Ultrastructural features of the salt gland of Tamarix aphylla L.

Summary The salt gland in Tamarix is a complex of eight cells composed of two inner, vacuolate, collecting cells and six outer, densely cytoplasmic, secretory cells. The secretory cells are completely enclosed by a cuticular layer except along part of the walls between the collecting cells and the inner secretory cell. This non-cuticularized wall region is termed the transfusion are (Ruhland, 1915) and numerous plasmodesmata connect the inner secretory cells with the collecting cells in this area. Plasmodesmata also connect the collecting cells with the adjacent mesophyll cells.There are numerous mitochondria in the secretory cells and in different glands they show wide variation in form. In some glands wall protuberances extend into the secretory cells forming a labyrinth-like structure; however, in other glands the protuberances are not extensively developed. Numerous small vacuoles are found in some glands and these generally are distributed around the periphery of the secretory cells in association with the wall protuberances. Further, an unusual structure or interfacial apparatus is located along the anticlinal walls of the inner secretory cells. The general structure of the gland including the cuticular encasement, connecting plasmodesmata, interfacial apparatus, and variations in mitochondria, vacuoles, and wall structures are discussed in relation to general glandular function.     

Ecological effects of the parasitic rust fungus Uromyces lineolatus (Pucciniaceae) on Glaux maritima (Primulaceae)

Disease incidence of the parasitic rust fungus Uromvces lineolatus (Pucciniaceae) on Glaux maritima (Primulaceae) was recorded in three transects across a Baltic sea shore meadow The effects of the fungus on growth, flowering, seed production and germinability were investigated No significant differences between healthy and diseased plants were found except for abortion rate, germinability and germination rate Incidence of the disease seems to be correlated with accumulation of litter from the winter host Scirpus mantimus (Cyperaceae)     

In vitro morphogenesis ofCrambe maritima L.

Summary Tissue cultures isolated from the root ofCrambe maritima have now undergone 17 transfers over two years on a medium containing 10% coconut milk, 2.0 mg/l IAA + 0.8 mg/l kinetin. The cultures consist predominantly of organized structures varying in complexity from nodular to root-like outgrowths and teratomatous leafy shoots. Embryoid-like structures also occur.     

Effect of drought on leaf gland secretion of the mangrove Avicennia germinans L.

This study assessed the effects of salinity changes over space and time upon leaf gland secretion in Avicennia germinans trees growing naturally in an area featuring markedly seasonal rainfall. Soil ? (, soil N MPa) during the wet season was -0.95ǂ.05 and -2.12ǂ.08 at low and high salinity sites, respectively. During the dry season, these values decreased to -3.24ǂ.09 at low salinity and to -5.75ǂ.06 at high salinity. Consequently, predawn and midday plant water potential were lowered during drought at both sites. The rates of secretion (mmol m^-2 h^-1 ) increased during drought from 0.91ǂ.12 during the wet season to 1.93ǂ.12 at low salinity, and from 1.69ǂ.12 during the wet season to 2.81ǂ.15 at high salinity. Conversely, stomatal conductance (g_s) was lowered by both salinity and drought. As xylem osmolality increased during drought, secretion tended to rise exponentially, and g_s decayed hyperbolically. Thus, a trade-off is obtained between enhancement in salt secretion and control of water loss suggested by g_s.     

The crystal structure of indoleglycerol-phosphate synthase from Thermotoga maritima. Kinetic stabilization by salt bridges.

The crystal structure of the thermostable indoleglycerol-phosphate synthase from Thermotoga maritima (tIGPS) was determined at 2.5 A resolution. It was compared with the structures of the thermostable sIGPS from Sulfolobus solfataricus and of the thermolabile eIGPS from Escherichia coli. The main chains of the three (beta alpha)(8)-barrel proteins superimpose closely, and the packing of side chains in the beta-barrel cores, as well as the architecture of surface loops, is very similar. Both thermostable proteins have, however, 17 strong salt bridges, compared with only 10 in eIGPS. The number of additional salt bridges in tIGPS and sIGPS correlates well with their reduced rate of irreversible thermal inactivation at 90 degrees C. Only 3 of 17 salt bridges in tIGPS and sIGPS are topologically conserved. The major difference between the two proteins is the preference for interhelical salt bridges in sIGPS and intrahelical ones in tIGPS. The different implementation of salt bridges in the closely related proteins suggests that the stabilizing effect of salt bridges depends rather on the sum of their individual contributions than on their location. This observation is consistent with a protein unfolding mechanism where the simultaneous breakdown of all salt bridges is the rate-determining step.     

Electrophysiological membrane characteristics of the salt tolerant Plantago maritima and the salt sensitive Plantago media

Plasmid pUCD607 was mobilized into the biocontrol agent Enterobacter cloacae strain E6 by conjugation and the resultant strain, E6(pUCD607), was bioluminescent. Biocontrol of Pythium ultimum by E6(pUCD607) was similar to that of the parent strain, E6. The location of E6(pUCD607) in the soil and in the rhizosphere of lettuce was readily determined by pressing agar medium against plant roots in a root box, allowing the bacteria to grow overnight on the medium, and detecting the presence of bioluminescence by autophotography. There was a positive, linear correlation between population sizes determined by dilution plating and the quantity of light emitted due to bioluminescence. However, both the intercept and slope of this line varied among experiments possibly due to the differing physiological states of cells recovered from soils. The amount of light emitted by the bioluminescent strain E6(pUCD607) was not quantitative. This technique is useful for qualitative determinations of populations and for photographically locating bacteria.     

An efficient autofluorescence method for screening Limonium bicolor mutants for abnormal salt gland density and salt secretion

With the spread of saline soils worldwide, it has become increasingly important to understand salt-tolerant mechanisms and to develop halophytes with increased salt tolerance. Limonium bicolor is a typical recretohalophyte and has a typical salt excretory structure in the epidermis called the salt gland. A method that can be used to screen a large population of L. bicolor mutants for altered salt gland density and altered salt secretion is needed but is currently unavailable. Leaves of 1-month-old L. bicolor seedlings were processed by three traditional methods [epidermal peel, nail impression, and clearing/differential interference contrast microscope (clearing/DIC) method] and a fluorescence method (fluorescence microscopic examination of cleared leaves). With the fluorescence method, the autofluorescence of salt glands under UV excitation (330–380 nm) was easily distinguished with the least labor and time. The fluorescence method was used to screen ~ 10,000 seedlings (which grew from gamma-irradiated seeds). Four mutants with reduced salt gland density and 15 with increased salt gland density were obtained. Both kinds of mutants will be useful for the isolation of genes involved in salt gland development and salt secretion in L. bicolor and other halophytes. The fluorescence method was also successfully used to observe the salt glands of Aegialitis rotundifolia and the stomata and trichomes of Arabidopsis. The fluorescence method described here will be useful for examining plant epidermal structures that have autofluorescence under UV or other wavelengths.     

Salt tolerance in the halophyte Suaeda maritima L. Dum.

Osmotic potentials and individual epidermal cell turgor pressures were measured in the leaves of seedlings of Suaeda maritima growing over a range of salinities. Leaf osmotic potentials were lower (more negative) the higher the salt concentration of the solution and were lowest in the youngest leaves and stem apices, producing a gradient of osmotic potential towards the apex of the plant. Epidermal cell turgor pressures were of the order of 0.25 to 0.3 MPa in the youngest leaves measured, decreasing to under 0.05 MPa for the oldest leaves. This pattern of turgor pressure was largely unaffected by external salinity. Calculation of leaf water potential indicated that the gradient between young leaves and the external medium was not altered by salinity, but with older leaves, however, this gradient diminished from being the same as that for young leaves in the absence of NaCl, to under 30% of this value at 400 mM NaCl. These results are discussed in relation to the growth response of S. maritima.     

Embryology and relationships ofSuriana maritima L. (Surianaceae)

An intensive study of the embryology ofSuriana maritima L. is made to provide the information for discussing relationships and systematic position of the genus which is uncertain yet. Notable embryological features ofSuriana include: ovular archesporium multi-celled; ovule unitegmic, campylotropous, and crassinucellate with a nucellar cap; obturator not formed; ovule and seed pachychalazal; chalazal haustorium of endosperm formed; mature seed exalbuminous. Comparisons with possibly related families suggest thatSuriana is distinct from any of the families discussed but best resembles Rutaceae (and Simaroubaceae). Until a study onStylobasium and several other genera, which might be closer toSuriana, comes up in future, we tentatively support the placement ofSuriana as a monotypic family Surianaceae in Rutalessens. Takhtajan.     

Ecophysiological and genomic analysis of salt tolerance of Cakile maritima

Arabidopsis thaliana L. (Brassicaceae) and its close relative Thellungiella salsuginea (Pallas) O.E. Schulz have been widely used as genetic models by researchers in their quest of understanding salt tolerance mechanisms in plants. Despite the fact that significant knowledge has been gained, both of these plants present some limitations mainly in relation to their response to salinity. Indeed, Arabidopsis is a glycophyte, whereas Thellungiella is a facultative halophyte. Among the Brassicaceae, Cakile maritima Scop. is an annual succulent obligate halophyte with a small size genome (1C = 719 Mb) and short life cycle. With these attributes, C. maritima presents a potential as a genetic model system to address salt stress adaptations at the molecular level in the quest to identify salt stress tolerance mechanisms. Beside their potential as promising model species, halophytes might also be valued for their potential as cash crops themselves. The present paper aims to highlight the main results gained on C. maritima using multidisciplinary approaches in complement to those obtained on plant model species of the Brassicaceae family.