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Immunogold localization of nodule‐enhanced phosphoenolpyruvate carboxylase in alfalfa
Author(s) -
Robinson D. L.,
Pathiran S. M.,
Gantt J. S.,
Vance C. P.
Publication year - 1996
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1996.tb00394.x
Subject(s) - phosphoenolpyruvate carboxylase , immunogold labelling , biology , pericycle , nodule (geology) , root nodule , lotus , phosphoenolpyruvate carboxykinase , nitrogenase , biochemistry , botany , enzyme , nitrogen fixation , gene , bacteria , paleontology , genetics , ultrastructure , arabidopsis , mutant
Phosphoenolpyruvate carboxylase (PEPC; EC 4‐1‐1‐31) plays a paramount role in providing carbon for synthesis of malate and aspartate in alfalfa ( Medicago sativa L.) root nodules. PEPC protein and activity levels are highly enhanced in N 2 ‐fixing alfalfa nodules. To ascertain the relationship between the cellular location of PEPC and root nodule metabolism, enzyme localization was evaluated by immunogold cytochemistry using alfalfa nodule PEPC antibodies. Gold labelling patterns in effective nodules showed that PEPC is a cytosolic enzyme and is distributed relatively equally in infected and uninfected cells of the nodule symbiotic zone. A high amount of labelling was also observed in pericycle cells of the nodule vascular system. Labelling was also detected within inner cortical cells, but the density was reduced by 60%. When Lotus corniculatus was transformed with a chimeric gene consisting of the 5′‐upstream region of the PEPC gene fused to β‐glucuronidase (GUS), GUS staining in nodules was consistent with immunogold localization patterns. The occurrence of PEPC in both infected and uninfected cells of the symbiotic zone of effective nodules coupled to the reduced amounts in ineffective nodules suggests a direct role for this enzyme in supporting N 2 ‐fixation. PEPC localization in the uninfected, interstitial cells of the symbiotic zone indicates that these cells may also have a role in nodule carbon metabolism. Moreover, the association of PEPC with the nodule vascular system implies a role for the enzyme in the transport of assimilates to and from the shoot.