Low Osmotic Potential Research Articles

Response of microbial activity and community structure to decreasing soil osmotic and matric potential

Low soil water content (low matric potential) and salinity (low osmotic potential) occur frequently in soils, particularly in arid and semi-arid regions. Although the effect of low matric or low osmotic potential on soil microorganisms have been studied before, this is the first report which compares the effect of the two stresses on microbial activity and community structure. A sand and a sandy loam, differing in pore size distribution, nutrient content and microbial biomass and community structure, were used. For the osmotic stress experiment, salt (NaCl) was added to achieve osmotic potentials from −0.99 to −13.13 MPa (sand) and from −0.21 to 3.41 MPa (sandy loam) after which the soils were pre-incubated at optimal water content for 10d. For the matric stress experiment, soils were also pre-incubated at optimal water content for 10d, after which the water content was adjusted to give matric potentials from −0.03 and −1.68 MPa (sand) and from −0.10 to 1.46 MPa (sandy loam). After amendment with 2% (w/w) pea straw (C/N 26), soil respiration was measured over 14d. Osmotic potential decreased with decreasing soil water content, particularly in the sand. Soil respiration decreased with decreasing water potential (osmotic + matric). At a given water potential, respiration decreased to a greater extent in the matric stress experiment than in the osmotic stress experiment. Decreasing osmotic and matric potential reduced microbial biomass (sum of phospholipid fatty acids measured after 14 days) and changed microbial community structure: fungi were less tolerant to decreasing osmotic potential than bacteria, but more tolerant to decreasing water content. It is concluded that low matric potential may be more detrimental than a corresponding low osmotic potential at optimal soil water content. This is likely to be a consequence of the restricted diffusion of substrates and thus a reduced ability of the microbes to synthesise osmolytes to help maintain cell water content. The study also highlighted that it needs to be considered that decreasing soil water content concentrates the salts, hence microorganisms in dry soils are exposed to two stressors.

Overexpression of the mitogen-activated protein kinase gene OsMAPK33 enhances sensitivity to salt stress in rice (Oryza sativa L.)

Mitogen-activated protein kinases (MAPK) signalling cascades are activated by extracellular stimuli such as environmental stresses and pathogens in higher eukaryotic plants. To know more about MAPK signalling in plants, aMAPK cDNA clone, OsMAPK33, was isolated from rice. The gene is mainly induced by drought stress. In phylogenetic analysis, OsMAPK33 (Os02g0148100) showed approximately 47-93% identity at the amino acid level with other plant MAPKs. It was found to exhibit organ-specific expression with relatively higher expression in leaves as compared with roots or stems, and to exist as a single copy in the rice genome. To investigate the biological functions of OsMAPK33 in rice MAPK signalling, transgenic rice plants that either overexpressed or suppressed OsMAPK33 were made. Under dehydration conditions, the suppressed lines showed lower osmotic potential compared with that of wild-type plants, suggesting a role of OsMAPK33 in osmotic homeostasis. Nonetheless, the suppressed lines did not display any significant difference in drought tolerance compared with their wild-type plants. With increased salinity, there was still no difference in salt tolerance between OsMAPK33-suppressed lines and their wild-type plants. However, the overexpressing lines showed greater reduction in biomass accumulation and higher sodium uptake into cells, resulting in a lower K+/Na+ ratio inside the cell than that in the wild-type plants and OsMAPK33-suppressed lines. These results suggest that OsMAPK33 could play a negative role in salt tolerance through unfavourable ion homeostasis. Gene expression profiling of OsMAPK33 transgenic lines through rice DNA chip analysis showed that OsMAPK33 altered expression of genes involved in ion transport. Further characterization of downstream components will elucidate various biological functions of this novel rice MAPK.

Analysis of osmotin, a PR protein as metabolic modulator in plants

Osmotin is an abundant cationic multifunctional protein discovered in cells of tobacco (Nicotiana tabacum L. var Wisconsin 38) adapted to an environment of low osmotic potential. Beside its role as osmoregulator, it provides plants protection from pathogens, hence also placed in the PRP family of proteins. The osmotin induced proline accumulation has been reported to confer tolerance against both biotic and abiotic stresses in plants including transgenic tomato and strawberry overexpressing osmotin gene. The exact mechanism of induction of proline by osmotin is however, not known till date. These observations have led us to hypothesize that osmotin could be regulating these plant responses through its involvement either as transcription factor, cell signal pathway modulator or both in plants. We have therefore, undertaken the present investigation to analyze the osmotin protein as transcription factor using bioinformatics tools. The results of available online DNA binding motif search programs revealed that osmotin does not contain DNAbinding motifs. The alignment results of osmotin protein with the protein sequence from DATF showed the homology in the range of 0-20%, suggesting that it might not contain a DNA binding motif. Further to find unique DNA-binding domain, the superimposition of osmotin 3D structure on modeled Arabidopsis transcription factors using Chimera also suggested absence of the same. However, evidence implicating osmotin in cell signaling were found during the study. With these results, we therefore, concluded that osmotin is not a transcription factor, but regulating plant responses to biotic and abiotic stresses through cell signaling.

Overexpression of a Common Wheat Gene TaSnRK2.8 Enhances Tolerance to Drought, Salt and Low Temperature in Arabidopsis

Drought, salinity and low temperatures are major factors limiting crop productivity and quality. Sucrose non-fermenting1-related protein kinase 2 (SnRK2) plays a key role in abiotic stress signaling in plants. In this study, TaSnRK2.8, a SnRK2 member in wheat, was cloned and its functions under multi-stress conditions were characterized. Subcellular localization showed the presence of TaSnRK2.8 in the cell membrane, cytoplasm and nucleus. Expression pattern analyses in wheat revealed that TaSnRK2.8 was involved in response to PEG, NaCl and cold stresses, and possibly participates in ABA-dependent signal transduction pathways. To investigate its role under various environmental stresses, TaSnRK2.8 was transferred to Arabidopsis under control of the CaMV-35S promoter. Overexpression of TaSnRK2.8 resulted in enhanced tolerance to drought, salt and cold stresses, further confirmed by longer primary roots and various physiological characteristics, including higher relative water content, strengthened cell membrane stability, significantly lower osmotic potential, more chlorophyll content, and enhanced PSII activity. Meanwhile, TaSnRK2.8 plants had significantly lower total soluble sugar levels under normal growing conditions, suggesting that TaSnRK2.8 might be involved in carbohydrate metabolism. Moreover, the transcript levels of ABA biosynthesis (ABA1, ABA2), ABA signaling (ABI3, ABI4, ABI5), stress-responsive genes, including two ABA-dependent genes (RD20A, RD29B) and three ABA-independent genes (CBF1, CBF2, CBF3), were generally higher in TaSnRK2.8 plants than in WT/GFP controls under normal/stress conditions. Our results suggest that TaSnRK2.8 may act as a regulatory factor involved in a multiple stress response pathways.

Increased gelling agent concentration promotes somatic embryo maturation in hybrid larch (Larix×eurolepsis): a 2‐DE proteomic analysis

An integrated physiological and proteomic approach was used to investigate the effects of high gellan gum concentration in the medium during maturation of somatic embryos (SE) of hybrid larch, by comparing embryos incubated in media with a high gellan gum concentration (8 g l(-1) ) and the standard concentration (4 g l(-1) ) after 1, 3, 6 and 8 weeks of maturation. Because of the reduced availability of water in the 8 g l(-1) medium, the cultured embryos had a lower osmotic water potential (Ψπ) and water contents, but higher dry weights (DWs), at 8 weeks compared with embryos cultured on the standard medium. The high gellan gum concentration induced a desiccation that is characteristic in zygotic embryo maturation. Total soluble proteins were extracted from SE with trichloroacetic acid (TCA)-acetone after 1 and 8 weeks of maturation on media with 4 and 8 g l(-1) of gellan gum, and separated by two-dimensional gel electrophoresis (2-DE) at pH 4-7. More than 1100 proteins were reproducibly detected on each gel. At 1 and 8 weeks respectively, the abundances of 62 and 49 spots detected in analyses of embryos matured at the two gellan gum concentrations, significantly differed. Among 62 significantly differing spots at 1 week of maturation, the corresponding proteins of 56 were reliably identified by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS), and were found to be mainly involved in 'carbohydrate metabolism', 'genetic information processing' or 'environmental information processing' according to kegg taxonomy. Both physiological parameters and the proteins identified suggested that the embryos were stressed when they were cultured on 4 g l(-1) of gellan gum.

Differential effects of two species of arbuscular mycorrhiza on the growth and water relations of Spartium junceum and Anthyllis cytisoides

Anthyllis cytisoides and Spartium junceum are two leguminous shrubs native of semiarid mediterranean areas, often used in revegetation strategies. Mycorrhization of both shrubs with Glomus intraradices BEG 72 enhanced both plants growth and water relations under drought stress. Root colonization achieved by Glomus mosseae was lower than the level achieved by G. intraradices in both plants studied, and the effects of the inoculation with G. mosseae BEG 116 were less positive than those observed for G. intraradices. Before the onset of the drought stress period the specific leaf weight (SLW) of S. junceum plants inoculated with G. mosseae was lower than the SLW of control and G. intraradices plants. At the end of the stress period, after 15 days of withholding water, the relative water content of S. junceum twigs was lower for G. mosseae inoculated plants and higher for G. intraradices inoculated plants, compared to control, non-inoculated plants. At the end of the recovery period, 15 days after the reestablishment of watering, there were no differences between inoculation treatments on the parameters related to the plants water status. Anthyllis cytisoides plants inoculated with G. intraradices had lower leaf osmotic potential, more leaves, and higher chlorophyll content (measured as SPAD values). Anthyllis cytisoides plants responded to drought defoliating, but defoliation was lower for the plants inoculated with G. intraradices. At the end of the drought, the leaf osmotic potential was lowest for G. intraradices plants as was the relative water content (RWC) whilst Glomus mosseae inoculated plants had the highest RWC, SLW and osmotic potential values. At the end of the recovery period, all plants recuperated the osmotic potential values measured at the pre-stress period. In our experiments, G. intraradices BEG 72 was found to be superior to G. mosseae BEG 116, this difference could be attributed to the origin of the fungus, native from a Mediterranean area, compared to G. mosseae (BEG116) isolated from the UK.

The effects of salinity and osmotic stress on barley germination rate: sodium as an osmotic regulator

Seed germination is negatively affected by salinity, which is thought to be due to both osmotic and ion-toxicity effects. We hypothesize that salt is absorbed by seeds, allowing them to generate additional osmotic potential, and to germinate in conditions under which they would otherwise not be able to germinate. Seeds of barley, Hordeum vulgare, were germinated in the presence of either pure water or one of five iso-osmotic solutions of polyethylene-glycol (PEG) or NaCl at 5, 12, 20 or 27 °C. Germination time courses were recorded and germination indices were calculated. Dry mass, water content and sodium concentration of germinating and non-germinating seeds in the NaCl treatments at 12 °C were measured. Fifty supplemental seeds were used to evaluate the changes in seed properties with time. Seeds incubated in saline conditions were able to germinate at lower osmotic potentials than those incubated in iso-osmotic PEG solutions and generally germinated faster. A positive correlation existed between external salinity and seed salt content in the saline-incubated seeds. Water content and sodium concentration increased with time for seeds incubated in NaCl. At higher temperatures, germination percentage and dry mass decreased whereas germination index and sodium concentration increased. The results suggest that barley seeds can take up sodium, allowing them to generate additional osmotic potential, absorb more water and germinate more rapidly in environments of lower water potential. This may have ecological implications, allowing halophytic species and varieties to out-compete glycophytes in saline soils.

Maternal effects and drought tolerance determine seedling establishment success in a common roadside plant,Dipsacus fullonumsubspsylvestris

Previous studies have demonstrated that plants collected as seeds from roadside populations of Dipsacus fullonum L. subsp sylvestris (Huds.) Claphamare more tolerant of high salinity, low osmotic potentials, and hypoxia during juvenile growth stages than those from oldfield populations. However, it is unclear how tolerance to these abiotic stressors translates into performance in the roadside environment. Here, we conducted a reciprocal transplant experiment between oldfield and roadside environments. Seeds from three roadside and three oldfield populations were planted into oldfield and roadside sites in late fall. Throughout the spring and summer, the survivorship and size of the seedlings were monitored to examine differences in performance in the two habitats. We also assessed the relation between performance in the field and previous in vitro measures of salt and drought tolerance of each population. A drought caused high mortality levels in the oldfield and roadside. Individuals from roadside populations did not exhibit increased growth or survivorship in the roadside environment. In the early months of seedling growth, neither salt nor drought tolerance were significantly correlated with performance in the roadside during seedling establishment. Rather, during these early months, the average size of individuals in each population in the field was positively correlated with the population’s average seed mass, indicating that maternal provisioning had a greater impact than tolerance to particular environmental stresses during the juvenile stages of development. However, later in the summer, after the drought began, the average size of individuals from each population in the field was positively correlated with that population’s average drought tolerance.

Effect of Salinity and Low Osmotic Potential on the Germination and Seedling Growth of Rapeseed Cultivars with Different Stress Tolerance

In mediterranean environments, rapeseed is grown in fall-winter with late-summer sowing and this implies that germination and initial seedling growth may occur in soils with low water content and/or high salinity. Lab experiments were carried out to study the effect of the level and timing of salt and osmotic stress application on the germination and seedling growth of rapeseed (Brassica napus var. oleifera Del.) cultivars with different stress tolerance. After a preliminary screening on eighteen cultivars, four hybrids with different stress tolerance during germination were chosen to study germination on Petri dishes at 14 increasing concentrations of PEG 6000 (ψs up to -1.5 MPa) and 12 increasing concentrations of NaCl (up to 600 mM). Seedlings from seeds germinated at 0 and 250 mM of NaCl were then grown into boxes for the slant test containing NaCl solutions 0 mM and 100 mM, while seedlings from seeds germinated -0.8 and -0.03 MPa (PEG) were grown in pots containing siliceous sand with a water content equivalent to field capacity or half of field capacity. In both experiments seedlings were grown for 11 days under controlled light/temperature conditions. Therefore, for both salt and osmotic stress experiments, the following four combinations for “germination-growth” conditions were obtained for each cultivar: optimum-optimum; optimum-stress; stress-optimum; stress-stress. The following determinations were performed: final percentage germination, time to 50% germination (T50), and base water potential of seeds; dry and fresh weights, and shoot and root lengths of seedlings at the end of the growth period (i.e. 11 days after plant transfer to the growth medium), and correspondent relative growth rates between the start and the end of the growth period. The different degree of stress tolerance observed among rapeseed cultivars for germination was in the order of 150 mMol for NaCl concentration and 0.2-0.3 MPa for osmotic potential. Nonetheless, cultivars did not differ substantially for growth parameters of seedlings exposed to stressing conditions, and in some cases cultivars with higher tolerance during germination resulted even more sensitive during growth, especially under salt stress. The severe stresses applied reduced seedling growth, and root more than shoot growth. Agronomic implications for the different stress tolerance of cultivars are discussed.

Ecophysiological response of Crambe maritima to airborne and soil-borne salinity

There is a need to evaluate the salt tolerance of plant species that can be cultivated as crops under saline conditions. Crambe maritima is a coastal plant, usually occurring on the driftline, with potential use as a vegetable crop. The aim of this experiment was to determine the growth response of Crambe maritima to various levels of airborne and soil-borne salinity and the ecophysiological mechanisms underlying these responses. In the greenhouse, plants were exposed to salt spray (400 mM NaCl) as well as to various levels of root-zone salinity (RZS) of 0, 50, 100, 200 and 300 mM NaCl during 40 d. The salt tolerance of Crambe maritima was assessed by the relative growth rate (RGR) and its components. To study possible salinity effects on the tissue and cellular level, the leaf succulence, tissue Na(+) concentrations, Na(+) : K(+) ratio, net K(+)/Na(+) selectivity, N, P, K(+), Ca(2+), Mg(2+), proline, soluble sugar concentrations, osmotic potential, total phenolics and antioxidant capacity were measured. Salt spray did not affect the RGR of Crambe maritima. However, leaf thickness and leaf succulence increased with salt spray. Root zone salinities up to 100 mM NaCl did not affect growth. However, at 200 mM NaCl RZS the RGR was reduced by 41 % compared with the control and by 56 % at 300 mM NaCl RZS. The reduced RGR with increasing RZS was largely due to the reduced specific leaf area, which was caused by increased leaf succulence as well as by increased leaf dry matter content. No changes in unit leaf rate were observed but increased RZS resulted in increased Na(+) and proline concentrations, reduced K(+), Ca(2+) and Mg(2+) concentrations, lower osmotic potential and increased antioxidant capacity. Proline concentrations of the leaves correlated strongly (r = 0.95) with RZS concentrations and not with plant growth. Based on its growth response, Crambe maritima can be classified as a salt spray tolerant plant that is sensitive to root zone salinities exceeding 100 mM NaCl.

Variations physiologiques dans des populations de thuyas géants (Thuja plicata Donn ex D. Don) en réponse à une sécheresse courte

• Variation in the ability of western redcedar ( Thuja plicata Donn ex D. Don) populations to withstand water stress may exist because this species is found in coastal and interior biogeoclimatic subzones representing the full range of precipitation regimes in British Columbia, Canada.• Seven western redcedar populations from locations in British Columbia, representing a wide range of habitat types, were assessed for their gas exchange and water relations response to controlled drought. • Before drought, population variation occurred in stomatal conductance, net CO 2 assimilation rate and intrinsic water use efficiency and the relative water content at turgor loss point. During drought, populations had different responses of net CO 2 assimilation to decreasing predawn shoot water potential. After drought, populations differed in stomatal conductance and intrinsic water use efficiency, plus osmotic potential at turgor loss point, osmotic potential at saturation and apparent cuticular transpiration. Western redcedar populations from drier-inland habitats had a lower osmotic potential at turgor loss point, lower relative water content at turgor loss point and lower apparent cuticular transpiration in response to drought than populations from coastal origin with temperate maritime habitat.• Reduction of cuticular water loss and adjustments of cellular water relations in response to drought was found to occur among seven western redcedar populations originating along a precipitation gradient while; there were minimal population differences in the gas exchange response to drought.

Profiling of mitochondrial transcriptome in germinating wheat embryos and seedlings subjected to cold, salinity and osmotic stresses

Mitochondrial functions are potential targets of abiotic stresses that are major environmental factors limiting plant development and productivity. To evaluate mitochondrial responses to abiotic stresses we studied mitochondrial transcriptome profiles at the early stages of wheat development after imbibition under normal and induced stress conditions. Three stresses given were low temperature (4 degrees C), high salinity (0.2 M NaCl) and high osmotic potential (0.3 M mannitol). All these stresses greatly reduced growth but dramatically increased respiration both via the cytochrome and alternative pathways. Macroarray analysis of the mitochondrial transcriptome revealed that most of the changes in transcript levels were stress specific but groups of genes responded commonly to different stresses. Under 3-days continuous stresses, 13 genes showed low temperature specific responses with either up- or down-regulation, while 14 and 23 genes showed responses specific to high salinity and high osmotic potential, respectively. On the other hand, 13 genes showed common responses, among which cob and ccmFn increased their transcript levels while transcripts of the other genes including nad6, atp4 and atp9 decreased. The differential profiles of mitochondrial transcriptome revealed by the macroarray analysis were verified by the quantitative reverse transcriptase PCR analysis. Taken together, three among five nuclear-encoded mitochondria-targeted genes included in the array showed decreases under the stresses, while MnSOD and AOX increased their transcript amounts. Our results indicated the existence of common and different regulatory mechanisms that can sense different abiotic stresses and modulate both nuclear and mitochondrial gene expression in germinating wheat embryos and seedlings.

Effects of NO 3 − -N on the growth and salinity tolerance of Tamarix laxa Willd

The influence of NO 3 − -N on growth and osmotic adjustment was studied in Tamarix laxa Willd., a halophyte with salt glands on its twigs. Seedlings of T. laxa Willd. were exposed to 1 mM (control) or 300 mM NaCl, with 0.05, 1 or 10 mM NO 3 − -N for 24 days. The relative growth rate of seedlings at 300 mM NaCl was lower than that of control plants at all NO 3 − -N levels, but the concentrations of organic N and total N in the twigs did not differ between the two NaCl treatments. Increasing NO 3 − supply under 300 mM NaCl improved the growth of T. laxa, indicating that NO 3 − played positive roles in improving salt resistance of the plant. The twigs of T. laxa Willd. accumulated mainly inorganic ions, especially Na+ and Cl−, to lower osmotic potential (Ψs): the contributions of Na+ and Cl− to Ψs were estimated at 31% and 27% respectively, at the highest levels of supply of both NaCl and NO 3 − -N. The estimated contribution of NO 3 − -N to Ψs was as high as 20% in the twigs in these conditions, indicating that NO 3 − was also involved in osmotic adjustment in the twigs. Furthermore, increases in tissue NO 3 − were accompanied by decreases in tissue Cl− and proline under 300 mM NaCl. The estimated contribution of proline to Ψs declined as with NO 3 − -N supply increased from 1 to 10 mM, while the contributions of nitrate to Ψs were enhanced under 300 mM NaCl. This suggested that higher accumulation of nitrate in the vacuole alleviated the effects of salinity stress on the plant by balancing the osmotic potential. In conclusion, NO 3 − -N played both nutritional and osmotic roles in T. laxa Willd. in saline conditions.

Comparing plant water relations for wheat with alternative pulse and oilseed crops grown in the semiarid Canadian prairie

Understanding the drought physiology of alternate crops is essential to assess the production risks of new cropping systems. We compared the water relations of dry (field) pea (Pisum sativum L.), chickpea (Cicer arietinum L.), canola (Brassica napus L.) and mustard (Brassica juncea L.) with spring wheat (Triticum aestivum L.) under different moisture availabilities in field trials conducted in 1997 and 1998 at Swift Current, SK. Stress experience and stress responses varied with crop type. In general, there were similarities in drought physiology between the two pulse crops and between the two oilseed crops. The mean predawn leaf water potential of pea was frequently lowest, while the mean midday leaf water potential of wheat was at least -0.40 MPa lower than for any other crop. The crops exhibited different strategies to overcome water stress. Wheat had the lowest osmotic potential at full turgor, except under drought when turgor was lowest for chickpea and wheat; the highest values were observed in Brassica spp. Mean midday pressure potentials were lowest in wheat (and mostly negative, indicating loss of turgor) and highest for the pulse crops. Mean midday pressure potential for canola was positive when well-watered, otherwise it was near 0. Despite lowering osmotic potential, wheat could not maintain positive turgor much of the time at midday. Pulse crops, with the contributions from both osmotic adjustment and cell elasticity, maintained positive turgor over a wider range of water potentials compared with the other crops. With regard to both osmotic adjustment and tissue elasticity, we ranked the crops from high to low ability to adjust to moderate to severe water stress as pulses > wheat > Brassica oilseeds. Key words: Leaf water, osmotic, turgor potentials, wheat, pulse, canola, semiarid prairie

Osmoregulation and nutritional relationships between Orobanche foetida and faba bean

The present study aims at comparing the phloem composition of the tolerant XBJ90.03-16-1-1-1 and the susceptible Bachaar genotypes and the impact of the faba bean genotype on the levels of the major solutes and invertase activities in the parasite Orobanche foetida. In comparison to Bachaar, the XBJ90.03-16-1-1-1 genotype limited the growth of orobanche tubercles under in vitro conditions. The limited growth was due to low soluble invertase activity, low osmotic potential of the infected roots and the organic nitrogen deficiency of the host phloem sap. The faba bean genotype did not affect the osmoregulation process of O. foetida. Among the organic solutes, stachyose, hexoses, starch and free amino acids, mainly asparagine and aspartate were highly accumulated in orobanche. However, asparagine/aspartate, glutamine/glutamate, alanine, serine, gamma amino butyric acid, stachyose, sucrose were identified as the main organic components in the host phloem exudates. The key role of the enzymes α-galactosidase, asparagine synthetase and aspartate oxaloglutarate aminotransferase in the utilization of the host solutes is proposed in O. foetida parasitizing faba bean.

Seed Germination and Seedling Emergence of Synedrella (Synedrella nodiflora) in a Tropical Environment

Synedrella is a tropical annual plant species of the family Asteraceae that is widely distributed in many crops in nearly 50 countries. Experiments were conducted to determine the influence of various environmental factors on seed germination and seedling emergence of synedrella. Germination response was greater at 30/20 C and 35/25 C than at 25/15 C fluctuating day/night temperatures. Light stimulated germination; however, a small proportion of after-ripened seeds germinated in the dark. Seedling emergence was greatest (96%) for seeds placed on the soil surface but declined with increased seed burial depth. No seedlings emerged from a depth of 4 cm. Seedling emergence and seedling dry matter declined with the addition of crop residue to the soil surface; however, higher quantities of residue than those normally found in low-yield systems were required to result in substantial reductions in emergence. Seed germination was tolerant of moderate salt concentrations (40 to 100 mM sodium chloride) and a broad range of pH (4 to 10) but was sensitive to low osmotic potentials (< −0.8 MPa). The information gained from this study could help predict the invasion potential of this species and could lead to improved management strategies.

Leaf cold acclimation and freezing injury in C3 and C4 grasses of the Mongolian Plateau

The scarcity of C4 plants in cool climates is usually attributed to their lower photosynthetic efficiency than C3 species at low temperatures. However, a lower freezing resistance may also decrease the competitive advantage of C4 plants by reducing canopy duration, especially in continental steppe grasslands, where a short, hot growing season is bracketed by frost events. This paper reports an experimental test of the hypothesis that cold acclimation is negligible in C4 grasses, leading to greater frost damage than in C3 species. The experiments exposed six C3 and three C4 Mongolian steppe grasses to 20 d chilling or control pre-treatments, followed by a high-light freezing event. Leaf resistance to freezing injury was independent of photosynthetic type. Three C3 species showed constitutive freezing resistance characterized by <20% leaf mortality, associated with high photosynthetic carbon fixation and electron transport rates and low leaf osmotic potential. One freezing-sensitive C4 species showed the expected pattern of chilling-induced damage to photosynthesis and >95% leaf mortality after the freezing event. However, three C3 and two C4 species displayed a cold acclimation response, showing significant decreases in osmotic potential and photosynthesis after exposure to chilling, and a 30–72% reduction of leaf freezing injury. This result suggested that down-regulation of osmotic potential may be involved in the cold acclimation process, and demonstrated that there is no inherent barrier to the development of cold acclimation in C4 species from this ecosystem. Cold acclimation via osmoregulation represents a previously undescribed mechanism to explain the persistence of C4 plants in cool climates.

Field evaluation of cotton near-isogenic lines introgressed with QTLs for productivity and drought related traits

Quantitative trait loci (QTLs) for yield and drought related physiological traits, osmotic potential (OP), carbon isotope ratio (d 13 C, an indica- tor of water use efficiency), and leaf chlorophyll content (Chl), were exchanged via marker-assisted selection (MAS) between elite cultivars of the two cotton species Gossypium barbadense cv. F-177 and G. hirsutum cv. Siv'on. The resulting near isogenic lines (NILs) were examined in two field trials, each with two irrigation regimes, in order to (1) evaluate the potential to improve cotton drought resistance by MAS and (2) test the role of physiological traits in plant productivity. NILs introgressed with QTLs for high yield rarely exhibited an advantage in yield relative to the recipient parent, whereas a considerable number of NILs exhibited the expected phenotype in terms of lower OP (5 out of 9), higher d 13 C (4 out of 6) or high Chl (2 out of 3). Several NILs exhibited considerable modifications in non-targeted traits including leaf morphology, stomatal conductance and specific leaf weight (SLW). In G. barbadense genotypes, yield was correlated negatively with d 13 C and OP and positively with stomatal conductance, SLW and Chl, whereas in G. hirsutum yield was negatively correlated with d 13 C, SLW and Chl. This dissimilarity suggests that each of the respective species has evolved different mechanisms underlying plant productivity. We conclude that the improvement of drought related traits in cotton NILs may lead to improved drought resistance via MAS, but that conventional breeding may be necessary to combine the introduced QTL(s) with high yield potential.

Germination, seedling growth and relative water content of shoot in different seed sizes of triticale under osmotic stress of water and NaCl

Effect of seed size (small, medium and large) on germination and seedling growth of triticale (xTriticosecale Witm. cv. Presto) at the different osmotic potential of NaCl and PEG solutions were determined in the present study. Germination tests were conducted under five osmotic potential levels (-0.45, -0.77, -1.03, -1.44 MPa, and Control) of PEG 6000 and NaCl. Germination percentage (%) at 4 and 8 th days and also seedling growth traits such as root and shoot length (mm), dry root and shoot weight (mg), root : shoot length (R:S) ratio, and relative water content of shoot (RWC, %) were investigated in this study. The results indicated that decreases in the osmotic potentials caused a reduction in germination percentage and seedling growth. It was seen that drought created by PEG 6000 had more negative effects on germination and seedling growth than that of NaCl. In consequence, the total germinability and seedling growth were higher in large seeds rather than in small seeds in control solution and under osmotic stress. In addition, it was observed that seedlings obtained from larger seeds survived even at the lower osmotic potential of PEG and NaCl; whereas, seedling obtained from small seeds did not survive in the intensive stress.

Improved frost tolerance and winter hardiness in proline overaccumulating winter wheat mutants obtained by in vitro-selection is associated with increased carbohydrate, soluble protein and abscisic acid (ABA) levels

In previous studies in vitro-selection of proline overaccumulating lines of winter wheat (Triticum sativum L. cv. Jo 3063) with increased frost tolerance was reported. These traits were found to be genetically stable. In the present study the improvement of frost tolerance (winter hardiness) under field conditions is confirmed for F7 progenies of the mutants. Moreover, the mutants accumulated higher levels of glucose and fructose, soluble protein and abscisic acid (ABA) in addition to proline than the wild type under cold hardening conditions in a growth chamber as well as under cold hardening field conditions. ABA and proline levels peaked when the temperature decreased, whereas carbohydrate levels increased more slowly at decreasing temperature. Soluble protein levels also increased during cold hardening, but in addition showed sharp declines during frost periods. Increased carbohydrate levels of the mutants were associated with lower osmotic potential values. The differences in carbohydrate, protein and ABA levels between the mutants and the wild type are probably due to pleiotropic effects of the mutation.