Soluble acid invertase determines the hexose-to-sucrose ratio in cold-stored potato tubers

Abstract

Cold storage of potato (Solanum tuberosum L.) tubers is known to cause accumulation of reducing sugars. Hexose accumulation has been shown to be cultivar-dependent and proposed to be the result of sucrose hydrolysis via invertase. To study whether hexose accumulation is indeed related to the amount of invertase activities, two different approaches were used: (i) neutral and acidic invertase activities as well as soluble sugars were measured in cold-stored tubers of 24 potato cultivars differing in the cold-induced accumulation of reducing sugars and (ii) antisense potato plants with reduced soluble acid invertase activities were created and the soluble sugar accumulation in cold-stored tubers was studied. The cold-induced hexose accumulation in tubers from the different potato cultivars varied strongly (up to eightfold). Large differences were also detected with respect to soluble acid (50-fold) and neutral (5-fold) invertase activities among the different cultivars. Although there was almost no correlation between the total amount of invertase activity and the accumulation of reducing sugars there was a striking correlation between the hexose/sucrose ratio and the extractable soluble invertase activity. To exclude the possibility that other cultivar-specific features could account for the obtained results, the antisense approach was used to decrease the amount of soluble acid invertase activity in a uniform genetic background. To this end the cDNA of a cold-inducible soluble acid invertase (EMBL nucleic-acid database accession no. X70368) was cloned from the cultivar Desirée, and transgenic potato plants were created expressing this cDNA in the antisense orientation under control of the constitutive 35S cauliflower mosaic virus promotor. Analysis of the harvested and cold-stored tubers showed that inhibition of the soluble acid invertase activity leads to a decreased hexose and an increased sucrose content compared with controls. As was already found for the different potato cultivars the hexose/sucrose ratio decreased with decreasing invertase activities but the total amount of soluble sugars did not significantly change. From these data we conclude that invertases do not control the total amount of soluble sugars in cold-stored potato tubers but are involved in the regulation of the ratio of hexose to sucrose.

Carboidratos e matéria seca de tubérculos de cultivares de batata influenciados por doses de nitrogênio

“…Valores médios de AST de 1,67 e 1,79 g/100g de MF em tubérculos das cultivares 'Atlantic' e Pérola, respectivamente, foram encontrados por Pastorini et al (2003). Além da temperatura do ambiente de armazenamento, fatores como a degradação do amido, exportação de açúcares para os amiloplastos ou a biossíntese de sacarose podem influenciar o acúmulo de açúcares solúveis totais em tubérculos de batata (Zrenner et al, 1996). O efeito de doses de N sobre o teor de açúcares redutores (AR) na polpa de tubérculos foi dependente de cultivar, não havendo efeito em Asterix e Atlantic.…”

Invertases. Primary Structures, Functions, and Roles in Plant Development and Sucrose Partitioning

“…Similar conclusions were drawn from a study of sugar accumulation during cold storage of mature potato tubers. Reduction of soluble acid invertase activity by an antisense approach was correlated with a decrease in the hexose to Suc ratio but did not alter the total amount of released sugars (Zrenner et al, 1996). Thus, a soluble acid invertase functions in this postharvest process as a regulator of sugar composition.…”

A Bypass of Sucrose Synthase Leads to Low Internal Oxygen and Impaired Metabolic Performance in Growing Potato Tubers

“…To investigate whether there is a similar response in growing potato tubers, we incubated wild-type tuber discs in various oxygen concentrations (0%, 1%, 4%, 8%, 12%, and 21% [v/v]) for 45 min or 2 h and analyzed steady-state mRNA levels of the potato SuSy genes Sus1 (Salanoubat and Belliard, 1989), Sus2 (Ehlers Loureiro, 1999), and Sus3 (Fu and Park, 1995), and the genes encoding vacuolar (Zrenner et al, 1996) and apoplastic invertase in potato tubers (Hedley et al, 1993). For comparison, expression of the lowoxygen-sensitive potato Adh1 gene (Matton et al, 1990) was monitored.…”

“…Radioactive hybridization probes were prepared by the random priming labeling system of Amersham-Buchler using P 32 -dCTP according to the manufacturer's instructions. The following hybridization probes were used: (a) a 430-bp EcoRI-StyI fragment of StSus1 (Fu and Park, 1995), (b) a 2.1-kb Asp718-Asp718 fragment of StSus2 (Ehlers Loureiro 1999), (c) a 185-bp EcoRI-EcoRI fragment of StSus3 (Fu and Park 1995), (d) a 2,063-bp EcoRI-NotI fragment of the potato gene encoding vacuolar invertase (Zrenner et al, 1996), (e) a 630-bp BamHI-BamHI fragment of the apoplastic potato invertase gene (Hedley et al, 1993), and (f) a 250-bp EcoRI-EcoRI fragment from the potato gene encoding the hypoxia-inducible ADH (Matton et al, 1990). Quantification was performed with an imaging system (Herolab, Wiesloch, Germany), and the signal of the specific transcript was normalized to the UV signal of the rRNA on the blotted membrane.…”