Quantitative NMR microscopy of osmotic stress responses in maize and pearl millet.

The effect of osmotic stress (-0.35 MPa) on the cell water balance and apical growth was studied non-invasively for maize (Zea mays L., cv. LG 11) and pearl millet (Pennisetum americanum L., cv. MH 179) by (1)H NMR microscopy in combination with water uptake measurements. Single parameter images of the water content and the transverse relaxation time (T(2)) were used to discriminate between the different tissues and to follow the water status of the apical region during osmotic stress. The T(2) values of non-stressed stem tissue turned out to be correlated to the cell dimensions as determined by optical microscopy. Growth was found to be strongly inhibited by mild stress in both species, whereas the water uptake was far less affected. During the experiment hardly any changes in water content or T(2) in the stem region of maize were observed. In contrast, the apical tissue of pearl millet showed a decrease in T(2) within 48 h of stress. This decrease in T(2) is interpreted as an increase in the membrane permeability for water.     

Host specificity of trichodinid ectoparasites of freshwater fish

Ciliophorons of the family Trichodinidoe comprise seven genera, all of which are commensolists or parasites - mainly on aquatic hosts such as other ciliophorans, coelenterates, planctonic crustaceans, molluscs, echinoderms, amphibians and fish. Although the first species of this family, Trichodina pediculus, was described from material collected from Hydra, most literature concerns the trichodinids of fish-particularly cultured freshwater fish. These ciliophorans have been implicated in severe disease and mortalities of fish, causing severe economic losses in various parts o f the world. In spite o f the confused taxonomy o f the Trichodinidae, it now appears that they fall into four distinct groups representing a line of specialization towards a more exclusive niche on the host fish. The more opportunistic species, with a broad host range, tend to be larger skin parasites, while the more specialized are smaller and usually only parasitize the gills o f their specific host.     

In vivo qualitative changes of 31P NMR in stressed maize roots vis-à-vis carbon substrate determining the degree of stress

High resolution 31P nuclear magnetic resonance spectroscopy was used to investigate the changes in phosphate metabolism and intracellular pH in intact maize (Zea mays L) root segments to hyper osmotic shock. The results were compared with the happenings under field conditions, when the stress was given gradually. Effect of sugar substrate on adaptation of tissue to both kinds of situations was also studied. The hyper osmotic shock resulted in large vacuolar alkalinization and a decrease in pH across tonoplast membrane. There was gradual build up of phosphocholine and decrease in glucose 6P and UPDG levels. In gradual stress, the root segments were able to adapt to the stress and maintained pH gradient across tonoplast, with marginal alkalinization of vacuoles. The presence of sugar substrate reduced the impact of stress significantly, commensurate with the increased activity of plasmalemma H(+)-ATPase. The latter providing the driving force for uptake of organic molecules and ions required for osmoregulation.     

Identification and genomic distribution of<Emphasis Type="Italic"> gypsy</Emphasis> like retrotransposons in<Emphasis Type="Italic"> Citrus</Emphasis> and<Emphasis Type="Italic"> Poncirus</Emphasis>

Transposable elements might be importantly involved in citrus genetic instability and genome evolution. The presence of gypsy like retrotransposons, their heterogeneity and genomic distribution in Citrus and Poncirus, have been investigated. Eight clones containing part of the POL coding region of gypsy like retrotransposons have been isolated from a commercial variety of Citrus clementina, one of the few sexual species in Citrus. Four of the eight clones might correspond to active elements given that they present all the conserved motifs described in the literature as essential for activity, no in-frame stop codon and no frame-shift mutation. High homology has been found between some of these citrus elements and retroelements within a resistance-gene cluster from potato, another from Poncirus trifoliata and two putative resistance polyproteins from rice. Nested copies of gypsy like elements are scattered along the Citrus and Poncirus genomes. The results on genomic distribution show that these elements were introduced before the divergence of both genera and evolved separately thereafter. IRAPs based on gypsy and copia types of retrotransposons seem to distribute differently, therefore gypsy based IRAPs prove a new, complementary set of molecular markers in Citrus to study and map genetic variability, especially for disease resistance. Similarly to copia-derived IRAPs, the number of copies and heterozygosity values found for gypsy derived IRAPs are lower in Poncirus than in Citrus aurantium, which is less apomictic and the most usual rootstock for clementines until 1970.Communicated by C. Möllers     

Occurrence of ovulation after intracerebroventricular infusion of substance P in 6-OHDA pretreated female rats.

Substance P (SP) infused into the third cerebral ventricle blocks spontaneous ovulation in female rats, probably through catecholaminergic neurons. The studies presented in this paper were undertaken to investigate whether SP exerts its suppressing effect on ovulation in 6-hydroxydopamine (6-OHDA) pretreated female rats. After 8-12 days following 6-OHDA pretreatment female rats were infused, on the day of proestrus, with vehicle and all animals were found to ovulate or with a solution containing 5 nmol of SP and 89% of female rats were then found to ovulate. In the group pretreated with vehicle and subsequently infused with SP, ovulation was found to occur only in 25% of animals. The obtained results indicate that spontaneous ovulation in 6-OHDA-pretreated female rats cannot be blocked by i.c.v. administration of SP, and it may be concluded that SP exerts its suppressing effect through the monoaminergic neurons.     

Genetic diversity in the orange subfamily Aurantioideae. II. Genetic relationships among genera and species

Genetic relationships were studied by means of ten isoenzymatic systems, at the genus and species level, using two distances and four methods of aggregation in a germplasm collection of 198 cultivars and accessions of 54 species belonging to Citrus and 13 related genera. The most consistent results were obtained by the chord distance and the neighbor-joining clustering method. Citrus species were distributed in two main groups: the orange-mandarin group and the lime lemon-citron-pummelo group. The species C. halimii and C. tachibana are not included in these groups. Mandarin species fall into three main subgroups: one includes C. sinensis; the second, C. aurantium, the third, small-fruit species. The citron, the pummelo and the ancient lemon subgroups form a cluster to which the species belonging to subgenus Papeda and the cultivated limes, lemons and bergamots are related. Microcitrus spp, to which Severinia buxifolia and Atalantia ceylanica seem to be related, cluster with the lime lemon-citron-pummelo group while Fortunella is close to the orange-mandarin group. Poncirus trifoliata, the most important species for citrus rootstock improvement is located far from Citrus but connected to it through Fortunella spp. A broad distribution of species has been found that should be taken into account to sample new genotypes in the search of desired characters in order to fully and efficiently use genetic resources for citrus improvement.     

In situ plant water balance studies using a portable NMR spectrometer

A portable ¹H NMR spectrometer has been applied to whole plantsin situ, i.e. in climate rooms and in a greenhouse, to studyplant water relations under these conditions. The spectrometerconsists of a 30 kg permanent magnet system of 0.235 T, modifiedBruker Minispec electronics, and a standard XT pc for spectrometercontrol. Unattended, the system automatically measures the xylemsap stream and tissue water content in a well-defined sectionof the plant stem. Because of the small size of the magnet thesemeasurements can be made at different positions on the plantstem or on different plants in succession. Magnetic field driftdue to the varying climates that occur in greenhouses was correctedby field locking. Results are presented for a single plant ina climate room, demonstrating a method for the study of plantwater hydraulics. In addition, a single plant in a greenhousecrop was measured, and the NMR results were compared with thewater uptake and transpiration rates under (natural) variationof light intensity and relative humidity, demonstrating thereliability of the portable NMR under realistic greenhouse conditions.Finally, the application for the measurement of the root wateruptake efficiency is demonstrated for a number of grafted cucumberplants under constant climatic conditions in a phytotron. Key words: Portable NMR system, plant water balance sensor, greenhouse applications, flow, water content