Boosting species evenness, productivity and weed control in a mixed meadow by promoting arbuscular mycorrhizas

Lowland meadows represent aboveground and belowground biodiversity reservoirs in intensive agricultural areas, improving water retention and filtration, ensuring forage production, contrasting erosion and contributing to soil fertility and carbon sequestration. Besides such major ecosystem services, the presence of functionally different plant species improves forage quality, nutritional value and productivity, also limiting the establishment of weeds and alien species. Here, we tested the effectiveness of a commercial seed mixture in restoring a lowland mixed meadow in the presence or absence of inoculation with arbuscular mycorrhizal (AM) fungi and biostimulation of symbiosis development with the addition of short chain chito-oligosaccharides (CO). Plant community composition, phenology and productivity were regularly monitored alongside AM colonization in control, inoculated and CO-treated inoculated plots. Our analyses revealed that the CO treatment accelerated symbiosis development significantly increasing root colonization by AM fungi. Moreover, the combination of AM fungal inoculation and CO treatment improved plant species evenness and productivity with more balanced composition in forage species. Altogether, our study presented a successful and scalable strategy for the reintroduction of mixed meadows as valuable sources of forage biomass; demonstrated the positive impact of CO treatment on AM development in an agronomic context, extending previous observations developed under controlled laboratory conditions and leading the way to the application in sustainable agricultural practices.

Aspects of campus climate and mental health threats: The role of hypervigilance

Objective: This study sought to examine if hypervigilance is one mechanism through which aspects of less supportive campus climates are associated with mental health symptoms for college students. Participants: Data from 386 undergraduate college students attending a small college in the northeastern United States were collected. Methods: Participants completed online surveys which employed established measures of study variables. Results: Hypervigilance mediated the association between subjective social status and symptoms of anxiety and depression; lower subjective social status was associated with greater hypervigilance and greater hypervigilance was associated with more symptoms of anxiety and depression. Less sense of community was also directly associated with more anxiety, depression, and somatic symptoms. Conclusions: Hypervigilance may be an adaptive strategy to protect against psychosocial harm for low status members of the campus community, but may damage longer-term mental health. Implications for higher education administrators are discussed.

Long-lasting impact of chitooligosaccharide application on strigolactone biosynthesis and fungal accommodation promotes arbuscular mycorrhiza in Medicago truncatula

The establishment of arbuscular mycorrhiza (AM) between plants and Glomeromycotina fungi is preceded by the exchange of chemical signals: fungal released Myc-factors, including chitooligosaccharides (CO) and lipo-chitooligosaccharides (LCO), activate plant symbiotic responses, while root-exuded strigolactones stimulate hyphal branching and boost CO release. Furthermore, fungal signaling reinforcement through CO application was shown to promote AM development in Medicago truncatula, but the cellular and molecular bases of this effect remained unclear. Here, we focused on long-term M. truncatula responses to CO treatment, demonstrating its impact on the transcriptome of both mycorrhizal and nonmycorrhizal roots over several weeks and providing an insight into the mechanistic bases of the CO-dependent promotion of AM colonization. CO treatment caused the long-lasting regulation of strigolactone biosynthesis and fungal accommodation-related genes. This was mirrored by an increase in root didehydro-orobanchol content, and the promotion of accommodation responses to AM fungi in root epidermal cells. Lastly, an advanced downregulation of AM symbiosis marker genes was observed at the latest time point in CO-treated plants, in line with an increased number of senescent arbuscules. Overall, CO treatment triggered molecular, metabolic, and cellular responses underpinning a protracted acceleration of AM development.

Extraction of short chain chitooligosaccharides from fungal biomass and their use as promoters of arbuscular mycorrhizal symbiosis

Short chain chitooligosaccharides (COs) are chitin derivative molecules involved in plant-fungus signaling during arbuscular mycorrhizal (AM) interactions. In host plants, COs activate a symbiotic signalling pathway that regulates AM-related gene expression. Furthermore, exogenous CO application was shown to promote AM establishment, with a major interest for agricultural applications of AM fungi as biofertilizers. Currently, the main source of commercial COs is from the shrimp processing industry, but purification costs and environmental concerns limit the convenience of this approach. In an attempt to find a low cost and low impact alternative, this work aimed to isolate, characterize and test the bioactivity of COs from selected strains of phylogenetically distant filamentous fungi: Pleurotus ostreatus, Cunninghamella bertholletiae and Trichoderma viride. Our optimized protocol successfully isolated short chain COs from lyophilized fungal biomass. Fungal COs were more acetylated and displayed a higher biological activity compared to shrimp-derived COs, a feature that-alongside low production costs-opens promising perspectives for the large scale use of COs in agriculture.

TPLATE Recruitment Reveals Endocytic Dynamics at Sites of Symbiotic Interface Assembly in Arbuscular Mycorrhizal Interactions

Introduction: Arbuscular mycorrhizal (AM) symbiosis between soil fungi and the majority of plants is based on a mutualistic exchange of organic and inorganic nutrients. This takes place inside root cortical cells that harbor an arbuscule: a highly branched intracellular fungal hypha enveloped by an extension of the host cell membrane-the perifungal membrane-which outlines a specialized symbiotic interface compartment. The perifungal membrane develops around each intracellular hypha as the symbiotic fungus proceeds across the root tissues; its biogenesis is the result of an extensive exocytic process and shows a few similarities with cell plate insertion which occurs at the end of somatic cytokinesis. Materials and Methods: We here analyzed the subcellular localization of a GFP fusion with TPLATE, a subunit of the endocytic TPLATE complex (TPC), a central actor in plant clathrin-mediated endocytosis with a role in cell plate anchoring with the parental plasma membrane. Results: Our observations demonstrate that Daucus carota and Medicago truncatula root organ cultures expressing a 35S::AtTPLATE-GFP construct accumulate strong fluorescent green signal at sites of symbiotic interface construction, along recently formed perifungal membranes and at sites of cell-to-cell hyphal passage between adjacent cortical cells, where the perifungal membrane fuses with the plasmalemma. Discussion: Our results strongly suggest that TPC-mediated endocytic processes are active during perifungal membrane interface biogenesis-alongside exocytic transport. This novel conclusion, which might be correlated to the accumulation of late endosomes in the vicinity of the developing interface, hints at the involvement of TPC-dependent membrane remodeling during the intracellular accommodation of AM fungi.

Local endoreduplication as a feature of intracellular fungal accommodation in arbuscular mycorrhizas

The intracellular accommodation of arbuscular mycorrhizal (AM) fungi is a paradigmatic feature of this plant symbiosis that depends on the activation of a dedicated signaling pathway and the extensive reprogramming of host cells, including striking changes in nuclear size and transcriptional activity. By combining targeted sampling of early root colonization sites, detailed confocal imaging, flow cytometry and gene expression analyses, we demonstrate that local, recursive events of endoreduplication are triggered in the Medicago truncatula root cortex during AM colonization. AM colonization induces an increase in ploidy levels and the activation of endocycle specific markers. This response anticipates the progression of fungal colonization and is limited to arbusculated and neighboring cells in the cortical tissue. Furthermore, endoreduplication is not induced in M. truncatula mutants for symbiotic signaling pathway genes. On this basis, we propose endoreduplication as part of the host cell prepenetration responses that anticipate AM fungal accommodation in the root cortex.

Size matters: three methods for estimating nuclear size in mycorrhizal roots of Medicago truncatula by image analysis

BACKGROUND

The intracellular accommodation of arbuscular mycorrhizal (AM) fungi involves a profound molecular reprogramming of the host cell architecture and metabolism, based on the activation of a symbiotic signaling pathway. In analogy with other plant biotrophs, AM fungi are reported to trigger cell cycle reactivation in their host tissues, possibly in support of the enhanced metabolic demand required for the symbiosis.

RESULTS

We here compare the efficiency of three Fiji/ImageJ image analysis plugins in localizing and quantifying the increase in nuclear size - a hallmark of recursive events of endoreduplication - in M. truncatula roots colonized by the AM fungus Gigaspora margarita. All three approaches proved to be versatile and upgradeable, allowing the investigation of nuclear changes in a complex tissue; 3D Object Counter provided more detailed information than both TrackMate and Round Surface Detector plugins. On this base we challenged 3D Object Counter with two case studies: verifying the lack of endoreduplication-triggering responses in Medicago truncatula mutants with a known non-symbiotic phenotype; and analysing the correlation in space and time between the induction of cortical cell division and endoreduplication upon AM colonization. Both case studies revealed important biological aspects. Mutant phenotype analyses have demonstrated that the knock-out mutation of different key genes in the symbiotic signaling pathway block AM-associated endoreduplication. Furthermore, our data show that cell divisions occur during initial stages of root colonization and are followed by recursive activation of the endocycle in preparation for arbuscule accommodation.

CONCLUSIONS

In conclusion, our results indicate 3D Object Counter as the best performing Fiji/ImageJ image analysis script in plant root thick sections and its application highlighted endoreduplication as a major feature of the AM pre-penetration response in root cortical cells.

Size matters: three methods for estimating nuclear size in mycorrhizal roots of Medicago truncatula by image analysis

BACKGROUND

The intracellular accommodation of arbuscular mycorrhizal (AM) fungi involves a profound molecular reprogramming of the host cell architecture and metabolism, based on the activation of a symbiotic signaling pathway. In analogy with other plant biotrophs, AM fungi are reported to trigger cell cycle reactivation in their host tissues, possibly in support of the enhanced metabolic demand required for the symbiosis.

RESULTS

We here compare the efficiency of three Fiji/ImageJ image analysis plugins in localizing and quantifying the increase in nuclear size - a hallmark of recursive events of endoreduplication - in M. truncatula roots colonized by the AM fungus Gigaspora margarita. All three approaches proved to be versatile and upgradeable, allowing the investigation of nuclear changes in a complex tissue; 3D Object Counter provided more detailed information than both TrackMate and Round Surface Detector plugins. On this base we challenged 3D Object Counter with two case studies: verifying the lack of endoreduplication-triggering responses in Medicago truncatula mutants with a known non-symbiotic phenotype; and analysing the correlation in space and time between the induction of cortical cell division and endoreduplication upon AM colonization. Both case studies revealed important biological aspects. Mutant phenotype analyses have demonstrated that the knock-out mutation of different key genes in the symbiotic signaling pathway block AM-associated endoreduplication. Furthermore, our data show that cell divisions occur during initial stages of root colonization and are followed by recursive activation of the endocycle in preparation for arbuscule accommodation.

CONCLUSIONS

In conclusion, our results indicate 3D Object Counter as the best performing Fiji/ImageJ image analysis script in plant root thick sections and its application highlighted endoreduplication as a major feature of the AM pre-penetration response in root cortical cells.

The apocarotenoid metabolite zaxinone regulates growth and strigolactone biosynthesis in rice

Carotenoid cleavage dioxygenases (CCDs) form hormones and signaling molecules. Here we show that a member of an overlooked plant CCD subfamily from rice, that we name Zaxinone Synthase (ZAS), can produce zaxinone, a novel apocarotenoid metabolite in vitro. Loss-of-function mutants (zas) contain less zaxinone, exhibit retarded growth and showed elevated levels of strigolactones (SLs), a hormone that determines plant architecture, mediates mycorrhization and facilitates infestation by root parasitic weeds, such as Striga spp. Application of zaxinone can rescue zas phenotypes, decrease SL content and release and promote root growth in wild-type seedlings. In conclusion, we show that zaxinone is a key regulator of rice development and biotic interactions and has potential for increasing crop growth and combating Striga, a severe threat to global food security.

Ectopic activation of cortical cell division during the accommodation of arbuscular mycorrhizal fungi

Arbuscular mycorrhizas (AMs) between plants and soil fungi are widespread symbioses with a major role in soil nutrient uptake. In this study we investigated the induction of root cortical cell division during AM colonization by combining morphometric and gene expression analyses with promoter activation and protein localization studies of the cell-plate-associated exocytic marker TPLATE. Our results show that TPLATE promoter is activated in colonized cells of the root cortex where we also observed the appearance of cells that are half the size of the surrounding cells. Furthermore, TPLATE-green fluorescent protein recruitment to developing cell plates highlighted ectopic cell division events in the inner root cortex during early AM colonization. Lastly, transcripts of TPLATE, KNOLLE and Cyclinlike 1 (CYC1) are all upregulated in the same context, alongside endocytic markers Adaptor-Related Protein complex 2 alpha 1 subunit (AP2A1) and Clathrin Heavy Chain 2 (CHC2), known to be active during cell plate formation. This pattern of gene expression was recorded in wild-type Medicago truncatula roots, but not in a common symbiotic signalling pathway mutant where fungal colonization is blocked at the epidermal level. Altogether, these results suggest the activation of cell-division-related mechanisms by AM hosts during the accommodation of the symbiotic fungus.

The Association With Two Different Arbuscular Mycorrhizal Fungi Differently Affects Water Stress Tolerance in Tomato

Arbuscular mycorrhizal (AM) fungi are very widespread, forming symbiotic associations with ∼80% of land plant species, including almost all crop plants. These fungi are considered of great interest for their use as biofertilizer in low-input and organic agriculture. In addition to an improvement in plant nutrition, AM fungi have been reported to enhance plant tolerance to important abiotic and biotic environmental conditions, especially to a reduced availability of resources. These features, to be exploited and applied in the field, require a thorough identification of mechanisms involved in nutrient transfer, metabolic pathways induced by single and multiple stresses, physiological and eco-physiological mechanisms resulting in improved tolerance. However, cooperation between host plants and AM fungi is often related to the specificity of symbiotic partners, the environmental conditions and the availability of resources. In this study, the impact of two AM fungal species (Funneliformis mosseae and Rhizophagus intraradices) on the water stress tolerance of a commercial tomato cultivar (San Marzano nano) has been evaluated in pots. Biometric and eco-physiological parameters have been recorded and gene expression analyses in tomato roots have been focused on plant and fungal genes involved in inorganic phosphate (Pi) uptake and transport. R. intraradices, which resulted to be more efficient than F. mosseae to improve physiological performances, was selected to assess the role of AM symbiosis on tomato plants subjected to combined stresses (moderate water stress and aphid infestation) in controlled conditions. A positive effect on the tomato indirect defense toward aphids in terms of enhanced attraction of their natural enemies was observed, in agreement with the characterization of volatile organic compound (VOC) released. In conclusion, our results offer new insights for understanding the molecular and physiological mechanisms involved in the tolerance toward water deficit as mediated by a specific AM fungus. Moreover, they open new perspectives for the exploitation of AM symbiosis to enhance crop tolerance to abiotic and biotic stresses in a scenario of global change.

Intraradical colonization by arbuscular mycorrhizal fungi triggers induction of a lipochitooligosaccharide receptor

Functional divergence of paralogs following gene duplication is one of the mechanisms leading to evolution of novel pathways and traits. Here we show that divergence of Lys11 and Nfr5 LysM receptor kinase paralogs of Lotus japonicus has affected their specificity for lipochitooligosaccharides (LCOs) decorations, while the innate capacity to recognize and induce a downstream signalling after perception of rhizobial LCOs (Nod factors) was maintained. Regardless of this conserved ability, Lys11 was found neither expressed, nor essential during nitrogen-fixing symbiosis, providing an explanation for the determinant role of Nfr5 gene during Lotus-rhizobia interaction. Lys11 was expressed in root cortex cells associated with intraradical colonizing arbuscular mycorrhizal fungi. Detailed analyses of lys11 single and nfr1nfr5lys11 triple mutants revealed a functional arbuscular mycorrhizal symbiosis, indicating that Lys11 alone, or its possible shared function with the Nod factor receptors is not essential for the presymbiotic phases of AM symbiosis. Hence, both subfunctionalization and specialization appear to have shaped the function of these paralogs where Lys11 acts as an AM-inducible gene, possibly to fine-tune later stages of this interaction.

The phosphate transporters LjPT4 and MtPT4 mediate early root responses to phosphate status in non mycorrhizal roots

Arbuscular mycorrhizal (AM) symbiosis improves host plant phosphorous (P) status and elicits the expression of AM-inducible phosphate transporters (PTs) in arbuscule-containing cells, where they control arbuscule morphogenesis and P release. We confirmed such functions for LjPT4 in mycorrhizal Lotus japonicus. Promoter-GUS experiments showed LjPT4 transcription not only in arbusculated cells but also in root tips, in the absence of the fungus: here LjPT4 transcription profile depended on the phosphate level. In addition, quantitative RT-PCR confirmed the expression of Lotus and Medicago truncatula PT4 in the tips of non-mycorrhizal roots. Starting from these observations, we hypothesized that AM-inducible PTs may have a regulatory role in plant development, irrespective of the fungal presence. Firstly, we focused on root development responses to different phosphate treatments in both plants demonstrating that phosphate starvation induced a higher number of lateral roots. By contrast, Lotus PT4i plants and Medicago mtpt4 mutants did not show any differential response to phosphate levels, suggesting that PT4 genes affect early root branching. Phosphate starvation-induced genes and a key auxin receptor, MtTIR1, showed an impaired expression in mtpt4 plants. We suggest PT4 genes as novel components of the P-sensing machinery at the root tip level, independently of AM fungi.

Identification and functional characterization of a sulfate transporter induced by both sulfur starvation and mycorrhiza formation in Lotus japonicus

Arbuscular mycorrhizas (AMs) are one of the most widespread symbioses in the world. They allow plants to receive mineral nutrients from the symbiotic fungus which in turn gets back up to 20% of plant carbon and completes its life cycle. Especially in low-nutrient conditions, AM fungi are capable of significantly improving plant phosphate and nitrogen acquisition, but fewer data are available about sulfur (S) nutrition. We focused on S metabolism in Lotus japonicus upon mycorrhizal colonization under sulfur starvation or repletion. We investigated both tissue sulfate concentrations and S-related gene expression, at cell-type or whole-organ level. Gene expression and sulfate tissue concentration showed that Rhizophagus irregularis colonization can improve plant S nutritional status under S starvation. A group 1 sulfate transporter, LjSultr1;2, induced by both S starvation and mycorrhiza formation, was identified. Its transcript was localized in arbuscule-containing cells, which was confirmed with a promoter-GUS assay, and its function was verified through phenotyping of TILLING mutants in nonmycorrhizal seedlings. LjSultr1;2 thus appears to encode a key protein involved in plant sulfate uptake. In contrast to phosphate transporters, a single gene, LjSultr1;2, seems to mediate both direct and symbiotic pathways of S uptake in L. japonicus.

The Lotus japonicus MAMI gene links root development, arbuscular mycorrhizal symbiosis and phosphate availability

The arbuscular mycorrhizal-induced LjMAMI gene is phylogenetically related to GARP transcription factors involved in Pi-starvation responses such as AtPHR1. The gene is strongly upregulated in arbusculated cells from mycorrhizal plants and in root meristems, irrespectively of the fungal presence. A further expression analysis revealed a similar expression pattern for LjPT4, considered a marker gene for mycorrhizal functionality. Here we show that the LjPT4 promoter contains two conserved cis-acting elements typically found in Pi-starvation induced Pi transporters. One of these is strongly related to the binding site of AtPHR1, suggesting a direct regulation of LjPT4 by LjMAMI. The expression of both genes in non-mycorrhizal tissues leads to the hypothesis that these symbiosis-inducible genes are also involved in Pi starvation responses in root meristems in an AM-independent manner.

An AM-induced, MYB-family gene of Lotus japonicus (LjMAMI) affects root growth in an AM-independent manner

The interaction between legumes and arbuscular mycorrhizal (AM) fungi is vital to the development of sustainable plant production systems. Here, we focus on a putative MYB-like (LjMAMI) transcription factor (TF) previously reported to be highly upregulated in Lotus japonicus mycorrhizal roots. Phylogenetic analyses revealed that the protein is related to a group of TFs involved in phosphate (Pi) starvation responses, the expression of which is independent of the Pi level, such as PHR1. GUS transformed plants and quantitative reverse transcription PCR revealed strong gene induction in arbusculated cells, as well as the presence of LjMAMI transcripts in lateral root primordia and root meristems, even in the absence of the fungus, and independently of Pi concentration. In agreement with its putative identification as a TF, an eGFP-LjMAMI chimera was localized to the nuclei of plant protoplasts, whereas in transgenic Lotus roots expressing the eGFP-LjMAMI fusion protein under the control of the native promoter, the protein was located in the nuclei of the arbusculated cells. Further expression analyses revealed a correlation between LjMAMI and LjPT4, a marker gene for mycorrhizal function. To elucidate the role of the LjMAMI gene in the mycorrhizal process, RNAi and overexpressing root lines were generated. All the lines retained their symbiotic capacity; however, RNAi root lines and composite plants showed an important reduction in root elongation and branching in the absence of the symbiont. The results support the involvement of the AM-responsive LjMAMI in non-symbiotic functions: i.e. root growth.

Two putative-aquaporin genes are differentially expressed during arbuscular mycorrhizal symbiosis in Lotus japonicus

BACKGROUND

Arbuscular mycorrhizas (AM) are widespread symbioses that provide great advantages to the plant, improving its nutritional status and allowing the fungus to complete its life cycle. Nevertheless, molecular mechanisms that lead to the development of AM symbiosis are not yet fully deciphered. Here, we have focused on two putative aquaporin genes, LjNIP1 and LjXIP1, which resulted to be upregulated in a transcriptomic analysis performed on mycorrhizal roots of Lotus japonicus.

RESULTS

A phylogenetic analysis has shown that the two putative aquaporins belong to different functional families: NIPs and XIPs. Transcriptomic experiments have shown the independence of their expression from their nutritional status but also a close correlation with mycorrhizal and rhizobial interaction. Further transcript quantification has revealed a good correlation between the expression of one of them, LjNIP1, and LjPT4, the phosphate transporter which is considered a marker gene for mycorrhizal functionality. By using laser microdissection, we have demonstrated that one of the two genes, LjNIP1, is expressed exclusively in arbuscule-containing cells. LjNIP1, in agreement with its putative role as an aquaporin, is capable of transferring water when expressed in yeast protoplasts. Confocal analysis have demonstrated that eGFP-LjNIP1, under its endogenous promoter, accumulates in the inner membrane system of arbusculated cells.

CONCLUSIONS

Overall, the results have shown different functionality and expression specificity of two mycorrhiza-inducible aquaporins in L. japonicus. One of them, LjNIP1 can be considered a novel molecular marker of mycorrhizal status at different developmental stages of the arbuscule. At the same time, LjXIP1 results to be the first XIP family aquaporin to be transcriptionally regulated during symbiosis.

Effects of feeding Spodoptera littoralis on lima bean leaves: IV. Diurnal and nocturnal damage differentially initiate plant volatile emission

Continuous mechanical damage initiates the rhythmic emission of volatiles in lima bean (Phaseolus lunatus) leaves; the emission resembles that induced by herbivore damage. The effect of diurnal versus nocturnal damage on the initiation of plant defense responses was investigated using MecWorm, a robotic device designed to reproduce tissue damage caused by herbivore attack. Lima bean leaves that were damaged by MecWorm during the photophase emitted maximal levels of beta-ocimene and (Z)-3-hexenyl acetate in the late photophase. Leaves damaged during the dark phase responded with the nocturnal emission of (Z)-3-hexenyl acetate, but with only low amounts of beta-ocimene; this emission was followed by an emission burst directly after the onset of light. In the presence of (13)CO(2), this light-dependent synthesis of beta-ocimene resulted in incorporation of 75% to 85% of (13)C, demonstrating that biosynthesis of beta-ocimene is almost exclusively fueled by the photosynthetic fixation of CO(2) along the plastidial 2-C-methyl-D-erythritol 4-P pathway. Jasmonic acid (JA) accumulated locally in direct response to the damage and led to immediate up-regulation of the P. lunatus beta-ocimene synthase gene (PlOS) independent of the phase, that is, light or dark. Nocturnal damage caused significantly higher concentrations of JA (approximately 2-3 times) along with enhanced expression levels of PlOS. Transgenic Arabidopsis thaliana transformed with PlOS promoter :: beta-glucuronidase fusion constructs confirmed expression of the enzyme at the wounded sites. In summary, damage-dependent JA levels directly control the expression level of PlOS, regardless of light or dark conditions, and photosynthesis is the major source for the early precursors of the 2-C-methyl-D-erythritol 4-P pathway.

Effects of feeding Spodoptera littoralis on lima bean leaves. III. Membrane depolarization and involvement of hydrogen peroxide

In response to herbivore (Spodoptera littoralis) attack, lima bean (Phaseolus lunatus) leaves produced hydrogen peroxide (H(2)O(2)) in concentrations that were higher when compared to mechanically damaged (MD) leaves. Cellular and subcellular localization analyses revealed that H(2)O(2) was mainly localized in MD and herbivore-wounded (HW) zones and spread throughout the veins and tissues. Preferentially, H(2)O(2) was found in cell walls of spongy and mesophyll cells facing intercellular spaces, even though confocal laser scanning microscopy analyses also revealed the presence of H(2)O(2) in mitochondria/peroxisomes. Increased gene and enzyme activations of superoxide dismutase after HW were in agreement with confocal laser scanning microscopy data. After MD, additional application of H(2)O(2) prompted a transient transmembrane potential (V(m)) depolarization, with a V(m) depolarization rate that was higher when compared to HW leaves. In transgenic soybean (Glycine max) suspension cells expressing the Ca(2+)-sensing aequorin system, increasing amounts of added H(2)O(2) correlated with a higher cytosolic calcium ([Ca(2+)](cyt)) concentration. In MD and HW leaves, H(2)O(2) also triggered the increase of [Ca(2+)](cyt), but MD-elicited [Ca(2+)](cyt) increase was more pronounced when compared to HW leaves after addition of exogenous H(2)O(2). The results clearly indicate that V(m) depolarization caused by HW makes the membrane potential more positive and reduces the ability of lima bean leaves to react to signaling molecules.

Influence of metabolic syndrome on hypertension-related target organ damage

OBJECTIVES

The aim of our study was to analyse, in a wide group of essential hypertensive patients without diabetes mellitus, the influence of metabolic syndrome (MS) (defined according to the criteria laid down in the Third Report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults) on markers of preclinical cardiac, renal and retinal damage.

DESIGN

Cross-sectional study.

SETTING

Outpatient hypertension clinic.

SUBJECTS AND METHODS

A total of 353 young and middle-aged hypertensives, free from cardiovascular and renal diseases (and 37% of whom had MS), underwent echocardiographic examination, microalbuminuria determination and non-mydriatic retinography.

RESULTS

When compared with subjects without MS, hypertensive patients with MS exhibited more elevated left ventricular (LV) mass (either normalized by body surface area or by height elevated by a power of 2.7), higher myocardial relative wall thickness, albumin excretion rate (AER) and a greater prevalence of LV hypertrophy (57.7% vs. 25.1%; P < 0.00001), of microalbuminuria (36.2% vs. 19.3%; P = 0.002) and of hypertensive retinopathy (87.7% vs. 48.4%; P < 0.00001). These results held even after correction for age, 24-h blood pressures, duration of hypertension, previous antihypertensive therapy, and gender distribution. The independent relationships between LV mass and MS, and between AER and MS, were confirmed in multivariate regression models including MS together with its individual components.

CONCLUSIONS

MS may amplify hypertension-related cardiac and renal changes, over and above the potential contribution of each single component of this syndrome. As these markers of target organ damage are well-known predictors of cardiovascular events, our results may partly explain the enhanced cardiovascular risk associated with MS.

Relationship between albumin excretion rate and aortic stiffness in untreated essential hypertensive patients

OBJECTIVES

To evaluate, in a group of nondiabetic essential hypertensive patients with normal renal function, the relationship between albumin excretion rate (AER) and carotid-femoral pulse wave velocity (PWV), as an index of aortic stiffness.

DESIGN

Cross-sectional study.

SETTING

Outpatient hypertension clinic.

SUBJECTS

Seventy patients with mild-to-moderate essential hypertension, aged 42 +/- 8 years, never pharmacologically treated. All subjects underwent routine laboratory tests, 24-h ambulatory blood pressure (BP) monitoring, measurement of carotid-femoral PWV, by means of a computerized method, and AER.

RESULTS

Microalbuminuric patients (AER > or = 20 microg min(-1); n = 19), when compared with normoalbuminuric subjects, showed more elevated 24-h BP (136/88 +/- 10/10 vs. 128/83 +/- 7/6 mmHg; P < 0.001 and P = 0.013, for systolic and diastolic BP respectively) and higher values of carotid-femoral PWV (10.4 +/- 2 m s(-1) vs. 9.2 +/- 1.3; P = 0.006). This latter difference remained statistically significant, even after correction by ancova for 24-h systolic and diastolic BP, and body mass index (BMI, P = 0.016). Univariate regression analysis disclosed a tight correlation between AER and carotid-femoral PWV (r = 0.42; P = 0.0003). This association was confirmed in a multiple regression model (beta = 0.35; P = 0.009) in which, as independent variables, besides PWV, 24-h BP, age, serum glucose values, smoking status, gender and BMI, were added.

CONCLUSIONS

Our results seem to confirm that microalbuminuria may represent the early renal manifestation of a widespread vascular dysfunction, and therefore it is an integrated marker of cardiovascular risk.

Pulsatile and steady 24-h blood pressure components as determinants of left ventricular mass in young and middle-aged essential hypertensives

In order to explore the relations between left ventricular mass (LVM) and the pulsatile (pulse pressure) and steady (mean pressure) components of the blood pressure (BP) curve, 304 young and middle-aged essential hypertensive patients were studied by means of 24-h ambulatory BP monitoring and echocardiography. In the overall study population, both the BP components showed significant correlations with LVM. These correlations were unevenly distributed in the subgroups of subjects younger and in those older than 50 years. While in this latter subgroup, in multivariate analysis, both 24-h mean BP (24-MBP) (beta = 0.27; P = 0.008) and 24-h pulse pressure (24-h PP) (beta = 0.23; P = 0.02) were associated with LVM, in the subset of younger hypertensives only 24-h MBP (beta = 0.21; P = 0.009) was related to LVM, independent of other covariates. The relations observed between 24-h PP and LVM in the entire study population and in the patients older than 50 years lost statistical significance when the effect of 24-h systolic blood pressure (24-h SBP) was taken into account, in a multiple regression model in which 24-h MBP was replaced by 24-h SBP. Our findings seem to suggest that the association of PP with LVM in middle-aged hypertensives may partially explain the increased cardiovascular risk, documented in subjects with high PP. However, this relation is not independent, but is mediated by SBP.

Using artificial neural networks to model the urinary excretion of total and purine derivative nitrogen fractions in cows

A dataset of 177 individual nitrogen balances from dry and lactating cows was split in two independent groups: training dataset (n = 130) and challenge dataset (n = 47). The training dataset was used to develop multiple linear regressions (MLR) and artificial neural networks (ANN) aimed at predicting the urinary excretion of total (NURI) and that of purine derivative nitrogen (PDN). Input variables for the prediction of NURI were crude protein (CP) intake, effective degradability of non-protein dry matter (DM), neutral detergent fiber (NDF) content of the diet, live weight and milk yield. Live weight, total carbohydrate intake, the ratio of non-protein DM degraded to CP degraded and milk yield corrected for DM intake were entered to predict PDN. The regression between predicted and observed values for the training dataset showed a better statistical accuracy of ANN than did MLR models, especially for PDN. The evaluation of the two models on the challenge dataset showed similar determination coefficients, either when predicting total nitrogen excretion (0.623 and 0.614 for ANN and MLR, respectively) or PDN (0.688 and 0.666, for ANN and MLR, respectively). Moreover, both approaches were affected by a tendency to under-predict both targets at high levels of NURI and PDN. However, with the ANN approach, it is possible to study the response of the model to modifications of individual inputs by the so-called response analysis. This unique feature could be used to study the effect of different physiological situations as well as providing hypotheses for additional research.

Relationships between 24 h blood pressure load and target organ damage in patients with mild-to-moderate essential hypertension

OBJECTIVE

To analyse the relationships between 24 h blood pressure load (the percentage of systolic/diastolic blood pressures exceeding 140/90 mmHg while awake and 120/80 mmHg during sleep) and some indices of hypertensive target organ involvement, independently of the mean level of 24 h blood pressure.

METHODS

One hundred and thirty patients with mild-to-moderate hypertension underwent 24 h ambulatory blood pressure monitoring, ocular fundus examination, microalbuminuria assay and two-dimensional guided M-mode echocardiography. The study population was divided into subsets according to the systolic and diastolic 24 h blood pressure load values predicted from the regression equation relating 24 h blood pressure load to 24 h mean blood pressure. The subjects with an observed load above this predicted value were included in the higher blood pressure load groups, the remaining ones being included in the lower groups.

RESULTS

Relative myocardial wall thickness and total peripheral resistance were greater, and mid-wall fractional shortening, end-systolic stress-corrected mid-wall fractional shortening and cardiac index lower, in the subjects with a higher systolic blood pressure load. Moreover, the stroke index:pulse pressure ratio was reduced, and a greater prevalence of hypertensive retinopathy was observed in the higher systolic load group. On the contrary, no statistically significant difference was found for any of the cardiac, renal and funduscopic parameters examined when the two groups with a higher and lower 24 h diastolic blood pressure load were compared.

CONCLUSIONS

Our results seem to suggest that, in mild-to-moderate arterial hypertension, a high 24 h systolic blood pressure load may be associated, independently of the average level of 24 h systolic ambulatory blood pressure, with an adverse cardiovascular risk profile.

Microalbuminuria, renal dysfunction and cardiovascular complication in essential hypertension

OBJECTIVE

To evaluate the prevalence of microalbuminuria (albumin excretion rate, AER) in a wide hypertensive population, and to evaluate any relationship with cardiovascular damage and renal dysfunction.

DESIGN

A transversal study.

SUBJECTS AND METHODS

In 383 hospitalized Caucasian essential hypertensives (198 men, 185 women) of mean age 44 +/- 0.5 years and mean clinic blood pressure 170.3 +/- 0.95/ 103.4 +/- 0.47 mmHg, metabolic parameters, serum creatinine level (Cs), creatinine clearance rate (Ccs), 24 AER and plasma renin activity (PRA) were measured. Furthermore, each patient underwent 24 h ambulatory blood pressure monitoring (ABPM) and echocardiography to measure left ventricular mass, which was indexed both by body surface area to obtain left ventricular mass index (LVMI) and by height to obtain the left ventricular mass indexed for height (LVMH). By Doppler echocardiography, the diastolic compliance by early:late peak filling velocity ratio was analysed. The fundus oculi was also observed. Three subsets of hypertensives were obtained by dividing the 383 essential hypertensives on the basis of their AER: < or = 11 (group A), 11 < or = 20 (group B) and > 20 micrograms/min (group C).

MAIN OUTCOME MEASURES

Microalbuminuria, creatinine clearance, PRA, ABPM, LVMI, LVMH, early:late peak filling velocity ratio, hypertensive retinopathy.

RESULTS

Among the 383 essential hypertensives, AER was < 11 micrograms/min in 55% of the patients (group A), 18% had AER in the range 11-20 micrograms/min (group B) and 27% had AER > 20 micrograms/min (group C). In the entire essential hypertensive population the prevalence of left ventricular hypertrophy was 44.39% and hypertensive retinopathy was observed in 54.83%. Moreover, AER significantly correlated with clinic systolic blood pressure (SBP) and diastolic blood pressure (DBP), with 24 SBP and DBP and with 24 h daytime and night-time mean blood pressure (MBP). AER was correlated also with LVMH and creatinine clearance. The analysis of the three subsets revealed no differences in age, body mass index, serum creatinine level and PRA. Group C in comparison with group A showed higher values of clinic SBP, 24 h SBP, DBP and MBP, and of daytime and night-time MBP. Furthermore, in group C, LVMI and LVMH were significantly greater than in group A, with a prevalence of left ventricular hypertrophy of 55% in the former group. Group C showed a prevalence of hypertensive retinopathy of 69% whereas in group A the prevalence was 48%. In group C, AER was significantly correlated with serum creatinine level.

CONCLUSIONS

The transversal phase of our research, performed in a homogeneous population of Caucasian essential hypertensives with no metabolic disturbances, confirms the relationship between blood pressure pattern and early glomerular changes in essential hypertensives without overt proteinuria. Furthermore, these results emphasize the role of microalbuminuria as a marker of early cardiac, renal and retinal structural and functional changes in essential hypertension. The longitudinal study, which is in progress, will confirm the prognostic value of microalbuminuria in essential hypertension.

White-coat hypertension and cardiovascular risk

OBJECTIVE

To compare cardiovascular risk in white-coat hypertensives, normotensives and established hypertensives.

METHODS

We studied 61 hypertensive individuals, 27 of whom were white-coat hypertensives, and 35 normotensives. All subjects underwent 24 h noninvasive blood pressure monitoring and Doppler echocardiographic examination of the heart; urine was tested for microalbuminuria and the fundi of the eyes examined for retinopathy.

RESULTS

The 24 h as well as the day- and night-time mean systolic blood pressure (SBP) was slightly but significantly higher in white-coat hypertensives than in normotensives; no significant difference was observed in diastolic blood pressure (DBP) between these groups. In white-coat hypertensives, 24 h SBP and DBP were lower than in established hypertensives (P < 0.001). The echocardiographic study showed higher values of posterior wall thickness, left ventricular mass index (LVMI), and ventricular septum thickness (P < 0.05) in white-coat hypertensives than in normotensives; fractional shortening and ejection fraction were similar. The E:A ratio, obtained from the Doppler study, was lower in white-coat hypertensives than in normotensives (1.14 +/- 0.3 versus 1.24 +/- 0.25; P < 0.05). LVMI values were smaller in white-coat hypertensives than in established hypertensives (P < 0.05), and both ejection fraction and fractional shortening were similar in the two groups. Among white-coat hypertensives, eight out of 27 showed hypertensive retinal damage; microalbuminuria values were similar to those obtained in normotensives.

CONCLUSIONS

The results of this cross-sectional and therefore limited study lead us to hypothesize that white-coat hypertensives are at higher risk than normotensives and lower risk than established hypertensives for developing cardiovascular damage.

Sympathetic overactivity and 24-hour blood pressure pattern in hypertensives with chronic renal failure

In order to assess the activity of the sympathetic system and to evaluate the 24-h blood pressure pattern in hypertensives with chronic renal failure (CRF), 12 CRF patients and 16 essential hypertensives (EHs) were studied. In all subjects, plasma samples for catecholamines and renin activity were obtained both in the basal condition and after standing, and 24-h blood pressure monitoring (ABPM) was performed. The 24-h mean blood pressure results were quite similar between CRFs and EHs. In 50% of the CRFs, ABPM showed a nighttime decrease in diastolic BP (DBP) greater than 10%, while in the remaining 50% the ABPM indicated a nondipper blood pressure pattern. Of the 16 EHs, 4 had a nighttime decrease in DBP < 10%, that is, nondippers. The study of circulating catecholamines showed no significant differences in plasma epinephrine between CRFs and EHs, while plasma norepinephrine (NE) was significantly higher in hypertensives with CRF than in EHs, both at rest and after standing (p < 0.05 and 0.02, respectively). Among dipper hypertensives, subjects with CRF showed greater values of basal plasma NE than EHs (535 +/- 67 vs. 412 +/- 24.5 pg/mL, p < 0.05); the comparison between dipper and nondipper CRFs showed no differences in circulating NE levels (535 vs. 516 pg/mL). The present study shows that CRFs are characterized by higher values of plasma NE than EHs, and that there are no differences in sympathetic activity between dipper and nondipper hypertensives with CRF.

Blood pressure pattern importance in the development of left ventricular hypertrophy in hypertension

Heterogeneous results regarding correlations between blood pressure, (measured by various methods and in different conditions), and left ventricular mass in arterial hypertension have been reported. Fifty-three essential hypertensives, I-II WHO stage, have been studied in order to verify the relationship between office and average 24-hour blood pressure, and its day- and night-time pattern with left ventricular hypertrophy. All patients had newly diagnosed essential hypertension, and no subject had received any antihypertensive therapy before entry. The subjects underwent 24-hour blood pressure monitoring, evaluating the average of 24 hours, day- and night-time blood pressures, and M-mode echocardiography. Neither subjects with nor without left ventricular hypertrophy showed correlations between office blood pressure and left ventricular mass. On the contrary, average 24-hour systolic and diastolic blood pressure resulted related to left ventricular mass (r = 0.36 and 0.40, p less than 0.01 respectively). Furthermore, in the subgroup with left ventricular hypertrophy, left ventricular mass was correlated directly with nocturnal systolic blood pressure (r = 0.46) and inversely with the rate of nocturnal decrease in systolic pressure (r = -0.60, p less than 0.01). These results appear to confirm the usefulness of 24-hour blood pressure monitoring in evaluating cardiac afterload in essential hypertension, and the important role that the 24-hour systolic pressure has in the development of left ventricular hypertrophy in these subjects.