Gene transcript accumulation and in situ mRNA hybridization of two putative glutamate dehydrogenase genes in etiolated Glycine max seedlings.

Glutamate dehydrogenase (EC 1.4.1.2) is a multimeric enzyme that catalyzes the reversible amination of α-ketoglutarate to form glutamate. We characterized cDNA clones of two Glycine max sequences, GmGDH1 and GmGDH2, that code for putative α- and ß-subunits, respectively, of the NADH dependent enzyme. Temporal and spatial gene transcript accumulation studies using semiquantitative RT-PCR and in situ hybridization have shown an overlapping gene transcript accumulation pattern with differences in relative gene transcript accumulation in the organs examined. Detection of NADH-dependent glutamate dehydrogenase activity in situ using a histochemical method showed concordance with the spatial gene transcript accumulation patterns. Our findings suggest that although the two gene transcripts are co-localized in roots of etiolated soybean seedlings, the ratio of the two subunits of the active holoenzyme may vary among tissues.

Expression of three ß-type carbonic anhydrases in tomato fruits.

Carbonic anhydrase (CA) and phosphoenolpyruvate carboxylase (PEPC) activity were found in different Solanum lycopersicum fruit tissues, predominantly in the locular parenchyma and pericarp. The distribution of the CA and PEPC proteins in the tomato fruit tissues was examined by immunohistolocalization. CA and PEPC proteins were found in all fruit tissues examined as well as in the seeds. Three full length cDNA clones designated SlCA1, SlCA2 and SlCA3 coding for ß-carbonic anhydrases (CA; EC 4.2.1.1) were identified and characterized from tomato fruit. SlCA1 and SlCA3 encode two putative cytosolic isoforms whereas SlCA2 encodes a putative plastidial isoform. Quantitative real time RT-PCR analysis revealed that accumulation of SlCA1 mRNA transcripts was detected in all examined tomato fruit tissues or organs, whereas SlCA2 gene transcripts were found in abundance in leaves. Stems also had SlCA2 transcripts, with transcript levels being higher in flowers than in stems. The SlCA3 gene transcripts were found only in the flowers and the roots. The SlPEPC1 and SlPEPC2 gene transcript levels in different fruit tissues of the tomato were also examined. Τhe possible role of CA isoforms in relation to PEPC in tomato fruit is discussed.

Carbon metabolism in developing soybean root nodules: the role of carbonic anhydrase.

A full-length cDNA clone encoding carbonic anhydrase (CA) was isolated from a soybean nodule cDNA library. In situ hybridization and immunolocalization were performed in order to assess the location of CA transcripts and protein in developing soybean nodules. CA transcripts and protein were present at high levels in all cell types of young nodules, whereas in mature nodules they were absent from the central tissue and were concentrated in cortical cells. The results suggested that, in the earlier stages of nodule development, CA might facilitate the recycling of CO2 while at later stages it may facilitate the diffusion of CO2 out of the nodule system. In parallel, sucrose metabolism was investigated by examination of the temporal and spatial transcript accumulation of sucrose synthase (SS) and phosphoenolpyruvate carboxylase (PEPC) genes, with in situ hybridization. In young nodules, high levels of SS gene transcripts were found in the central tissue as well as in the parenchymateous cells and the vascular bundles, while in mature nodules the levels of SS gene transcripts were much lower, with the majority of the transcripts located in the parenchyma and the pericycle cells of the vascular bundles. High levels of expression of PEPC gene transcripts were found in mature nodules, in almost all cell types, while in young nodules lower levels of transcripts were detected, with the majority of them located in parenchymateous cells as well as in the vascular bundles. These data suggest that breakdown of sucrose may take place in different sites during nodule development.