Subcellular volumes and metabolite concentrations in spinach leaves

Abstract

Abstract. Cellular and subcellular volumes in mature leaves of spinach (Spinacia oteracea L. US Hybrid 424) were determined stereologically from light and electron micrographs. Forty-nine-day-old leaves of spinach with a total leaf volume of 1177 gL per mg chlorophyll (Chl) were found to be composed of 3% epidermis, 58% mesophyll, 1% vascular tissue, 5% apoplasm and 32% gas space. In the epidermal cells 89% of the volume was occupied by the vacuole. The mesophyll cells consisted, expressed in mg-Chl -~, of 546 gL (79%) vacuole, 66 ~tL (9.5%) chloroplast stroma, 24 gL (3.4%) cytosol, 3.7 ~tL (0.5%) mitochondria and 2.1 gL (0.3%) nucleus. From previous measurements of the subcellular levels of sucrose, of phosphorylated intermediates of carbohydrate metabolism, of malate, oxoglutarate and various amino acids in illuminated leaves, and the above subcellular volumes, the corresponding subcellular metabolite concentrations have been determined. Of the substances measured, only with malate was the concentration higher in the vacuole than in the cytosol. The concentration of sucrose in the cytosol was 5 times, and that of amino acids even 30 times higher than in the vacuole.

Differential Accumulation of Dimethylallyl Diphosphate in Leaves and Needles of Isoprene- and Methylbutenol-Emitting and Nonemitting Species

“…This estimate is consistent with the relatively high K m values that have been reported for isoprene synthase (0.5-8 mm; Silver and Fall, 1995;Schnitzler et al, 1996) and MBO synthase (5 mm; Fisher et al, 2000). The concentration of chloroplastic DMAPP is similar to those reported for other chloroplastic phosphorylated intermediates, including 3-phosphoglycerate (2.0-4.3 mm), dihydroxyacetone phosphate (0.21-0.32 mm), and Fru-1,6-bisphosphate (0.55-1.04 mm; Winter et al, 1993Winter et al, , 1994Leidreiter et al, 1995). When taken together, the large diurnal variation in DMAPP content associated with isoprene and MBOemission, as well as the localization of DMAPP to the cottonwood chloroplast, suggests that the production of DMAPP may participate in the regulation of isoprene and MBO emission from plant leaves.…”

Feedback Inhibition of Deoxy-d-xylulose-5-phosphate Synthase Regulates the Methylerythritol 4-Phosphate Pathway

“…Non-aqueous fractionation to measure the chloroplastic DMADP pool of kudzu leaves has estimated a range of ϳ0.25 to ϳ3.5 mM (34). Measurement of the chloroplastic DMADP pool by postillumination isoprene emission estimated a concentration of ϳ43 M in oak leaves (53,54). Metabolic profiling studies by LC-MS/MS estimated the chloroplastic IDP/DMADP pool to be ϳ30 M in poplar leaves (37).…”

Leaf anatomy enables more equal access to light and CO2 between chloroplasts

“…Detailed stereological quantification of the volume fractions occupied by the vacuole, chloroplast and other organelles has been carried out on mesophyll cells from Hordeum (Winter et al, 1993), Spinacia (Winter et al, 1994) and Solanum (Leidreiter et al, 1995). The fraction of an average mesophyll cell occupied by chloroplasts varied little, ranging between 16.4 and 19% for these species.…”