Cobalt and nitrogen fixation in Lupinus angustifolius L. I. Growth, nitrogen concentrations and cobalt distribution

Cobalt application markedly increased the growth of and nitrogen concentrations in tops of Lupinus angustifolius irrespective of inoculation with an effective strain of Rhizobium. Cobalt‐deficient plants produced a greater weight of lateral nodules and total nodule weight than cobalt‐adequate plants. Cobalt‐sufficient plants produced more crown nodule weight than cobalt‐deficient plants. Cobalt concentrations were higher in roots and nodules than in tops irrespective of cobalt application. In plant tops cobalt concentrations in young leaves were considerably lower than those in old leaves at both cobalt levels. Cobalt concentrations and contents increased in old leaves throughout the experiment. Under cobalt deficiency cobalt appeared to be preferentially distributed to nodules. Six weeks after sowing cobalt contents of nodules of cobalt‐deficient plants were similar to those in whole tops. By contrast at this time cobalt contents of nodules of cobalt‐adequate plants were only approximately one‐third those of whole tops

The role of iron in nodulation and nitrogen fixation in Lupinus angustifolius L

The effects of iron concentration in solution on nodulation and symbiotic N2 fixation in lupins (Lupinus angustifolius L. ev. Yandee) were studied in solution culture in the glasshouse by comparing plants supplied with NH4NO3 with those reliant on N2 fixation. At very low iron supply, adding NH4NO2 did not increase shoot growth. Under moderate iron deficiency, where plants were pale green, adding NH4NO3 increased shoot growth, implying that moderate iron deficiency was, operationally, nitrogen deficiency. Higher iron concentrations in solution were required for maximum growth of plants reliant on symbiotic N2 fixation than for those supplied with NH4NO3 Iron deficiency depressed nodule initiation earlier than host plant growth, resulting in decreased nodule number and mass. Alleviating iron deficiency enhanced leghaemoglobin production in nodules and increased nitrogen concentrations in the shoots. Iron concentration in the youngest fully expanded leaves provided a good indication of the severity of iron deficiency‐caused chlorosis. The results suggest that iron is involved in symbiotic N2 fixation through effects on both nodule initiation and nodule function, and that the symbiosis has a higher iron requirement than that needed for host plant growth

Impaired nodule function in Medicago polymorpha L. infected with alfalfa mosaic virus

The effects of alfalfa mosaic virus (AMV) on growth, nodule formation and nodule function in the annual burr medic, Medicago polymorpha cv. Circle Valley, were investigated in glasshouse pot experiments. Systemically‐infected plants from AMV‐infected seed produced 21% less shoot dry weight and accumulated 24% less fixed nitrogen in shoots than healthy plants when harvested 53 d after germination. At day 75, infected plants showed similar shoot dry weight losses (22%), but the quantity of nitrogen fixed fell by only 15%. At day 53, soluble sugar, starch and bacteroid concentrations in nodules were unaffected by AMV infection, but nitrogenase specific activity was decreased by 25% and soluble amino acids by 20%. Although AMV infection resulted in no differences in the number of nodules formed in the first 11 d after germination or at any harvest thereafter, nodule mass was decreased by 23% for virus‐infected plants at day 53. However this difference disappeared by day 75. Growth of AMV‐infected plants was decreased probably because of impaired N2 fixation with nodule function affected rather than nodulation. Increased nodule mass relative to plant weight in virus‐infected plants, seen at day 75, implied some degree of compensation for the limitation in N2‐fixing capacity. ELISAs for AMV antigen indicated that nodules were active sites of virus multiplication

Which stage of nodule initiation in Lupinus angustifolius L. is sensitive to iron deficiency?

Transfer experiments in solution culture were conducted to establish the stage of nodulation in lupins (Lupinus angustifolius L. cv. Yandee) most sensitive to iron deficiency. In all experiments, iron deficiency had a much greater effect on nodule number than on host plant growth. Irrespective of the iron treatment of either the Bradyrhizobium or the lupin plant prior to inoculation, plants receiving 2.5 μM iron after inoculation successfully formed nodule initials and nodules while those receiving 0.05 μM iron almost completely failed to initiate nodules. Thus, the prevention of nodulation by iron deficiency is not a consequence of either an inadequate number of infective bradyrhizobia surviving in the solution or an alteration in the iron status of the host root. Supply of 2.5 μM iron for 4 d or more after inoculation produced a similar number of nodule initials and nodules as did continuous supply of 2.5 μMiron. Delaying supply of 2.5 μM iron for 3 d or less after inoculation did not delay or prevent nodule initiation and formation. One‐day exposure of plants to 2.5μM iron on day 4 after inoculation induced the highest number of nodules of any 1 d treatment although this short exposure was not enough to allow the full complement of nodules to form. Hence, the impairment of the nodulation process by iron deficiency can be attributed to the prevention of a step at day 4, the stage just before nodule initials are formed. A further study was conducted to examine the effect of iron on nodule formation by using a vertical split‐root technique in which Bradyrhizobium sp. (Lupinus) was added to the upper compartment. Compared to plants receiving 0.05 μM iron in both compartments, plants receiving 0.05 μM in the upper and 5 5 μM iron in the lower compartments had only a slightly higher concentration of iron in the cortex of the upper part of the root. Furthermore, supplying 5 μM iron to the lower part of a root did not permit nodulation on the upper part of the root receiving 0.05 μMiron. Low concentration of iron in the cortex of roots may limit nodule formation

Cobalt and nitrogen fixation in Lupinus angustifolius L. II. nodule formation and function

The effects of cobalt deficiency on nodule formation and function in sweet lupin (Lupinus angustifotius L. cv. Unicrop) were studied in cobalt‐deficient Lancelin sand in the glasshouse. Bacteroid densities in cobalt‐deficient nodules were lower than in normal nodules. Recovery from cobalt deficiency in inoculated treatments was associated with increases in bacteroid density and cobalt accumulation in lateral nodules. Such changes did not occur in treatments infected with rhizobia from the soil. Acetylene‐reducing activity of cobalt‐deficient plants was not initiated until plants were nearly 6 weeks old, at which time cobalt‐treated plants were at their peak of activity. Specific activities of cobalt‐deficient nodules remained very low even when nitrogenase did develop. Their large mass of nodules allowed cobalt‐deficient plants to reach 20 to 50 % of the normal activity per plant, but specific activities were only 5 to 13 % of peak activities in cobalt‐treated nodules. Nodule bacteroid content and leghaemoglobin content were linearly related to cobalamin content, each with a single relationship. Plotting acetylene‐reducing activity against cobalamin content or leghaemoglobin content generated two different linear response curves in each case; the slopes of the lines were different, depending on the presence or absence of cobalt. It is suggested that there may be a function in N, fixation in legume nodules for a non‐cobalamin form of cobalt

Complete genome sequence of the Medicago microsymbiont Ensifer (Sinorhizobium) medicae strain WSM419

Ensifer (Sinorhizobium) medicae is an effective nitrogen fixing microsymbiont of a diverse range of annual Medicago (medic) species. Strain WSM419 is an aerobic, motile, non-spore forming, Gram-negative rod isolated from a M. murex root nodule collected in Sardinia, Italy in 1981. WSM419 was manufactured commercially in Australia as an inoculant for annual medics during 1985 to 1993 due to its nitrogen fixation, saprophytic competence and acid tolerance properties. Here we describe the basic features of this organism, together with the complete genome sequence, and annotation. This is the first report of a complete genome se-quence for a microsymbiont of the group of annual medic species adapted to acid soils. We reveal that its genome size is 6,817,576 bp encoding 6,518 protein-coding genes and 81 RNA only encoding genes. The genome contains a chromosome of size 3,781,904 bp and 3 plasmids of size 1,570,951 bp, 1,245,408 bp and 219,313 bp. The smallest plasmid is a fea-ture unique to this medic microsymbiont

A descriptive pilot study of structural and functional social network ties among women in the women’s health initiative (WHI) study

Few studies examine the network structure and function of older women’s health discussion networks. We sought to assess the feasibility and acceptability of collecting social network data via telephone from 72 women from the Women’s Health Initiative study and to describe structural and functional characteristics. Women were socially connected and had dense networks. Women were emotionally close to network members, but their networks were not used to facilitate communication with health-care providers. One-third of network members was not influential on health-related decision-making. Collecting social network data via telephone is feasible and an acceptable, though un-preferred, mode of data collection

Internalized HIV stigma predicts subsequent viremia in US HIV patients through depressive symptoms and antiretroviral therapy adherence

Objective:We sought to examine the prospective association between internalized HIV stigma and unsuppressed viral load and to investigate whether this relationship was sequentially mediated by depressive symptoms and antiretroviral therapy (ART) adherence.Design:Longitudinal study in a multisite observational clinical cohort.Methods:The Center for AIDS Research Network of Integrated Clinical Systems patient-reported outcomes survey measures internalized HIV stigma yearly using a four-item assessment (response scale 1 = strongly disagree to 5 = strongly agree). We obtained patient-reported outcome, lab, and appointment data from six center for AIDS research network of integrated clinical systems sites. We used multivariable logistic regression to examine the association between mean stigma and subsequent viremia. We then used Bayesian sequential mediation to fit a longitudinal sequential path model spanning four time points to test if depressive symptoms at T1and ART adherence at T2mediated the effect of stigma at T0on viral load at T3, adjusting for baseline covariates.Results:Between February 2016 and November 2018, 6859 patients underwent stigma assessment and were 81% cis-men, 38% Black, 16% Latinx, 32% heterosexual-identified, and 49% at least 50 years of age. Mean stigma level was 2.00 (SD 1.08). Stigma was significantly associated with subsequent viremia (adjusted odds ratio = 1.16, 95% confidence interval: 1.05-1.28, P = 0.004), as were younger age and Black race. The chained indirect effect from stigma to unsuppressed viral load through depressive symptoms and then adherence was significant (standardized β = 0.002; SD = 0.001).Conclusion:Internalized HIV stigma positively predicts subsequent viremia through depressive symptoms and ART adherence. Addressing the link between stigma and depressive symptoms could help improve viral suppression

Internalized HIV Stigma Predicts Suboptimal Retention in Care among People Living with HIV in the United States

HIV-related stigma is a known barrier to retention in care. However, no large-scale, multi-site studies have prospectively evaluated the effect of internalized stigma on retention in care. The Centers for AIDS Research Network of Integrated Clinical Systems (CNICS) cohort study integrates medical record and survey data from people living with HIV (PLWH) seen in HIV primary care clinics across the United States, and assesses internalized stigma yearly using a validated 4-item Likert scale. We used multivariable logistic regression models to evaluate associations between mean internalized stigma and two prospective retention in care outcomes: keeping the next primary care appointment and keeping all scheduled primary care appointments in the 12 months following stigma assessment. From February 2016 to November 2017, 5968 PLWH completed the stigma assessment and had adequate follow-up time. Mean stigma was 1.9 (standard deviation 1.08). Increased mean stigma scores were associated with decreased odds of attending the next primary care appointment [adjusted odds ratio (aOR) = 0.93, 95% confidence interval (CI) 0.88-0.99, p = 0.02], and all primary care appointments in the subsequent 12 months (aOR = 0.94, 95% CI 0.89-0.99, p = 0.02). In both models, younger age and Black race were also independently associated with suboptimal appointment attendance. There was no support for interactions between internalized stigma and covariates. Internalized HIV stigma had an independent negative effect on the odds of subsequent appointment attendance. This study highlights the importance of identifying even low levels of internalized stigma. Interventions to address internalized HIV stigma are critical to supporting retention in care and improving clinical outcomes