Regulation of sucrose and starch metabolism in potato tubers in response to short-term water deficit

Abstract

To investigate the effect of water stress on carbon metabolism in growing potato tubers (Solanum tuberosum L.), freshly cut and washed discs were incubated in a range of mannitol concentrations corresponding to external water potential between 0 and )1.2 MPa. (i) Incorporation of [ 14 C]glucose into starch was inhibited in water-stressed discs, and labeling of sucrose was increased. High glucose overrode the changes at low water stress (up to )0.5 MPa) but not at high water stress. (ii) Although [ 14 C]sucrose uptake increased in water-stressed discs, less of the absorbed [ 14 C]sucrose was metabolised. (iii) Analysis of the sucrose content of the discs confirmed that increasing water deficit leads to a switch, from net sucrose degradation to net sucrose synthesis. (iv) In parallel incubations containing identical concentrations of sugars but differing in which sugar was labeled, degradation of [ 14 C]sucrose and labeling of sucrose from [ 14 C]glucose and fructose was found at each mannitol concentration. This shows that there is a cycle of sucrose degradation and resynthesis in these tuber discs. Increasing the extent of water stress changed the relation between sucrose breakdown and sucrose synthesis, in favour of synthesis. (v) Analysis of metabolites showed a biphasic response to increasing water deficit. Moderate water stress (0-200 mM mannitol) led to a decrease of the phosphorylated intermediates, especially 3-phosphoglycerate (3PGA). The decrease of metabolites at moderate water stress was not seen when high concentrations of glucose were supplied to the discs. More extreme water stress (300-500 mM mannitol) was accompanied by an accumulation of metabolites at low and high glucose. (vi) Moderate water stress led to an activation of sucrose phosphate synthase (SPS) in discs, and in intact tubers. The stimulation involved a change in the kinetic properties of SPS, and was blocked by protein phosphatase inhibitors. (vii) The amount of ADP-glucose (ADPGlc) decreased when discs were incubated on 100 or 200 mM mannitol. There was a strong correlation between the in vivo levels of ADPGlc and 3PGA when discs were subjected to moderate water stress, and when the sugar supply was varied. (viii) The level of ADPGlc increased and starch synthesis was further inhibited when discs were incubated in 300-500 mM mannitol. (ix) It is proposed that moderate water stress leads to an activation of SPS and stimulates sucrose synthesis. The resulting decline of 3PGA leads to a partial inhibition of ADP-glucose pyrophosphorylase and starch synthesis. More-extreme water stress leads to a further alteration of partitioning, because it inhibits the activities of one or more of the enzymes involved in the terminal reactions of starch synthesis. Abbreviations: ADPGlc = ADP-glucose; AGPase = ADP-glucose pyrophosphorylase; Fru6P = fructose-6-phosphate; Glc6P = glucose-6-phosphate; 3PGA = 3-phosphoglycerate; P i = inorganic phosphate; SPS = sucrose-phosphate synthase; UDPGlc = uridine-5′-diphosphoglucose; V max = activity of SPS assaye...

Regulation of Leaf Starch Degradation by Abscisic Acid Is Important for Osmotic Stress Tolerance in Plants

“…In response to acute temperature shock, plants mobilize starch at time when biosynthesis would be expected (e.g., in the middle of the light period), resulting in the accumulation of maltose, the major starch catabolite, and of its deriving sugars (Usadel et al, 2008a;Purdy et al, 2013;Guy, 2005, 2004;Sitnicka and Orzechowski, 2014;Yano et al, 2005;Kaplan et al, 2007). Similar rearrangements of starch metabolism are observed when plants are subject to short periods of oxidative or osmotic stress (Scarpeci and Valle, 2008;Zanella et al, 2016;Valerio et al, 2011;Geigenberger et al, 1997). It is proposed that soluble sugars and other charged metabolites, such as proline or glycine, may function as osmoprotectants during stress responses.…”

“…Consistent with this, we observed that osmotic stress caused only a transient decrease in the PSII operating efficiency (FPSII), which was similar in the two genotypes (Supplemental Table 3) and, importantly, did not hinder the capacity of the plants to assimilate 14 CO 2 . However, sugars may also accumulate in leaves because of decreased demand, as a consequence of shoot growth limitation (Hummel et al, 2010), or because of decreased starch biosynthesis (Geigenberger et al, 1997). This might be caused by changes in phosphorylated intermediates, especially 3-phosphoglycerate, reduction of which would inactivate ADP-glucose pyrophosphorylase, the regulated enzyme of starch biosynthesis (Heldt et al, 1977).…”

“…This might be caused by changes in phosphorylated intermediates, especially 3-phosphoglycerate, reduction of which would inactivate ADP-glucose pyrophosphorylase, the regulated enzyme of starch biosynthesis (Heldt et al, 1977). A decline in 3-phosphoglycerate under stress could result from impaired photosynthesis (Kaplan and Guy, 2005;Scarpeci and Valle, 2008) or from the activation of the sucrose biosynthesis in response to stress through sucrose synthase phosphate (Geigenberger et al, 1997), which would compete for assimilates. It was indeed demonstrated that phosphorylation of sucrose synthase phosphate is a mechanism for osmotic stress activation of this enzyme in spinach leaves (Toroser and Huber, 1997).…”

Combined expression of glucokinase and invertase in potato tubers leads to a dramatic reduction in starch accumulation and a stimulation of glycolysis

“…Nucleotides were determined in the TCA extracts by high pressure liquid chromatography (HPLC) (Geigenberger et al, 1997), using a Kontron HPLC system (Kontron Instruments, Eching, Germany) fitted with a Partisil-SAX anion exchange column (Knauer, Berlin, Germany). An aliquot of the TCA extract (250 µl) was freeze-dried and re-dissolved in a volume of 50 µl, from which 20 µl was injected.…”

Aspectos fisiológicos, anatômicos e ultra-estruturais do rizoma de Costus arabicus L. (Costaceae) sob condições de déficit hídrico

“…No entanto, a maioria deles utiliza como modelo espécies de interesse agronômico, tais como milho (Sharp & Lenoble 2002, Sharp et al 2004, Fan & Neumann 2004, trigo (Asseng et al 1998, Morillon & Lassalles 2002, Piro et al 2003, grão-de-bico (Basu et al 2007), mandioca (Santisopasri et al 2001) e batata (Geigenberger et al 1997). Especifi camente no caso da batata (Solanum tuberosum L.), que acumula amido como principal carboidrato de reserva em seus órgãos subterrâneos (tubérculos) e também uma das mais estudadas sob condições de estresse hídrico, os trabalhos realizados demonstram que a disponibilidade hídrica regula as taxas de síntese de amido e crescimento dos tubérculos (Oparka & Wright 1988a, b) e que tanto a síntese como a degradação desse carboidrato são alteradas sob condições de déficit hídrico, com respostas, em geral, associadas ao aumento nos níveis de açúcares solúveis e inibição da síntese de amido (Geigenberger et al 1997). De acordo com esses autores, a direção da via metabólica para síntese de sacarose ou amido representam uma estratégia importante sob condições de défi cit hídrico, visto que infl uenciam a regulação do potencial osmótico interno, das relações hídricas e, por extensão, do crescimento da planta.…”