Organization of the photosynthetic membrane in maize mesophyll and bundle sheath chloroplasts

The ultrastructure of the thylakoids of barley chloroplasts was examined by freeze-fractfiring and freeze-etching. Thylakoid fracture faces were objectively characterised in terms of the numbers of particles per square micron, average particle size and size distribution. Chloroplast envelope membranes were similarly examined and characterised. The changes in freeze-fracture appearance that occurred during greening are discussed in relation to current theories regarding thylakoid membrane structure. A procedure was developed that enables the induction of large numbers of particle arrays on the EF and PF faces and ES and PS surfaces of barley thylakoids. Measurements of the particles in these arrays revealed the asymmetric nature of EFs particles and confirmed that they span the thylakoid membrane.

Section: Discussionsupporting

confidence: 79%

Freeze-fracture studies on barley plastid membranes II. Wild-type chloroplast

Simpson

1978

“…This is indicated by the short incubation time (20-30 min) used for enzymatic digestion (l 2). Bundle sheath chloroplasts from the basal half of the leaf have numerous small grana, which contain the PSII-containing EFs particles (11). As the leaves develop, the grana and PSII activity disappear (3).…”

Section: Resultsmentioning

confidence: 99%

Differential expression of LHCII genes in mesophyll and bundle sheath cells of maize

Bassi

Simpson

1986

The properties and composition of bundle sheath and mesophyl! thylakoids from maize leaves are compared. This was possible because of the isolation of large amounts of purified material obtained by enzymatic digestion of mechanically disrupted leaves. Bundle sheath thylakoids from mature leaves, lack the chlorophyll-proteins and polypeptides associated with the reaction centre ofphotosystem II. They do, however, contain significant amounts of LHCII, which transfers excitation energy to photosystem I. LHCII isolated from bundle sheath thylakoids had a different freeze-fracture ultrastructure and a different polypeptide composition from LHCII isolated from mesophyll thylakoids, indicating a differential expression of the LHCII gene family in mesophyll and bundle sheath cells of maize leaves. INTRODUCI'IONThe photosynthetic membranes of higher plants are now thought to be characterised by extreme lateral heterogeneity with respect to composition and function, with all photosystem I (PSI) in the unstacked membrane regions (stroma la'mellae) and most, if not all photosystern II (PSII) in the appressed regions (grana) (1). The locations of some of the minor components remain in doubt because the methods used for the isolation of stroma and grana lamellae requires either mechanical disruption or detergent fractionation. Both procedures can generate artefacts due to cross-contamination or selective removal of some components.Chloroplasts containing no grana lamellae can therefore be very useful for studying thylakoid composition since their isolation avoids these procedures. Such chloroplasts are found in the bundle sheath cells (l l) of some C4 plants (e.g., maize and sorghum) characterised by high levels of NADPH-malic enzyme. In the leaves of such plants, CO2 is fixed by phosphoenolpyruvate c~rboxylase in mesophyll cells and transported as malate to bundle sheath cells, where decarboxylation yields CO2 and NADPH. The Abbreviations: BS = bundle sheath; Chl = chlorophyll; DCPIP = 2,6-di-chlorophenol indophenol; DPC = 1,5-diphenyi carbazide; EDTA = ethylenediamine tetraacetate; Hepes = N-2-(hydroxyethyl)-piperazine-N'-2-ethanesulphonic acid; LHC = light-harvesting complex; Mes = 2-(N-morpholino)-ethanesulphonic acid; PS = photosystem; SDS = sodium dodecyl sulphate; Tricine = N-(tris-(hydroxymethyl)-methyl)-glycine.Springer-Verlag

“…MILLER et al (39) showed by freeze-fracturing that bundle sheath membranes of maize are virtually identical in structure to the stroma membrane of mesophyll thylakoids. GHIRARDI and MELIS (23) suggested that the functional antenna size of the PSI is the same in mesophyll and bundle sheath chloroplasts.…”

Section: Discussionmentioning

confidence: 99%

Spectral properties and polypeptide composition of the chlorophyll-proteins from thylakoids of granal and agranal chloroplasts of maize (Zea mays L.)

Bassi

1985

Keywords: Bundle sheath and mesophyll thylakoids, absorption spectra, fluorescence emission spectra, circular dichroism spectra, light harvesting complex I and IIIn contrast to the granal thylakoids of mesophyll cells, the bundle sheath thylakoids of maize lack photosystem I1 activity and both of the chlorophyll a binding proteins ofphotosystem II. The chlorophyll-proteins from bundle sheath and mesophyll thylakoids are separated by undenaturing electrophoresis and after isolation characterized by SDS-urea-PAGE and spectroscopy. The chlorophyll-protein with the highest molecular mass (Chla-Pl*) is shown to consist of the reaction centre I containing chlorophyll-protein (Chl~-PI) and 12 other polypeptides. Three of the polypeptides are components of the chlorophyll a/b-protein P3, which by its fluorescence emission and absorption spectrum is recognized as PSI antenna.The oligomeric chlorophyll a/b-protein 2** consists of the Chlo/~-P2 polypeptides plus a polypeptide R with an apparent molecular weight of 7.800.The bundle sheath thylakoids contain large amounts of the light harvesting complex of the photosystem II which transfers energy efficiently to the PSI reaction centre in absence of the PSII reaction centre.