Structural and molecular strategy of photosynthetic apparatus organisation of wild flora halophytes.

Structural and molecular parameters of photosynthetic apparatus in plants with different strategies for the accumulation of salts were investigated. CO2 gas exchange rate, content of pigments, mesostructure, chloroplast ultrastructure and the biochemical composition of the membrane structural components in leaves were measured. The objects of the study were euhalophytes (Salicornia perennans, Suaeda salsa, Halocnemum strobilaceum), crynohalophyte (Limonium gmelinii), glycohalophyte (Artemisia santonica). Euhalophytes S. perennans and S. salsa belong to the plants of the halosucculent type, three other species represent the xerophilic type. The highest photosynthetic activity estimated by the average parameters of CO2 gas exchange rate in the leaves was observed in S. perennans plants. Plants of the xerophyte type including both H. strobilaceum euhalophyte and cryno- and glycohalophytes are described by lower values of these characteristics. Larger cells with a great number of chloroplasts and a high content of membrane glycerolipids and unsaturated C18:3 fatty acid, but with smaller pigment and light-harvesting complexes size characterise the features of euhalophytes with a succulent leaf type. Thus, features of the mesostructure, ultrastructure, and supramolecular interactions of the halophyte PA were closely related to the functional parameters of gas exchange, and were characterised by the strategy of species in relation to the accumulation of salts, the life form of plants, and the attitude to the method of water regulation.

The salt glands of Tamarix usneoides E. Mey. ex Bunge (South African Salt Cedar).

Tamarix usneoides is a halophyte tree endemic to south-western Africa. This species is known to excrete a range of ions from specialized glandular structures on its leaves. To understand the mechanisms involved in the transport, sequestration and excretion of ions by the glands, a study was performed on salt gland distribution and ultrastructure. The glands are vesiculated trichomes, comprised of eight cells viz. two basal collecting cells and six excretory cells, partially bounded by a secondary cell wall that could serve as an impermeable barrier, forcing excess ions to move from the apoplast of the surrounding tissue into the cytoplasm of the basal excretory cells. It was hypothesized that the ions are moved across the excretory cells in endocytotic vesicles that fuse with the plasmalemma or form junctional complexes, allowing ion movement from one excretory cell to the next. In the apical cell, the vesicles fuse with the plasmalemma, releasing the ions into the network of cell wall ingrowths which channel the ions to the outside surface of the cell. This study shows that there are distinct structural adaptations for the processing of ions for excretion, although the mechanism by which ions enter the cells still needs to be determined.

The influence of salinity on growth, morphology, leaf ultrastructure, and cell viability of the seagrass Halodule wrightii Ascherson.

Halodule wrightii is an ecologically important seagrass; however, little is known about the adaptation of this species in the context of environmental change, particularly changes arising from alterations in salinity of coastal ecosystems. This study aimed to determine the effects of different salinities on growth, morphology, leaf ultrastructure, and cell viability of H. wrightii. To accomplish this, plants were cultivated for 21 days in salinities of 25, 35, and 45. More hydropotens were observed in samples exposed to salinity of 45 with increased invagination of the plasma membrane and cell wall. These invaginations were also observed in other epidermal cells of the leaf blade. In particular, a significant retraction of plasma membrane was seen in samples exposed to salinity of 45, with possible deposition of compounds between the membrane and cell wall. Osmotic stress in samples exposed to salinity of 45 affected the chloroplasts through an increase in plastoglobules and thylakoids by granum in the epidermal chloroplasts of the leaf and decrease in the number of chloroplasts. Overall, this study showed that H. wrightii can survive within salinities that range between 25 and 45 without changing growth rate. However, the plant did have higher cell viability at salinity of 35. Salt stress in mesocosms, at both salinity of 25 and 45, decreased cell viability in this species. H . wrightii had greater changes in salinity of 45; this showed that the species is more tolerant of salinities below this value.

Phylogeography and modes of reproduction in diploid and tetraploid halophytes of Limonium species (Plumbaginaceae): evidence for a pattern of geographical parthenogenesis.

BACKGROUND AND AIMS: The genus Limonium (Plumbaginaceae) has long been recognized to have sexual and apomictic (asexual seed formation) modes of reproduction. This study aimed to elucidate phylogeographical patterns and modes of reproduction in diploid and tetraploid Limonium species, namely three putative sexual diploid species with morphological affinities (L. nydeggeri, L. ovalifolium, L. lanceolatum) and three related, probably apomict tetraploid species (L. binervosum, L. dodartii, L. multiflorum). METHODS: cpDNA diversity and differentiation between natural populations of the species were investigated using two chloroplast sequence regions (trnL intron and trnL-trnF intergenic spacer). Floral heteromorphies, ovule cytoembryological analyses and pollination and crossing tests were performed in representative species of each ploidy group, namely diploid L. ovalifolium and tetraploid L. multiflorum, using plants from greenhouse collections. KEY RESULTS AND CONCLUSIONS: Genetic analyses showed that diploid species have a higher haplotype diversity and a higher number of unique (endemic) haplotypes than tetraploid species. Network analysis revealed correlations between cpDNA haplotype distribution and ploidy groups, species groups and geographical origin, and haplotype sharing within and among species with distinct ploidy levels. Reproductive biology analyses showed that diploid L. ovalifolium mainly forms meiotically reduced tetrasporic embryo sacs of Gagea ova, Adoxa and Drusa types. Limonium multiflorum, however, has only unreduced, diplosporic (apomictic) embryo sacs of Rudbeckia type, and autonomous apomictic development seems to occur. Taken together, the findings provide evidence of a pattern of 'geographical parthenogenesis' in which quaternary climatic oscillations appear to be involved in the geographical patterns of coastal diploid and tetraploid Limonium species.

Sex-specific responses and tolerances of Populus cathayana to salinity.

Responses of males and females to salinity were studied in order to reveal sex-specific adaptation and evolution in Populus cathayana Rehd cuttings. This dioecious tree species plays an important role in maintaining ecological stability and providing commercial raw material in southwest China. Female and male cuttings of P. cathayana were treated for about 1 month with 0, 75 and 150 mM NaCl. Plant growth traits, gas exchange parameters, chlorophyll pigments, intrinsic water use efficiency (WUEi), membrane system injuries, ion transport and ultrastructural morphology were assessed and compared between sexes. Salt stress caused less negative effects on the dry matter accumulation, growth rate of height, growth rate of stem base diameter, total number of leaves and photosynthetic abilities in males than in females. Relative electrolyte leakage increased more in females than in males under salinity stress. Soil salinity reduced the amounts of leaf chlorophyll a, chlorophyll b and total chlorophyll, and the chlorophyll a/b ratio more in females than in males. WUEi decreased in both sexes under salinity. Regarding the ultrastructural morphology, thylakoid swelling in chloroplasts and degrading structures in mitochondria were more frequent in females than in males. Moreover, females exhibited significantly higher Na(+) and Cl(-) concentrations in leaves and stems, but lower concentrations in roots than did males under salinity. In all, female cuttings of P. cathayana are more sensitive to salinity stress than males, which could be partially due to males having a better ability to restrain Na(+) transport from roots to shoots than do females.

The extreme halophyte Salicornia veneta is depleted of the extrinsic PsbQ and PsbP proteins of the oxygen-evolving complex without loss of functional activity.

BACKGROUND AND AIMS: Photosystem II of oxygenic organisms is a multi-subunit protein complex made up of at least 20 subunits and requires Ca(2+) and Cl(-) as essential co-factors. While most subunits form the catalytic core responsible for water oxidation, PsbO, PsbP and PsbQ form an extrinsic domain exposed to the luminal side of the membrane. In vitro studies have shown that these subunits have a role in modulating the function of Cl(-) and Ca(2+), but their role(s) in vivo remains to be elucidated, as the relationships between ion concentrations and extrinsic polypeptides are not clear. With the aim of understanding these relationships, the photosynthetic apparatus of the extreme halophyte Salicornia veneta has been compared with that of spinach. Compared to glycophytes, halophytes have a different ionic composition, which could be expected to modulate the role of extrinsic polypeptides. METHODS: Structure and function of in vivo and in vitro PSII in S. veneta were investigated and compared to spinach. Light and electron microscopy, oxygen evolution, gel electrophoresis, immunoblotting, DNA sequencing, RT-PCR and time-resolved chlorophyll fluorescence were used. KEY RESULTS: Thylakoids of S. veneta did not contain PsbQ protein and its mRNA was absent. When compared to spinach, PsbP was partly depleted (30 %), as was its mRNA. All other thylakoid subunits were present in similar amounts in both species. PSII electron transfer was not affected. Fluorescence was strongly quenched upon irradiation of plants with high light, and relaxed only after prolonged dark incubation. Quenching of fluorescence was not linked to degradation of D1 protein. CONCLUSIONS: In S. veneta the PsbQ protein is not necessary for photosynthesis in vivo. As the amount of PsbP is sub-stoichiometric with other PSII subunits, this protein too is largely dispensable from a catalytic standpoint. One possibility is that PsbP acts as an assembly factor for PSII.