The water status of the roots of soil-grown maize in relation to the maturity of their xylem

The long delayed maturation of the late metaxylem of maize ( Zea mays ) roots imposes a high-resistance barrier between the immature apices and the negative water potential of the leaves. These apices (20+ cm) bear strongly adhering soil sheaths to within 0.5 to 2 cm of the distal end. It was hypothesized that the sheathed immature apices should show less response to transpiration stress than bare regions. Measurements were made of the relative water content (RWC) of the sheathed and bare zones of the axile roots, both at different ages of the plant, and early and late in the day's transpiration. Sheathed roots maintained a steady RWC of about 83% irrespective of age or transpiration. Bare roots had RWCs of about 63% in the morning, but this fell to 55% in the afternoon. The first-order branches on the bare roots in the morning had still lower values of RWC, near 50%. Plots of RWC against water potential were indistinguishable for the three root types. It is concluded that the immature apices are indeed relatively isolated from the fluctuating tensions in the stem xylem, and that these tensions reduce the water content of bare roots and their branches to low values.     

Retention in Situ and Spectral Analysis of Fluorescent Vacuole Components in Sections of Plant Tissues

The contents of plant vacuoles vary in different organs and with the health of the plant, but little is known of the cell-to-cell distribution of soluble organic compounds within plant tissues. Soluble fluorescent phenolic compounds can be immobilized in plant tissues using an anhydrous freeze-substitution and resin embedment process. The vacuolar fluorescence can be characterized in fluorescence photomicrographs for variations in color and intensity, or more quantitatively with spectra obtained using a microspectrofluorometer. This is demonstrated here in freeze-substituted roots and leaves of soybean. Excitation and emission spectra of individual vacuoles can be compared with spectra of pure compounds to form profiles of the varied phenolic contents of plant vacuoles. Such analyses will add an important anatomical dimension to the study of plant defense and stress responses.     

THE OCCURRENCE OF WALL PAPILLAE IN ROOT EPIDERMAL CELLS OF AXENICALLY GROWN SEEDLINGS OF ZEA MAYS

Lens-shaped wall papillae, resembling those known to form in response to fungi or mechanical damage, occur in root epidermal cells of axenically grown seedlings of Zea mays. Papillae are most common in the tabular epidermal cells but also occur in younger cells. Not all tabular cells have papillae, and they are more frequent in some seedlings. Where present, there is usually only one papilla per cell and it lies against the outer periclinal wall just proximal to an emerged root hair or near the position where a hair would be expected to form. Electron micrographs show that a papilla is structurally heterogeneous. Papillae fluoresce strongly in the presence of aniline blue even in freeze-substituted material.     

Distribution of glucosinolates and sulphur-rich cells in roots of field-grown canola (Brassica napus)

To investigate the role played by the distribution pattern of glucosinolates (GSLs) in root systems in the release of biocides to the rhizosphere, GSLs have been localized, for the first time, to specific regions and cells in field-grown roots. GSL concentrations in separated tissues of canola (Brassica napus) were determined by chemical analysis, and cell-specific concentrations by extrapolation from sulphur concentrations obtained by quantitative cryo-analytical scanning electron microscopy (SEM). In roots with secondary growth, GSL concentrations in the outer secondary tissues were up to 5x those of the inner core. The highest GSL concentrations (from sulphur measurements) were in two cell layers just under the outermost periderm layer, with up to 100x published concentrations for whole roots. Primary tissues had negligible GSL. Release and renewal of the peripheral GSLs is probably a normal developmental process as secondary thickening continues and surface cells senesce, accounting for published observations that intact roots release GSLs and their biocide hydrolosates to the rhizosphere. Absence of myrosin idioblasts close to the root surface suggests that GSLs released developmentally are hydrolysed by myrosinase in the rhizosphere, ensuring a continuous localized source of biotoxic hydrolysates which can deter soil-borne pests, and influence microbial populations associated with long-lived components of the root system.     

Microscopic reversibility of protein folding in molecular dynamics simulations of the engrailed homeodomain

The principle of microscopic reversibility states that at equilibrium the number of molecules entering a state by a given path must equal those exiting the state via the same path under identical conditions or, in structural terms, that the conformations along the two pathways are the same. There has been some indirect evidence indicating that protein folding is such a process, but there have been few conclusive findings. In this study, we performed molecular dynamics simulations of an ultrafast unfolding and folding protein at its melting temperature to observe, on an atom-by-atom basis, the pathways the protein followed as it unfolded and folded within a continuous trajectory. In a total of 0.67 micros of simulation in water, we found six transient denaturing events near the melting temperature (323 and 330 K) and an additional refolding event following a previously identified unfolding event at a high temperature (373 K). In each case, unfolding and refolding transition state ensembles were identified, and they agreed well with experiment on the basis of a comparison of S and Phi values. On the basis of several structural properties, these 13 transition state ensembles agreed very well with each other and with four previously identified transition states from high-temperature denaturing simulations. Thus, not only were the unfolding and refolding transition states part of the same ensemble, but in five of the seven cases, the pathway the protein took as it unfolded was nearly identical to the subsequent refolding pathway. These events provide compelling evidence that protein folding is a microscopically reversible process. In the other two cases, the folding and unfolding transition states were remarkably similar to each other but the paths deviated.     

Vascular development of the grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L.) inflorescence rachis in response to flower number,plant growth regulators and defoliation

The grapevine inflorescence is a determinate panicle and as buds emerge, shoot, flower and rachis development occur simultaneously. The growth and architecture of the rachis is determined by genetic and environmental factors but here we examined the role of flower and leaf number as well as hormones on its elongation and vascular development. The consequences of rachis morphology and vascular area on berry size and composition were also assessed. One week prior to anthesis, Merlot and Cabernet Sauvignon field vines were exposed to manual flower removal, exogenous plant growth regulators or pre-bloom leaf removal. Manual removal of half the flowers along the vertical axis of the inflorescence resulted in a shorter rachis in both cultivars. Conversely, inflorescences treated with gibberellic acid (GA₃) and the synthetic cytokinin, 6-benzylaminopurine (BAP) resulted in a longer rachis while pre-bloom removal of all leaves on the inflorescence-bearing shoot did not alter rachis length relative to untreated inflorescences. Across the treatments, the cross-sectional areas of the conducting xylem and phloem in the rachis were positively correlated to rachis girth, flower number at anthesis, bunch berry number, bunch berry fresh mass and bunch sugar content at harvest. Conversely, average berry size and sugar content were not linked to rachis vascular area. These data indicate that the morphological and vascular development of the rachis was more responsive to flower number and plant growth regulators than to leaf removal.     

Increased daily physical activity and fatigue symptoms in chronic fatigue syndrome

Individuals with chronic fatigue syndrome (CFS) have been shown to have reduced activity levels associated with heightened feelings of fatigue. Previous research has demonstrated that exercise training has beneficial effects on fatigue-related symptoms in individuals with CFS. PURPOSE: The aim of this study was to sustain an increase in daily physical activity in CFS patients for 4 weeks and assess the effects on fatigue, muscle pain and overall mood. METHODS: Six CFS and seven sedentary controls were studied. Daily activity was assessed by a CSA accelerometer. Following a two week baseline period, CFS subjects were asked to increase their daily physical activity by 30% over baseline by walking a prescribed amount each day for a period of four weeks. Fatigue, muscle pain and overall mood were reported daily using a 0 to 100 visual analog scale and weekly using the Profile of Mood States (Bipolar) questionnaire. RESULTS: CFS patients had significantly lower daily activity counts than controls (162.5 +/- 51.7 x 103 counts/day vs. 267.2 +/- 79.5 x 103 counts/day) during a 2-week baseline period. At baseline, the CFS patients reported significantly (P < 0.01) higher fatigue and muscle pain intensity compared to controls but the groups did not differ in overall mood. CFS subjects increased their daily activity by 28 +/- 19.7% over a 4 week period. Overall mood and muscle pain worsened in the CFS patients with increased activity. CONCLUSION: CFS patients were able to increase their daily physical activity for a period of four weeks. In contrast to previous studies fatigue, muscle pain, and overall mood did not improve with increased activity. Increased activity was not presented as a treatment which may account for the differential findings between this and previous studies. The results suggest that a daily "activity limit" may exist in this population. Future studies on the impact of physical activity on the symptoms of CFS patients are needed.