Subcellular volumes and metabolite concentrations in barley leaves

Abstract

Abstract. Metabolite concentrations in subcellular compartments from mature barley (Hordeum vulgare L. cv.Apex) leaves after 9 h of illumination and 5 h of darkness were determined by nonaqueous fractionation and by the stereological evaluation of cellular and subcellular volumes from light and electron micrographs. Twenty oneday-old primary leaves of barley with a total leaf volume of 902 gL per mg chlorophyll were found to be composed of 27% epidermis, 42% mesophyll cells, 6% veins, 4.5% apoplast and 23% gas space. While in epidermal cells 99% of the volume was occupied by the vacuole, mesophyll cells with an average volume of 31.3 pL consisted of 23 pL (73%) vacuole, 4.6 pL (19%) chloroplasts, 2.06 pL (6,7%) cytosol (including smaller organelles and vesicles), 0.34 pL (1%) mitochondria and 107 fL (0.34%) nucleus. The differences between leaves harvested after 9 h of illumination and after 5 h of darkness were in the size of the stromal compartment and the starch grains therein. Subcellular metabolite concentrations were calculated from the compartmental volumes and metabolite contents of the compartments as determined by nonaqueous fractionation. The amino-acid concentrations in stroma and eytosol were rather similar after 9 h of illumination and 5 h of darkness. In contrast, the vacuolar amino-acid concentrations were about one order of magnitude lower than the stroma and cytosol values, and there was a slight increase in concentration after 5 h of darkness.

Patterns of solute in individual mesophyll, bundle sheath and epidermal cells of barley leaves induced to accumulate carbohydrate

“…Samples from bundle sheath cells are also likely to be predominantly vacuoiar (Williams et al, 1989) and the solutes measured are likely to approximate the value of the vacuoiar sap. The mesophyll samples, on the other hand, are likely to contain 26% of cytoplasm (Winter, Robinson & Heldt, 1993) and a precise estiniation of vacuoiar sucrose is not possible. It is thought, however, that the sucrose and fructose values are representative of the vacuole.…”

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.…”

Elements Required for an Efficient NADP-Malic Enzyme Type C4 Photosynthesis

“…The proportion of MC and BSC volume was based on maize (Zea mays) leaf cross sections, and subcellular volumes were based on barley (Hordeum vulgare) leaf (Winter et al, 1993). All of the volume-related parameters are listed in Supplemental Data File S3.…”