Evidence that arbuscular mycorrhizal and phosphate-solubilizing fungi alleviate NaCl stress in the halophyte Kosteletzkya virginica: nutrient uptake and ion distribution within root tissues

The effects of an arbuscular mycorrhizal (AM) fungus, Glomus mosseae, and a phosphate-solubilizing microorganism (PSM), Mortierella sp., and their interactions, on nutrient (N, P and K) uptake and the ionic composition of different root tissues of the halophyte Kosteletzkya virginica (L.), cultured with or without NaCl, were evaluated. Plant biomass, AM colonization and PSM populations were also assessed. Salt stress adversely affected plant nutrient acquisition, especially root P and K, resulting in an important reduction in shoot dry biomass. Inoculation of the AM fungus or/and PSM strongly promoted AM colonization, PSM populations, plant dry biomass, root/shoot dry weight ratio and nutrient uptake by K. virginica, regardless of salinity level. Ion accumulation in root tissues was inhibited by salt stress. However, dual inoculation of the AM fungus and PSM significantly enhanced ion (e.g., Na⁺, Cl^?, K⁺, Ca²⁺, Mg²⁺) accumulation in different root tissues, and maintained lower Na⁺/K⁺ and Ca²⁺/Mg²⁺ ratios and a higher Na⁺/Ca²⁺ ratio, compared to non-inoculated plants under 100 mM NaCl conditions. Correlation coefficient analysis demonstrated that plant (shoot or root) dry biomass correlated positively with plant nutrient uptake and ion (e.g., Na⁺, K⁺, Mg²⁺ and Cl^?) concentrations of different root tissues, and correlated negatively with Na⁺/K⁺ ratios in the epidermis and cortex. Simultaneously, root/shoot dry weight ratio correlated positively with Na⁺/Ca²⁺ ratios in most root tissues. These findings suggest that combined AM fungus and PSM inoculation alleviates the deleterious effects of salt on plant growth by enabling greater nutrient (e.g., P, N and K) absorption, higher accumulation of Na⁺, K⁺, Mg²⁺ and Cl^? in different root tissues, and maintenance of lower root Na⁺/K⁺ and higher Na⁺/Ca²⁺ ratios when salinity is within acceptable limits.     

Osmolyte accumulation in different rape genotypes under sodium chloride salinity

Physiological mechanisms of two rape (Brassica napus L.) genotype adaptation to chlorine salinity were investigated. The plants of two cultivars (Olga and Westar) differing in salt tolerance were grown in the pots filled with Perlite on the Hoagland and Snyder’s medium under controlled conditions. At a stage of 3–4 true leaves, the plants experienced 7-day-long salinity induced by a single addition of NaCl to the nutrient medium in order to attain desired final salt concentration (from 50 to 400 mM). The obtained results showed that a greater salt tolerance of cv. Olga plants (as compared with cv. Westar) could be accounted for by a capability of their root cells to uptake water under high salinity (300–400 mM NaCl), which is evident from a greater content of water in the tissues of cv. Olga. This was ensured by a sharp fall of the osmotic potential of the cellular contents (down to −2.3 MPa) at a low water potential of nutrient solution owing to more active uptake of Na⁺ (57–61 μeq/g fr wt) and K⁺ (210–270 μeq/g fr wt) as well as active accumulation of proline (30–50 μmol/g fr wt). The latter is caused by a reduced activity of proline dehydrogenase and retarded degradation of this osmolyte. It is important that, in contrast to less tolerant genotype, the rape plants of salt-resistant cultivar were able to maintain the K⁺/Na⁺ ratio at a rather high level at salinity of different degree, which made it possible to preserve ionic homeostasis under adverse conditions. Original Russian Text ? A.M. Mokhamed, G.N. Raldugina, V.P. Kholodova, Vl.V. Kuznetsov, 2006, published in Fiziologiya Rastenii, 2006, Vol. 53, No. 5, pp. 732–738.     

Colonization with arbuscular mycorrhizal fungi improves salinity tolerance of tomato (Solanum lycopersicum L.) plants

The purpose of this study was to investigate the mechanisms underlying alleviation of salt stress by mycorrhization. Solanum lycopersicum L. cultivars Behta and Piazar with different salinity tolerance were cultivated in soil without salt (EC?=?0.63 dSm^?1), with low (EC?=?5 dSm^?1), or high (EC?=?10 dSm^?1) salinity. Plants inoculated with the arbuscular mycorrhizal fungi Glomus intraradices (+AMF) were compared to non-inoculated plants (?AMF). Under salinity, AMF-mediated growth stimulation was higher in more salt tolerant Piazar than in sensitive Behta. Mycorrhization alleviated salt-induced reduction of P, Ca, and K uptake. Ca/Na and K/Na ratios were also better in +AMF. However, growth improvement by AMF was independent from plant P nutrition under high salinity. Mycorrhization improved the net assimilation rates through both elevating stomatal conductance and protecting photochemical processes of PSII against salinity. Higher activity of ROS scavenging enzymes was concomitant with lowering of H₂O_2, less lipid peroxidation, and higher proline in +AMF. Cultivar differences in growth responses to salinity and mycorrhization could be well explained by differences in ion balance, photochemistry, and gas exchange of leaves. Function of antioxidant defenses seemed responsible for different AMF-responsiveness of cultivars under salinity. In conclusion, AMF may protect plants against salinity by alleviating the salt-induced oxidative stress.     

Evaluation of salinity tolerance in seedlings of sugar beet (Beta vulgaris L.) cultivars using proline, soluble sugars and cation accumulation criteria

Salinity tolerance of sugar beet (Beta vulgaris L.) cultivars in terms of growth, proline and soluble sugars concentrations, and Na⁺/K⁺ and Na⁺/Ca²⁺ ratios were analyzed in this study. Three-week-old seedlings of three sugar beet cultivars, ‘Gantang7’, ‘SD13829’, and ‘ST21916’, differing in salinity tolerance, were treated with 0, 50, 100, and 200 mM NaCl. Plant shoots and roots were harvested at 7 days after treatment and subjected to analysis. Low concentration of NaCl (50 mM) enhanced fresh and dry weights of shoot and root in ‘Gantang7’, whereas high one (200 mM) reduced growth in all cultivars and the less reduction was observed in ‘ST21916’. Shoot proline was strongly induced by salinity stress in both ‘Gantang7’ and ‘SD13829’, while it remained unchanged in ‘ST21916’. The addition of 50 mM NaCl significantly increased shoot soluble sugars concentrations in ‘Gantang7’ while it had no significant effects in the other two cultivars. ‘Gantang7’ also showed a higher level of root soluble sugars concentration as compared to the other two cultivars. At 50 mM NaCl, the lower shoot Na⁺ concentration, and the higher shoot K⁺ and root Ca²⁺ concentration in ‘Gantang7’ resulted in the lower shoot Na⁺/K⁺ and root Na⁺/Ca²⁺ ratio. However, ‘SD13829’ maintained a lower Na⁺/K⁺ ratio in both shoot and root when subjected to 200 mM NaCl treatment. According to comprehensive evaluation on salinity tolerance, it is clear that ‘Gantang7’ is more tolerant to salinity than the other two cultivars. Therefore, it is suggested that ‘Gantang7’ should be more suitable for cultivating in the arid and semi-arid irrigated regions.     

Arbuscular mycorrhizal symbiosis regulates the physiological responses,ion distribution and relevant gene expression to trigger salt stress tolerance in pistachio

Mycorrhizal symbiosis is generally considered effective in ameliorating plant tolerance to abiotic stress by altering gene expression, and evaluation of genes involved in ion homeostasis and nutrient uptake. This study aimed to use arbuscular mycorrhizal fungus (AMF) to alleviate salinity stress and analyse relevant gene expression in pistachio plants under No/NaCl stress in greenhouse conditions. Arbuscular mycorrhizal symbiosis was used to study the physiological responses, ion distribution and relevant gene expression in pistachio plants under salinity stress. After four months of symbiosis, mycorrhizal root colonization showed a significant reduction in all tested parameters under salt stress treatment compared to non-saline treatment. Salinity affected the morphological traits, and decreased the nutrient content including N, P, Mg and Fe as well as K/Na and Ca/Na ratios, relative water content (RWC), membrane stability index (MSI), and increased the concentration of K, Ca and Na nutrient, glycine betaine, ROS and MDA. Inoculation of seedlings with AMF mitigated the negative effects of salinity on plant growth as indicated by increasing the root colonization, morphological traits, glycine betaine, RWC and MSI. Specifically, under salinity stress, shoot and root dry weight, P and Fe nutrient content, K/Na and Ca/Na ratio of AMF plants were increased by 53.2, 48.6, 71.6, 60.2, 87.5, and 80.1% respectively, in contrast to those of the NMF plants. The contents of Na, O^2•− and MDA in AMF plants were significantly decreased by 66.8, 36.8, and 23.1%, respectively at 250 mM NaCl. Moreover, salinity markedly increased SOS1, CCX2 and SKOR genes expression and the inoculation with AMF modulated these genes expression; however, NRT2.4, PHO1 and PIP2.4 gene expressions were increased by salinity and AMF. It could be concluded that inoculation of AMF with Rhizophagus irregularis conferred a larger endurance towards soil salinity in pistachio plants and stimulate the nutrient uptake and ionic homeostasis maintenance, superior RWC and osmoprotection, toxic ion partitioning, maintaining membrane integrity and the ion-relevant genes expression.     

Root apoplastic transport and water relations cannot account for differences in Cl− transport and Cl−/NO3 − interactions of two grapevine rootstocks differing in salt tolerance

Grapevine is moderately sensitive to salinity and accumulation of toxic levels of Cl^? in leaves is the major reason for salt-induced symptoms. In this study, apoplastic Cl^? uptake and transport mechanism(s) were investigated in two grapevine (Vitis sp.) rootstock hybrids differing in salt tolerance; 1103 Paulsen (salt tolerant) and K 51–40 (salt sensitive). Increased external salinity caused high Cl^? accumulation in shoots of the salt sensitive K 51–40 in comparison to Paulsen. Measurement of ¹⁵NO₃ ^? net fluxes under high salinity showed that by increasing external Cl^? concentrations K 51–40 roots showed reduced NO₃ ^? accumulation. This was associated with increased accumulation of Cl^?. In comparison to Paulsen, K 51–40 showed reduced NO₃ ^?/Cl^? root selectivity with increased salinity, but Paulsen had lower selectivity over the whole salinity range (0–45 mM). To examine if root hydraulic and permeability characterisations accounted for differences between varieties, the root pressure probe was used on excised roots. This showed that the osmotic Lp_r was significantly smaller than hydrostatic Lp_r, but no obvious difference was observed between the rootstocks. The reflection coefficient (σ) values (0.48–0.59) were the same for both rootstocks, and root anatomical studies showed no obvious difference in apoplastic barriers of the main and lateral roots. Comparing the uptake of Cl^? with an apoplastic tracer, PTS (3-hydroxy-5,8,10-pyrentrisulphonic acid), showed that there was no correlation between Cl^? and PTS transport. These results indicated that bypass flow of salts to the xylem is the same for both rootstocks (0.77 ± 0.2 and 1.05 ± 0.12 %) and hence pointed to differences in membrane transport to explain difference in Cl^? transport to the shoot.     

Growth and proline accumulation in mungbean seedlings as affected by sodium chloride

Mungbean (Vigna radiata L. Wilczek cv. Sujata and cv. K851) seedlings were grown in paper towelins in dark under 0, 0.5, 1, 2 and 3 % (m/v) NaCl salinity. Germination percentage, shoot and root length, fresh mass of both cultivars decreased with salinity. Total soluble saccharides and proline accumulated in the root and shoot of salt stressed seedlings. The proline accumulation in the root was four to five times higher than that of the shoot of NaCl treated etiolated mungbean seedlings.     

Influence of saline drip-irrigation on fine root and sap-flow densities of two mature olive varieties

Salt stress is known to influence water use and carbon allocation in trees; however, information about the effects of salt exposure on water uptake and below-ground carbon investment is scant, especially for adult trees. Consequently, this study examined these variables in two mature olive varieties (Olea europaea L.) that differ in their NaCl tolerance: Barnea (tolerant) and Proline (sensitive). Trees were irrigated using water with electrical conductivities of 1.2, 4.2 (both varieties) and 7.5 dS m⁻¹ (Barnea only) for 11 years. At each treatment level, we measured soil properties, root morphology, root biomass:necromass ratio, root xylem sap osmolality, and root sap-flow as well as leaf conductance and morphology. Both varieties exhibited reduced fine root biomass under salinity which was only partially compensated for by higher specific root areas under moderate salinity. Proline variety exhibited a smaller fine root system under moderate salinity than Barnea trees, likely causing the lower sap-flow density in coarse roots of Proline compared to Barnea. The higher biomass:necromass ratio of the Barnea root system under moderate salinity is indicative of lower root turnover rates and thus a more efficient carbon use than in Proline trees. Besides differences in ion exclusion capacities, the ability of the fine root system to resist the deleterious effects of salinity seems to affect the salt resistance of mature olive varieties by influencing water uptake and carbon allocation.     

Effects of salinity and nitrogen on cotton growth in arid environment

The influences of different N fertilization rates and soil salinity levels on the growth and nitrogen uptake of cotton was evaluated with a pot experiment under greenhouse conditions. Results showed that cotton growth measured as plant height was significantly affected by the soil salinity and N-salinity interaction, but not by N alone. Cotton was more sensitive to salinity during the emergence and early growth stages than the later developmental stages. At low to moderate soil salinity, the growth inhibition could be alleviated by fertilizer application. Soil salinity was a dominated factor affecting cotton’s above-ground dry mass and root development. Dry mass of seed was reduced by 22%, 52%, and 84% respectively, when the soil salinity level increased from control level of 2.4 dS m^?1 to 7.7 dS m^?1, 12.5 dS m^?1 and to 17.1 dS m^?1, respectively. N uptake increased with N fertilization at adequate rates at both low and medium soil salinities but was not influenced by over N fertilization. At higher salinities, N uptake was independent of N rates and mainly influenced by soil salinity. The uptake of K decreased with soil salinity. The concentration of Na, Cl and Ca in plant tissues increased with soil salinity with highest concentrations in the cotton leaf.     

The response of Mo-hydroxylases and abscisic acid to salinity in wheat genotypes with differing salt tolerances

The differential responses of the wheat cultivars Shi4185 and Yumai47 to salinity were studied. The higher sensitivity of Yumai47 to salinity was linked to a greater growth reduction under salt stress, compared to more salt-tolerant Shi4185. Salinity increased the Na⁺, proline and superoxide anion radical (O₂ ^?) contents in both cultivars. Leaf Na⁺ content increased less in the more salt-tolerant cultivar Shi4185 than salt-sensitive Yumai47. The proline content increased more significantly in Shi4185 than Yumai47; on the contrary, superoxide anion radical content increased less in Shi4185 than Yumai47. This data indicated that wheat salinity tolerance can be increased by controlling Na⁺ transport from the root to shoot, associated with higher osmotic adjustment capability and antioxidant activity. Although salinity increased aldehyde oxidase (AO) activity and abscisic acid (ABA) content in the leaves and roots of both cultivars following the addition of NaCl to the growth medium, AO and ABA increased more in the salt-sensitive cultivar Yumai47 than the more salt-tolerant cultivar Shi4185. Xanthine dehydrogenase (XDH) activity in the leaves of both cultivars increased with increasing concentrations of NaCl; however, leaf XDH activity increased more significantly in Yumai47 than Shi4185. Root XDH activity in Shi4185 decreased with increasing NaCl concentrations, whereas salinity induced an increased root XDH activity in Yumai47. The involvement of AO and XDH enzymatic activities and altered ABA content in the response mechanisms of wheat to salinity are discussed herein.     

Lisianthus response to salinity stress

The effect of salinity on some morpho-physiological characteristics in lisianthus cultivars was investigated. Cultivars namely, Blue Picotee (C1), Champagne (C₂), Lime Green (C₃), and Pure White (C₄), were subjected to salt stress (0–60 mM NaCl) in a sand culture and their responses were measured. Our results showed that as a salinity level increased, growth parameters, relative water content, photosynthetic pigments, and gas-exchange characteristics decreased in all cultivars, while root fresh mass, root/shoot length ratio, electrolyte leakage, and a malondialdehyde content increased. However, the changes were less pronounced in C₃ and C₄ compared to C1 and C₂. The regression analysis of the relationship between salinity levels and seedling height or root/shoot length ratio defined two groups with different slope coefficients: C1 and C₂ as salt-sensitive cultivars and C₃ and C₄ as salt-tolerant cultivars. Shoot dry mass and leaf area tolerance indices were less affected by salinity in C₃ and C₄ compared to those in C1 and C₂. Further, C₃ and C₄ showed higher photosynthetic rates, greater stomatal conductances, and accumulated greater K+ and Ca2+ contents and K+/Na+ ratios in roots and shoots compared to those in C1 and C₂. The results suggests that C₃ and C₄ could be recommended as resistant cultivars due to maintaining higher growth, water balance, leaf gas exchange, ion compartmentalization, and lower lipid peroxidation in response to salinity compared to C1 and C₂.     

Isolation and characterization of variant wheat cultivars for ABA sensitivity

Genetic variants for abscisic acid (ABA) sensitivity are important for investigating the role of ABA sensitivity in conditioning plant response to environmental stress, and especially to those soil conditions that may elicit a root-mediated hormonal signal. This study was performed in order to isolate variation in ABA sensitivity among wheat (Triticum aestivum and T. durum) cultivars, as characterized by two plant responses: (i) shoot growth reduction in response to 5×10^?2mol m^?3 ABA (racemic) in the root medium of hydroponically grown plants, and (ii) changes in transpiration and gas exchange in a bioassay of detached leaves (leaflaminac) infused with 10^?4mol m^?3 ABA. Very significant (P≤0.01) and repeatable differences were found among 36 wheat cultivars and 19 landraces in the growth rate in ABA-containing nutrient solutions, expressed as a percentage of the growth rate in control nutrient solutions (ABA/control ratio). In duplicate experiments, the ABA/control ratio ranged between 60 and 83% for the least sensitive cultivars (V2151-3, Bethlehem, K1056 and Sunstar) and between 9 and 19% for the most sensitive cultivars (Sundor, Comet, Barkaec and V5). In the transpiration bioassay, performed with seven selected cultivars, it was found that the reductions in transpiration of ABA-infused leaves corresponded very well with the reductions in growth in response to ABA in the root media. Measurement of gas exchange in the detached leaves of two cultivars differing in ABA sensitivity (Bethlehem and Sundor) showed that variable ABA sensitivity was expressed very well in the stomatal conductance, carbon exchange rate (CER) and photosynthetic capacity (CER/C_i ratio) of the leaf. These results therefore allowed us to isolate wheat variants for ABA sensitivity and to conclude that, while ABA sensitivity is expressed in the growth of plants challenged by ABA in the root medium, the control of sensitivity resides, at least partly, in the leaf.     

Improved Tolerance of <Emphasis Type="Italic">Acacia nilotica</Emphasis> to Salt Stress by Arbuscular Mycorrhiza, <Emphasis Type="Italic">Glomus fasciculatum</Emphasis> may be Partly Related to Elevated K/Na Ratios in Root and Shoot Tissues

A pot experiment was conducted to examine the effect of arbuscular mycorrhizal fungus, Glomus fasciculatum, and salinity on the growth of Acacia nilotica. Plants were grown in soil under different salinity levels (1.2, 4.0, 6.5, and 9.5 dS m⁻¹). In saline soil, mycorrhizal colonization was higher at 1.2, 4.0, and 6.5 dS m⁻¹ salinity levels in AM-inoculated plants, which decreased as salinity levels further increased (9.5 dS m⁻¹). Mycorrhizal plants maintained greater root and shoot biomass at all salinity levels compared to nonmycorrhizal plants. AM-inoculated plants had higher P, Zn, and Cu concentrations than uninoculated plants. In mycorrhizal plants, nutrient concentrations decreased with the increasing levels of salinity, but were higher than those of the nonmycorrhizal plants. Mycorrhizal plants had greater Na concentration at low salinity levels (1.2, 4.0 dS m⁻¹), which lowered as salinity levels increased (6.5, 9.5 dS m⁻¹), whereas Na concentration increased in control plants. Mycorrhizal plants accumulated a higher concentration of K at all salinity levels. Unlike Na, the uptake of K increased in shoot tissues of mycorrhizal plants with the increasing levels of salinity. Our results indicate that mycorrhizal fungus alleviates deleterious effects of saline soils on plant growth that could be primarily related to improved P nutrition. The improved K/Na ratios in root and shoot tissues of mycorrhizal plants may help in protecting disruption of K-mediated enzymatic processes under salt stress conditions.     

Growth and phosphorus uptake ofAtriplex amnicola at different levels of NaCI

Growthof Atriplex amnicola P.G. Wilson was not affected by different levels (10, 100, and 200 mM) of NaCI. Na concentrations in roots and shoots increased significantly at higher levels of NaCI. K/Na ratios in plant parts were higher compared to those in the external solutions, indicating selectivity for K over Na. P uptake, as determined using³²P, was not affected by increasing NaCl in the root medium.     

High external phosphate (Pi) increases sodium ion uptake and reduces salt tolerance of 'Pi-tolerant' soybean

Previous studies on the interaction between environmental inorganic phosphate (Pi) and salinity stress using soybean cultivars sensitive to high external Pi had two limitations: (1) the phenotype was dominated by overaccumulation of phosphorus (P); and (2) no detailed analysis was performed for sodium ion uptake. In this study, we focused on the effects of high external Pi on the sodium ion uptake in 'Pi-tolerant' soybean cultivars. The P accumulation in Pi-tolerant soybean Union was much lower [9.0 mg g⁻¹ dry weight (DW); contrasting to 38–76 mg g⁻¹ DW in the 'Pi-sensitive' soybean cultivars]. At in planta level, high level of external Pi significantly ( P  < 0.001) increased net sodium ion uptake and aggravated salinity stress symptoms. The effects of high external Pi diminished when de-rooted plants were used, suggesting that root is the primary organ interacting with Pi in the growth medium. Two-cell models, including soybean suspension cells and the tobacco Bright Yellow-2 cell line, were also employed to study the effects of high external Pi at the cellular level. Consistent to in planta results, high external Pi uplifted cellular sodium ion uptake and reduced cell viability under salinity stress. Gene expression analyses further showed that HPi (2 m M Pi supplements; excessive level of Pi) could reduce the fold of induction of GmSOS1 and GmCNGC under salinity stress, suggesting that they may be possible molecular targets involved in the interaction between high external Pi and Na⁺ uptake.     

Indirect monitoring of root activity in soybean cultivars under contrasting moisture regimes by measuring electrical capacitance

The applicability of root electrical capacitance (EC) measurement for in situ investigation of root activity and drought tolerance was tested in soybean cultivars. Well-watered and drought-stressed plants were grown in pots with repeated EC measurements, followed terminally by harvest to determine root dry mass (RDM), shoot dry mass (SDM), root/shoot ratio (RSR) and leaf area (LA). EC measurement showed the cultivar differences in root growth and biomass production. EC increased till the beginning of flowering, then became nearly constant. Terminal EC was highly correlated with RDM for non-stressed (R ² = 0.844) and stressed plants (R ² = 0.936). Drought reduced the EC of cultivars by 28.8–50.5 %, consistently with the corresponding changes of SDM (25.5–49.1 %) and LA (23.6–51.5 %), but considerably exceeded the loss of RDM (12.6–47.3 %) in some cultivars. The reason is drought increased the RSR (by 3.9–21.9 %), leading to decreased water uptake, and thus EC per unit of RDM. This was confirmed by the significantly decreased slope of EC–RDM regression line from 0.437 to 0.317 nF g^?1 RDM calculated for well-watered and drought-stressed plants, respectively. As EC referred to root uptake activity, it was better indicator of the actual root status than RDM. EC measurement was adequate for monitoring the cultivar-specific differences in root growth and for estimation of biomass loss caused by drought. By supplementing the conventional methods, this in situ technique could be useful for various fields of agriculture, including cultivar selection or stress tolerance studies.     

Modelling zinc uptake by rice crop using a Barber-Cushman approach

The Barber-Cushman mechanistic nutrient uptake model which has been utilized extensively to describe and predict nutrient uptake by crop plants at different stages of crop growth was evaluated for its ability to predict the Zn uptake by rice seedlings. Uptake of the nutrient is, therefore, determined by the rate of nutrient supply to the root surface by mass flow and diffusion. Inter root competition and time dependent root density are accounted for by soil volume that delivers nutrients. The radii of these cylinders decline with increasing density. Since mass flow and diffusion each supply zinc to the root, the process can be described mathematically using the model of Barber-Cushman (1984). The 11 parameters of the model for the uptake by rice cultivars were measured by established experimental techniques. Zinc uptake at different growth stages predicted by the model was compared to measured zinc uptake by rice cultivars grown on sandy loam soil in a green house. Predicted zinc uptake was significantly correlated with observed uptake r ²=0.99^**. Sensitivity analysis was also used to investigate the impact of changes in soil nutrient supply, root morphological and root uptake kinetic parameters on simulated nutrient uptake. Overall results of sensitivity analysis indicate that the half distance between root axes, rate of root growth and water flux affect the uptake of zinc particularly at their higher values rather than at lower values and DaZn is the most sensitive parameter for zinc uptake at its lower values.     

Genotypic difference in salinity tolerance in quinoa is determined by differential control of xylem Na loading and stomatal density

Quinoa is regarded as a highly salt tolerant halophyte crop, of great potential for cultivation on saline areas around the world. Fourteen quinoa genotypes of different geographical origin, differing in salinity tolerance, were grown under greenhouse conditions. Salinity treatment started on 10 day old seedlings. Six weeks after the treatment commenced, leaf sap Na and K content and osmolality, stomatal density, chlorophyll fluorescence characteristics, and xylem sap Na and K composition were measured. Responses to salinity differed greatly among the varieties. All cultivars had substantially increased K⁺ concentrations in the leaf sap, but the most tolerant cultivars had lower xylem Na⁺ content at the time of sampling. Most tolerant cultivars had lowest leaf sap osmolality. All varieties reduced stomata density when grown under saline conditions. All varieties clustered into two groups (includers and excluders) depending on their strategy of handling Na⁺ under saline conditions. Under control (non-saline) conditions, a strong positive correlation was observed between salinity tolerance and plants ability to accumulate Na⁺ in the shoot. Increased leaf sap K⁺, controlled Na⁺ loading to the xylem, and reduced stomata density are important physiological traits contributing to genotypic differences in salinity tolerance in quinoa, a halophyte species from Chenopodium family.     

Getting to the roots of Cicer arietinum L. (chickpea) to study the effect of salinity on morpho-physiological,biochemical and molecular traits

The effect of saline irrigation (EC_iw 6 dS m^?1 and 9 dS m^?1) on the roots of Cicer arietinum L. genotypes was examined at morpho-physiological, biochemical and molecular levels. Reduction in root growth due to salinity was observed, but less effect was seen on the roots of genotypes KWR 108, ICCV 10, CSG 8962, and S7 as compared to the other genotypes. Cell turgor was maintained in tolerant genotypes through optimum water relations and osmoprotectants (proline and total soluble sugars) than the sensitive cultivars. Salinity caused oxidative stress as increased hydrogen peroxide and malondialdehyde were noticed, where low accumulation was observed in tolerant genotypes due to the higher activity of enzymatic antioxidants (superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and peroxidase). Na⁺/K⁺ ratio increased, but more increment was reported in sensitive cultivars. Gene expression studies depicted that genes encoding pyrroline-5-carboxylate synthetase and pyrroline-5-carboxylate reductase got upregulated and that of proline dehydrogenase was downregulated and more fold change with respect to control was in the salt tolerant check CSG 8962 and the genotype KWR 108. Higher expression of the genes encoding reactive oxygen species scavenging enzymes namely, superoxide dismutase, catalase, peroxidase, and those involved in the ascorbate–glutathione cycle was noticed in KWR 108 and CSG 8962 than ICC 4463. Enhanced expression of sodium transporter HKT1 due to salinity can be correlated with ion homeostasis maintenance. Cumulative effects of osmolytes, enzymatic antioxidants and maintaining ion homeostasis in root enable chickpea plants to survive in saline environments.     

Uptake and partitioning of cadmium by cultivars of peanut (Arachis hypogaea L.)

Cadmium has been found to accumulate in peanut (Arachis hypogaea) kernels to levels exceeding the current maximum permitted concentration in Australia of 0.1 mg kg^-1. Little is known of the mechanisms of Cd uptake into kernels by cultivars of peanut, so the aims of the experiments reported here were to determine if Cd is absorbed directly through the pod wall or via the main root system, and if differences exist between cultivars in this respect. Split-pot soil and sand/nutrient solution experiments were performed with two cultivars of peanut (cv. NC7 and Streeton) known to accumulate Cd to different levels in the kernel. The growth medium was separated into pod and root zones with Cd concentrations in each zone varied. In confirmation of previous field trial results, cv. NC7 had higher concentrations of Cd in kernels, given the same Cd levels in the external medium (solution or soil). Despite total Cd uptake by cv. NC7 being similar to cv. Streeton, cv. NC7 appeared to retain more Cd in the roots and translocate less Cd to shoots. Results from both soil and sand/solution culture indicated that the dominant path of Cd uptake by peanut was via the main root system, with direct pod uptake contributing less than 5% of the total Cd in the kernel. There was little difference between cultivars in this characteristic. This indicates that unlike Ca nutrition of peanuts, agronomic techniques to manage Cd uptake will require modification of soil to the full depth of root exploration, rather than just the surface strata where pods develop. Cadmium concentrations in testa were up to an order of magnitude higher than in the kernel, indicating that blanching of kernels would be effective in reducing Cd in the marketed product. This revised version was published online in June 2006 with corrections to the Cover Date.