on the steady state metabolism of xylem-borne [U-14C]glutamate
by young transpiring shoots of tobacco seedlings has been determined.
During a 90 min time-course, aminoacetonitrile causes
glycine accumulation, decreases the 14C-radioactivity in glutamine,
and increases the 14C-radioactivity in glutamate, succinate and
other Krebs-cycle organic acids. Furthermore, the early precursor–
product relations indicate that succinate is derived primarily
via the GABA shunt rather than from a-ketoglutarate. Thus,
recyling of photorespiratory NH3 via glutamine synthetase is
restricted by aminoacetonitrile, thereby enhancing the availability
of glutamate for use by GAD. This study also provides experimental
support for the suggestion that elevated glutamate levels
stimulate GABA synthesis in isolated Asparagus mesophyll
cells13,31. Similarly, elevated GABA levels occur under long-term
on the steady state metabolism of xylem-borne [U-14C]glutamateby young transpiring shoots of tobacco seedlings has been determined.During a 90 min time-course, aminoacetonitrile causesglycine accumulation, decreases the 14C-radioactivity in glutamine,and increases the 14C-radioactivity in glutamate, succinate andother Krebs-cycle organic acids. Furthermore, the early precursor–product relations indicate that succinate is derived primarilyvia the GABA shunt rather than from a-ketoglutarate. Thus,recyling of photorespiratory NH3 via glutamine synthetase isrestricted by aminoacetonitrile, thereby enhancing the availabilityof glutamate for use by GAD. This study also provides experimentalsupport for the suggestion that elevated glutamate levelsstimulate GABA synthesis in isolated Asparagus mesophyllcells13,31. Similarly, elevated GABA levels occur under long-term
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