Haramonas dimorpha gen. et sp. nov. (Raphidophyceae), a new marine raphidophyte from Australian mangrove*

A new raphidophyte flagellate is described from the river mouth of the Daintree River, north-east Australia where there are extensive mangrove forests. The organism has two distinct phases: a club-shaped motile form, and a more or less spherical benthic non-motile form. The motile cell is metabolic and possesses 10–20 chloroplasts. The chloroplasts are imbricated, somewhat reminiscent of roofing tiles. A unique structure has been found at the posterior end of the cell. It is a tubular invagination, which consists of a single membrane supported by many small flattened vesicles. In addition, the structure is surrounded by many fibril-containing vesicles. The tubular invagination is different from both the contractile vacuoles and the pusules of dinoflagellates in both behavior and structure. Based on the possession of these unique features, it is concluded that the this mangrove flagellate should be described as a new species in a new genus and the name Haramonas dimorpha Horiguchi gen. et sp. nov. is proposed.     

Hydraulic conductance, stomatal conductance, and maximal photosynthetic rate in bean leaves

A positive correlation was found between steady state values of hydraulic (L _pA) and stomatal conductance (g _s) of French bean leaves: both were lower in the dark than in the light and lower in water-deficient plants than in the well-watered ones. The relative rate of stomatal opening after a pressure rise in the xylem was also positively related to L _pA. The L _pA and g _s were both related to the maximal photosynthetic rate at saturating CO2 concentrations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Distribution of plant functional types along gradients of disturbance intensity and resource supply in an agricultural landscape

Abstract. In this study, plant functional types are understood as groups of plants with similar biological traits displaying significant optima or maxima on a gradient plane of resource supply and disturbance intensity. The biological traits refer to expansion, vegetative regeneration, generative reproduction, dispersal and seed bank longevity. 129 vegetation samples were taken in an agricultural landscape in southwestern Germany, covering a wide range of terrestrial vegetation types – but with the exception of forests and wetlands. For each site, also soil data were recorded. Mean daily soil moisture was estimated with a simple model. Soil moisture, balanced nitrogen supply and available phosphorus were combined into a factor ‘resource supply’. In addition, disturbance intensity was estimated for each site. This factor was based on (1) frequency of disturbance, (2) disturbance depth below or above the soil surface, and (3) proportion of the area affected by a discrete disturbance event. 30 plant groups with similar biological characteristics resulted from a cluster analysis, based on a compilation of 19 biological traits for a regional species pool. Logistic regression on a gradient plane of disturbance intensity and resource supply yielded response curves for 28 groups. The dependent variable was defined as the probability of encountering all members of a group in a sample. 17 groups display a significant response curve on the gradient plane. Plants with a potential for long- range dispersal are concentrated on sites with low or high disturbance intensities (e.g. fallow land, fields, lawns). On sites with medium disturbance intensity (e.g. meadows) and low to medium resource supply, small-range dispersal predominates. There are no distinct trends concerning seed bank longevity. The potential for vertical and lateral expansion increases with decreasing disturbance intensity. Only at medium disturbance intensities does vertical expansion correlate positively with resource supply. Rapid detachment of daughter individuals occurs more often on productive sites than on less productive sites. Diversity of groups with similar biological traits is highest on sites with medium disturbance intensities.     

Direct somatic embryogenesis from axes of mature peanut embryos

Summary Plant regeneration via somatic embryogenesis was obtained in peanut (Arachis hypogaea L.) from axes of mature zygotic embryos. The area of greatest embryogenic activity was a 2-mm region adjacent to and encircling the epicotyl. Somatic embryogenesis was evaluated on Murashige and Skoog media supplemented with a variety of auxin treatments. Maximum production occurred on medium supplemented with 3 mg · liter⁻¹ 4-amino-3,5,6-trichloropicolinic acid. Explant cultures were transferred to half-strength medium supplemented with 1 mg · liter⁻¹ gibberellic acid for somatic embryo germination and early plantlet growth. Plantlets, transferred to soil, were placed in a greenhouse and grown to maturity.     

Study of thiol proteases of normal human skin fibroblasts

The protease activity of cultured normal human skin fibroblasts was studied using the synthetic fluorigenic peptides, the modified protein 4-methylumbelliferyl-casein, the thiol inhibitors and the affinity for concanavalin A-Sepharose. The majority of the activity to N-benzyloxycarbonyl-L-phenylalanyl-L-arginyl-7-amido-4-methyl-coumarin and N-a-benzyloxycarbonyl-L-arginyl-arginyl-7-amido-4-methylcoumarin had a pH optimum of 6.0, and was thiol-dependent and inhibited by leupeptin and antipain. The activity toward N-benzyloxycarbonyl-L-phenylalanyl-L-arginyl-7-amido-4-methylcoumarin represents both cathepsin B and cathepsin L, whereas the activity towards 4-methylumbelliferyl-casein represent only cathepsin L. Cathepsin H could not be detected when assayed with L-arginine-7-amido-4-methylcoumarin substrate. Cathepsin D was present in comparatively small amounts when assayed with 4-methylumbelliferyl-casein. Activity towards 4-methylumbelliferyl-casein had pH optima at 3 and 6 and was stimulated by dithiothreitol. A proportion of the activity at pH 6.0 was not dependent on thiols and not inhibited by leupeptin, and had the general characteristics of a carboxyl proteinase. Over 70 per cent of the activity was in the lysosomal fraction and showed structure-linked latency. All the detectable protein emerged from the immobilized concanavalin A column and the fractions eluted by alpha-methyl-D-mannoside were significantly hydrolysed the synthetic peptides. Only that fraction which bound to concanavalin A was active towards 4-methylumbelliferyl-casein. Cathepsin B had no affinity for concanavalin A-Sepharose due to the absence of glycoprotein content, unlike cathepsin L which showed a strong affinity for concanavalin A-Sepharose.     

Relative growth rate correlates negatively with pathogen resistance in radish: the role of plant chemistry

Plant growth rate has frequently been associated with herbivore defence: a large investment in quantitative defence compounds occurs at the expense of growth. We tested whether such a relationship also holds for growth rate and pathogen resistance. For 15 radish (Raphanus sativus L.) cultivars, we determined the potential growth rate and the resistance to fungal wilt disease caused by Fusarium oxysporum. We subsequently aimed to explain a putative negative relationship between growth rate and resistance based on plant chemical composition. Both growth rate and resistance level varied greatly among cultivars. Moreover, there was a strong negative correlation between growth rate and resistance, i.e. there are costs associated with a high resistance level. Roots of slow-growing, resistant cultivars have a higher biomass density. Using pyrolysis mass spectrometry. we part1y explained variation in both growth rate and resistance in terms of the same change in chemical composition. Leaves of slow-growing, resistant cultivars contained more cell wall material. Surprisingly, roots of slow-growing, highly resistant cultivars contained significantly less cell wall material, and more cytoplasmic elements (proteins). We speculate that this higher protein concentration is related to high construction and turn-over costs and high metabolic activity. The latter in turn is thought to be responsible for a rapid and adequate resistance reaction, in which phenols may be involved.     

The different effects of PEG 6000 and NaCI on leaf development are associated with differential inhibition of root water transport

The inhibitory effects of PEG on whole-plant growth can exceed the effects of other osmolytes such as NaCI, and this has been ascribed to toxic contaminants, or to reduced oxygen availability in PEG solutions. We investigated another possibility, namely that PEG has an additional inhibitory effect on root water transport which in turn affects leaf development. The effects on first-leaf growth of applications of PEG 6000 or isoosmotic NaCI to the roots were determined using hydroponically grown maize (Zea mays L.) seedlings. Leaf growth rates were inhibited within minutes of PEG application to the roots and remained inhibited for days. The inhibitory effects on growth of NaCI, and also of KCl and mannitol, were much smaller. The comparative effects of NaCI and PEG on root water transport were determined by assaying pressurized flow through excised roots. PEG induced a 7-fold greater inhibition of flow through live roots than NaCI. Killing of the roots by heat treatment, to reduce cell membrane resistances to solute penetration, nearly doubled the flow rate for roots in NaCI, but not for roots in PEG. We suggest that the greater viscosity of PEG solutions, as compared with NaCI, may be a primary factor contributing to the additional inhibition of water flow through live and killed roots. PEG did not have additional effects on leaf turgor but had a 3 times greater inhibitory effect than NaCI on the irreversible extensibility of the leaves and induced 16 times more leaf accumulation of the growth inhibitory stress hormone abscisic acid (ABA). We conclude that greater inhibition of root water transport by PEG 6000, as compared with NaCI, leads to additional reductions in extensibility, additional ABA accumulation, and a greater inhibition of leaf growth.