Robert R. Wise

Chilling-enhanced photooxidation: The production, action and study of reactive oxygen species produced during chilling in the light

Chilling-enhanced photooxidation is the light- and oxygen-dependent bleaching of photosynthetic pigments that occurs upon the exposure of chilling-sensitive plants to temperatures below approximately 10 °C. The oxidants responsible for the bleaching are the reactive oxygen species (ROS) singlet oxygen (1O2), superoxide anion radical (O2∸,hydrogen peroxide (H2O2), the hydroxyl radical (OH·), and the monodehydroascorbate radical (MDA) which are generated by a leakage of absorbed light energy from the photosynthetic electron transport chain. Cold temperatures slow the energy-consuming Calvin-Benson Cycle enzymes more than the energy-transducing light reactions, thus causing leakage of energy to oxygen. ROS and MDA are removed, in part, by the action of antioxidant enzymes of the Halliwell/Foyer/Asada Cycle. Chloroplasts also contain high levels of both lipid- and water-soluble antioxidants that act alone or in concert with the HFA Cycle enzymes to scavenge ROS. The ability of chilling-resistant plants to maintain active HFA Cycle enzymes and adequate levels of antioxidants in the cold and light contributes to their ability to resist chilling-enhanced photooxidation. The absence of this ability in chilling-sensitive species makes them susceptible to chilling-enhanced photooxidation. Chloroplasts may reduce the generation of ROS by dissipating the absorbed energy through a number of quenching mechanisms involving zeaxanthin formation, state changes and the increased usage of reducing equivalents by other anabolic pathways found in the stroma. During chilling in the light, ROS produced in chilling-sensitive plants lower the redox potential of the chloroplast stroma to such a degree that reductively-activated regulatory enzymes of the Calvin Cycle, sedohepulose 1,7 bisphosphatase (EC 3.1.3.37) and fructose 1,6 bisphosphatase (EC 3.1.3.11), are oxidatively inhibited. This inhibition is reversible in vitro with a DTT treatment indicating that the enzymes themselves are not permanently damaged. The inhibition of SBPase and FBPase may fully explain the inhibition in whole leaf gas exchange seen upon the rewarming of chilling-sensitive plants chilled in the light. Methods for the study of ROS in chilling-enhanced photooxidation and challenges for the future are discussed.

Leaf Growth Development in Relation to Gas Exchange in Quercus marilandica Muenchh.

Summary Photosynthesis, transpiration rates and stomatal conductances were measured using a portable infra-red gas analyzer and then correlated with structural changes occurring during the development of Quercus marilandica Muenchh. leaves. Q. marilandica was found to synthesize high levels of leaf anthocyanins (0.79 ± 0.13gkg −1 fresh weight) during the period immediately following bud break. Carbon assimilation rates showed net respiration (−1.3 ± 1.6μmolm −2 s −1 ) when measured in anthocyanin-containing leaves seven days after bud break (DAB), but to be near the compensation point at 17 DAB (1.1 ± 1.4 μmol m −2 s −1 ) when most of the anthocyanins were metabolized away, but the leaves not yet fully expanded. The maximum rate (8.3 ± 2.6 μmol m −2 s −1 ) was observed in fully expanded leaves at 37 DAB and was eight-fold higher than at 17 DAB. Transpiration rates and stomatal conductances were low at 7 DAB, but then increased 250 and 160 %, respectively, at 17 DAB, but only 22 and 43 % from 17 to 37 DAB. Ultrastructural analysis showed the leaves had small intercellular air spaces and underdeveloped chloroplasts at both 7 and 17 DAB; the leaves not appearing fully mature until expansion was complete at 37 DAB. SEM images showed 7 DAB leaves to be extensively covered with trichomes on both abaxial and adaxial surfaces. The trichomes were mostly shed by 17 DAB revealing the extensive development of sto- mates. It is concluded that transpiration and stomatal conductances were controlled primarily by the boundary layer resistance associated with the trichome layer at 7 DAB and the low carbon assimilation rates seen at 17 DAB were likely a consequence of sub-optimal chloroplast function and/or limitations in CO2 uptake associated with the lack of intercellular air spaces.

Seed coat morphology and its systematic implications in Cyanea and other genera of Lobelioideae (Campanulaceae)

Recent surveys of seed coat morphology in Lobelioideae (Campanulaceae) have demonstrated the systematic utility of such data in the subfamily and led to a revision of the supraspecific classification of Lobelia. Expanding upon these studies, we examined via scanning electron microscopy 41 seed accessions, emphasizing lobelioid genera in which only one or no species had been examined. Most conformed to previously described testal patterns. However, five species of the endemic Hawaiian genus Cyanea, comprising the molecularly defined Hardyi Clade, had a unique testal pattern (here termed Type F), characterized by laterally compressed, almost linear, areoles with rounded, knob-like protuberances on the radial walls at opposite ends. This offered a convenient synapomorphy for recognition of a clade originally defined on a molecular basis. A second unique testal pattern was found in the related Hawaiian endemics Brighamia and Delissea, thus supporting their close relationship. In this type (here termed Type G), the seed coat is irregularly wrinkled (rugose), creating broad, rounded ridges that run more-or-less perpendicular to the long axis of the seed and thus to the long axis of the testal cells. Seed coat morphology also supported the monophyly of all 124 species of Hawaiian Lobelioideae and their probable derivation from Asian species of Lobelia subg. Tupa. Additional studies supported close relationships between (1) the neotropical genera Centropogon and Siphocampylus; (2) the western American genera Legenere and Downingia; and (3) Jamaican Hippobroma and Lobelia sect. Tylomium, a group endemic to the West Indies.

Juvenile Rhus glabra leaves have higher temperatures and lower gas exchange rates than mature leaves when compared in the field during periods of high irradiance.

We sought to test the hypothesis that stomatal development determines the timing of gas exchange competency, which then influences leaf temperature through transpirationally driven leaf cooling. To test this idea, daily patterns of gas exchange and leaflet temperature were obtained from leaves of two distinctively different developmental stages of smooth sumac (Rhus glabra) grown in its native habitat. Juvenile and mature leaves were also sampled for ultrastructural studies of stomatal development. When plants were sampled in May-June, the hypothesis was supported: juvenile leaflets were (for part of the day) from 1.4 to 6.0 degrees C warmer than mature leaflets and as much as 2.0 degrees C above ambient air temperature with lower stomatal conductance and photosynthetic rates than mature leaflets. When measurements were taken from July to October, no significant differences were observed, although mature leaflet gas exchange rates declined to the levels of the juvenile leaves. The gas exchange data were supported by the observations that juvenile leaves had approximately half the number of functional stomata on a leaf surface area basis as did mature leaves. It was concluded that leaf temperature and stage of leaf development in sumac are strongly linked with the higher surface temperatures observed in juvenile leaflets in the early spring possibly being involved in promoting photosynthesis and leaf expansion when air temperatures are cooler.

PARP2 Is the Predominant Poly(ADP-Ribose) Polymerase in Arabidopsis DNA Damage and Immune Responses

Poly (ADP-ribose) polymerases (PARPs) catalyze the transfer of multiple poly(ADP-ribose) units onto target proteins. Poly(ADP-ribosyl)ation plays a crucial role in a variety of cellular processes including, most prominently, auto-activation of PARP at sites of DNA breaks to activate DNA repair processes. In humans, PARP1 (the founding and most characterized member of the PARP family) accounts for more than 90% of overall cellular PARP activity in response to DNA damage. We have found that, in contrast with animals, in Arabidopsis thaliana PARP2 (At4g02390), rather than PARP1 (At2g31320), makes the greatest contribution to PARP activity and organismal viability in response to genotoxic stresses caused by bleomycin, mitomycin C or gamma-radiation. Plant PARP2 proteins carry SAP DNA binding motifs rather than the zinc finger domains common in plant and animal PARP1 proteins. PARP2 also makes stronger contributions than PARP1 to plant immune responses including restriction of pathogenic Pseudomonas syringae pv. tomato growth and reduction of infection-associated DNA double-strand break abundance. For poly(ADP-ribose) glycohydrolase (PARG) enzymes, we find that Arabidopsis PARG1 and not PARG2 is the major contributor to poly(ADP-ribose) removal from acceptor proteins. The activity or abundance of PARP2 is influenced by PARP1 and PARG1. PARP2 and PARP1 physically interact with each other, and with PARG1 and PARG2, suggesting relatively direct regulatory interactions among these mediators of the balance of poly(ADP-ribosyl)ation. As with plant PARP2, plant PARG proteins are also structurally distinct from their animal counterparts. Hence core aspects of plant poly(ADP-ribosyl)ation are mediated by substantially different enzymes than in animals, suggesting the likelihood of substantial differences in regulation.

Ultrastructure of echimyid and murid rodent spines

Aristiform spines of the rodents Niviventer fulvescens, Maxomys surifer, Hoplomys gymnurus and 17 species of Proechimys (representing both recognized subgenera and all nine species groups) were studied qualitatively using scanning electron microscopy (SEM) and quantitatively by measuring seven linear dimensions. SEM was used to examine spine tips, bases, longitudinal furrows and cross sections. Spines of the murid rodents N. fulvescens and M. surifer differed from those of the echimyid rodents H. gymnurus and Proechimys spp. in possessing a smaller base with a longer, narrower neck, scaled rather than ridged longitudinal furrows, and a solid internal core and large lacunae at the spine margins. Spines of H. gymnurus differed from those of Proechimys spp. in being considerably more robust with a stout neck at the base, an abruptly-tapering tip and a dense inner layer with a series of smaller lacunae at the spine margins. A factor analysis of spine measurements revealed major differences among N. fulvescens, M. surifer, H. gymnurus ,t heProechimys subgenus Trinomys and the nine Proechimys species groups within the subgenus Proechimys .H owever, allProechimys species groups clustered closely together. A discriminant function analysis of the nine Proechimys species groups provided generally limited discriminatory power. Although spines are distinct at the generic and subgeneric levels, spines may possess limited diagnostic structure at the level of species within the subgenus Proechimys.

Morphological Deformities in Chironomus (Chironomidae: Diptera) Larvae as Indicators of Pollution in Lake Winnebago, Wisconsin

Lake Winnebago, a large, shallow lake in east-central Wisconsin, supports substantial populations of several different chironomid species (the larvae of which inhabit bottom sediments) and has been the repository of substantial amounts of lead from non-point sources. Larval morphological characters, in particular mouthpart deformities, have been used in other systems as sensitive, but non-specific, indicators of anthropogenic pollution. Forty-eight percent of the lake fly (Chironomus spp.) larvae collected from Lake Winnebago had either a deformed mentum or a deformed mandible. That level of deformities is taken as strong evidence of polluted bottom sediments. Lake Winnebago sediments were found to contain approximately 50 ppm lead. In laboratory experiments, Chironomus pallidivittatus larvae were cultured in Lake Winnebago sediments supplemented with different concentrations of lead as high as 20,000 ppm. Less than 10% of the larvae in those experiments had either a deformed mentum or a deformed mandible. These results suggest that lead alone is unlikely to be the cause of the high levels of deformities seen in the Chironomus spp. larvae collected from the Lake Winnebago sediments.

Development of ultrastructural damage to chloroplasts in a plastoquinone-deficient mutant of maize

Abstract The ultrastructure of a recently discovered mutant of maize (mutant hcf103-114 ) that is completely lacking plastoquinone (Cook, W.B., Miles, D., 1992. Nuclear mutations affecting plastoquinone accumulation in maize. Photosyn. Res. 31, 99–111) was investigated. This mutant fails to green and dies at an early age. Tissues along a developmental gradient (from base to tip of a maize leaf) were fixed and prepared for examination via electron microscopy. Initial development was normal in both mesophyll cell (MC) and bundle sheath cell (BSC) chloroplasts. Starch, which was abundant in BSC chloroplasts of wild type maize, did not accumulate in the mutant. As tissue aging progressed, both plastid types exhibited symptoms typical of photooxidative injury. Injury, seen as chloroplast swelling, lipid accumulation and envelope disruption, appeared sooner in BSC chloroplasts than in MC chloroplasts. Chloroplasts in guard cells possessed starch granules and only showed ultrastructural injury after the starch granules disappeared. Stomata developed normally in the hcf103-114 mutant. The results are discussed in terms of the known roles of plastoquinone in chloroplast metabolism.

Simple light guide for measuring irradiance in an aqueous oxygen electrode chamber.

The light-dependent reactions of photosynthesis are often measured with Clark-type oxygen electrodes yet the irradiance level inside aqueous oxygen electrode reaction vessels is seldom reported due to the difficulty of measuring light inside a small volume chamber. We describe a simple light guide terminating in a 90° prism that can be inserted into a reaction vessel. Incoming irradiation is directed to a commercially available quantum sensor positioned at the other end of the light guide. Both materials for and construction of the device are inexpensive.

David T. Hanson and Steven K. Rice (eds): Photosynthesis in bryophytes and early land plants

With the publication of ‘‘Photosynthesis in Bryophytes and Early Land Plants,’’ the continually expanding Advances in Photosynthesis and Respiration Series have reached back to the very base of the Embryophyte clade. To quote from the volume’s website (http://www.springer.com/us/book/97894 00769878#aboutBook), ‘‘Bryophytes, which are important constituents of ecosystems globally and often dominate carbon and water dynamics at high latitudes and elevations, were also among the pioneers of terrestrial photosynthesis. Consequently, in addition to their present day ecological value, modern representatives of these groups contain the legacy of adaptations that led to the greening of Earth. This volume brings together experts on bryophyte photosynthesis whose research spans the genome and cell through whole plant and ecosystem function and combines that with historical perspectives on the role of algal, bryophyte and vascular plant ancestors on terrestrialization of the Earth. The eighteen wellillustrated chapters reveal unique physiological approaches to achieving carbon balance and dealing with environmental limitations and stresses that present an alternative, yet successful strategy for land plants.’’ This volume has 342 pages and is arranged into 18 chapters: Chapter 1 (What Can We Learn From Bryophyte Photosynthesis?); Chapter 2 (Early Terrestrialization: Transition from Algal to Bryophyte Grade); Chapter 3 (Photosynthesis in Early Land Plants: Adapting to the Terrestrial Environment); Chapter 4 (The Diversification of Bryophytes and Vascular Plants in Evolving Terrestrial Environments); Chapter 5 (Best Practices for Measuring Photosynthesis at Multiple Scales); Chapter 6 (Diffusion Limitation and CO2 Concentrating Mechanisms in Bryophytes); Chapter 7 (Sunsafe Bryophytes: Photoprotection from Excess and Damaging Solar Radiatio); Chapter 8 (Chloroplast Movement in Higher Plants, Ferns and Bryophytes: A Comparative Point of View); Chapter 9 (Scaling Light Harvesting from Moss ‘‘Leaves’’ to Canopies); Chapter 10 (Structural and Functional Analyses of Bryophyte Canopies); Chapter 11 (Genetics and Genomics of Moss Models: Physiology Enters the Twenty-first Century); Chapter 12 (Photosynthesis in Aquatic Bryophytes); Chapter 13 (Physiological Ecology of Peatland Bryophytes); Chapter 14 (Interacting Controls on Ecosystem Photosynthesis and Respiration in Contrasting Peatland Ecosystems); Chapter 15 (Physiological Ecology of Tropical Bryophytes); Chapter 16 (Physiological Ecology of Dryland Biocrust Mosses); Chapter 17 (Dominating the Antarctic Environment: Bryophytes in a Time of Change); and Chapter 18 (Opportunities in Bryophyte Photosynthesis Research). A comprehensive Subject Index completes the volume. Two previous reviews, Hereford (2014) and Wise (2015), have favorably critiqued the volume and provide strong support for both the choice of topic—bryophytes are indeed worthy of more attention—and the broad, balanced, and in-depth coverage. David Hanson and Steven Rice deserve much credit for outlining the book and then assembling a quality group of international authors to undertake the research and writing. I particularly like use of the opening chapter (What can we learn from Bryophyte photosynthesis?) and closing chapter (18: Opportunities in Bryophyte research); they orient the reader, point the way forward, and tie the volume together. Evolutionary issues are the focus of Chapters 2–4, while Chapters 5–12 center around the many unique aspects of carbon acquisition in & Robert R. Wise wise@uwosh.edu