Root Cell Ultrastructure in Developing Aerenchyma Tissue of Three Wetland Species

Patterns of root cortex cell development and ultrastructurewere analysed in Sagittaria lancifolia L., Thalia geniculataL. and Pontederia cordata L. using scanning and transmissionelectron microscopy (SEM, TEM). In all three species, cortexcells were arranged in radial columns extending from the endodermisto the hypodermis/epidermis. During gas space formation, thecortex cells elongated parallel to the root radius and shrankin the plane perpendicular to the radius leaving long and thinrows of cortex cells extending from the endodermis to the epidermis.Although the cortex cells appeared collapsed in tissue withwell-developed gas spaces, TEM revealed that the cortical cellsas well as the epidermal cells maintained intact membranes andmany normal organelles. Formation of root cortex tissue withwell-developed gas spaces does not require cell death in thesespecies. Living cortex cells in root tissue with mature gasspaces could provide a symplastic pathway for transport betweenthe root stele and the living epidermal cells. Copyright 2000Annals of Botany Company Sagittaria lancifolia, Thalia geniculata, Pontederia cordata, aerenchyma, root, wetland, development     

Fine needle aspiration of Actinomyces infection of the breast. A novel presentation of thoracopleural actinomycosis.

A case of Actinomyces infection of the breast secondary to thoracopleural disease was initially diagnosed by fine needle aspiration biopsy. The tender, hard, swollen left breast was clinically suspected of harboring an inflammatory carcinoma. Cell block sections of the aspirate showed polymorphonuclear leukocytes surrounding a typical "sulphur granule" composed of branching filaments. The diagnosis was confirmed by culture of material obtained at subsequent surgery.     

Light effects on leaf development and photosynthetic capacity of Hydrocotyle bonariensis Lam.

Rates of net CO₂ uptake were examined in developing leaves of Hydrocotyle bonariensis. Leaves that developed under high photosynthetically active radiation (48 mol m^-2 day^-1 PAR) were smaller, thicker, and reached maximum size sooner than did leaves that developed under low PAR (4.8 mol m^-2 day^-1). Maximum net CO₂ uptake rates were reached after 5 to 6 days expansion for both the low and the high PAR leaves. Leaves grown at high PAR had higher maximum photosynthetic rates and a higher PAR required for light saturation but showed a more rapid decline in rate with age than did low PAR leaves. To assess the basis for the difference observed in photosynthetic rates, CO₂ diffusion conductances and the mesophyll surface available for CO₂ absorption were examined for mature leaves. Stomatal conductance was the largest conductance in all treatments and did not vary appreciably with growth PAR. Mesophyll conductance progressively increased with growth PAR (up to 48 mol m^-2 day^-1) as did the mesophyll surface area per unit leaf area, but the cellular conductance exhibited most of its increase at low PAR (up to 4.8 mol m^-2 day^-1).     

Changes in cell structure during the formation of root aerenchyma inSAGITTARIA LANCIFOLIA (Alismataceae)

In many wetland species, root aerenchyma is produced by the predictable collapse of root cortex cells, indicating a programmed cell death (PCD). The objective of this study was to characterize the cellular changes that accompany this PCD in the marsh species Sagittaria lancifolia. Structural changes in membranes and organelles were examined during development of root cortex cells to compare with previous examples of PCD. The organization of cortical microtubule (CMT) arrays in root cells from S. lancifolia was also evaluated as a possible predictor of cell lysis. Nuclear fragmentation and condensation were the earliest changes observed in cells undergoing lysis. Breakdown of the tonoplast and other organelles and disruption of the plasma membrane followed. After loss of cytoplasm, cells collapsed to form gas spaces. These results were compared to collapse of root cortical cells of Zea mays and Oryza sativa during aerenchyma development. Changes in the appearance of the cytoplasm of all three species were similar at later stages of aerenchyma development. The relative timing of disintegration of the tonoplast and middle lamella appeared to differ among the three species. Changes in the organization of CMT arrays did not appear to be a predictor of PCD in S. lancifolia. Aerenchyma production in plants involves a type of PCD that is morphologically distinct from PCD described from many animals.     

HIGH CARBON DIOXIDE CONCENTRATIONS IN AERENCHYMA OF TYPHA LATIFOLIA

Diurnal and seasonal patterns of CO₂ concentration ([CO₂]) in leaf gas spaces were measured to better understand the relationship of sediment-derived CO₂ to photosynthesis in the emergent wetland species, Typha latifolia L. (cattail). Leaf [CO₂] was above 2,000 μl/liter at dawn on all but the first sampling date. At all sampling dates, leaf [CO₂] declined to near atmospheric [CO₂] at midday and rose to well above atmospheric [CO₂] in the late afternoon. The maximum leaf [CO₂] varied with sampling date and was over 18 times atmospheric levels (over 6,300 μl/liter) in August. Based on measurement of photon flux density and temperature, the diurnal pattern in leaf [CO₂] may be generally controlled by expected photosynthetic rates. It is hypothesized that seasonal variation in leaf [CO₂] may be a function of variation in microbial (soil) respiration. Using dye and slight pressurization, it was confirmed that gas spaces in rhizomes were interconnected with the gas spaces in leaves through the rhizome-shoot transition. From anatomical measurements, it was also estimated that over 50% of total leaf volume was occupied by gas spaces and that most of the total gas-space volume in plants was in the shoot. Photosynthetic rate in C3 plants, like cattail, can increase with increasing [CO₂] under natural conditions. For this reason, cattail and other emergent wetland plants possessing continuous gas-space pathways appear to have a significant carbon supplement as compared to other C3 plants growing in well-aerated soils.     

Nutrient Influences on Leaf Photosynthesis: EFFECTS OF NITROGEN, PHOSPHORUS, AND POTASSIUM FOR GOSSYPIUM HIRSUTUM L

The net rate of CO₂ uptake for leaves of Gossypium hirsutum L. was reduced when the plants were grown at low concentrations of NO₃^-, PO₄^2-, or K⁺. The water vapor conductance was relatively constant for all nutrient levels, indicating little effect on stomatal response. Although leaves under nutrient stress tended to be lower in chlorophyll and thinner, the ratio of mesophyll surface area to leaf area did not change appreciably. Thus, the reduction in CO₂ uptake rate at low nutrient levels was due to a decrease in the CO₂ conductance expressed per unit mesophyll cell wall area (g^cell_CO2). The use of g^cell_CO2 and nutrient levels expressed per unit of mesophyll cell wall provides a new means of assessing nutrient effects on CO₂ uptake of leaves.     

Salinity Effects on Photosynthesis and Growth in Alternanthera philoxeroides (Mart.) Griseb

Alternanthera philoxeroides, alligator weed, was grown at five different NaCl concentrations to determine the effect of salinity on factors related to the net rate of CO₂ uptake (P_n). Over the range of 0 to 400 millimolar NaCl, P_n declined 51%. Stomatal conductance declined in parallel with P_n and as a result there was no reduction in intercellular CO₂ concentration and therefore no reduction in the amount of CO₂ available for photosynthesis. The CO₂ compensation point did not change with salt stress. Increases in leaf thickness tended to compensate slightly for the negative effects of salinity on leaf cell metabolism, at least in relation to P_n. On a mesophyll cell area basis, soluble protein was relatively constant in leaves developed at 100 to 400 millimolar NaCl while total chlorophyll decreased at all salinities. Dry weight production and P_n were closely correlated in alligator weed grown at different salinities. Plants produced less leaf area per unit dry weight as salinity increased, which may aid in water conservation.     

Environmental effects of ozone depletion and its interactions with climate change: progress report, 2011

The parties to the Montreal Protocol are informed by three panels of experts. One of these is the Environmental Effects Assessment Panel (EEAP), which deals with two focal issues. The first focus is the effects of increased UV radiation on human health, animals, plants, biogeochemistry, air quality, and materials. The second focus is on interactions between UV radiation and global climate change and how these may affect humans and the environment. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than believed previously. As a result of this, human health and environmental problems will be longer-lasting and more regionally variable. Like the other panels, the EEAP produces a detailed report every four years; the most recent was published in 2010 (Photochem. Photobiol. Sci., 2011, 10, 173-300). In the years in between, the EEAP produces less detailed and shorter progress reports, which highlight and assess the significance of developments in key areas of importance to the parties. The next full quadrennial report will be published in 2014-2015.     

PHOTOSYNTHETIC RATE AND MESOPHYLL SURFACE AREA IN EXPANDING LEAVES OF ALTERNANTHERA PHILOXEROIDES GROWN AT TWO LIGHT LEVELS

Leaves of Alternanthera philoxeroides, alligator weed, developed at a photosynthetic photon flux density (PPFD, light energy at wavelengths of 400 to 700 nm) of 790 μmol sec⁻¹ m⁻² (High Light) had less surface area, were thicker, had a higher maximum P_n (net rate of CO₂ uptake), and required a higher PPFD for saturation of P_n, than leaves developed at 160 μmol sec⁻¹ m⁻² (Low Light). Mesophyll thickness at Low Light was within 19% of maximum 2 days after emergence but at High Light, thickness increased 79% between 2 and 16 days after leaf emergence. The ratio of mesophyll surface area to leaf surface area decreased during development in both light treatments; the ratio, however, was over 70% greater in fully expanded High Light leaves than in Low Light leaves. Maximum P_n expressed on a leaf surface area basis was 158% greater in High Light leaves than in Low Light leaves, but P_n was only 58% greater when expressed on a mesophyll surface area basis. It was estimated that fully expanded High Light leaves fixed 72% more CO₂ per leaf (P_n expressed per unit surface area times the total surface area per leaf) than fully expanded Low Light leaves when P_n was measured at the PPFD leaves expanded under. Both High and Low Light leaves would fix about the same amount of CO₂ per leaf when P_n was measured at 160 μmol sec⁻¹ m⁻² because the larger surface area of the Low Light leaves offset small differences in P_n.