Wayne R. Fagerberg

Exposure to low levels of photosynthetically active radiation induces rapid increases in palisade cell chloroplast volume and thylakoid surface area in sunflower (Helianthus annuus L.).

SummarySudden changes in photoactive radiation (PAR) (wavelength, 400–700 nm) induces rapid surface area changes in chloroplast thylakoid membranes. Although this response may have important photo-acclimative functions for the plant, little is known about the mechanisms by which changes in irradiance are detected or how thylakoid membranes actually increase or decrease surface area. Knowledge of the time required for significant changes in thylakoid area would help eliminate or support several possible mechanisms that may be involved in this aspect of photo-acclimation in plants. Leaf tissues were acclimated to a PAR of 500 μmol quanta per m2 per s then exposed to low irradiance (PAR, 50 μmol quanta per m2 per s) and sampled at 5, 15, 30, and 60 min post exposure. Tissue and cell structure were quantified and results showed a significant increase in the surface-to-volume ratio and surface area per unit of standard leaf volume for both appressed and nonappressed thylakoids within 5 min of exposure to low irradiance. On the basis of the ratios of appressed to nonappressed thylakoids, the surface area of the nonappressed thylakoids was found to increase faster than that of the appressed thylakoids throughout the sample period. The portion of the appressed thylakoids in contact with the stroma was defined as margin thylakoids. Margin thylakoid surface-to-volume ratio did not change relative to the high-irradiance control during the sample period but did remain significantly lower than the low-irradiance control during the sample period. The ratio of appressed to margin thylakoids indicated a broadening and shortening of the appressed thylakoid stack within the first 5 min of low-irradiance exposure. The rapidity of the shade response indicates that the early events in this response probably do not directly involve gene activation pathways.

Evidence for Bicarbonate Active Transport in Elodea Nuttallii

In aquatic wastewater treatment systems, submerged aquatic macrophytes can be exposed to high oxygen and low CT (see abbreviations below) concentrations which are detrimentally conducive to photorespiration. Many macrophytes adapt to such conditions by entering a low photorespiratory state which involves a decrease in the CO2 compensation point (Γ) and consequently an increase In the affinity (Km) for CO2. Two seChapaute Inducible enzyme mechanisms are utilized (1,2). Both utilize HCO2 -, which can be the only available inorganic carbon species, and both promote carbcxylatlon over oxygenation at RUBISCO. Hydrilla synthesizes PEPcase which fixes HCO3 - into C4 acids which can then be decarboxylated as a CO2 source for RUBISCO (2). Conversely, Myriophyllum synthesizes CA which is thought to be involved in a HCO3 - active transport system (1). We have grown Elodea nuttallii in aquatic treatment systems; the macrophyte exhibits low photorespiratory and HCO33- utilization characteristics (3)Γ=44 μL L-1, Km [C2]=98μ M, RUBISCO/PEPcase=6.6, CA=14 EU mg Chl-1, acid and alkaline banding, and 1:1 HCO3 - utilization: OH- production stolchlometries. The purpose of this study was to determine if E. nuttallii employs a HCO3 - active transport system as part of its adaptive response to photorespiratory conditions. The data suggests the E. nuttallii possesses a HOO3 - proton symport to accumulate CT.

Comprehensive histological and immunological studies reveal a novel glycoprotein hormone and thyrostimulin expressing proto-glycotrope in the sea lamprey pituitary

In the adenohypophysis (anterior pituitary) of all gnathostomes, there are six tropic cell types: corticotropes, melanotropes, somatotropes, lactotropes, gonadotropes and thyrotropes; each cell type produces specific tropic hormones. In contrast, we report in this study that there are only four tropic cell types in the sea lamprey (Petromyzon marinus) adenohypophysis. We specifically focused on the cell types that produce the glycoprotein hormones (GpHs). The gnathostome adenohypophyseal GpHs are follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyroid-stimulating hormone (TSH), and thyrostimulin. However, lampreys only have two heterodimeric adenohypophyseal GpHs consisting of unique α and β subunits, lamprey GpH (lGpH) (lGpA2/lGpHβ) and thyrostimulin (lGpA2/lGpB5). We used an array of histological techniques to determine the (co)-localization and (co)-expression of the lGpH and thyrostimulin subunits in the lamprey adenohypophysis at different life stages (larval, parasitic, adult) and to identify their synthesizing cell(s). The thyrostimulin subunits (lGpA2/lGpB5) were co-expressed throughout the adenohypophysis (larval, parasitic, and adult), while the GpH β-subunit (lGpHβ) exhibited localized distribution (adult); all three subunits were co-localized and co-expressed, suggesting that both GpHs are synthesized in the same cells, novel proto-glycotropes, in specific adenohypophyseal regions at different life stages. In summary, we provide the first comprehensive study using histology, transmission electron microscopy, in situ hybridization and immunohistochemistry that strongly supports further evidence for four definitive adenohypophyseal cell types in the lamprey, including: corticotropes, somatotropes, melanotropes, and the first identification of a novel proto-glycotrope. In addition, our studies show that there is developmental and region-specific co-localization and co-expression of lGpH and thyrostimulin in the lamprey adenohypophysis.

The Development and Potential Roles of Cell-Wall Trabeculae in Caulerpa Mexicana (Chlorophyta)

Siphonous plants represent an alternate scheme to the way most macroscopic plants are constructed. They are single, often large (1–2 m), sometimes morphologically complex, multinucleate (coenocytic) cells where the whole of the cytoplasm is a continuum. Caulerpa mexicana Sond. ex Kütz. is a siphonous tropical marine green alga characterized by four morphologically distinct regions and, as with other members of the genus, by the presence of a dense network of anastomosing cylindrical cell wall in growths called trabeculae. Based on the results of this study, we propose several roles for trabeculae: (i) They are structural components, which likely add some small amount of support in compression but add considerable strength in tension. (ii) As extensions of the cell wall and plasma membrane, they act as diffusion channels from the cell exterior to the interior cytoplasm. It is possible that trabeculae also play a role in determining cell shape through developmental positioning and placement patterns, thus facilitating the diverse shapes found in the morphologically distinct regions of Caulerpa sp.

Below-ambient levels of UV induce chloroplast structural change and alter starch metabolism.

Summary.Electromagnetic radiation (EMR) in the 400–700 nm bandwidth of photosynthetically active radiation (PAR) has been established as an important source of energy for photosynthesis and environmental signals regulating many aspects of green-plant life. Above-ambient levels of UV-B radiation (290–320 nm) under high-PAR conditions have been shown to elicit responses in chloroplasts of Brassica napus similar to those of chloroplasts at low-PAR exposure (W. Fagerberg and J. Bornman, Physiol. Plant. 101: 833–844, 1997). The question arises as to whether UV at normal levels can also evoke similar responses. Here we provide evidence that even below-ambient levels of UV-B (1/28 ambient; Durham, N.H., U.S.A., 1200 hours, March) were capable of inducing an increase in thylakoid surface area relative to the chloroplast volume typical of a low-PAR response (shade response) in sunflowers. This response occurred even though leaves were concurrently exposed to PAR levels that normally induce a “sun” or high-PAR response in the absence of UV-B. Subambient levels of UV-B were also associated with a decrease in chloroplast and starch volume. Exposure to levels of UV-A 1/10 of ambient appeared to enhance the high-PAR response of the chloroplast, characterized by an increase in the amounts of stored starch, an increase in chloroplast volume density ratio values, and a decrease in thylakoid surface area density ratios relative to the high-light controls. These effects were opposite to those seen in UV-B-exposed tissue. In a general sense, subambient levels of UV-B evoked a response similar to that elicited by low-PAR irradiance, while subambient UV-A elicited responses similar to those typical of high-PAR irradiance. The fact that below-ambient levels of UV altered a normal chloroplast structural response to PAR provides evidence that UV may be an important environmental signal for plants.

BIOADHESION IN CAULERPA MEXICANA (CHLOROPHYTA): RHIZOID-SUBSTRATE ADHESION†

The attachment of the psammophytic alga Caulerpa mexicana Sond. ex Kütz., a coenocytic green alga, to crushed CaCO3 particles was examined utilizing the scanning electron microscope and fluorescently tagged antivitronectin antibodies. Plants attached to the substrate through morphologically variable tubular rhizoidal extensions that grew from the stolon. In this study, we describe two means of attachment: (i) the rhizoid attachment to limestone gravel by thigmoconstriction, where tubular extensions of the rhizoid wrapped tightly around the substrate and changed morphology to fit tightly into crevices in the limestone, and (ii) through adhesion pads that formed in contact with the limestone granules. Flattened rhizoidal pads were observed to secrete a fibrillar material that contained vitronectin‐like proteins identified through immunolocialization and that facilitated binding of the rhizoid to the substrate.

Survey for the presence of a vitronectin-like protein in micro- and macroalgae and cyanobacteria

Vitronectin (Vn) is a glycoprotein that serves a wide variety of roles in multicellular organisms. It was first identified in multicellular animals but has also been isolated from land plants and some algae, where it appears to serve as an extracellular adhesive molecule. In order to further elucidate presence and localization of a Vn–like protein and its potential role in algae, we surveyed different morphological regions of 24 species of macro‐ and microalgae and three species of cyanobacteria for the presence of a Vn–like protein. Vn–like proteins were not detected in any of the species of cyanobacteria, microalgae or Rhodophyta investigated. They were detected in several species of the Phaeophyceae and Chlorophyta where their localization was limited to the holdfast and rhizoids of these organisms, respectively. Detection of a Vn–like protein (between 0.0125 and 0.097 μg · μL−1 protein extract) was therefore limited to locations associated with substrate attachment.

Changes in Thylakoid Surface Area when Shade Acclimated Helianthus Annuus L. Chloroplasts are Exposed to High P.F.D.

Mature mesophyll cells in sunflower (Helianthus annuus L.) are capable of dynamic alterations in cell and tissue structure in response to changes in light environment (1,2) and as a normal part of diel behavior (3). Many of these rapid alteration in cell structure are related to changes in irradiance levels and are presumably adaptive (1.2).