Ultrastructure of the Lamellae and Grana in the Chloroplasts of Zea Mays L

Abstract

Electron microscope studies of chloroplasts have confirmed the lamellar structure postulated from polarization optical and other studies (9). In the chloroplasts of lower plants, e.g., Euglena (28), Chlamydomonas (22), Chlorella (1), S~rogyra (25), and Nitella (18), and in the chromoplasts of brown algae (Fucus (17)), the lamellae are fairly well ordered, but grana have not been demonstrated. In the higher plants, grana are present in the chloroplasts, and both the grana and the intervening regions (intergrana regions) are laminated. The grana consist of well ordered stacks of lameUae, e.g., Beta (15), Aspidistra (7,15,16,26), Nicotiana (4), and Zea (12).The present paper is concerned with the finer structural details of the lamellae and grana, and with the interrelationships existing between the lamellae of the grana and those of the intergrana regions. It will be shown that the individual lamellae of both the grana and intergrana regions of Zea exhibit a characteristic compound layer structure when ultrathin sections are examined in the electron microscope. A possible interpretation of this compound structure in terms of the lipide, protein, and other components of the chloroplast will be given. Materials and MethodsThe chloroplasts were examined in situ. Small portions of the leaves of 3 to 4 week old maize plants were excised and fixed for 3 to 6 hours in 2 per cent osmium tetroxide solutions buffered to pH 7.2 with acetate-veronal (19) and adjusted to 0.2 ~ with sodium chloride. After washing and dehydration in an ethanol series, the leaf portions were embedded in n-butyl methacrylate, with or without the addition of up to 10 per cent of the methyl monomer. Portions of the leaves of efiolated seedlings were excised at various time intervals after exposure of the plants to daylight, and were prepared for examination in a similar manner. Thin sections were obtained using a microtome and the technique already described (11), and were examined in the electron microscope (RCA model EMU-I, fitted with an externally centerable objective aperture) without removal of the embedding medium. 6O5J.

P700 Activity and Chlorophyll Content of Plants with Different Photosynthetic Carbon Dioxide Fixation Cycles

“…Therefore, the present experiments strongly support the possibility that plants with the C4 cycle of CO2 fixation contain more Photosystem I than pentose phosphate cycle plants as evidenced by the increased amount of P700 and chlorophyll a. One should also note that these differences in pigment concentration may reflect on a molecular level the striking differences in chloroplast and cell anatomy which have been observed in these two groups of plants (4,10; Black, C. C. and Mollenhauer, H. H., manuscript in preparation). Furthermore, the data suggest that the photosynthetic unit in C4 cycle plants may have a distinct size and/or composition, i.e., C4 cycle plants appear to have a smaller photosynthetic unit than pentose cycle plants.…”

Accumulation of δ-Aminolevulinic Acid and Its Relation to Chlorophyll Synthesis and Development of Plastid Structure in Greening Leaves

“…In green leaves, the elongated, ellipsoidal BS chloroplasts contain single thylakoids which extend through the entire length of the plastids and rudimentary grana. MP chloroplasts are more rounded and contain well developed grana stacks interconnected by stroma thylakoids (18 (Table IV). The approximate doubling of the length of the thylakoidal membranes during this period (Table V) is probably related to the diminution of the PLBs.…”

Spectral, Physical, and Electron Transport Activities in the Photosynthetic Apparatus of Mesophyll Cells and Bundle Sheath Cells of Digitaria sanguinalis (L.) Scop.

“…In plants which fix carbon dioxide via the C4 cycle there are two major types of chloroplast containing cells (19,22); mesophyll cells which may fix carbon via the C4 cycle and bundle sheath cells which may fix carbon via the pentose cycle (16,21). Recently we developed a method for separating the two cell types (14,15), and have undertaken an investigation of the properties of each cell type.…”