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Operation of the glycolate pathway in isolated bundle sheath strands of maize and Panicum maximum
Author(s) -
Farineau Jack,
MorotGaudry JeanFrançois,
Lelandais Maud
Publication year - 1984
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1984.tb04566.x
Subject(s) - glycine , serine , photorespiration , glycine cleavage system , labelling , biochemistry , amino acid , chemistry , photosynthesis , enzyme
Operation of the glycolate pathway in isolated bundle sheath (BS) strands of two C 4 species was demonstrated from 14 C incorporation into two intermediates, glycine and serine, under conditions favourable for photorespiratory activity. Isolated BS strands fixing 14 CO 2 under light at physiological rates incorporate respectively 3% ( Zea mays L., cv. INRA 258) and 7% ( Panicum maximum Jacq.) of total 14 C fixed into glycine + serine, at low bicarbonate levels (less than the Km for CO 2 fixation, 0.8 m M ). Higher bicarbonate concentrations depressed the percentage of incorporation into the two amino acids. No labelling was observed in the absence of added glutamate. Oxygen was required for glycine + serine labelling, since 14 C incorporation into glycine was largely depressed by argon flushing, and labelling of the two amino acids was nearly suppressed by the addition of the strong reductant, dithionite, especially in maize. Two inhibitors of the glycolate pathway were tested. With α‐hydroxypyridine‐methanesulfonic acid, an inhibitor of glycolate oxidase, labelling of glycine and serine remained minimal whereas glycolate was accumulated. Isoniazid, an inhibitor of the transformation of glycine to serine induced a 50% increased labelling of glycine in maize BS, and a large decrease in serine labelling. In Panicum , the increase in [ 14 C]‐glycine was 90%. These results suggest that the pathway glycolate → glycine → serine operates in these plants. However, leakage of metabolites occurs in BS cells, especially in maize and a large part of newly formed glycolate, glycine and serine is exported out of the cells. Operation of ribulose‐1,5‐bisphosphate oxygenase activity in competition with ribulose‐1,5‐bisphosphate carboxylase is demonstrated by the lowering of total 14 CO 2 fixation when O 2 is increased at low bicarbonate concentration. An interesting feature observed in maize BS, at low bicarbonate concentration, was an increase in ribulose‐1,5‐bisphosphate labelling when the O 2 level was decreased. This was accompanied by an increase in CO 2 fixation. This could indicate an increased rate in synthesis of ribulose‐1,5‐bisphosphate (which accumulated) due to a stimulation of ATP synthesis by cyclic photophosphorylation under anaerobic conditions.