Decreased expression of sucrose phosphate synthase strongly inhibits the water stress‐induced synthesis of sucrose in growing potato tubers

Abstract

SummaryWater stress stimulates sucrose synthesis and inhibits starch synthesis in wild-type tubers. Antisense and cosuppression potato transformants with decreased expression of sucrose±phosphate synthase (SPS) have been used to analyse the importance of SPS for the regulation of this water-stress induced change in partitioning. (i) In the absence of water stress, a 70±80% decrease in SPS activity led to a 30±50% inhibition of sucrose synthesis and a slight (10±20%) increase of starch synthesis in tuber discs in short-term labelling experiments with low concentrations of labelled glucose. Similar changes were seen in short-term labelling experiments with intact tubers attached to well-watered plants. Provided plants were grown with ample light and water, transformant tubers had a slightly lower water and sucrose content and a similar or even marginally higher starch content than wild-type tubers. (ii) When wild-type tuber slices were incubated with labelled glucose in the presence of mannitol to generate a moderate water de®cit (between ±0.12 and ±0.72 MPa), there was a marked stimulation of sucrose synthesis and inhibition of starch synthesis. A similar stimulation was seen in labelling experiments with wild-type tubers that were attached to waterstressed wild-type plants. These changes were almost completely suppressed in transformants with a 70±80% reduction of SPS activity. (iii) Decreased irrigation led to an increase in the fraction of the dry-matter allocated to tubers in wild-type plants. This shift in allocation was prevented in transformants with reduced expression of SPS. (iv) The results show that operation of SPS and the sucrose cycle in growing potato tubers may lead to a marginal decrease in starch accumulation in non-stressed plants. However, SPS becomes a crucial factor in waterstressed plants because it is required for adaptive changes in tuber metabolism and whole plant allocation.

Detection of Sugar Accumulation and Expression Levels of Correlative Key Enzymes in Winter Wheat (Triticum aestivum) at Low Temperatures

“…The function of this phenomenon is unknown, but researchers have found that sucrose phosphate synthase is a crucial factor in adapting to some forms of abiotic stress in plants. 41) Analysis of the expression levels of genes whose products located in the chloroplast…”

Starch Synthesis in Potato Tubers Is Regulated by Post-Translational Redox Modification of ADP-Glucose Pyrophosphorylase

“…Instead, it adjusts the rate of starch synthesis to the balance between Suc breakdown and carbon use. Conditions in which changes in the 3PGA/ Pi ratio correlate with starch synthesis include high temperature, during which an increasing rate of respiration leads to a depletion of phosphorylated intermediates and an inhibition of starch synthesis (Geigenberger et al, 1998a), and mild water stress, during which post-transcriptional activation of Suc phosphate synthase stimulates the resynthesis of Suc and leads to a decrease of phosphorylated intermediates and an inhibition of starch synthesis (Geigenberger et al, 1997(Geigenberger et al, , 1999b.…”

“…First, lower levels of phosphorylated intermediates will favor Suc breakdown via the reversible reactions catalyzed by SuSy and UGPase , will relieve feedback inhibition of fructokinase by Fru-6-P (Renz and Stitt, 1993), and will decrease Suc resynthesis by inhibiting Suc phosphate synthase (Geigenberger et al, 1999b). Second, stimulation of starch synthesis via a mechanism that simultaneously decreases glycolytic intermediate levels may channel Suc toward starch without this leading to a stimulation of glycolysis and respiration.…”

Differential Expression of Sucrose-Phosphate Synthase Isoenzymes in Tobacco Reflects Their Functional Specialization during Dark-Governed Starch Mobilization in Source Leaves

“…While this led to an inhibition of Suc synthesis in leaves, photosynthetic carbon partitioning was not redirected toward starch (Strand et al, 2000). Antisense or cosuppression of SPS A in potato (Solanum tuberosum) and the examination of the transgenic tubers revealed a crucial role for this enzyme during the adaptation to water stress and low temperature (Krause et al, 1998;Geigenberger et al, 1999); however, in these studies no data on any effects on photosynthetic carbon metabolism have been reported.…”