Function of polyphenol oxidase in higher plants

Recent evidence has supported the folllowing views:
1. Polyphenol oxidase (PPO) is a plastidic enzyme that is unclear-coded, but is inactive until incorporated into the plastid.
2. In healthy green tissues PPO exists in a latent form on the thylakoid membrane and is not involved in synthesis of phenolic compounds. In leucoplasts, proplastids, or amyloplasts PPO is often present in a latent form in rudimentary thylakoids.
3. PPO normally functions as a phenol oxidase in vivo only in sencent or damaged cells.
4. In the functional chloroplast, PPO may be involved in some aspect of oxygen chemistry – pherhaps mediation of pseudocyclic photophosphorylation.     

Gas exchange and habitat selection in the aquatic salamanders Necturus maculosus and Cryptobranchus alleganiensis

Summary The standard metabolic rate (SMR) and critical O₂ tension (P_c) of water-breathing mudpuppies and hellbenders were determined at 20° C using open-system respirometry. Both species are metabolic O₂ regulators, although the P_c of hellbenders (90 mmHg) is much higher than that of mudpuppies (40 mmHg). The SMR of the two species in water saturated with air was similar (19.5 and 20.0 l O₂/g·h for Cryptobranchus and Necturus, respectively) and not different from that of salamanders in general. Both species were able to survive for at least 5–11 days in severely hypoxic water (9–10 mmHg) by breathing air, indicating that the lungs are functional accessory respiratory structures.We conclude that hellbenders are restricted to relatively cool and flowing waters because of their limited gas exchange capabilities, particularly with regard to their limited aerobic scope for activity and slow recovery from exercise. Necturus maculosus is much more tolerant of hypoxia, but it is not known if they can inhabit areas were hypoxia is combined with hypercarbia.     

Purification and Characterization of Pea Epicotyl beta-Amylase

The most abundant β-amylase (EC 3.2.1.2) in pea (Pisum sativum L.) was purified greater than 880-fold from epicotyls of etiolated germinating seedlings by anion exchange and gel filtration chromatography, glycogen precipitation, and preparative electrophoresis. The electrophoretic mobility and relative abundance of this β-amylase are the same as that of an exoamylase previously reported to be primarily vacuolar. The enzyme was determined to be a β-amylase by end product analysis and by its inability to hydrolyze β-limit dextrin and to release dye from starch azure. Pea β-amylase is an approximate 55 to 57 kilodalton monomer with a pl of 4.35, a pH optimum of 6.0 (soluble starch substrate), an Arrhenius energy of activation of 6.28 kilocalories per mole, and a K_m of 1.67 milligrams per milliliter (soluble starch). The enzyme is strongly inhibited by heavy metals, p-chloromer-curiphenylsulfonic acid and N-ethylmaleimide, but much less strongly by iodoacetamide and iodoacetic acid, indicating cysteinyl sulfhydryls are not directly involved in catalysis. Pea β-amylase is competitively inhibited by its end product, maltose, with a K_i of 11.5 millimolar. The enzyme is partially inhibited by Schardinger maltodextrins, with α-cyclohexaamylose being a stronger inhibitor than β-cycloheptaamylose. Moderately branched glucans (e.g. amylopectin) were better substrates for pea β-amylase than less branched or non-branched (amyloses) or highly branched (glycogens) glucans. The enzyme failed to hydrolyze native starch grains from pea and glucans smaller than maltotetraose. The mechanism of pea β-amylase is the multichain type. Possible roles of pea β-amylase in cellular glucan metabolism are discussed.     

The small-subunit ribosomal RNA gene sequences from the hypotrichous ciliates Oxytricha nova and Stylonychia pustulata

We have determined the complete nucleotide sequence of the small- subunit ribosomal RNA genes for the ciliate protozoans Stylonychia pustulata and Oxytricha nova. The sequences are homologous and sufficiently similar that these organisms must be closely related. In a phylogeny inferred from comparisons of several eukaryotic small-subunit ribosomal RNAs, the divergence of the ciliates from the eukaryotic line of descent is seen to coincide with the radiation of the plants, the animals, and the fungi. This radiation is preceded by the divergence of the slime mold, Dictyostelium discoideum.      

Extremely low genetic diversity across mangrove taxa reflects past sea level changes and hints at poor future responses

The projected increases in sea levels are expected to affect coastal ecosystems. Tropical communities, anchored by mangrove trees and having experienced frequent past sea level changes, appear to be vibrant at present. However, any optimism about the resilience of these ecosystems is premature because the impact of past climate events may not be reflected in the current abundance. To assess the impact of historical sea level changes, we conducted an extensive genetic diversity survey on the Indo‐Malayan coast, a hotspot with a large global mangrove distribution. A survey of 26 populations in six species reveals extremely low genome‐wide nucleotide diversity and hence very small effective population sizes (N_e) in all populations. Whole‐genome sequencing of three mangrove species further shows the decline in N_e to be strongly associated with the speed of past changes in sea level. We also used a recent series of flooding events in Yalong Bay, southern China, to test the robustness of mangroves to sea level changes in relation to their genetic diversity. The events resulted in the death of half of the mangrove trees in this area. Significantly, less genetically diverse mangrove species suffered much greater destruction. The dieback was accompanied by a drastic reduction in local invertebrate biodiversity. We thus predict that tropical coastal communities will be seriously endangered as the global sea level rises. Well‐planned coastal development near mangrove forests will be essential to avert this crisis.     

CHROMOSOME NUMBERS IN SPHAERALCEA SECTION FENDLERIANAE

Chromosome numbers are reported for ten taxa in Sphaeralcea section Fendlerianae (Malvaceae). New ploidy levels are reported for six taxa, with one species not previously reported, and extensive polyploidy at all taxonomic levels is documented. The geographic and taxonomic distribution of polyploids suggests that polyploidy arose many times in the taxa of Sphaeralcea. Sphaeralcea fendleri var. venusta, S. polychroma, and S. wrightii populations have yielded exclusively tetraploid counts. Tetraploidy is correlated with taxa having lavender petals. Polyploidy has also allowed the taxa to expand their distributions without resulting in speciation.     

Correlates of Marijuana Drugged Driving and Openness to Driving While High: Evidence from Colorado and Washington

Aims

A potential unintended consequence of legalizing recreational marijuana is increased marijuana-related driving impairment. Some states where recreational marijuana is legal have begun implementing interventions to mitigate driving under the influence (DUI) of marijuana, including media campaigns to increase knowledge about DUI laws. However, little is known about the associations between knowledge of DUI laws and marijuana DUI behavior. In this study, we provide new data from a survey of marijuana users in Colorado and Washington to examine associations between marijuana drugged driving and two potential behavioral precursors of marijuana DUI. We also explore other factors that may influence marijuana DUI.

Methods

Data are from an online survey of marijuana users in Colorado and Washington. Respondents who reported any marijuana use in the past 30 days (n = 865) served as the analytic sample. We examined prevalence of two behavioral outcomes: (1) any driving of a motor vehicle while high in the past year and (2) driving a motor vehicle within 1 hour of using marijuana 5 or more times in the past month. Additional outcomes measuring willingness to drive while high were also assessed. Logistic regressions were used to estimate each outcome as a function of two multi-item scales measuring knowledge of the legal consequences of driving high and perceptions that driving while high is not safe. Additional covariates for potential confounders were included in each model.

Results

Prevalence of past-year driving while under the influence of marijuana was 43.6% among respondents. The prevalence of driving within 1 hour of using marijuana at least 5 times in the past month was 23.9%. Increased perception that driving high is unsafe was associated with lower odds of past-year marijuana DUI (OR = 0.31, P < 0.01) and lower past-month odds of driving 5 or more times within 1 hour of using marijuana (OR = 0.26, P < 0.01). Increased knowledge of marijuana DUI laws was also associated with lower odds of each of these outcomes (OR = 0.63, P < 0.01, OR = 0.69, P = 0.02, respectively). Post-estimation Wald tests confirmed the negative associations with marijuana DUI were greater in magnitude for safety perceptions than knowledge of DUI laws. Increased perceptions that driving while high is unsafe was associated with significantly lower willingness to drive after using marijuana while increased knowledge of marijuana DUI laws was not associated with these outcomes.

Conclusions

Despite recent interventions targeting public awareness of the legal consequences of marijuana DUI, our results suggest that knowledge of these laws is a weaker predictor of DUI behavior than perceptions that driving high is unsafe. In addition, safety perceptions predict decreased openness to driving high while knowledge of DUI laws was not associated with openness. These findings suggest that interventions for reducing the incidence of marijuana DUI are likely to be more successful by targeting safety perceptions related to marijuana DUI rather than knowledge of DUI laws. We caution that because these data are limited to an online convenience sample, results may not be generalizable beyond our sample.