Ascorbic acid biosynthesis: a precursor study on plants

Abstract

Since the first isolation of ascorbic acid (AsA) in 1928, few papers have been published regarding the biosynthesis of AsA in plants, especially in fruits. It took as long as 1998, before Wheeler, Jones and Smirnoff, based on a study with Arabidopsis leaves, proposed what can be considered the main pathway of biosynthesis of AsA, in which L-galactose (L-GAL) is a key precursor. This paper reports the effectiveness of some precursors (cold or radiolabeled) in the biosynthesis of AsA in different plants: green sweet pepper, white-pulp guava, red-pulp guava, papaya and strawberry at two ripening stages (mature green and ripe for papaya and mature green and half red for strawberry) and broccoli. The 'Smirnoff-Wheeler' pathway was functioning and active in all sources studied, as demonstrated by the increase in AsA contents and incorporation of labeled precursors into AsA. In papaya, the AsA content in the ripe fruit was higher than in the mature green, indicating the synthesis of AsA during ripening. On the other hand, the AsA content in the mature green strawberry was similar to that of the half red fruits. Our data demonstrate that L-GAL and L-Galactono-1,4-lactone (L-GL) are effective precursors for the biosynthesis of AsA in fruits and also provided additional evidence for the participation of D-mannose (D-MAN) and D-glucose-1P in the biosynthesis of AsA in plants.

Correlações entre compostos fenólicos e atividade antioxidante em casca e polpa de variedades de uva de mesa

“…Esta promove proteção contra espécies reativas produzidas durante os processos de fotossíntese e de respiração, e está envolvida no crescimento celular, bem como atua como cofator de importantes enzimas na síntese de antocianidina e outros metabólitos secundários (SOARES et al, 2004 …”

Effects of Cultural Practices on Total Phenolics and Vitamin C Content of Organic Table Grapes

“…In this respect, vitamin C is another very important compound in the protection against oxidative stress in plants (Rock et al, 1996). It also is a co-factor of several enzymes that participate in the synthesis of anthocyanidins (Barata-Soares et al, 2004). Table grape production usually involves treatments such as adjusting crop load by cultivar thinning and shoot topping, as well as increasing crop quality by girdling, topping or tipping, and using growth regulators, mainly gibberellic acid.…”

Efeito do corte como dano mecânico na qualidade e na fisiologia de mamões 'golden'

“…Também se observou que, após o sexto dia de armazenamento, frutos com 3 e 4 cortes apresentaram teor de ácido ascórbico menor que os demais tratamentos . Provavelmente, isso ocorreu porque esses frutos apresentaram maiores danos oxidativos, cuja ação antioxidante foi fornecida, especialmente, pelo ascorbato, derivado do ácido ascórbico (BARATA-SOARES et al, 2004).…”