Coarse control of sucrose-phosphate synthase in leaves: Alterations of the kinetic properties in response to the rate of photosynthesis and the accumulation of sucrose

Abstract

It has been investigated whether diurnal rhythms of sucrose-phosphate synthase (SPS) are involved in controlling the rate of photosynthetic sucrose synthesis. Extracts were prepared from spinach (Spinacia oleracea L.) and barley (Hordeum vulgare L.) leaves and assayed for enzyme activity. The activity of SPS increased in parallel with a rising rate of photosynthesis, and was increased by feeding mannose and decreased by supplying inorganic phosphate. In leaf material where sucrose had accumulated during the photoperiod or when sucrose was supplied exogenously, SPS activity decreased. During a diurnal rhythm, SPS activity increased after illumination, declined gradually during the light period, decreased further after darkening and then recovered gradually during the night. These changes did not involve an alteration of the maximal activity, but were caused by changes in the kinetic properties, revealed as a change in sensitivity to inhibition by inorganic phosphate. In experiments which modelled the response of SPS to changing metabolite concentrations, it was shown that these alterations of kinetic properties would strongly modify the activity of SPS in vivo. It is proposed that SPS can exist in kinetically distinct forms in vivo, and that the distribution between these forms can be rapidly altered. As the rate of photosynthesis increases there is an activation of SPS, which may be directly or indirectly linked to changes in the availability of Pi. This activation can be modified by factors related to the accumulation of sucrose. Under normal conditions there is a balance between these factors, and the leaf contains a mixture of the different forms of SPS.

Sucrose‐phosphate synthase is dephosphorylated by protein phosphatase 2A in spinach leaves

“…Spinach (Spinacia oleracea US Hybrid 424, Ferry Morse Seed Company, Modesto, CA) was grown hydroponically in a 9 h light/l5 h dark cycle [9]. The catalytic subunits of PPl and PP2A [18], and inhibitors-l and -2 [IS] were purified to homogeneity from rabbit skeletal muscle; okadaic acid was a gift from Dr Y. Tsukitani, Fujisawa Pharmaceutical Company, Japan, and microcystin-LR was provided by Professor G. Codd, Department of Biological Sciences, University of Dundee.…”

Fructan metabolism in two species of Bromus subjected to chilling and water stress

“…However, the greater activity of INV and SS found in B. auleticus than in B. pictus might explain the lower con- centration of sucrose found in the northern species. Stitt (1988) showed that in order to see a modification of SPS activity, measurements had to be made with limiting substrate conditions. However, under low temperature, growth is severely reduced.…”

Potato plants contain multiple forms of sucrose phosphate synthase, which differ in their tissue distributions, their levels during development, and their responses to low temperature

“…Phosphorylation leads to a lowering of the substrate affinity of the enzyme, and makes it more susceptible to inhibition by Pj and more dependent on Glc6P Siegl, Mackintosh & Stitt 1990). Reversible phosphorylation is involved in the regulation of SPS in response to rising rates of photosynthesis (Stitt et al 1988), accumulation of sucrose (Stitt et al 1988), the assimilation of nitrate (Van Quy & Champigny 1992) and water stress (Quick et al 1989;Zrenner & Stitt 1991;, although all the details of the regulation circuits have not yet been elucidated (see Huber & Huber 1996).…”