William P. Sharp

Seed Coat Characters of Some American Myrtinae (Myrtaceae): Psidium and Related Genera

Psidium (Myrtaceae: Myrtinae) has long been one of the most difficult genera of American Myrtaceae to define. We here describe and illustrate, with SEM photographs, four char- acteristics of seed coats that help to distinguish Psidium from its American relatives: 1) seed coat surface dull or rough with an external layer of pulpy tissue; 2) hard portion of outer seed coat usually 8-30 cells thick at narrowest point; 3) prevalent shape of cells in the outer seed coat elongate; and 4) lumen of cells in the outer seed coat tending to be less than 1/2 as wide as the cell. Recognition of these characters allows extraction of certain anomalous groups from Psidium.

Gross morphological changes in thylakoid membrane structure are associated with photosystem I deletion in Synechocystis sp. PCC 6803

Cells of Synechocystis sp. PCC 6803 lacking photosystem I (PSI-less) and containing only photosystem II (PSII) or lacking both photosystems I and II (PSI/PSII-less) were compared to wild type (WT) cells to investigate the role of the photosystems in the architecture, structure, and number of thylakoid membranes. All cells were grown at 0.5μmol photons m(-2)s(-1). The lumen of the thylakoid membranes of the WT cells grown at this low light intensity were inflated compared to cells grown at higher light intensity. Tubular as well as sheet-like thylakoid membranes were found in the PSI-less strain at all stages of development with organized regular arrays of phycobilisomes on the surface of the thylakoid membranes. Tubular structures were also found in the PSI/PSII-less strain, but these were smaller in diameter to those found in the PSI-less strain with what appeared to be a different internal structure and were less common. There were fewer and smaller thylakoid membrane sheets in the double mutant and the phycobilisomes were found on the surface in more disordered arrays. These differences in thylakoid membrane structure most likely reflect the altered composition of photosynthetic particles and distribution of other integral membrane proteins and their interaction with the lipid bilayer. These results suggest an important role for the presence of PSII in the formation of the highly ordered tubular structures.

Element absorption and hydration potential of polyacrylamide gels

Abstract Element absorption and hydration potential (HP) of two polyacrylamide gels (Aa and Bb) were studied after incubation in Hoaglands nutrient solution concentrations of either 2X, 1X, 0.5X, 0.25X, 0.125X, or 0X (deionized water). Element absorption was observed and analyzed by making transects from the gel granule surface to center on a Phillips CM12S scanning transmission electron microscope (STEM) equipped with an EDAX 9800 plus EDS unit for x‐ray micro analysis. Thick sections were cut on dry glass knives using an RMC MT6000 ultramicrotome. Surface analysis of bulk specimens was also made with an AMR 1000A scanning electron microscope plus PGT1000 EDS unit. Overall, gel HP decreased curvilinearly as solution concentration increased linearly; however, HP was generally higher for gel Bb than for Aa. Surface analysis of both gels compounds (1X concentration) revealed the presence Ca, Zn, and K. Additionally, Mn, S, and P in trace amounts, and Fe were found at the surface of gel Aa. Furthermore, Fe ...

LIGHT-HARVESTING COMPLEX AF'OPROTEINS IN CYTOPLASMIC VACUOLES IN CHLAMYDOMONAS REINHARDTII (CHLOROPHYTA)1

Cells of Chlamydomonas reinhardtii Dangeard strain cw15arg7A contain electron‐opaque material, often in the form of large granules, within cytoplasmic vacuoles. Immunoelectron microscopy with antibodies to polypeptide 11, a component of the major light‐harvesting chlorophyll (Chl) a/b‐protein complex (LHCII,) of thylakoid membranes, revealed the presence of LHCII Polypeptides within the chloroplast and in vacuolar material in cells grown in the light. Vacuolar material was also heavily immunodecorated in dark‐grown cells that did not synthesize Chl. Accumulation of LHCII polypeptides was further studied in greening and light‐grown cells of a pale green mutant, deficient in LHCII, that was derived from cu15arg7A by insertional mutagenesis. Light‐grown cells of this mutant strain contained relatively few thylakoid membranes and synthesized LHCII polypeptides at a low rate. However, cytoplasmic vacuoles were immunoreactive. Appearance of mature‐sized LHCII polypeptides in vacuoles suggested that these proteins were partially translocated across the envelope but not retained by the chloroplast without assembly of LHCII.

Manganese and iron encrustations and other features ofPlanctomyces crassus Hortobágyi 1965, morphotype Ib of theBlastocaulis-Planctomyces group of budding and appendaged bacteria, examined by electron microscopy and X-ray micro-analysis

Water samples collected in August, 1980, from a pond in Budapest, Hungary, have permitted transmission and scanning electron microscopic observations to be made ofPlanctomyces crassus Hortobágyi 1965, which—to remain taxonomically noncommittal—we designated as morphotype Ib of theBlastocaulis-Planctomyces group of appendaged and budding bacteria. The detailed cell morphology of morphotype Ib (cellular shape, size and distribution pattern of crateriform structures, pili, spires) was similar to that of morphotype Ia,Planctomyces bekefii Gimesi 1924. The major appendage—a seemingly tubular, multifibrillar stalk—differed somewhat from the stalk of morphotype Ia, in that the morphotype Ib stalk was generally shorter than the morphotype Ia stalk, was tapered (the morphotype Ia stalk was uniformly cylindrical), and apparently lacked the organizing matrix of the morphotype Ia stalk. Energy-dispersive X-ray spectroscopy of the metallic-oxide encrustations of morphotype Ib rosettes revealed manganese and iron to be the predominant elements present. Moreover, localized differences were found in the relative amounts of the two elements deposited in different rosettes and at different loci on the same rosette.

Metallic-Oxide encrustations of the nonprosthecate stalks of naturally occurring populations ofPlanctomyces bekefii

Naturally occurring metallic-oxide encrustations of the multifibrillar stalks of morphotype Ia (Planctomyces bekefii) of theBlastocaulis-Planctomyces group of budding and nonprosthecately appendaged prokaryotes from two sources-a pond in Budapest, Hungary (containing topotypical material) and Gebharts Teich, a fishpond in Austria-have been examined by energy-dispersive X-ray spectroscopy. Some rosettes of morphotype Ib (Planctomyces crassus) also occurred in the Budapest pond; only morphotype Ia was found in Gebharts Teich. Manganese was the major metallic element in the morphotype Ia stalk encrustations from the Budapest pond; iron was not detected. However, morphotype Ib rosettes occurring in the same Budapest pond sampes contained both manganese and iron in their stalk encrustations. Both iron and manganese were present in the morphotype Ia stalk encrustation of rosettes from Gebharts Teich.

Hybridization betweenPsidium guajava andP. guineense (Myrtaceae)

Psidium guajava andP. guineense are characterized, illustrated and contrasted. Population samples ofPsidium guajava andP. guineense and apparent hybrids were collected from four localities: two in Mexico, one in Honduras, and one in Argentina. Seven morphological characters, one micromorphological (stomatal density), and one chemical character (presence or absence of myricetin) that distinguish the parent species were found to be useful in the evaluation of specimens and population variation. Results were consistent with the hypothesis that hybridization occurs between these species, but in three localities it may not go beyond Fl ’s. Back crossing between hybrids andP. guajava was not detected at any locality.RésuméSe recolectaron muestras de poblaciones dePsidium guajava, P. guineense y posibles híbridos en cuatro localidades: dos en México, una en Honduras, una en Argentina. Se encontraron útiles en la evaluación de especímenes y variación de poblaciones siete características morfológicas, una micromorfológica (densidad de stomata), y una química (presencia o ausencia de myricetin) que distinguen las especies padres. Los resultados indican que hibridación ocurre entre las especies, pero en tres localidades es posible que hay solamente Fl ’s. No se detectaron cruces entre híbridos yP. guajava en ninguna localidad.

Freeze Fracture and Freeze Etching

Freeze fracture depends on the property of frozen tissues or cells, when cracked open, to split along the hydrophobic interior of membranes, thus revealing broad panoramas of membrane interior. These large panoramas reveal the three-dimensional contours of membranes making the methods well suited to studying changes in membrane architecture. Freshly split membrane faces are visualized by platinum or tungsten shadowing and carbon backing to form a replica that is then cleaned of tissue and imaged by TEM. Etching, i.e., removal of ice from the frozen fractured specimen by sublimation prior to shadowing, can also reveal the true surfaces of the membrane as well as the extracellular matrix and cytoskeletal networks that contact the membranes. Since the resolution of detail in the metal replicas formed is 1-2 nm, these methods can also be used to visualize macromolecules or macromolecular assemblies either in situ or displayed on a mica surface. These methods are available for either specimens that have been chemically fixed or specimens that have been rapidly frozen without chemical intervention.