research Blackwell Science Ltd Carbohydrate–ethanol transition in cereal grains under anoxia Lorenzo Guglielminetti 1 , Héctor Abel Busilacchi 1,3 , Pierdomenico Perata 2 and Amedeo Alpi 1 1 Dipartimento di Biologia delle Piante Agrarie, Sezione Fisiologia Vegetale, Via Mariscoglio 34, I-56124 Pisa, Italy; 2 Dipartimento di Scienze Agrarie, Università di Modena & Reggio Emilia, Via Kennedy 17, Reggio Emilia, Italy; 3 Present address: Facultad de Ciencias Agrarias, University of Rosario, CC 14 CP (2123) Zavalla, Pcia de Santa Fe, Argentina Summary • Cereal grains differ greatly in their reponses to anaerobiosis. Here, the in vivo conversion of carbohydrates to ethanol and CO 2 under anoxia is reported for three cereal grains. • The conversion of glucose, fructose or sucrose to ethanol under anaerobic condi- tions was investigated in rice (Oryza sativa), barley (Hordeum vulgare) and wheat (Triticum aestivum) grains; alcohol dehydrogenase (EC 1.1.1.1) and pyruvate decar- boxylase (EC 4.1.1.1) activities were also analysed under aerobic and anaerobic incubation. • Our data suggest that rice grains are able to produce ethanol under anoxia for the whole period of anoxic treatment, whereas barley and wheat grains can produce this terminal product of fermentation only during the first days of anaerobiosis. The level of enzymes involved in the fermentation pathway increases strongly under anoxic conditions in all three cereals. • Conversion of hexose to CO 2 is nearly unaffected by anoxia in wheat, barley and rice, whereas only rice grains are able to degrade and utilize sucrose efficiently under anoxia. By contrast, wheat and barley do not utilize sucrose efficiently under anaerobic conditions. Key words: alcohol dehydrogenase (ADH), anoxia, fermentation, Hordeum vulgare (barley), Oryza sativa (rice), pyruvate decarboxylase (PDC), Triticum aestivum (wheat). © New Phytologist (2001) 151: 607– 612 Author for correspondence: Amedeo Alpi Tel: +39 050 542898 Fax: +39 050 540296 Email: aalpi@agr.unipi.it Received: 28 November 2000 Accepted: 2 May 2001 Introduction Cereal grains differ greatly in their responses to anaerobiosis. Rice grains represent an example of metabolic adaptation to anoxia, being able to germinate and elongate the coleoptile in an oxygen-free environment (Alpi & Beevers, 1983). By contrast, grains of barley and wheat are severely injured when imbibed under anoxia, fail to elongate coleoptile and root and cannot recover when transferred to air after a few days of anoxic treat- ment (Perata et al., 1996). The availability of fermentable carbohydrates appears to be one of the biochemical parameters correlating with anoxia- tolerance in cereal grains. Indeed, rice can take advantage of the starchy reserves present in the endosperm as a consequence of the successful anaerobic induction of the complete set of starch-degrading enzymes (Perata et al., 1992; Perata et al., 1993; Guglielminetti et al., 1995b). On the contrary, wheat and barley do not induce these enzymes, and the embryos soon suffer from sugar starvation which may account for the decline in viability (Guglielminetti et al., 1995b). The main fate of carbohydrates under anoxia is very likely to be their utilization through glycolysis and fermentation leading to ethanol as the main end product (Mayne & Kende, 1986; Bouny & Saglio, 1996). The analysis of several enzymatic activities in anaerobically germinating cereal grains revealed the absence of striking differences between the tolerant species (rice) and the intolerant species (wheat and barley). An excep- tion was the induction of enzymes involved in the sucrose synthase pathway for sucrose utilization, which was detected in rice grains but not in wheat and barley grains, suggesting