Cold responses of Arabidopsis mutants impaired in freezing tolerance

Mutants of Arabidopsis thaliana L. (Heynh), characterized asdeficient in their freezing tolerance after cold acclimation,were surveyed for some of the normal responses to cold exposure.In foliar tissue, the coldinducibility of three proteins, thelevels of sucrose and glucose, the fatty acyl composition oflipids, and the accumulation of anthocyanin was examined. Fourmutations (sfr3, sfr4, sfr6, and sfr7) reduced or eliminatedthe accumulation of anthocyanin during cold acclimation. Onemutation (sfr4) prevented the normally cold-induced elevationof sucrose and glucose levels; both sfr4 and another mutation(sfr7) affected fatty acid composition after (and only after)cold acclimation. On the other hand mutations sfr1, sfr2 andsfr5 did not differ significantly from the wild type in anyof the parameters tested, suggesting that they have other, perhapshighly specific, effects on lowtemperature responses. Key words: Arabidopsis thaliana, cold acclimation, freezing tolerance, mutation     

Effect of Metalaxyl on the incidence and severity of Pearl millet downy mildew disease in Northern Nigeria

Pearl millet downy mildew (DM) incidence, severity and yield losses of two pearl millet varieties (local and improved) due to the disease were determined in the field. Significant differences in the disease incidence and severity were recorded in the plots sown with metalaxyl-treated seeds and those sown with non-treated seeds, indicating the efficacy of the fungicide on the fungus. Yield losses due to non-treatment of seeds with metalaxyl was 40.88 and 45.39% in a local variety and 43.00 and 18.60% in an improved variety in the 2000 and 2001 cropping seasons respectively. Significant differences between plots sown with metalaxyl-treated and those sown with non-treated seeds were obtained for other yield components such as 1000-grains weight, panicle length and weight.     

Gene expression and the evolution of phenotypic diversity in social wasps

Background  

Organisms are capable of developing different phenotypes by altering the genes they express. This phenotypic plasticity provides a means for species to respond effectively to environmental conditions. One of the most dramatic examples of phenotypic plasticity occurs in the highly social hymenopteran insects (ants, social bees, and social wasps), where distinct castes and sexes all arise from the same genes. To elucidate how variation in patterns of gene expression affects phenotypic variation, we conducted a study to simultaneously address the influence of developmental stage, sex, and caste on patterns of gene expression in Vespula wasps. Furthermore, we compared the patterns found in this species to those found in other taxa in order to investigate how variation in gene expression leads to phenotypic evolution.     

The action of soybean lipoxygenase-1 on 12-iodo-cis-9-octadecenoic acid: the importance of C11-H bond breaking

Previous work has demonstrated that the ferric form of soybean lipoxygenase-1 will catalyze an elimination reaction on 12-iodo-cis-9-octadecenoic acid (12-IODE) to produce 9, 11-octadecadienoic acid and iodide ion. Elimination is accompanied by irreversible inactivation of the enzyme on 1 out of 10 turnovers. In the present work, 11,11-dideuterio-12-IODE (D(2)-12-IODE) was synthesized and used to demonstrate that both the elimination reaction and inactivation of the enzyme exhibit very large kinetic isotope effects. The rates with the deuterated compound are so low that the isotope effects are difficult to quantify, but they appear to be comparable to the isotope effects previously observed for the normal reaction catalyzed by lipoxygenase and much larger than can be explained by zero-point energy considerations. ESR spectroscopy was used to demonstrate that 12-IODE can reduce ferric lipoxygenase to the ferrous form, and a large isotope effect on this process was observed with D(2)-12-IODE. It is proposed that the pathway leading to reduction and inactivation by 12-IODE is initiated by homolytic cleavage of the C(11)-H bond. Elimination could be initiated either by homolytic or by heterolytic cleavage of this bond. The results suggest that very large isotope effects may be a general feature of C-H bond cleavages catalyzed by this enzyme.     

Restricted epithelial proliferation by lacritin via PKCalpha-dependent NFAT and mTOR pathways

Renewal of nongermative epithelia is poorly understood. The novel mitogen "lacritin" is apically secreted by several nongermative epithelia. We tested 17 different cell types and discovered that lacritin is preferentially mitogenic or prosecretory for those types that normally contact lacritin during its glandular outward flow. Mitogenesis is dependent on lacritin's C-terminal domain, which can form an alpha-helix with a hydrophobic face, as per VEGF's and PTHLP's respective dimerization or receptor-binding domain. Lacritin targets downstream NFATC1 and mTOR. The use of inhibitors or siRNA suggests that lacritin mitogenic signaling involves Galpha(i) or Galpha(o)-PKCalpha-PLC-Ca2+-calcineurin-NFATC1 and Galpha(i) or Galpha(o)-PKCalpha-PLC-phospholipase D (PLD)-mTOR in a bell-shaped, dose-dependent manner requiring the Ca2+ sensor STIM1, but not TRPC1. This pathway suggests the placement of transiently dephosphorylated and perinuclear Golgi-translocated PKCalpha upstream of both Ca2+ mobilization and PLD activation in a complex with PLCgamma2. Outward flow of lacritin from secretory cells through ducts may generate a proliferative/secretory field as a different unit of cellular renewal in nongermative epithelia where luminal structures predominate.     

Dynamics of leaf hydraulic conductance with water status: quantification and analysis of species differences under steady state

Leaf hydraulic conductance (K(leaf)) is a major determinant of photosynthetic rate in well-watered and drought-stressed plants. Previous work assessed the decline of K(leaf) with decreasing leaf water potential (Ψ(leaf)), most typically using rehydration kinetics methods, and found that species varied in the shape of their vulnerability curve, and that hydraulic vulnerability correlated with other leaf functional traits and with drought sensitivity. These findings were tested and extended, using a new steady-state evaporative flux method under high irradiance, and the function for the vulnerability curve of each species was determined individually using maximum likelihood for 10 species varying strongly in drought tolerance. Additionally, the ability of excised leaves to recover in K(leaf) with rehydration was assessed, and a new theoretical framework was developed to estimate how rehydration of measured leaves may affect estimation of hydraulic parameters. As hypothesized, species differed in their vulnerability function. Drought-tolerant species showed shallow linear declines and more negative Ψ(leaf) at 80% loss of K(leaf) (P(80)), whereas drought-sensitive species showed steeper, non-linear declines, and less negative P(80). Across species, the maximum K(leaf) was independent of hydraulic vulnerability. Recovery of K(leaf) after 1 h rehydration of leaves dehydrated below their turgor loss point occurred only for four of 10 species. Across species without recovery, a more negative P(80) correlated with the ability to maintain K(leaf) through both dehydration and rehydration. These findings indicate that resistance to K(leaf) decline is important not only in maintaining open stomata during the onset of drought, but also in enabling sustained function during drought recovery.     

Photosynthetic pathway influences xylem structure and function in Flaveria (Asteraceae)

Higher water use efficiency (WUE) in C(4) plants may allow for greater xylem safety because transpiration rates are reduced. To evaluate this hypothesis, stem hydraulics and anatomy were compared in 16 C(3), C(3)-C(4) intermediate, C(4)-like and C(4) species in the genus Flaveria. The C(3) species had the highest leaf-specific conductivity (K(L)) compared with intermediate and C(4) species, with the perennial C(4) and C(4)-like species having the lowest K(L) values. Xylem-specific conductivity (K(S)) was generally highest in the C(3) species and lower in intermediate and C(4) species. Xylem vessels were shorter, narrower and more frequent in C(3)-C(4) intermediate, C(4)-like and C(4) species compared with C(3) species. WUE values were approximately double in the C(4)-like and C(4) species relative to the C(3)-C(4) and C(3) species. C(4)-like photosynthesis arose independently at least twice in Flaveria, and the trends in WUE and K(L) were consistent in both lineages. These correlated changes in WUE and K(L) indicate WUE increase promoted K(L) decline during C(4) evolution; however, any involvement of WUE comes late in the evolutionary sequence. C(3)-C(4) species exhibited reduced K(L) but little change in WUE compared to C(3) species, indicating that some reduction in hydraulic efficiency preceded increases in WUE.     

Passive recovery of an island bird community after rodent eradication

The number and scale of island invasive species eradications is growing, but quantitative evidence of the conservation efficacy of passive recovery is limited. We compare relative abundances of breeding birds on Hawadax Island (formerly named Rat island), Aleutian Archipelago, Alaska, pre- and post- rat eradication to examine short-term (<1 year post-eradication) changes due to rodenticide application, and medium-term (5 years post-eradication) changes due to the absence of invasive rats. In the short term, Bald Eagle (Haliaeetus leucocephalus) numbers decreased from 24 individuals pre-eradication to two individuals <1 year post-eradication, but recovered to 10 individuals (42 % of pre-eradication) 5 years post-eradication, with all individuals nesting (63 % of the pre-eradication nesting). Five years post-eradication relative abundances of most terrestrial birds surveyed using point counts either significantly increased [Gray-crowned Rosy Finch (Leucosticte tephrocotis), Lapland Longspur (Calcarius lapponicus), Snow Bunting (Plectrophenax nivalis), Song Sparrow (Melospiza melodia)] or did not differ [Pacific Wren (Troglodytes troglodytes)]. Shorebirds also increased 5 years post-eradication with Black Oystercatchers (Haematopus palliates) increasing fivefold, and Rock Sandpiper (Calidris ptilocnemis) nesting increasing from one to five nests. We confirmed two species of ground nesting seabirds [Tufted Puffin (Fratercula cirrhata) and Leach’s Storm-petrel (Oceanodroma leucohoa)] as nesting (puffin) or engaged in courtship behavior (Storm-petrel) 5 years post-eradication. Our results indicate that despite the short-term impact on Bald Eagles, and without further human intervention, most terrestrial and marine birds have newly-colonized, re-colonized, or increased in abundance following the eradication of invasive rats.     

A randomised, blinded, placebo-controlled trial in dementia patients continuing or stopping neuroleptics (the DART-AD trial)

Background

There have been increasing concerns regarding the safety and efficacy of neuroleptics in people with dementia, but there are very few long-term trials to inform clinical practice. The aim of this study was to determine the impact of long-term treatment with neuroleptic agents upon global cognitive decline and neuropsychiatric symptoms in patients with Alzheimer disease.

Methods and Findings

Design: Randomised, blinded, placebo-controlled parallel two-group treatment discontinuation trial.Setting: Oxfordshire, Newcastle and Gateshead, London and Edinburgh, United Kingdom.Participants: Patients currently prescribed the neuroleptics thioridazine, chlorpromazine, haloperidol trifluoperazine or risperidone for behavioural or psychiatric disturbance in dementia for at least 3 mo.Interventions: Continue neuroleptic treatment for 12 mo or switch to an identical placebo.Outcome measures: Primary outcome was total Severe Impairment Battery (SIB) score. Neuropsychiatric symptoms were evaluated with the Neuropsychiatric Inventory (NPI).Results: 165 patients were randomised (83 to continue treatment and 82 to placebo, i.e., discontinue treatment), of whom 128 (78%) commenced treatment (64 continue/64 placebo). Of those, 26 were lost to follow-up (13 per arm), resulting in 51 patients per arm analysed for the primary outcome. There was no significant difference between the continue treatment and placebo groups in the estimated mean change in SIB scores between baseline and 6 mo; estimated mean difference in deterioration (favouring placebo) −0.4 (95% confidence interval [CI] −6.4 to 5.5), adjusted for baseline value (p = 0.9). For neuropsychiatric symptoms, there was no significant difference between the continue treatment and placebo groups (n = 56 and 53, respectively) in the estimated mean change in NPI scores between baseline and 6 mo; estimated mean difference in deterioration (favouring continue treatment) −2.4 (95% CI −8.2 to 3.5), adjusted for baseline value (p = 0.4). Both results became more pronounced at 12 mo. There was some evidence to suggest that those patients with initial NPI ≥ 15 benefited on neuropsychiatric symptoms from continuing treatment.

Conclusions

For most patients with AD, withdrawal of neuroleptics had no overall detrimental effect on functional and cognitive status. Neuroleptics may have some value in the maintenance treatment of more severe neuropsychiatric symptoms, but this benefit must be weighed against the side effects of therapy.Trial registration: Cochrane Central Registry of Controlled Trials/National Research Register (#ISRCTN33368770).