THE ULTRASTRUCTURE OF PORPHYRIDIUM CRUENTUM

An electron microscopic examination of Porphyridium cruentum revealed the presence of mitochondria which had been reported absent in this aerobic organism. The chloroplast in this red alga was found to contain small granules (about 320 A) regularly arranged along the parallel chloroplast lamellae. The chloroplast granules differ in size and staining intensity from the ribosomes located in the cytoplasm. Two tubular elements are described. One type (450 to 550 A) is associated with the Golgi bodies. Another type (350 A), in the cell periphery, is believed to connect the endoplasmic reticulum and the cell membrane. Daughter nuclei were found to be positioned at opposite ends of the cell prior to commencement of cell division. Cytokinesis is accomplished by an annular median constriction causing the gradual separation of the chloroplast, pyrenoid, and other cell organelles, resulting in two equal daughter cells. No appreciable differences were observed between cells grown in high light (400 ft-c) and low light (40 ft-c). Structural differences between young and old cells were compared.     

ELECTRON MICROSCOPY OF THE PACINIAN CORPUSCLE

The Pacinian corpuscle has a framework of cytoplasmic lamellae arranged concentrically in the outer zone, and bilaterally in the core. Between these is an intermediate growth zone. The inner core shows an unexpected complexity in that its component lamellae are arranged in two symmetrical groups of nested cytoplasmic sheets. Longitudinal tissue spaces form clefts separating the two groups. The perikarya of the core lamellae lie in or near the intermediate growth zone, and send arms into the clefts. The arms then branch and terminate as lamellae which interdigitate with those of neighboring cells. The single nerve fiber loses its myelin sheath just before it reaches the inner core but retains its Schwann cell cytoplasmic covering for a short additional distance. The Schwann sheath is not continuous with the lamellae of the inner core. Inside the core the fiber contains a striking circumferential palisade of radially disposed mitochondria. The fiber does not arborize. Vascular capillaries penetrate the hilar region of the corpuscle only as far as the myelinated sheath of the nerve, and they have not been seen elsewhere in the corpuscle. There is direct continuity between the clefts of the core and tissue spaces in the vicinity of the capillaries. It is likely that this provides a route whereby metabolites reach the active nerve ending, as well as the cells of the growth zone. The outer zone consists of at least 30 flattened concentric cytoplasmic lamellae separated from one another by relatively wide fluid-filled spaces. Collagenous fibrils are present, particularly on the outer surface of lamellae, and tend to be oriented circularly. The girdle of proliferating cells constituting the growth zone, which is prominent in corpuscles from young animals, is the layer from which the outer lamellae are derived. Osmotic forces probably elevate the lamellae, and maintain turgor pressure.     

THE FINE STRUCTURE OF RHODOSPIRILLUM RUBRUM

The fine structure of Rhodospirillum rubrum grown under a series of defined conditions has been examined in thin sections prepared by the methods of Ryter and Kellenberger. In cells grown anaerobically at different light intensities, the abundance of 500 A membrane-bounded vesicles in the cytoplasm is inversely related to light intensity, and directly related to cellular chlorophyll content. When the chlorophyll content of the cell is low, the vesicles are exclusively peripheral in location; they extend more deeply into the cytoplasm when the chlorophyll content is high. Typical vesicles also occur, though rarely, in cells grown aerobically in the dark, which have a negligible chlorophyll content. When synthesis of the photosynthetic pigment system is induced in a population of aerobically grown cells by incubation under semianaerobic conditions in the dark, the vesicles become increasingly abundant with increasing cellular chlorophyll content, and the cells eventually acquire the cytoplasmic structure that is characteristic of cells growing anaerobically at a high light intensity. Poststaining with lead hydroxide reveals that the membranes surrounding the 500 A vesicles are indistinguishable in structure from the cytoplasmic membrane, and continuous with it in some areas of the sections. The bearing of these observations on current notions concerning the organization of the bacterial photosynthetic apparatus is discussed.     

THE FINE STRUCTURE OF NERVE CELL BODIES AND THEIR MYELIN SHEATHS IN THE EIGHTH NERVE GANGLION OF THE GOLDFISH

The eighth cranial nerve ganglion consists of bipolar nerve cell bodies each occupying part of an internodal segment. The perikaryal sheaths range from a single layer of Schwann cell cytoplasm on the smallest cells to typical thick compact myelin on the largest. On most perikarya, the sheath displays an intermediate form, consisting of multiple layers of Schwann cell cytoplasm (loose myelin), or of loose and compact myelin continuous with each other. Internodes beyond the one containing the cell body bear only compact myelin. In loose myelin the thickness of each layer of Schwann cell cytoplasm is about 100 A. It may be much greater (~ 3000 A) particularly in the outermost layers of the sheath, or the cytoplasm may thin and even disappear with formation of a major dense line. The cytoplasmic layers are separated from each other by a light zone, 40 to 200 A wide, which in its broader portions may contain an intermediate line. Desmosomes sometimes occur between lamellae. In addition to the usual organelles, the perikaryal cytoplasm contains granular and membranous inclusions. Large cells covered by compact myelin have a consistently higher concentration of neurofilaments, and some of the largest cells, in addition, show a reduced concentration of ribosomes. The functional significance and possible origins of perikaryal myelin sheaths are discussed.     

THE FINE STRUCTURE OF ACOUSTIC GANGLIA IN THE RAT

Nerve cell bodies in the spiral and vestibular ganglia of the adult rat are surrounded by thin (about ten lamellae) myelin sheaths which differ in several respects from typical axonal myelin. In some instances lamellae surrounding perikarya appear as typical major dense lines, and in others as thin Schwann cell sheets in which cytoplasm persists. Discontinuities and irregularities appear in the structure of perikaryal myelin. Lamellae may terminate anywhere within the sheaths; they may bifurcate; they may reverse their direction; or they may merge with each other. The number of lamellae varies from one part of a sheath to another. In addition, the myelin of a single perikaryal sheath may receive contributions from more than one Schwann cell, which overlap and interleave with each other. The ganglion cells are of two types: those which are densely packed with the usual cytoplasmic organelles but have few neurofilaments (granular neurons), and those which exhibit large areas containing few organelles but have a high concentration of neurofilaments (filamented neurons). The latter cell type is ensheathed by myelin which is generally more compact that that surrounding the former. The formation and the physiologic significance of perikaryal myelin are discussed.     

Fine Structure of Blue-Green Algae and the Cells Lined along the Endophyte Cavity in the Coralloid Root of Cycas

The ultrastructure of vegetative cells of blue-green alga, Anabaena cycadae, in the coralloid root of Cycas revoluta has the general characteristics of the cyanophycean cells. Their heterocysts are characterized by heavy envelope deposition, well developed pore channel with its plug, absence of large granules as inclusions and reduced and flattened photosynthetic thylakoids. By these characteristical features, the frequency of heterocysts occurring in this algal population of the coralloid root may be estimated to ca. 40%. This high heterocyst frequency is a sign of relatively high activity of nitrogen fixation in this symbiont. The ultrastructure of the cells lined along the endophyte cavity in the coralloid root shows that they have the function to maintain vigorous nutritional transport in short distance. These cells are especially characterized by the presence of numerious outgrowths on the cell wall into the endophyte cavity. Correspondingly, there are abundant mitochondria, dictyosomes and numerious vesicles in the cytoplasm. The plasma membrane becomes tortuous along the cell wall and many secretory granules are present between the plasma membrane and cell wall in the cytoplasm amyloplasts and starch granules also occur constantly. The ultrastructure observed above indicates the fact that there is sound structural basis for the metabolic relationship between the host cells and the symbiont.     

ULTRASTRUCTURE OF CARPOSPOROGENESIS IN THE PARASITIC RED ALGA FAUCHEOCOLAX ATTENUATA SETCH. (RHODYMENIALES,RHODYMENIACEAE)

Carpospore differentiation in Faucheocolax attenuata Setch. can be separated into three developmental stages. Immediately after cleaving from the multinucleate gonimoblast cell, young carpospores are embedded within confluent mucilage produced by gonimoblast cells. These carpospores contain a large nucleus, few starch grains, concentric lamellae, as well as proplastids with a peripheral thylakoid and occasionally some internal (photosynthetic) thylakoids. Proplastids also contain concentric lamellar bodies. Mucilage with a reticulate fibrous substructure is formed within cytoplasmic concentric membranes, thus giving rise to mucilage sacs. Subsequently, these mucilage sacs release their contents, forming an initial reticulate deposition of carpospore wall material. Dictyosome vesicles with large, single dark-staining granules also contribute to wall formation and may create a separating layer between the mucilage and carpospore wall. During the latter stages of young carpospores, starch is polymerized in the perinuclear cytoplasmic area and is in close contact with endoplasmic reticulum. Intermediate-aged carpospores continue their starch polymerization. Dictyosomes deposit more wall material, in addition to forming fibrous vacuoles. Proplastids form thylakoids from concentric lamellar bodies. Mature carpospores are surrounded by a two-layered carpospore wall. Cytoplasmic constituents include large floridean starch granules, peripheral fibrous vacuoles, mature chloroplasts and curved dictyosomes that produce cored vesicles which in turn are transformed into adhesive vesicles. Pit connections remain intact between carpospores but begin to degenerate. This degeneration appears to be mediated by microtubules.     

CHLOROPLAST STRUCTURE AND PIGMENT COMPOSITION IN THE RED ALGA GRIFFITHSIA PACIFICA: REGULATION BY LIGHT INTENSITY1

The ratio of accessory phycobiliproteins to chlorophyll a is controlled by light intensity in the marine red alga Griffithsia pacifica. The greatest changes in pigment ratios are observed below 300 ft-c; above 300 ft-c the response approaches saturation. Ultrastructural examination of chloroplasts of plants grown at different intensities reveals that the number of phycobilisomes per unit of photosynthetic thylakoid changes in direct proportion to the pigment ratios and in inverse proportion to the light intensity.     

SPECIALIZATION OF MESOPHYLL MORPHOLOGY IN RELATION TO C4 PHOTOSYNTHESIS IN THE POACEAE

Our current understanding of the photosynthetic process in species utilizing the C₄ photosynthetic pathway suggests that photosynthetic efficiency should be enhanced by: 1) maximizing the conductance of the gas phase transport pathway from the leaf exterior to the mesophyll cell surfaces; 2) maximizing cytoplasmic connections and metabolite transport between bundle sheath and mesophyll parenchyma cells; and 3) minimizing the conductance of the gas phase transport pathway from the bundle sheath cells to the leaf exterior. In this study we have examined several species in the Poaceae with C₄ photosynthesis to determine if there is any evidence for anatomical specialization which would lead to enhanced photosynthetic efficiency by these processes. Observations with light and scanning electron microscopes revealed specializations in mesophyll cell morphology and arrangement which include branched cells forming intercellular channels. These specializations are hypothesized to contribute to photosynthetic efficiency through its influence on the above transport processes.     

THE ULTRASTRUCTURE OF THE VITELLINE BODY IN THE OOCYTE OF THE SPIDER TEGENARIA PARIETINA

The vitelline body in the mature oocyte of the spider Tegenaria parietina is composed of 4 different zones. 1. The central zone contains granular areas, vesicles, and a few lamellae. 2. The lamellar zone consists of numerous concentric lamellae. These sheets, 45 A in thickness, are stacked in groups. The fine structure and the regular arrangement recall those of myelin sheets, retinal rods, and chloroplasts. Between the stacks of lamellae, finely granular masses and various vesicles are to be found. 3. The "zone of transition" consists of a finely granular substance accumulated in abundant masses. This substance is composed of very closely packed granules about 50 to 60 A in diameter. Very often, near the lamellae, the granules show alignment giving a gradual transition from grains to lamellae. 4. The vesicular zone contains ergastoplasm, dense particles, mitochondria, and Golgi material. It is suggested that the peculiar ultrastructure of these cytoplasmic components may be related to an intense metabolic activity.     

Observations on Cellular Structures of Porphyridium cruentum

The cellular structure of Porphyridium cruentum was studied with both light and electron microscope. The photosynthetic plastid in this red alga was found to be structurally similar to that in the Chlorophyceae and higher green plants. The phycobilins, as well as the chlorophyll, seem to be associated with the lamellae of the plastid. The pyrenoid, a region of low lamellar density, contains no tubules, and does not appear to function in synthesis or storage of reserve material. Grains of floridean starch are located in the cytoplasm, outside the plastid. Typical mitochondrial organelles were not observed. The nucleus is eccentric, and contains a nucleolus located on the inner face of the nucleus, nearest the plastid. The schedule for staining the nucleus is given in detail. Other cell structures (sheath, dictyosomes, etc.) are described. Growing cells in light of intensity leads to disruption of the parallel arrangement of the lamellar characteristic of cells grown in moderate light.     

A possible optical role of the bundle sheath extensions of the heterobaric leaves of Vitis vinifera and Quercus coccifera

Heterobaric leaves are characterized by transparent regions in their lamina, due to the occurrence of bundle sheath extensions. Fused silica fibre‐optic microprobes were used to monitor light gradients and part of the spectral regime along the bundle sheath extensions, as well as along the mesophyll in the heterobaric leaves of two representative plants, one mesomorphic (Vitis vinifera L.) and one xeromorphic (Quercus coccifera L.). It was found that the attenuation of collimated visible light by the bundle sheath extensions of both plants was weaker than the attenuation by the photosynthetic parenchyma layers. However, only a small portion of the amount of light that strikes the leaf surface is transmitted through these structures. The adaxial epidermis covering the bundle sheath extensions, as well as the mesophyll, afforded similar effective protection against UV radiation in both tissues. The relative amount of the forward‐scattered visible light inside the bundle sheath extensions approached that detected by the microprobe at the adaxial illuminated leaf surface. Moreover, light transmitted through the bundle sheath extensions was enriched mainly in the blue and red regions, compared to light transmitted through the photosynthetic tissue. The time course of photosynthetic starch formation in the leaves of V. vinifera detected by iodine staining showed that the accumulation of starch during the first minutes of illumination was high within photosynthetic parenchyma cells adjacent to the bundle sheath extensions. The data showed that bundle sheath extensions act as transparent ‘windows’ which enrich the neighbouring mesophyll areas with high levels of photosynthetically active radiation (400–700 nm). The phenomenon was more pronounced in the thick and compact sclerophyllous leaves of Q. coccifera by virtue of the greater abundance of bundle sheath extensions as compared to that in V. vinifera. The enhancement of the light micro‐environment within the deep internal layers of the mesophyll may affect the photosynthetic performance of such leaves, giving adaptive advantages.     

ULTRASTRUCTURAL STUDIES ON THE CYANELLES OF GLAUCOCYSTIS NOSTOCHINEARUM ITZIGSOHN1

Ultrastructural studies conducted on the intracellular symbiont of Glaucocystis nostochinearum Itz., a unicellular alga with a debated taxonomic position, have shown that the endosymbiont, although somewhat aberrant, is a blue-green alga. Due possibly to its intracellular habitat, it lacks the characteristic cyanophycean double-layered cell wall and the cells appear to be completely naked, bound only by a single plasma membrane. The protoplasm of the cell is differentiated into the lamellated chromatoplasm, which contains the photosynthetic pigments and polyphosphate granules, and a nonlamellar ccntroplasm, in which the nucleic material is dispersed. The usual cyanophycean organelles, as well as the different vacuoles and granules, with the exception of the formed bodies, are missing. Approximately 10% of the cells sliows a peculiar homogeneous area at one tip, the nature of which is unknown. Binary fission of the organism is mentioned. Since this cyanelle has not yet been classified, we name it Skujapelta nuda nov. gen., nov. sp.; and because of its structural peculiarities we find it necessary to create a new family for it, Skujapeltaceae in the order Chroococcales.     

Observations on cellular structures of Porphyridium cruentum

The cellular structure of Porphyridium cruentum was studied with both light and electron microscope. The photosynthetic plastid in this red alga was found to be structurally similar to that in the Chlorophyceae and higher green plants. The phycobilins, as well as the chlorophyll, seem to be associated with the lamellae of the plastid. The pyrenoid, a region of low lamellar density, contains no tubules, and does not appear to function in synthesis or storage of reserve material. Grains of floridean starch are located in the cytoplasm, outside the plastid. Typical mitochondrial organelles were not observed. The nucleus is eccentric, and contains a nucleolus located on the inner face of the nucleus, nearest the plastid. The schedule for staining the nucleus is given in detail. Other cell structures (sheath, dictyosomes, etc.) are described. Growing cells in light of intensity leads to disruption of the parallel arrangement of the lamellar characteristic of cells grown in moderate light.     

Iron Deficiency in the Blue-Green Alga Anacystis nidulans: Changes in Pigmentation and Photosynthesis

Phycocyanin-free photosynthetic lamellae (PSI-particles) were prepared from Anacystis nidulans, grown in complete and iron-deficient media. French press treatment and fractionated centrifugation were used. Absorption studies of the particles revealed an iron deficiency-induced shift of the main red chlorophyll a absorption peak from 679 to 673 nm as reported before for whole cells. The shift may reflect a changed distribution between different chlorophyll a forms. Action spectra for photo-oxidation of mammalian cytochrome c with photosynthetic lamellae revealed an iron deficiency-induced shift, corresponding to that found in the absorption spectra. As photo-oxidation of cytochrome c is mediated by PSI, it is believed that chlorophyll a also after the shift towards shorter wavelengths, is active in PSI. A decreased photosynthetic capacity of PSI, due to iron deficiency, was shown by time course studies of photosynthetic oxygen evolution, by photo-oxidation studies of P700 and mammalian cytochrome c, by photo-reduction studies of NADP and by combined studies of light-induced and chemical oxidation of P700. The ration chlorophyll a/700 was also determined for whole cells, lyophilized cells and PSI-particles. Iron deficiency caused an increased ratio in all studied fractions. The results of this work imply that energy is transferred with less efficiency within the photosynthetic units of PSI in iron-deficient A. nidulans than in iron-supplied algae.     

CHLOROPLAST SPECIALIZATION IN DICOTYLEDONS POSSESSING THE C4-DICARBOXYLIC ACID PATHWAY OF PHOTOSYNTHETIC CO2 FIXATION

The C₄-dicarboxylic-acid pathway of photosynthetic CO₂ fixation found in tropical grasses has recently been demonstrated in members of the Amaranthaceae and Chenopodiaceae. In the tropical grasses this CO₂-fixation pathway is correlated with specialized leaf anatomy and chloroplast structure. This investigation was undertaken to determine if leaf cells of some representatives of these other families had structural features similar to those of tropical grasses. The leaf anatomy of Amaranthus edulis and a variety of Atriplex species is very similar and it resembles that of grasses such as sugar cane. Prominent bundle sheaths are surrounded by a layer of palisade cells. Bundle-sheath cells of Am. edulis have large chloroplasts containing much starch, but the chloroplasts have grana. The palisade cells have much smaller chloroplasts containing very little starch. The bundle-sheath cell chloroplasts of At. lentiformis have grana, their profiles tend to be ovoid, and they contain abundant starch grains. The palisade cell chloroplasts contain little starch and their profiles are discoid. The bundle-sheath cells of both species contain mitochondria which are much larger than those in the palisade cells. The chloroplasts in both types of cells in both species have a highly developed peripheral reticulum. This reticulum is composed of anastomosing tubules which are contiguous with the inner plastid membrane. The leaf anatomy and cell ultrastructure of these dicots are similar to those of the tropical grasses possessing this new photosynthetic carbon-fixation pathway. These morphological features are interpreted as adaptations for the rapid transport of precursors and end products of photosynthesis. A hypothesis is presented stating that the unique morphological and biochemical characters of these plants represent adaptations for efficient and rapid carbon fixation in environments where water stress frequently limits photosynthesis.     

DEVELOPMENT OF THE DIMORPHIC CHLOROPLASTS OF SUGAR CANE

The vascular bundle sheath cells of sugar cane contain starch-storing chloroplasts lacking grana, whereas the adjacent mesophyll cells contain chloroplasts which store very little starch and possess abundant grana. This study was undertaken to determine the ontogeny of these dimorphic chloroplasts. Proplastids in the two cell types in the meristematic region of light-grown leaves cannot be distinguished morphologically. Bundle sheath cell chloroplasts in tissue with 50% of its future chlorophyll possess grana consisting of 2-8 thylakoids/granum. Mesophyll cell chloroplasts of the same age have better developed grana and large, well structured prolamellar bodies. A few grana are still present in bundle sheath cell chloroplasts when the leaf tissue has 75% of its eventual chlorophyll, and prolamellar bodies are also found in mesophyll cell chloroplasts at this stage. The two cell layers in mature dark-grown leaves contain morphologically distinct etio-plasts. The response of these two plastids to light treatment also differs. Plastids in tissue treated with light for short periods exhibit protrusions resembling mitochondria. Plastids in bundle sheath cells of dark-grown leaves do not go through a grana-forming stage. It is concluded that the structure of the specialized chloroplasts in bundle sheath cells of sugar cane is a result of reduction, and that the development of chloroplast dimorphism is related in some way to leaf cell differentiation.     

CYTOLOGY OF BLUE-GREEN ALGAE. I. THE CELLS OF SYMPLOCA MUSCORUM

Pankratz , H. S., and C. C. Bowen . (Iowa State U., Ames.) Cytology of blue-green algae. I. The cells of Symploca muscorum . Amer. Jour. Bot. 50(4): 387–399. Illus. 1963.—The cellular morphology of Symploca muscorum is described, based upon electron micrographs utilizing improved techniques of specimen preparation. Except for a limiting plasma membrane, ribosomes, and Feulgen-positive chromatin, the cells have little resemblance to those of higher organisms. The longitudinal components of the cellular envelope consist of a 200–300 mμ fibrous sheath and a complex inner investment about 35 mμ thick which includes at least 3 distinctly layered wall elements in addition to the typical 7-mμ unit membrane forming the plasma membrane. A row of very small elongate “pores” pierce the inner investment on each side of, and immediately adjacent to, the junction of the longitudinal walls and the crosswalls. Crosswalls vary in thickness from 3 to 20 mμ, depending upon their age, and arise as elaborations of the inner layers of the longitudinal inner investment. The photosynthetic lamellar component of the cytoplasm consists of flattened sacs formed from unit membranes. The lamellae are concentrated in the peripheral region of the cell and usually are parallel to the longitudinal wall. These often extend from one crosswall to the next but, except for a few cases, are not continuous with the plasma membrane at either end. The Feulgen-positive nucleoplasm appears as an anastomosing system of lightstaining regions containing fibrils 2–5 mμ in diameter. The morphology and interrelationship of a number of other cellular elements are described: (1) structured granules range up to 0.5μ in diameter and occur near crosswalls; (2) polyhedral bodies, 0.2–0.5μ in diameter, are closely associated with the nucleoplasm; (3) “cylindrical bodies” characteristically consist of 2 concentric cylinders, are about 13 mμ in diameter and up to lμ in length; (4) “α granules” are spherical or somewhat elongate elements about 30 mμ in diameter and characteristically associated with the photosynthetic lamellae and structured granules; (5) “β granules” are spherical, highly osmiophilic granules which range from 30 to 90 mμ in diameter; (6) ribosomes, 10–15 mμ, in diameter, are most numerous near the nucleoplasm; (7) plasmodesms penetrate the crosswalls between adjacent cells. The cells of this organism can best be described as being in a “steady state” of division, and there is no evidence of any kind of organized distribution of the nucleoplasm to daughter cells during the constant progress of cytokinesis.     

Ultrastructure of leaves in C4 Cyperus iria and C3 Carex siderosticta

The ultrastructural aspects ofCyperus iria leaves showing the C₄ syndrome and the typical C₃ species,Carex siderosticta, in the Cyperaceae family were examined.C. iria exhibited the chlorocyperoid type, showing an unusual Kranz structure with vascular bundles completely surrounded by two bundle sheaths. The cellular components of the inner Kranz bundle sheath cells were similar to those found in the NADP-ME C₄ subtype, having centrifugally arranged chloroplasts with greatly reduced grana and numerous starch grains. Their chloroplasts contained convoluted thyla-koids and a weakly-developed peripheral reticulum, although it was extensive mostly in mesophyll cell chloroplasts. The outer mestome bundle sheath layer was sclerenchymatous and generally devoid of organelles, but had unevenly thickened walls. Suberized lamellae were present on its cell walls, and they became polylamellate when traversed by plasmodesmata. Mesophyll cell chloroplasts showed well-stacked grana with small starch grains. InC. siderosticta, vascular bundles were surrounded by the inner mestome sheath and the outer parenchymatous bundle sheath with intercellular spaces. The mestome sheath cells degraded in their early development and remained in a collapsed state, although the suberized lamellae retained polylamellate features. Plastids with a crystalline structure, sometimes membrane-bounded, were found in the epidermal cells. The close interveinal distance was 35–50 μm inC. iria, whereas it was 157–218 μm inC. siderosticta. These ultrastructural characteristics were discussed in relation to their photosynthetic functions.     

玉米叶肉细胞和维管束鞘细胞中光合产物的分析

玉米苗照光后,叶肉细胞和维管束鞘细胞大量积累淀粉和可溶性糖(包括蔗糖),其中淀粉95％以上在维管束鞘细胞中。阻断光合产物输出时,两类细胞中蔗糖和淀粉积累都显著增加。离体维管束鞘细胞也能合成蔗糖。离体玉米叶内原生质体饲喂NaH~(14)CO_3并照光后,通常90％以上的~(14)C参入到有机酸和氨基酸中,3～10％参入糖和淀粉中。玉米叶肉原生质体具有直接利用CO_2合成碳水化合物的能力。