Immunocytochemical localization of phosphoenolpyruvate carboxylase and photosynthetic gas-exchange characteristics in ears of Triticum durum Desf.

Abstract

Abstract. The presence and distribution of phosphoenolpyruvate carboxylase (PEPCase) in the glumes and immature grains of durum wheat (Triticum durum Desf.) were studied by electron-microscopical immunolabeling of PEPCase with polyclonal antibodies followed by protein A-gold. Plants were grown under mediterranean field conditions and samples were obtained two weeks after anthesis. In the kernels, high gold label was associated with the unstained areas of the protein bodies of aleurone cells, whereas labeling in the cytoplasm and chloroplasts of the pericarp was slight, although significantly above the background. In the glumes, high gold label was only located in cytoplasmic granules (vesicles) of the mesophyll cells, although labeling in the cytoplasm and chloroplasts was also significantly above the background. These observations in immature kernels and glumes are in accordance with the anaplerotic role of this enzyme, as evidenced in C 3 plants. Measurements of apparent photosynthesis and its 02 dependence and CO 2 compensation concentration were made on ears and flag leaves of durum wheat. In addition, an analog of phosphoenolpyruvate, 3,3-dichloro-2-dihydroxy-phosphinoylmethyl-2-propenoate, was used to inhibit PEPCase and, thereby, to assess the contribution of the PEPCase to photosynthesis in detached ears. There was no effect of the inhibitor on the apparent photosynthesis of ears. Whereas inhibition of apparent photosynthesis by 210 mL 9 L 1 02 in flag leaves was typical of C 3 species, inhibition in ears was even greater. The CO 2 compensation concentrations in different ear parts were similar to or higher than in flag leaves and the 02 dependence was also comparable (about 70%). Therefore, gas-exchange data give further support to the assumption that a C4 cycle is Abbreviations and symbol: AP=apparent photosynthesis; BSA=bovine serum albumin; DCDP=3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate; PBS=phosphate-buffered saline; PEP=phosphoenolpyruvate; PEPCase=PEP carboxylase; F = CO2 compensation concentration Correspondence to: J.L. Araus; FAX: 34(3)4112842 absent or limited to very low rates in ears of durum wheat.

Phosphoenolpyruvate carboxylase in developing seeds of Vicia faba L.: gene expression and metabolic regulation

“…4). All these properties are consistent with the proposed role of PEPCase in the cotyledons to provide carbon skeletons for amino acid biosynthesis (Flinn 1985;Smith et al 1989;Araus et al 1993).…”

“…The pathway requires the anaplerotic carbon¯ow catalyzed by PEPCase. Using immunolocalization, PEPCase was detected in the protein bodies of developing wheat grains, possibly contributing to storage-protein biosynthesis (Araus et al 1993). A strong correlation between PEPCase activity and protein concentration in seeds of 13 soybean cultivars (Sugimoto et al 1989) indicates a possible rate-limiting role of the enzyme in seed storage-protein accumulation.…”

Influence of water deficit on photosynthetic activity, dry matter partitioning and grain yield of different durum and bread wheat genotypes

“…Stem and spike provide 40-50% of the required photosynthetic products during grain formation and filling (Evans and Rawson 1970;Araus et al 1993). The importance of the total biomass in the improvement of productivity (Reynolds et al 2007), especially under drought (Quarrie et al 1999) was reported.…”

Poor Evidence for C4 Photosynthesis in the Wheat Grain

“…Immunolabeling studies in wheat grains have shown that PEPC is not localized in the cross-cells of the pericarp, as suggested by Rangan et al (2016), but in the aleurone layer and endosperm (Araus et al, 1993;González et al, 1998), the sites where one would expect the highest concentration of respiratory CO 2 . With Rubisco located in the chloroplasts of the pericarp (Tambussi et al, 2005), this would render a C 4 -like CO 2 pump ineffective.…”