Reduced Water Potential Research Articles

Tree responses to an invasive sap-feeding insect

Although sap-feeding insects are known to negatively affect plant growth and physiology, less is known about sap-feeding insects on woody plants. Adelges tsugae (Annand Hemiptera: Adelgidae), the hemlock woolly adelgid, is an invasive sap-feeding insect in eastern North America that feeds on and kills Tsuga canadensis (L. Carriere), eastern hemlock. Newly hatched adelgid nymphs crawl to young unattacked tissue, settle and immediately enter diapause (aestivation) while attached to hemlock in summer. We assessed the effect of A. tsugae infestation on T. canadensis growth and physiology by analyzing hemlock growth on lateral and terminal branches, water potential, photosynthesis, stomatal conductance, and foliar nitrogen (%N). A. tsugae infestation greatly decreased terminal and lateral growth of eastern hemlock. In addition, A. tsugae presence reduced photosynthesis by 10 % in September and 36 % in October. Adelgid-infested hemlocks also exhibited signs of water stress that included notable reductions in water potential and stomatal conductance. These responses shed light on possible mechanisms of adelgid-induced mortality.

Functional mechanisms of drought tolerance in subtropical maize (Zea mays L.) identified using genome-wide association mapping.

BackgroundEarlier studies were focused on the genetics of temperate and tropical maize under drought. We identified genetic loci and their association with functional mechanisms in 240 accessions of subtropical maize using a high-density marker set under water stress.ResultsOut of 61 significant SNPs (11 were false-discovery-rate-corrected associations), identified across agronomic traits, models, and locations by subjecting the accessions to water stress at flowering stage, 48% were associated with drought-tolerant genes. Maize gene models revealed that SNPs mapped for agronomic traits were in fact associated with number of functional traits as follows: stomatal closure, 28; flowering, 15; root development, 5; detoxification, 4; and reduced water potential, 2. Interactions of these SNPS through the functional traits could lead to drought tolerance. The SNPs associated with ABA-dependent signalling pathways played a major role in the plant’s response to stress by regulating a series of functions including flowering, root development, auxin metabolism, guard cell functions, and scavenging reactive oxygen species (ROS). ABA signalling genes regulate flowering through epigenetic changes in stress-responsive genes. ROS generated by ABA signalling are reduced by the interplay between ethylene, ABA, and detoxification signalling transductions. Integration of ABA-signalling genes with auxin-inducible genes regulates root development which in turn, maintains the water balance by regulating electrochemical gradient in plant.ConclusionsSeveral genes are directly or indirectly involved in the functioning of agronomic traits related to water stress. Genes involved in these crucial biological functions interacted significantly in order to maintain the primary as well as exclusive functions related to coping with water stress. SNPs associated with drought-tolerant genes involved in strategic biological functions will be useful to understand the mechanisms of drought tolerance in subtropical maize.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-1182) contains supplementary material, which is available to authorized users.

THE ROLE OF SOME SOLUBLE METABOLITES IN OSMOTIC ADJUSTMENT TO REDUCED MATRIC AND OSMOTIC WATER POTENTIAL IN TWO SOYBEAN CULTIVARS دور بعض المواد الايضيه الذائبة في الانضباط الاسموزي لسلالتين من نبات فول الصويا تحت النقص في الجهد المائي للتربة

This work aimed to study the effect of reduced matric- and osmotic water potential on changes of some parameters affecting plant water potential related to metabolism. The experimental plants are two cultivars of soybean (Giza 111 and Giza 21). The study is concerned mainly with internal adjustment in soluble metabolites affecting plant water relation. Such as soluble sugars (SS), hydrolysable carbohydrates (HC) among carbon metabolites and total free amino acids (AA) as nitrogenous components as well as soluble proteins which contribute water conservation in the plant. Statistical treatment of data helped much in clarifying the role of each of the four metabolic components in adjusting to the reduced water potential in the soil (water stress).

Predicting seed germination of slender wheatgrass [Elymus trachycaulus (Link) Gould subsp. trachycaulus] using thermal and hydro time models

Schellenberg, M. P., Biligetu, B. and Wei, Y. 2013. Predicting seed germination of slender wheatgrass [Elymus trachycaulus (Link) Gould subsp. trachycaulus] using thermal and hydro time models. Can. J. Plant Sci. 93: 793–798. Slender wheatgrass [Elymus trachycaulus (Link) Gould subsp. trachycaulus] is a native caespitose grass used for forage production and reclamation. The objective of this study was to quantify seed germination requirements of slender wheatgrass using thermal and hydro time models. Slender wheatgrass, San Luis, had a base temperature (Tb) of 9.48°C, and required 946.8°C h to reach 50% of seed germination. Seed germination of San Lius occurred at a temperature range of 10–30°C, with the highest germination rate being achieved at 20°C, and the highest final germination percentage being achieved at 25°C. At 20 and 25°C, San Luis had a hydro time constant of 61 MPa h, and a median base water potential of approximately 1.0 MPa, but the germination had low uniformity in reduced water potentials. Final germination was reduced at or lower than –0.6 MPa. Compared with many other cool-season native grasses of Northern Great Plains, a relatively warm temperature would be necessary for uniform seedling establishment of this grass. In reclamation seeding, the seedling emergence could reach the highest level at a temperature of 25°C.

Hydrotime model can describe the response of common bean (Phaseolus vulgaris L.) seeds to temperature and reduced water potential

Germination parameters of the response to temperature and water potential from four common bean (Phaseolus vulgaris) lines based on thermal-time and hydrotime concepts were estimated to verify to what extent they can predict germination under different thermal and water conditions. The cultivars IPR Uirapuru and IAPAR 81 (drought-tolerant), and Grauna and Carioca (not tolerant) were used. The isothermal assays were performed in a temperature gradient block, and the assays with different osmotic potentials (PEG 6000) were performed in germination chambers. Seeds from drought-tolerant cultivars spent less time to germinate at supra-optimum temperatures than non-tolerant ones, and the cultivar Uirapuru (drought-tolerant) germinated faster in response to reduced Ψ and low temperatures. The parameter Ψb(50) did not discriminate between drought-tolerant and non-tolerant lines at the infra- optimum temperature range, but it can be used to identify drought-tolerant lines at high temperatures. In general, the hydrotime model reproduced the actual germination data relatively well, chiefly at higher temperatures. This study evidenced that the hydrotime model can be used to describe the germination of common bean seeds under reduced water potentials, and as a screening tool for drought-tolerant bean genotypes.

The role of mesophyll conductance in the economics of nitrogen and water use in photosynthesis

A recent resurgence of interest in formal optimisation theory has begun to improve our understanding of how variations in stomatal conductance and photosynthetic capacity control the response of whole plant photosynthesis and growth to the environment. However, mesophyll conductance exhibits similar variation and has similar impact on photosynthesis as stomatal conductance; yet, the role of mesophyll conductance in the economics of photosynthetic resource use has not been thoroughly explored. In this article, we first briefly summarise the knowledge of how mesophyll conductance varies in relation to environmental factors that also affect stomatal conductance and photosynthetic capacity, and then we use a simple analytical approach to begin to explore how these important controls on photosynthesis should mutually co-vary in a plant canopy in the optimum. Our analysis predicts that when either stomatal or mesophyll conductance is limited by fundamental biophysical constraints in some areas of a canopy, e.g. reduced stomatal conductance in upper canopy leaves due to reduced water potential, the other of the two conductances should increase in those leaves, while photosynthetic capacity should decrease. Our analysis also predicts that if mesophyll conductance depends on nitrogen investment in one or more proteins, then nitrogen investment should shift away from Rubisco and towards mesophyll conductance if hydraulic or other constraints cause chloroplastic CO2 concentration to decline. Thorough exploration of these issues awaits better knowledge of whether and how mesophyll conductance is itself limited by nitrogen investment, and about how these determinants of photosynthetic CO2 supply and demand co-vary among leaves in real plant canopies.

Effects of salt stress on wild type and vte4 mutant Arabidopsis thaliana: Model plant to engineer tolerance towards salinity

One of the major environmental constraints impairing plant distribution and yield is believed to be salt stress. Additionally, engineered abiotic stress resistance or/and tolerance is considered as an indispensable target in order to enhance plant productivity. In this study, the effects of salinity on physiological and morphological of wild type (Columbia-0) and vte4 mutant Arabidopsis thaliana were investigated under different NaCl concentrations. These salt treatments, including control condition, 50mM and 100mM NaCl were imposed on the plants. Each salt treatment was replicated three times in a complete randomized design with factorial arrangement. Wild type and mutant A.thaliana plants were subjected to the abiotic stress (salinity) for up to 11 days to evaluate the parameters of growth, development and water relations. As a result, the performance of wild type plants was stronger than vte4 mutant under different salt treatments. Under control condition, rosette dry weight, maximum quantum efficiency (PSII) and specific leaf area obtained the highest values of 13.85 mg, considered, wild type A.thaliana recorded higher value of 0.82 gW/gFW for relative water content (RWC) under 50mM NaCl whereas mutant plants gained the value of 0.78 gW/gFW under the same condition. However, root mass fraction indicated an increase for both wild type and vte4 mutant plants after 11 days of salt stress onset. The reduction of water potential was observed for wild type and mutant A.thaliana where it scored -1.3 MPa and -1.4, respectively. As a conclusion, these findings implied that under different salt treatments morphological and physiological responses of wild type and vte4 mutant were affected in which wild type plants showed more tolerance. Lack of ?-tocopherol methyltransferase (? -TMT) gene in vte4 seemed to impair defence mechanism of this mutant against salinity.

Environmental factors influencing Pyrenophora semeniperda-caused seed mortality in Bromus tectorum

AbstractTemperature and water potential strongly influence seed dormancy status and germination of Bromus tectorum. As seeds of this plant can be killed by the ascomycete fungus Pyrenophora semeniperda, this study was conducted to learn how water potential and temperature influence mortality levels in this pathosystem. Separate experiments were conducted to determine: (1) if P. semeniperda can kill dormant or non-dormant seeds across a range of water potentials (0 to − 2 MPa) at constant temperature (20°C); and (2) how temperature (5–20°C) and duration at reduced water potentials (0–28 days) affect the outcome. When inoculated with the fungus at 20°C, all dormant seeds were killed, but fungal stromata appeared more quickly at higher water potentials. For non-dormant seeds, decreasing water potentials led to reduced germination and greater seed mortality. Results were similar at 10 and 15°C. Incubation at 5°C prevented stromatal development on both non-dormant and dormant seeds regardless of water potential, but when seeds were transferred to 20°C, dormant seeds evidenced high mortality. For non-dormant seeds, exposure to low water potential at 5°C resulted in secondary dormancy and increased seed mortality. Increasing incubation temperature, decreasing water potential and increasing duration at negative water potentials all led to increased mortality for non-dormant seeds. The results are consistent with field observations that pathogen-caused mortality is greatest when dormant seeds imbibe, or when non-dormant seeds experience prolonged or repeated exposure to low water potentials. We propose a conceptual model to explain the annual cycle of interaction in the Bromus tectorum–Pyrenophora semeniperda pathosystem.

Effect of salt stress on physiological response of tomato fruit grown in hydroponic culture system

The effect of salt stress on physiological response of hydroponically grown tomato fruit was investigated. Fruit growth rate, water status, cuticle permeability and induction of blossom-end rot (BER) of tomato fruit were considered for this study. Salt stress was applied by using Ca salt treatment and it plays an important role on all parameters studied in this experiment. Fruit growth rate, predawn water potential, osmotic potential and cuticle permeability were significantly lower in treated plants than in control plants. On the other hand, tissue turgor of control and treated fruit showed almost similar values 12 days after flowering (DAF). This result indicated that turgor was osmotically regulated in fruit under stress condition. Fruit growth rate was found to decline from 12 DAF and eventually ceased when BER externally appeared on fruit surface at the age of 19 DAF in this experiment. The reduction of growth rate coincided with the reduction of water potential in fruit tissue due to salt stress. Although BER externally appeared at 19 DAF anatomical investigation showed that intercellular air space becomes discoloured at least one week before external symptoms appeared on fruit tip. Different levels of cuticular permeability indicated that the deposition of cuticular wax on fruit surface was enhanced by the salt stress condition in tomato fruit. Since, BER was found to appear on fruit tip under high calcium concentration in solution it can be concluded that calcium deficiency was not the only the cause of BER in tomato, rather salt stress might alter metabolic activity in developing tomato fruit.

Partitioning Water Potential and Specific Salt Effects on Seed Germination of Kochia scoparia

Salinity is one of the environmental factors that have a critical influence on the germination of halophyte seeds and plant establishment. Salinity affects imbibitions, germination and root elongation. However, the way in which NaCl exerts its influence on these vital processes (seed germination), whether it is through an osmotic effect or specific ion toxicity, is still not resolved. Seeds of the halophyte Kochia scoparia were treated with various iso-osmotic solutions of NaCl and polyethylene glycol 6000 (PEG) over the water potential range of 0 to -1.9 MPa. After 10d of treatment, the ungerminated seeds were transferred to distilled water for 3 d. The germination results revealed that both NaCl and PEG inhibited germination and seedling growth, but the effects of NaCl compared to PEG were less on final germination. The seeds of kochia differ in their response to salinity and failure of seeds to recover from high salinity when transferred to deionized water, revealed the toxicity of NaCl. In contrast, the increase in germination and during the recovery period after exposure of PEG suggested that PEG was not toxic. It was concluded that at low levels of salinity the main effect of NaCl was to reduce the rate of germination due to the reduce water potential and at a higher salinity NaCl had a toxic effect since many seeds failed to germinate even salinity stress was removed.

Cadmium Tolerance in Mustard Cultivars: Dependence on Proline Accumulation and Nitrogen Assimilation

Cadmium [Cd] is a heavy metal, which reduces crop productivity even at low doses and reduces overall performance of the crop plants. Four mustard [Brassica juncea L. Czern and Coss.] cultivars, Alankar, Pusa Bold, Rohini and SS2 differing in Cd tolerance were treated with different doses 0, 50 and 100 mg Cd kg -1 soil. Cultivar SS2 [Cd sensitive] accumulated greater Cd in roots and leaves than Alankar [Cd tolerant]. Furthermore, SS2 also exhibited higher contents of thiobarbituric acid reactive substances [TBARS], hydrogen peroxide [H2O2] and electrolyte leakage. Photosynthesis and growth were adversely and maximally decreased by 100 mg Cd kg -1 soil treatment in all four of the cultivars, but SS2 exhibited greater reductions. Increasing concentrations of Cd in the soil result in decreased net photosynthesis [Pn], stomatal conductance [gs] and intercellular CO2 [Ci], but increase in proline content. Cultivars Alankar with higher proline content and greater nitrogen and nitrate reductase activity are efficient in controlling the Cd-induced oxidative stress as compared to least tolerant SS2, whereas tolerance capacity of Pusa Bold and Rohini lie in between the two. The tolerance index of Alankar was found to be higher among all the studied mustard cultivars, which indicate its higher tolerance to Cd toxicity. Tolerance index has been used as a good criterion to select the tolerant genotypes under high Cd stress. Leaf area and dry mass also decrease maximally at 100 mg Cd kg -1 soil with highest reduction in SS2. Maximum reduction of water potential and osmotic potential occur in SS2 and least in Alankar.

Influência do déficit hídrico na germinação de sementes e no desenvolvimento inicial de três espécies de Pleurothallidinae (Orchidaceae)

A subtribo Pleurothallidinae possui cerca de 4.100 especies em 36 generos, e ocorre somente nas Americas. Acianthera teres (Lindl.) Borba e rupicola e exposta a luz e a altas temperaturas. Octomeria gracilis Lood. ex Lindl. e Octomeria crassifolia Lindl. sao epifitas de florestas, porem, a primeira ocorre em areas umidas e a segunda em locais mais secos. A disponibilidade de agua influencia o metabolismo nas diversas etapas do desenvolvimento vegetal. Objetivou-se com este trabalho avaliar a influencia do deficit hidrico, induzido pela adicao de polietileno glicol 6000 (PEG) ao meio de cultura, na germinacao e desenvolvimento inicial em A. teres, O. crassifolia e O. gracilis. A semeadura foi efetuada em meio MS/2, sob quatro tratamentos: controle (sem adicao de PEG), e com 50 g L-1, 100 g L-1 e 200 g L-1 de PEG, induzindo potenciais hidricos de -0,53, -0,70, -0,86 e -1,60 MPa, respectivamente. Foram realizadas analises aos 45, 120 e 180 dias de cultivo. Em A. teres, observou se que o menor potencial hidrico do meio resulta em menor taxa de germinacao e maior retardo do desenvolvimento inicial das plantas. Em O. crassifolia, quanto menor o potencial hidrico do meio, maior a taxa de germinacao, contudo, o desenvolvimento foi semelhante entre os tratamentos aos 180 dias. Octomeria gracilis possui certa tolerância a reducao do potencial hidrico ate 120 dias, e desenvolvimento mais rapido em potenciais hidricos de -0,53 e -0,70 MPa.

SKRINING UNTUK TOLERANSI TERHADAP STRES KEKERINGAN PADA 36 VARIETAS KEDELAI PADA FASE PERKECAMBAHAN

Water stress due to drought is the most significant abiotic factor limiting crop growth and development. Drought stress inhibit germination and seedling growth, and extention of inhibition in germination under drought stress condition is varying in varieties. The previous research result showed that the differences in germination response under drought stress can be used as early test for screening to drought tolerance in plants. The objectives of this experiment were to evaluate the germination response of 36 soybean varieties under drought stress simulated by polyethylene glycol (PEG), to know the drought-stress tolerance level of 36 soybean varieties based on germination response in medium containing PEG, and to identify drought tolerant varieties. Soybean seeds were germinated in sand medium containing several PEG (6000) at concentration 0%, 15% and 20% which equivalent to 0, -0,41 and -0,67 MPa during 5 days. Germination responses were observed by calculating vigor index, germination percentage, lateral root number and measuring hypocotyl and root lenght and seedling dry weight. The level of drought stress tolerance of soybean varieties were evaluated based on index of reduction and drought sensitivity on germination variables in stres and non-stres conditions. The research result showed that drought stress on germination media simulated by PEG decreased vigor index, germination percentage, lateral root number, hypocotyl and root lengths and dry weight of seedling. The inhibition of germination increased with reduction of water potential. The water potential -0,41 MPa inhibited vigor index and hypocotyls length in all tested varieties, but inhibited germination percentage, lateral root number and dry weight of seedling in some varieties. However, decreasing of water potential -0,67 MPa inhibited almost germination variables in all varieties, except root length. Each tested soybean variety showed differences of germination response to drought stres. Varieties of Dieng, Tidar and Sibayak showed less inhibition than others, but Anjasmoro, Burangrang, Galunggung, Kipas Putih and Tambora showed more inhibition in seedling growth. Based on index of reduction and drought sensitivity on germination variables, Dieng and Tidar were identified as tolerant varieties, while sixteen varieties as medium tolerant and seventeen varieties as sensitive ones.

Quantification of solid pressure in the concentration polarization (CP) layer of colloidal particles and its impact on ultrafiltration

Here we describe the nature and implications of the “concentration polarization” (CP) layer that is formed during ultrafiltration of colloidal particles using a new approach in which the solid pressure, which arises from inter-particle interactions, and the inherent osmotic pressure are separately considered. The approach makes use of the particle transport mass balance between the convective and diffusive fluxes. The particle convection rate is hindered when inter-particle interactions take effect by reducing the particle velocities while the particle diffusion is solely controlled by the Brownian motion. An increase in solid pressure accounts for the reduction of the water potential caused by the relative motions of the particles and the surrounding water. A cell model is adopted to relate the local solid pressure with the local solid fraction and inter-particle interactions. The inter-particle interactions critically determine the form of particle accumulation (i.e. CP or gel/cake) on the membrane. The Shirato–Darcy equation is employed to relate the rate of increase in solid pressure, the relative liquid velocity and the solid fraction. Numerical integration approaches are employed to quantify the properties of the CP layer during both the development as well as the steady state phases (with steady state normally being achieved in a few minutes). The solid fractions are always no higher than those obtained when the inter-particle interactions are not considered. The decrease of the water potential caused by CP formation leads to the increase of both the solid pressure and the osmotic pressure. The dependence of the solid pressure on the solid fraction is usually stronger than that of the osmotic pressure. It is thus apparent that the solid pressure would be expected to dominate water potential reduction for solid fractions above a certain value though the solid pressure will be negligible when the solid fraction is relatively low.

Expression of an Arabidopsis vacuolar H+‐pyrophosphatase gene (AVP1) in cotton improves drought‐ and salt tolerance and increases fibre yield in the field conditions

The Arabidopsis gene AVP1 encodes a vacuolar pyrophosphatase that functions as a proton pump on the vacuolar membrane. Overexpression of AVP1 in Arabidopsis, tomato and rice enhances plant performance under salt and drought stress conditions, because up-regulation of the type I H+-PPase from Arabidopsis may result in a higher proton electrochemical gradient, which facilitates enhanced sequestering of ions and sugars into the vacuole, reducing water potential and resulting in increased drought- and salt tolerance when compared to wild-type plants. Furthermore, overexpression of AVP1 stimulates auxin transport in the root system and leads to larger root systems, which helps transgenic plants absorb water more efficiently under drought conditions. Using the same approach, AVP1-expressing cotton plants were created and tested for their performance under high-salt and reduced irrigation conditions. The AVP1-expressing cotton plants showed more vigorous growth than wild-type plants in the presence of 200 mM NaCl under hydroponic growth conditions. The soil-grown AVP1-expressing cotton plants also displayed significantly improved tolerance to both drought and salt stresses in greenhouse conditions. Furthermore, the fibre yield of AVP1-expressing cotton plants is at least 20% higher than that of wild-type plants under dry-land conditions in the field. This research indicates that AVP1 has the potential to be used for improving crop's drought- and salt tolerance in areas where water and salinity are limiting factors for agricultural productivity.

Group 1 and 2 LEA protein expression correlates with a decrease in water stress induced protein aggregation in horsegram during germination and seedling growth

Plants produce an array of proteins as a part of a global response to protect the cell metabolism when they grow under environmental conditions such as drought and salinity that generate reduced water potential. The synthesis of hydrophilic proteins is a major part of the response to water deficit conditions. An increased expression of LEA proteins is thought to be one of the primary lines of defense to prevent the loss of intercellular water during adverse conditions. These LEA proteins are known to prevent aggregation of a wide range of other proteins. In this study we report the water stress induced protein aggregation and its abrogation followed by expression of group 1 and group 2 LEA proteins of water soluble proteomes in horsegram. Water stress caused an increased protein aggregation with magnitude and duration of stress in horsegram seedlings. Tissue-specific expression of LEA 1 protein decreased in the embryonic axis when compared to cotyledons in 24 h stressed seedlings. We found no cross reaction of LEA 1 with proteome of 48 h stressed embryonic axis and 72 h stressed root and shoot samples. However, LEA 2 antibodies were cross reacted with four polypeptides with different molecular mass in shoot tissue samples and found no reaction with root proteome as evidenced from immuno-blot analysis. The role of LEA proteins in relation to protein aggregation during water stressed conditions was discussed.

Hydrotime Analysis of Ethiopian Mustard (Brassica carinata A. Braun) Seed Germination Under Different Temperatures

Ethiopian mustard (Brassica carinata A. Braun) is an oil-seed species that has recently become an object of great interest as a promising crop for energy purposes (biodiesel and biolubricant production). In semi-arid regions of South Italy, soil moisture at sowing time is often inadequate, delaying and reducing seed germination. In this study, the effect of reduced water potential on seed germination in three cultivars of B. carinata (ISCI 7, CT 180 and Sincron) was investigated in the laboratory. Germination behaviour at constant temperatures under low water availability was also analysed through the hydrotime model. Six water potentials (ψs) in PEG solution (0, −0.2, −0.4, −0.6, −0.8 and −1.0 MPa) and three temperatures (10, 20 and 30 °C) were used for the germination tests. A thermo-inhibiting effect was observed at the highest levels of water stress. The hydrotime analysis revealed that the increase of temperature to 30 °C reduced predicted hydrotime (θH) by hastening the rate of germination, but shifted median base water potential (ψb(50)) to higher values (less negative), whereas the lowering of temperature increased θH. These observations may have a great agronomic impact because although fewer seeds germinated at 30 °C at the highest levels of water stress, they may germinate faster in rapidly drying soil. However, genetic differences were observed among cultivars in terms of estimated θH and ψb(50). The hydrotime modelling approach offered in this study may help predict B. carinata seed germination under soil water deficit conditions occurring under early or late autumnal sowing.

EFFECT OF SALINIZATION OF SOIL ON GROWTH, WATER STATUS AND NUTRIENT ACCUMULATION IN SEEDLINGS OF ACACIA AURICULIFORMIS (FABACEAE)

Greenhouse experiments were conducted to assess the effects of salinization of soil on emergence, growth, water status, proline content, and mineral accumulation of seedlings of Acacia auriculiformis A. Cunn. ex Benth. (Fabaceae). Sodium chloride (NaCl) was added to the soil and salinity was maintained at 0.3, 3.9, 6.0, 7.9, 10.0, 12.1, and 13.9 dS m−1. Salinity caused reduction in water potential of tissues, which resulted in internal water deficit to plants. Consequently, seedling growth significantly decreased with increase in soil salinity. Proline content in tissues increased with increase in salinity. Potassium and sodium content significantly increased in tissues as salinity increased. Nitrogen content significantly increased in tissues with salinization of soil. Phosphorus, calcium and magnesium content significantly decreased as salinity increased. Changes in tissues and whole-plant accumulation patterns of other nutrients, as well as possible mechanisms for avoidance of sodium toxicity in this tree species in response to salinity, are discussed.

Germination response of Hylocereus setaceus (Salm-Dyck ex DC: ) Ralf Bauer (Cactaceae) seeds to temperature and reduced water potentials

The germination response of Hylocereus setaceus seeds to isothermic incubation at different water potentials was analysed by using the thermal time and hydrotime models, aiming to describe some germination parameters of the population and to test the validity of the models to describe the response of the seeds to temperature and water potential. Hylocereus setaceus seeds germinated relatively well in a wide range of temperatures and the germination was rate limited from 11 to 20 degrees C interval and beyond 30 degrees C until 40 degrees C, in which the germination rate respectively shifts positively and negatively with temperature. The minimum or base temperature (T(b)) for the germination of H. setaceus was 7 degrees C, and the ceiling temperature varied nearly from 43.5 to 59 degrees C depending on the percent fraction, with median set on 49.8 degrees C. The number of degrees day necessary for 50% of the seeds to germinate in the infra-optimum temperature range was 39.3 degrees C day, whereas at the supra-optimum interval the value of theta = 77 was assumed to be constant throughout. Germination was sensitive to decreasing values of psi in the medium, and both the germinability and the germination rate shift negatively with the reduction of psi, but the rate of reduction changed with temperature. The values of base water potential (psi(b)) shift to zero with increasing temperatures and such variation reflects in the relatively greater effect of low psi on germination in supra optimum range of T. In general, the model described better the germination time courses at lower than at higher water potentials. The analysis also suggest that Tb may not be independent of psi and that psi(b(g)) may change as a function of temperature at the infra-otimum temperature range.

Responses of Root Growth to Moderate Soil Water Deficit in Wheat Seedlings

In the field, plants show better root growth in drying soil than in wet soil. However, the root growth enhancement has not been demonstrated clearly in the laboratory. In this study, the root growth response of wheat seedlings to moderate soil water deficits was characterized quantitatively in an environment-controlled chamber. Germinated seeds of wheat were grown for 15 days in the soil with a water potential ranging from field capacity (FC) to approximately –0.08 MPa. Theleaf area decreased with reduction in soil water potential. By contrast, the root surface area increased upon reduction ofthe soil water potential to –0.04 MPa while it decreased significantly in soil with a water potential of –0.08 MPa. The increase in surface area was obvious in the roots with a diameter of 0.2 to 0.4 mm and larger than 0.7 mm. Root weight increased with the reduction of soil water potential to –0.04 MPa. While specific root length decreased significantly with the reduction of water potential to –0.06 MPa, the specific root surface area did not. Assimilatestransported from shoot might be used in roots to increae the surface area mainly by increasing the diameter rather than the length in response to a moderate soil water deficit in wheat seedlings. This might result from the drought tolerance mechanism of osmotic adjustment in roots.