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Compartmentation of metabolic steps in biosynthesis of 2- carboxyl-D-arabinitol-1 phosphate & consequences for regulation of photosynthetic metabolism

Reference	BBS/E/C/00011490
Principal Investigator / Supervisor	Professor Martin Parry
Co-Investigators / Co-Supervisors
Institution	Rothamsted Research
Department	Rothamsted Research Department
Funding type	Research
Value (£)	87,579
Status	Completed
Type	Institute Project
Start date	01/04/1997
End date	31/03/1999
Duration	24 months

Abstract

This project has evolved from project 011491 (BOMRIP grant) which is concerned with the biosynthesis of 2- carboxyarabinitol-1-phosphate (CA1P) a tight binding nocturnal inhibitor of Ribulose 1,5-bisphosphate carboxylase (Rubisco). In many but not all species, CA1P is synthesised during periods of prolonged darkness and stops the energy- dependent reactions of the Calvin cycle. In the light, CA1P is released from Rubisco and rendered non-inhibitory by CA1P- phosphatase which removes its phosphate group, to produce carboxyarabinitol, CA. The biosynthetic pathway is unclear. 2 Radiolabelled CA fed to leaf petioles in the light is converted to CA1P in the dark. Recently assimilated carbon is incorporated into CA1P and CA but the order in which CA and CA1P receive newly assimilated carbon has yet to be established. CA and CA1P-phosphatase are found in some species e.g Hordeum vulgare in which Rubisco is not inhibited by CA1P. Little is known about the intracellular distribution of CA1P, CA and CA1P- phosphatase in relation to the in vivo activity of Rubisco. Compartmentation may be important in the regulation of CA1P concentrations and thus regulation of Rubisco. A knowledge of the compartmentation of CA1P and its precursors may also reveal other metabolic/physiological functions; although CA, CA1P and related branched chain sugar derivatives are widespread in plants the only function ascribed to them is the regulation of Rubisco. 3 The subcellular distribution of CA, CA1P, and related compounds in the leaves of a species in which Rubisco is not inhibited by CA1P, Hordeum vulgare, and one where it is, Phaseolus vulgaris, will be determined using aqueous and non-aqueous density gradient fractionation. Isolated chloroplasts, mitochondria, nuclei and vacuoles will be incubated with radiolabelled potential precursors of CA1P to determine the potential role of each organelle in CA1P metabolism and their ability to accumulate different metabolites. The reactions of these compounds within, and transport between, metabolic pools will be examined. Determine the concentration of CA1P in different parts of Phaseolus vulgaris leaves. Establish methods for the routine quantification of CA, CA1P and CA1P- phosphatase. Evaluate and develop protocols for the aqueous or non-aqueous density gradient fractionation of leaf tissue to isolate chloroplasts, mitochondria, nuclei and vacuoles. To determine, in H. vulgare and P. vulgaris, the subcellular distribution of CA, CA1P and CA1P-phosphatase, and other enzymes and substrates involved in the regulation of Rubisco. The uptake of radiolabeled potential precursors of CA1P by chloroplasts will be examined. The transfer of radiolabel from hamamelose to CA and CA1P will be examined in isolated chloroplasts from P. vulgaris and Triticum aestivum. The activity of any enzymes (identified in project 001492) will be determined in P. vulgaris.

Summary

unavailable

Committee	Closed Committee - Plant & Microbial Sciences (PMS)
Research Topics	X – not assigned to a current Research Topic
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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