000			02443nam a2200277Ia 4500
008			220216s9999 xx 000 0 und d
100			_aClement Anne
245		0	_aGlutamine synthetase of hevea brasiliensis latex : characterisation and physiological regulation
260			_bJournal of Rubber Research _c2001
300			_a56-68
520			_aRegular exploitation of rubber tree causes intense metabolic activity in latex cells located in the phloem, associated with the regeneration of the latex cellular components removed by tapping. In this context, glutamine synthetase (GS) plays a prominent role by ensuring ammonium fixation necessary for the regeneration of latex nitrogeneous components. In latex, GS activity was detected in the cytosol only. The enzyme was purified and its main physico-chemical characteristics were determined. Its molecular mass was 450 kDa for the native form and 45kDa +_ 5kDa for the sub-unit. The pH optimum was found to be 8.0 and variaitons in the physiological pH range (6.4 to 7.2) strongly affected GS activity. Km for ammonium, glutamate and ATP were estimated at 8mM +_ 2 mM +_ 5 mM and 0.6 mM +_ 0.05 mM, respectively. Comparison with the cytosol physiological parameters showed the importance of ATP concentration for GS activity regulation. Functioning of the purified enzyme in a paraphysiological (ultrafiltrated, protein free) medium, as compared with an optimised control medium, demonstrated that physiological ATP concentrations were significantly limiting for GS potential activity. Treatment with ethephon increases latex production both by increasing latex flow duration and by stimulating the regeneration of metabolism. In this paper we demonstrated that ethephon treatment induced a concomitant increase in pH, ATP concentration and GS activity. These results suggest that biochemical mechanisms involving pH and ATP participate in the regulation of GS activity in response to ethylene, in addition to the previously observed stimulation of gene expression.
650			_aBiochemical analysis
650			_aCharacterisation
650			_aEthephon
650			_aGlutamine synthetase
650			_aGT1
650			_aHevea brasiliensis
650			_aLatex stimulation
650			_aPhysiological regulation
650			_aPurification
700			_aHirel B
700			_aJacob Jean-Louis
700			_aPrevot Jean-Claude
700			_aPujade-Renaud V
942			_cJS
999			_c60009 _d60009