Anti-hyperlipidemic Effect of Polyphenol Extract (Seapolynol(™)) and Dieckol Isolated from Ecklonia cava in in vivo and in vitro Models

The inhibitory effect of polyphenol extracts (Seapolynol^™, SPN) of the marine brown algae Ecklonia cava and dieckol, a major component of SPN, on hyperlipidemia was investigated in ICR mice fed a high-fat diet (HFD) for five weeks. For analysis of the anti-hyperlipidemic effects of SPN and dieckol, these two agents were given orally on a daily basis to HFD-fed mice for four weeks, starting one week after the beginning of HFD feeding. Groups administered with SPN as well as dieckol showed lower body weight gains than the HFD only group. Administration of SPN and dieckol also resulted in a significant reduction of the level of total cholesterol (TCHO), triglyceride (TG), and low-density lipoprotein (LDL) cholesterol in the serum of HFD-fed mice. In Oil Red O staining using 3T3-L1 preadipocytes, it was shown that both SPN and dieckol markedly inhibited lipid accumulation of 3T3-L1 cells. Furthermore, SPN and dieckol (50 μg/mL) significantly inhibited 3-hydroxyl-methyl glutaryl coenzyme A (HMGCoA) reductase activity in vitro. Taken together, these results suggest that polyphenols of Ecklonia cava (SPN) and dieckol reduce body weight gain and fat accumulation in HFD-induced obese mice, and that their hypolipidemic effect is related to the inhibition of adipogenesis of adipocytes and HMGCoA reductase activity.

Quantitative trait loci for component physiological traits determining salt tolerance in rice

Rice (Oryza sativa) is sensitive to salinity, which affects one-fifth of irrigated land worldwide. Reducing sodium and chloride uptake into rice while maintaining potassium uptake are characteristics that would aid growth under saline conditions. We describe genetic determinants of the net quantity of ions transported to the shoot, clearly distinguishing between quantitative trait loci (QTL) for the quantity of ions in a shoot and for those that affect the concentration of an ion in the shoot. The latter coincide with QTL for vegetative growth (vigor) and their interpretation is therefore ambiguous. We distinguished those QTL that are independent of vigor and thus directly indicate quantitative variation in the underlying mechanisms of ion uptake. These QTL independently govern sodium uptake, potassium uptake, and sodium:potassium selectivity. The QTL for sodium and potassium uptake are on different linkage groups (chromosomes). This is consistent with the independent inheritance of sodium and potassium uptake in the mapping population and with the mechanistically different uptake pathways for sodium and potassium in rice under saline conditions (apoplastic leakage and membrane transport, respectively). We report the chromosomal location of ion transport and selectivity traits that are compatible with agronomic needs and we indicate markers to assist selection in a breeding program. Based upon knowledge of the underlying mechanisms of ion uptake in rice, we argue that QTL for sodium transport are likely to act through the control of root development, whereas QTL for potassium uptake are likely to act through the structure or regulation of membrane-sited transport components.

QTL: their place in engineering tolerance of rice to salinity

Secondary salinization and its relationship to irrigation are strong incentives to improve the tolerance of crops to salinity and to drought. Achieving this through the pyramiding of physiological traits (phenotypic selection without knowledge of genotype) is feasible. However, wide application of this approach is limited by the practicalities of assessing not only the parents, but also large numbers of individuals and families in segregating generations. Genotypic information is required in the form of markers for any quantitative trait loci involved (marker-assisted selection) or of direct knowledge of the genes. In the absence of adequate candidate genes for salt tolerance, a quantitative trait locus/marker-assisted selection approach has been used here. Putative markers for ion transport and selectivity, identified from analysis of amplified fragment length polymorphism, had been discovered within a custom-made mapping population of rice. Here it is reported that none of these markers showed any association with similar traits in a closely related population of recombinant inbred lines or in selections of a cultivar. Whilst markers will be of value in using élite lines from the mapping population in backcrossing, this has to be considered alongside the effort required to develop and map any given population. This result cautions against any expectation of a general applicability of markers for physiological traits. It is concluded that direct knowledge of the genes involved is needed. This cannot be achieved at present by positional cloning. The elucidation of candidate genes is required. Here the problem lies not in the analysis of gene expression but in devising protocols in which only those genes of interest are differentially affected by the experimental treatments.

Additive and antagonistic effects of ozone and salinity on the growth, ion contents and gas exchange of five varieties of rice (Oryza sativa L.)

Five varieties of rice (Oryza sativa L.) of varying salinity resistance were grown in non-saline and in saline conditions, with and without a repeated exposure to ozone at a concentration of 83 nmol mol(-1) giving an AOT40 (cumulative exposure above 40 nmol mol(-1)) of 3600 nmol mol(-1) h. Salinity caused a substantial reduction in shoot and root dry weight in all varieties, but the effect on root growth was proportionately less than on shoot growth. Ozone reduced root dry weight but the treatment used did not significantly affect shoot dry weight. Both salinity and ozone reduced plant height. The potassium concentration in the leaves of all five varieties was reduced by salinity, and by ozone in both saline and non-saline treatments. Ozone reduced the sodium concentration in plants grown at 50 mM NaCl but had no effect upon the chloride concentration. Carbon dioxide assimilation, transpiration and stomatal conductance were all reduced by salinity and by ozone and there was close quantitative similarity between the effects of ozone and/or salinity upon assimilation, stomatal conductance and transpiration. There were some antagonistic effects but there were additive effects of salinity and of ozone on root dry weight, plant height, shoot potassium concentration, photosynthesis, transpiration and stomatal conductance. The possible basis of the additive effects of salinity and ozone on gas exchange and mineral uptake are discussed.

The effects of selection for sodium transport and of selection for agronomic characteristics upon salt resistance in rice (Oryza sativa L.)

A multiple cross was constructed with the aim of combining component traits for the complex salinity resistance character. The aim was to combine donors for physiological traits with the agronomically desirable semidwarf/intermediate plant type and with the overall salinity resistance of the traditional tall land races. We report a study of selection strategies in the resulting breeding population. The effects of early selection for agronomic traits and early selection for low sodium transport were compared with a control population in which minimal selection was practised. Conventional selection for agronomic characters at early generations selected against low sodium-transporting (and thus potentially salt-tolerant) genotypes. In contrast, mild early selection for low sodium transport enriched the population in potentially salt-resistant genotypes but did not select against agronomic (semi-dwarf/intermediate) genotypes. It is concluded that selection for agronomic traits should be made after selection for salt resistance and, ideally, should be delayed until the population has reached near-homozygosity.

Breeding for Salinity Resistance in Crop Plants: Where Next?

Soil salinity is widely reported to be a major agricultural problem, particularly in irrigated agriculture, and research on salinity in plants has produced a vast literature. However, there are only a handful of instances where cultivars have been developed which are resistant to saline soils. Reasons for the lack of success in developing salt-resistant genotypes, and for the low impact that plant physiological research has made, are explored. We conclude that soil salinity has not yet become a sufficient agricultural problem, other than on a local scale, to make salt resistance a high priority objective for plant breeders. The limited success of simple selection, where this has been practised in breeding programs, can be accounted for by the fact that research has consistently shown salt resistance is a complex character controlled by a number of genes or groups of genes and involves a number of component traits which are likely to be quantitative in nature. We also conclude that the results of physiological research have been poorly marketed by physiologists and, understandably, have failed to impress plant breeders. We anticipate that the importance of salinity as a breeding objective will increase in the future. Our assessment of reports of the degradation of irrigation systems, together with projections of the future demands of irrigated agriculture, is that enhancing the salt resistance of at least some crops will be necessary. Salinity resistance will both help provide stability of yield in subsistence agriculture and, through moderating inputs, help limit salinisation in irrigation systems with inadequate drainage. It is emphasised that plant improvement and drainage engineering should be seen as partners and not alternatives. We conclude with a personal view of one way forward for developing salt-resistant genotypes, through the pyramiding of physiological characters.

Screening of rice (Oryza sativa L.) genotypes for physiological characters contributing to salinity resistance, and their relationship to overall performance

Phenotypic resistance of salinity is expressed as the ability to survive and grow in a salinised medium. Some subjective measure of overall performance has normally been used in plant breeding programmes aimed at increasing salinity resistance, not only to evaluate progeny, but to select parents. Salinity resistance has, at least implicitly, been treated as a single trait. Physiological studies of rice suggest that a range of characteristics (such as low shoot sodium concentration, compartmentation of salt in older rather than younger leaves, tolerance to salt within leaves and plant vigour) would increase the ability of the plant to cope with salinity. We describe the screening of a large number of rice genotypes for overall performance (using an objective measure based on survival) and for the aforementioned physiological traits. There was wide variation in all the characters studied, but only vigour was strongly correlated with survival. Shoot sodium concentration, which a priori is expected to be important, accounted for only a small proportion of the variability in the survival of salinity. Tissue tolerance (the cellular component of resistance reflecting the ability to compartmentalise salt within leaves) revealed a fivefold range between genotypes in the tolerance of their leaves to salt, but this was not correlated positively with survival. On the basis of such (lack of) correlation, these traits would be rejected in normal plant breeding practice, but we discuss the fallacies involved in attempting correlation between individual traits and the overall performance of a salt-sensitive species in saline conditions. We conclude that whilst overall performance (survival) can be used to evaluate the salt resistance of a genotype, it is not the basis on which parents should be selected to construct a complex character through breeding. It was the norm for varieties which had one good characteristic affecting salt resistance to be unexceptional or poor in the others. This constitutes experimental evidence that the potential for salt resistance present in the rice genome has not been realised in genotypes currently extant. The results are discussed in relation to the use of physiological traits in plant breeding, with particular reference to environmental stresses that do not affect a significant part of a species' ecological range.

Nonosmotic Effects of Polyethylene Glycols upon Sodium Transport and Sodium-Potassium Selectivity by Rice Roots

Addition of polyethylene glycol (PEG) as an osmotic agent (at -230 kilopascals) dramatically lessened the toxicity of NaCl (at 50 moles per cubic meter) to rice (Oryza sativa L.) seedlings. This was explained by a reduction in the uptake of NaCl. This reduction was much greater than could be accounted for by the lowered transpiration rate resulting from the solute potential changes due to the PEG.Low concentrations of PEG (-33 kilopascals and less) had no effect upon transpiration rate but reduced sodium uptake (from 10-50 moles per cubic meter NaCl) by up to 80%. PEG (at -33 kilopascals) also reduced chloride uptake but had no effect upon the uptake of potassium from low (0.5-2.0 moles per cubic meter) external concentrations. However, the increased uptake of potassium occurring between 2 and 10 moles per cubic meter external concentration was abolished by PEG. Similar concentrations of mannitol had no effect upon sodium uptake in rice. PEG, in similar conditions, had much less effect upon sodium uptake by the more salt-resistant species, barley.(22)Na studies showed that PEG reduced the transport of sodium from root to shoot, but had a long half time for maximal effect (several days).(14)C-labeled PEG was shown to bind to microsomal membranes isolated from rice roots; it is suggested that this is due to multipoint attachment of the complex ions of PEG which exist in aqueous solutions. It is argued that this reduces passive membrane permeability, which accounts for the large effect of PEG on sodium influx in rice and the different effects on sodium influx and (carrier-dependent) potassium influx.

Ion measurements by X-ray microanalysis in unfixed, frozen, hydrated plant cells of species differing in salt tolerance

A technique is described for X-ray microanalysis of unfixed, frozen, hydrated higher plant cells using a scanning electron microscope in conjunction with a cryostage. Freezing in liquid N2 is the only preparative step required. Using this method, ion distribution was compared in the roots of Zea mays L. (termed a salt excluder) and Hordeum vulgare L. (which is rather more tolerant), both grown in the presence of NaCl. Distinct differences were observed between the two species in Na, K and Cl distribution. Evidence is presented to support the hypothesis that reabsorption of Na from the xylem sap in the mature regions of the root may occur in salt-sensitive glycophytes such as Z. mays.