Studies on growth and distribution of Na+, K+ and Cl− in soybean varieties differing in salt tolerance

Soybean plants, varieties “Lee”, “Jackson” and “Bragg” were grown in solution culture at various salinity levels. A NaCl concentration of 10 mM was already inhibitory to growth of “Jackson”; growth of “Lee”, however, was only reduced at a salt concentration of 50 mM or higher. The moderately salt tolerant variety “Lee” efficiently excluded Cl^? from the leaves up to about 50 mM NaCl in the medium, but showed high Cl^? contents in the root; exclusion of Na⁺ from the leaves was also apparent in this variety. On the other hand, the salt sensitive variety “Jackson” did not have the capacity for exclusion of Cl^? and Na⁺. The physiological behaviour of the variety “Bragg” resembled that of “Jackson”. It is suggested that the exclusion of Cl^? and Na⁺ from the leaves in the soybean variety “Lee” is regulated by the root.     

Effects of salt stress on distribution of Na+ and some other cations in two soybean varieties differing in salt tolerance

In the course of investigations on the impact of salinity on mineral ion transport in differentially salt susceptible soybeans (“Lee” and “Jackson”) short-term experiments were conducted to elucidate the distribution pattern of Na⁺ and some other cations. The results showed that low salinity (7.5 mM NaCl) did not induce varietal differences in Na⁺ content during a 30 hrs uptake period. At 66.5 mM NaCl, however, the Na⁺ contents increased more in the leaves of the salt sensitive variety “Jackson” than in “Lee”. Both soybean varieties retained Na⁺ in the proximal root and stem. Furthermore, they extruded considerable amounts of Na⁺ from the roots to the medium. Increasing the level of salinity in the solution substantially reduced the Ca²⁺ uptake of both soybean varieties. In an experiment with the salt sensitive variety under constant salinity but increasing Ca²⁺ concentration in the medium, the plants showed a reduction in Na⁺ uptake and translocation to stem and leaves and an enhanced Ca²⁺ uptake and translocation to the shoots. It is suggested that the injury observed in “Jackson” after salt treatment is not only related to the insufficient control of Cl^? transport. At higher salinity levels the increasing accumulation of Na⁺ in the leaves and the varietally independant depression of Ca²⁺ uptake and translocation may enhance the development of leaf necrosis.     

Wirkung einer Abscisinsäure-Applikation auf die Cl−Translokation in Sojabohnen bei niedriger und hoher Besalzung des Nährmediums

Effect of abscisic acid in the root medium on Cl^? translocation in soybeans under low and high salt conditions With soybeans of the varieties ?Lee”? and ?Jackson”? the effect of abscisic acid (ABA) applied to the root medium in different concentrations (10^?4, 10^?5 and 10^?6M) on Cl^? translocation was investigated. Under low salt conditions (0,5 mM NaCl) ABA, depending on its concentration, strongly decreased Cl^? translocation to the shoot. At the highest ABA concentration, within 24 h the Cl^? content of the shoots was reduced to about 40 % of the control, the Cl^? accumulation within the roots was reduced about 25 %. However, the 10^?5 and the 10^?6M ABA treatment increased Cl^? accumulation in the roots but decreased Cl^? translocation to the shoot. Under high salt conditions (75 mM NaCI) ABA had no measureable effect on CI- translocation to the shoot. It was found that the genetic mechanism responsible for high CI- accumulation within the roots of ?Lee”? and high CI- translocation to the shoot of ?Jackson”? was not affected by ABA. ABA strongly inhibited transpiration. High ABA concentration in combination with low salt treatment decreased the transpiration rate up to 50 % of the control. ABA also inhibited transpiration under high salt conditions. This result is discussed considering the fact, that ABA added to the highly saline nutrient solution did not decrease the CI- translocation to the shoot. An investigation using ¹⁴C-ABA showed, the radioactive substance was taken up by the roots and translocated to the shoot independently from the salt treatment. The metabolism of the radioactive substance was different for roots and leaves. However, no difference could be observed by comparing the two soybeans varieties with or without salt treatment.     

Auswirkungen hoher NaCl-Konzentration im Nährmedium auf die Transpiration,den Abscisinsäure-, Cytokinin- und Prolingehalt zweier Sojabohnensorten

Effect of high NaCl concentration in the nutrient medium on transpiration, abscisic acid, cytokinin and proline content of two soybean varieties With the differentially salt-sensitive soybean varieties ?Lee”? and ?Jackson”? the effect of salinization on transpiration, Cl^? and Na⁺ accumulation, and on abscisic acid (ABA), cytokinin and proline content was investigated. Salinization with 75 mM NaCl in the nutrient medium drastically inhibited the transpiration (about 40%) of both varieties but more so with the variety ?Jackson”?. Nevertheless this variety translocated substantially more Cl^? into the shoot than ?Lee”?. However, ?Lee”? accumulated more Cl^? into the roots and thus was able to effectively protect the shoot against a toxic Cl^? concentration. The Na⁺ distribution in the roots and shoots was nearly the same in both varieties. The ABA content of the leaves of both varieties increased 5-fold to 1200 ng × g^? dry weight after 48 h of salt stress. About the same time transpiration of the salt-stressed plants reached a minimum. Between 48 and 168 h the ABA content of ?Lee”? dropped to about half. The ABA level in ?Jackson”? remained higher which indicated that the shoot was stressed more intensely and/or longer. The results do not imply a causal relationship between the ABA concentration in the leaves and the exclusion of C1^? from the shoot of ?Lee”?. The cytokinin concentration of the two soybean varieties was not significantly affected by salinization. The proline content in the leaves increased markedly with salt stress in both varieties but much more so in ?Jackson”?. Proline content in the leaves increased from about 1.8 μmoles × g^?1 dr. w. before salt stress to 24.7 μmoles × g^?1 dr. w. after 168 h of stress. However, the proline concentration dropped to nearly the initial level within 48 h after a 120 h salt stress treatment was discontinued and the plants were returned to a control solution. In ?Lee”? salinization only doubled the amount of proline found initially. The highest value was observed after 120 h of salinization.     

Influence of extreme K:Na ratios and high substrate salinity on plant metabolism of crops differing in salt tolerance

Abstract

Ion‐specific initial salt effects due to supply of extreme K⁺, Na⁺, Cl or SO₄ ^2‐ combinations were studied on the carbohydrate pattern as well as on the activity of amylases, phosphorylase and invertase of two soybean varieties, Jackson and the more tolerant Lee.

Reducing sugars were little affected. Salinity increased leaf sucrose more in Jackson than in Lee, and more due to Cl^? than to SO₄ ^2‐ supply. Salinity increased the higher level of root sucrose in Lee less than the lower sucrose level in Jackson, independent of the nature of salination. Salinity increased leaf starch more in Jackson than in Lee. KCl increased leaf starch of Jackson most, Na₂SO₄. least. KCl increased leaf starch of Lee more than NaCl, while K₂SO₄ and Na₂SO₄ tended to decrease leaf starch. Only KCl stimulated amylases and phosphorylase in leaves of Jackson. Salinity changed amylases according to the starch content in leaves of Lee, while phosphorylase decreased independent of the ion combination supplied. Salinity decreased invertase in leaves of Jackson, it affected invertase in Lee only little.

It is suggested that the carbohydrate metabolism dependent and independent of ionic regulation contribute to physiological salt tolerance mechanisms of soybean varieties.     

Effect of grafting on the growth and ion concentrations of cucumber seedlings under NaCl stress

Abstract

To assess whether grafting raised the salt tolerance of cucumber seedlings by limiting transport of Na⁺ to the leaf and to test whether the salt tolerance of grafted plants was affected by the shoot genotype, two cucumber cultivars (“Jinchun No. 2”, a relatively salt-sensitive cultivar, and “Zaoduojia”, a relative salt-tolerant cultivar) were grafted onto rootstock pumpkin (Cucurbita moschata Duch. cv. “Chaojiquanwang”, a salt-tolerant cultivar). Ungrafted plants were used as controls. The effects of grafting on plant growth and ion concentrations were investigated under NaCl stress. Reductions in the shoot and root dry weights, leaf area and stem diameter of grafted plants were lower and concentrations of K⁺ and Cl^? in the leaves were higher than those of ungrafted plants under the same NaCl stress. The Na⁺ concentration and Na⁺/K⁺ ratio in scion leaves and in the stems of grafted plants were lower, whereas those in rootstock stems and roots were higher than in ungrafted plants under the same NaCl stress. Shoot and root dry weight, leaf area and stem diameter were negatively correlated with leaf Na⁺ concentrations and Na⁺/K⁺ ratio, but were positively correlated with leaf K⁺ concentrations. The Na⁺ concentrations and Na⁺/K⁺ ratio were lower, whereas the K⁺ concentrations in the leaves of grafted “Zaoduojia” plants were higher than those in grafted “Jinchun No. 2” plants under the same NaCl stress. The reductions in leaf area and stem diameter of grafted “Jinchun No. 2” plants were more severe than those of grafted “Zaoduojia” plants. These results indicate that: (1) the higher salt tolerance of grafted cucumber seedlings is associated with lower Na⁺ concentrations and Na⁺/K⁺ ratio and higher K⁺ concentrations in the leaves, (2) grafting improved the salt tolerance of cucumber seedlings by limiting the transport of Na⁺ to the leaves, (3) the salt tolerance of grafted cucumber seedlings is related to the shoot genotype.     

Influence of extreme K:Na ratios and high substrate salinity on plant metabolism of crops differing in salt tolerance

Mineral regulation of two soybean varieties Jackson and Lee was investigated in long term water culture experiments using saline solutions. The effects of extreme K:Na ratios using chloride and sulfate as counterions were studied in the early stages of salinity.

The growth rates of both varieties were not affected by salinization. A K⁺ stimulated, intensive acropetal Cl^‐ translocation was observed in the salt sensitive variety Jackson. The varieties did not differ in Na⁺ translocation and in the suppression of Ca²⁺ and Mg²⁺ in the leaves. But the effect of the nature of salinization indicates already differences in Na uptake and translocation of the cultivars.

The avoidance of Cl^‐, but also of Ha⁺, in connection with influences of the resulting ionic imbalance on metabolic pathways are probably the most causative factors for the different tolerance to salinity of the two soybean varieties.     

Adjustment of mineral ratio and composition in rice genotypes under varied salinity regimes

A study of the salinity effect on mineral content in rice genotypes differing in salt tolerance was conducted in a factorial Completely Randomized Design experiment. The results indicated that the genotypes developed differently by mutation conventional breeding. NS15 represented as salt-sensitive, Pokkali was included as an internationally salt-tolerant check and Iratom24 was moderately tolerant. The content of Na⁺, Ca²⁺, Mg²⁺ and Cl^? followed an increasing pattern in roots and shoots of all the rice genotypes due to increasing salinity levels except Ca²⁺ and Mg²⁺ in the root. However, the concentration of K⁺ showed more or less an increasing pattern in root and a decreasing pattern in shoot. The concentration of Na⁺ and Ca²⁺ sharply increased with increasing the salinity levels in both the roots and shoots of NS15. The concentration of K⁺ sharply decreased in shoot and increased in the root of susceptible genotype NS15 with increasing salinity over 6 dS m^?1 salinity levels, where the transformation of K⁺ from root to shoot was disrupted by Na⁺. The Cl^? content sharply increased with increasing salinity in the root of NS15 as compared to shoot. The effect of different salinity levels on Na⁺/K⁺ ratio in the shoots of the selected rice genotypes sharply increased in susceptible genotype NS15 as compared to the other genotypes.     

Salinity and Irrigation Method Affect Mineral Ion Relations of Soybean

Abstract

Soybean [Glycine max(L.) Merrill] is moderately salt tolerant, but the method of irrigation used for crop production under saline conditions may influence the uptake and distribution of potentially toxic salts. This field study was conducted to determine the effects of application of saline waters by different methods, namely, drip and above‐canopy sprinkler irrigation, on the ion relations of soybean cultivar “Manokin”. Salinity was imposed by adding NaCl and CaCl₂ (1:1 by weight) to nonsaline irrigation waters. Saline treatments with electrical conductivity (EC _i ) of 4 dS m^?1 were compared with nonsaline controls (EC _i  = 0.5 dS m^?1). Ion concentrations in leaves, stems, roots, and when present, pods were determined at four stages of growth: vegetative, flowering, podding, and grain filling. Both Na⁺ and Cl^? were excluded from the Manokin leaves and stems when plants were drip‐irrigated and the uptake of these ions occurred solely via the root pathway. However, when saline water was applied by sprinkling, the ions entered leaves by both foliar absorption and root uptake and their concentrations in the leaves were about 9‐fold higher than in those under saline drip irrigation. Regardless of treatment, leaf‐K was highest during the vegetative stage, then decreased with plant age as K⁺ was mobilized to meet nutrient demands of the developing reproductive structures.     

Na+ and Cl−: Leaf extrusion,retranslocation and root efflux in diplachne fusca (kallar grass) grown in NaCl

Abstract

Groups of “Kallar”; grass plants were subjected to various treatments of 100 mM NaCl simultaneously labelled with ²²Na⁺ and ³⁶Cl^?. On the basis of the specific activity, the distribution of Na and Cl^? in the tissue was followed during and after treatment, i.e. after transfer of some groups to an identical but inactive solution. Sequential collections of leaf washes showed that both Na and Cl^? were extruded at a somewhat constant rate. Leaf sheaths accumulated more Na⁺ and Cl^? than the leaf blades and the amounts of Na⁺ and Cl^? in the leaf sheaths as a percentage of their total plant content (i.e. 28% and 31%) approximated the amounts of Na and Cl^? extruded by the leaves (i.e. 23%). Moreover, almost equivalent amounts of Na⁺ (21%) and Cl^? (29%) were removed by root efflux which continued even several days after transfer of the plants to the inactive, saline solution. Part of the Na⁺ and Cl^? was retranslocated from the tops to the roots and was attributed to phloem export.

Tolerance of Kallar grass to NaCl was thus related to preventing the tissue from accumulating high concentration by extrusion of both Na⁺ and Cl^? by the leaves and their efflux by the roots in addition to an equivalent retention in the leaf sheaths.     

Time sequence studies on uptake and distribution of Na+ and Cl– in diplachne fusca (Kallar grass) grown in NaCl

Abstract

The time sequence of uptake and distribution of labelled Na and Cl^– in osmotically adjusted “Kallar”; grass was studied at low (10 mM) and moderately high salinity (100 mM) in nutrient solutions. Increasing NaCl raised the concentrations of Na⁺ and Cl^– in the tissue of tops and roots but had little or no effect on plant growth. On the leaves no toxic symptoms were obvious, not even in plants grown at salt stress of 200 mM NaCl. In all treatments, the young and the old leaves extruded 30–60% and 30–70% of their total Na⁺ and Cl^–. As the amounts of Na⁺ and Cl^– in the tissue increased with time, their extrusion also increased, however, as a proportion of the total Na⁺ and Cl^– it did not change much with time. Autoradiographs revealed that the extruded salts were distributed equally on the upper and lower surface of all leaves, parallel to veins. There seemed to be a more intense distribution of Na⁺ and Cl^– in the leaf sheaths as well as in the apical region of the roots. However, the net transfer rates, even after only 6 hours of uptake, did not indicate a strong retention mechanism in the roots.     

Growth,water use efficiency,and sodium and potassium acquisition by tomato cultivars grown under salt stress

Three cultivars of tomato (Lycopersicon esculentum Mill., cvs. Sera, 898, Rohaba) were grown under different levels of NaCl in nutrient solution to determine effects of salt stress on shoot and root dry matter (DM), plant height, water use efficiency (WUE, g DM kg^‐1 water evapotranspired), shoot sodium (Na) and potassium (K) concentrations, and K versus Na selectivity (S_K,Na). Increasing NaCl concentration in nutrient solution adversely affected shoot and root DM, plant height, WUE, K concentration, and K/Na ratio of all cultivars. Shoot Na concentrations increased with increasing NaCl concentration in the nutrient solution. Although increasing salt concentration in the solution adversely affected growth of all cultivars, the cultivar Sera had the highest shoot and root DM than the other two cultivars (898 and Rohaba). Shoot and root DM of cultivar 898 was most affected by salt, while cultivar Rohaba had an intermediate salt sensitivity. The cultivar Sera generally had higher WUE values, shoot K concentrations, and S_K,Na, but had lower shoot Na concentrations than the other two cultivars when plants were grown under different salt levels. Greater Na exclusion, higher K uptake and shoot S_K,Na are suggested as being plant strategies for salt tolerance.     

Effects of Salinity and Water Stress on Growth and Macro Nutrients Concentration of Pomegranate (Punica granatum L.)

In order to study the effects of salinity and water stress on growth and macronutrients concentration of pomegranate plant leaves, a factorial experiment was conducted based on completely randomized design with 0, 30, and 60 mM of salinity levels of sodium chloride and calcium chloride (1:1) and three irrigation intervals (2, 4, and 6 days) with 3 replications on ‘Rabab’ and ‘Shishegap’ cultivars of pomegranate. The results of the shoot and root analysis indicated that the salinity and drought affected the concentration and distribution of sodium (Na⁺), potassium (K⁺), chloride (Cl^?), calcium (Ca²⁺), magnesium (Mg²⁺), and phosphorus (P⁺) in pomegranate leaves. Mineral concentrations of sodium (Na⁺), chloride (Cl^-), potassium (K⁺), in shoots and roots were increased with increasing salinity. Drought treatments increased the concentration of Cl^?, Na⁺, and Mg²⁺ in the shoot. Both cultivars showed significant differences in the concentrations of elements, however the most accumulation of Na⁺ and Cl^? was observed in ‘Rabab,’ while the ‘Shishegap’ cultivar had the most absorption of K⁺. ‘Shishegap’ cultivar showed higher tolerance to salinity than ‘Rabab’ through maintaining the vegetative growth and lower chloride transport to the shoot, and improvement of potassium transport to shoot.     

Effects of NaHCO3 on photosynthetic characteristics,and iron and sodium transfer in pomegranate

In order to study effects of sodium bicarbonate (NaHCO₃) stress in irrigation water on photosynthetic characteristics and iron (Fe) and sodium (Na⁺) translocation content of pomegranate plants, a factorial experiment was conducted based on completely randomized design with three cultivars of pomegranate (“Gorch-e-Dadashi,” “Zagh-e-Yazdi,” and “Ghermez-e-Aliaghai”) and four concentrations of NaHCO₃ (0, 5, 10, and 15 mM), with three replications. The results of plant analysis indicated that NaHCO₃ affected chlorophyll index, F_v/F_m, and performance index (PI) in upper and lower leaves of shoots and also the translocation of Na⁺ and Fe. The results also showed that Fe translocation from root to shoot reduced at 15 mM level of NaHCO₃. The highest Na translocation and the lowest Fe translocation were observed in Zagh-e-Yazdi and Ghermez-e-Aliaghai cultivars, respectively. The ratio of sodium/potassium (Na⁺/K⁺) in stems was higher than that in roots and leaves, and the observed chlorophyll content of upper leaves was also lower than that of lower leaves. Based on the measured parameters Gorch-e-Dadashi cultivar showed less relative sensitivity than other cultivars to NaHCO₃ of irrigation water through maintaining the lower Na⁺ transport to the shoots, and improvement of Fe transport to shoots.     

Growth and chloride accumulation in soybean cultivars treated with excess KCl in solution culture

Abstract

Sensitivity to chloride was measured in soybean [Glycine max (L.) Merr.] cultivars Rinjani, Lokon, and Merbabu from Indonesia, and Lee from the United States. Plants were grown in solution culture to which KCl (0, 50, or 100 mol m^‐3) was added gradually during days 7–14 after emergence. Excess KCl reduced growth, measured as leaf area, shoot and root biomasses, total biomass, and root/shoot ratio in 24‐day‐old plants of all cultivars. The cultivar x KCl treatment interaction was significant for all growth parameters. The order of chloride tolerance at 50 mol m^‐3 Cl^‐, based on the mean of all growth parameters relative to the control, was Lee>Rinjani>Lokon=Merbabu. In the 50 mol m^‐3 Cl^‐ treatment Lee excluded Cl^‐ from the leaves, and accumulated Cl^‐ in the roots; Lokon, Rinjani, and Merbabu excluded less Cl^‐ from the leaves. At 100 mol m^‐3 KCl, cultivar Lee lost its capacity to exclude Cl^‐ from the leaves and its growth was poor. Chloride exclusion from the leaves at 100 mol m^‐3 KCl was most effective in Lokon, which corresponded to the relatively good growth of this cultivar in the high KCl treatment.     

Effect of salinity and soil temperature on the growth and physiology of drip-irrigated rice seedlings

Drip irrigation offers potential for rice (Oryza sativa L.) production in regions where water resources are limited. However, farmers in China’s Xinjiang Province report that drip-irrigated rice seedlings sometimes suffer salt damage. The objective of this study was to learn more about the effects of soil salinity and soil temperature on the growth of drip-irrigated rice seedlings. The study consisted of a two-factor design with two soil salinity treatments (0 and 1.8 g kg^?1 NaCl) and three soil temperature treatments (18°C, 28°C and 36°C). The results showed that shoot biomass, root biomass and root vigor were greatest when seedlings were grown with no salt stress (0 g kg^?1 NaCl) at 28°C. Moderate salt stress (1.8 g kg^?1 NaCl) combined with high temperature (36°C) significantly reduced root and shoot biomass by 39–53%. Moderate salt stress and high temperature also increased root proline concentration by 77%, root malonyldialdehyde concentration by 60% and seedling mortality by 60%. Shoot and root Na⁺ concentrations, shoot and root Na⁺ uptake and the Na⁺ distribution ratio in shoots were all the greatest when moderate salt stress was combined with high temperature. In conclusion, high soil temperature aggravates salt damage to drip-irrigated rice seedlings. Therefore, soil salinity should be considered before adopting drip-irrigation for rice production.     

Screening of tomato genotypes for salinity tolerance based on early growth attributes and leaf inorganic osmolytes

The experiment containing three replicates of completely randomized factorial treatments was conducted in a glasshouse under controlled conditions with three simulated soil salinity levels (control, 10 and 15 dS m^?1). Morpho-physiological traits (i.e. lengths, fresh weights and dry weights of root and shoot, number of leaves, root/shoot ratio, shoot Na⁺ accumulation, K⁺/Na⁺ ratio, Ca²⁺/Na⁺ ratio, membrane stability index, lycopene contents, chlorophyll-a and -b) were recorded to determine mechanism of salt tolerance of tomato at seedling stage. Principal component analysis (PCA) was used to express a three-way interaction of genotype × salinity level × traits that scattered the 25 tomato genotypes based on their morpho-physiological response to different NaCl levels. The negative association of Na⁺ with all other traits except root/shoot ratio and the morpho-physiological response trend of genotypes exposed that probable mechanism of salt tolerance was initially Na⁺ exclusion by abscising older leaves to have younger physiologically energetic, and lastly a higher activity of plants for root development to sustain them in saline soil. PCA three-way biplot efficiently recognized ANAHU, LA-2821, LO-2752, LO-2707, PB-017909, LO-2831-23 and 017860 as salt tolerant genotypes. On the other hand, ZARNITZA, GLACIER, LO-2692, LO-2576, BL-1079, 006233, 006232, 017856, NUTYT-701 and NAGINA were found to be salt susceptible.     

Salt-induced perturbation in growth,physiological attributes,activities of antioxidant enzymes and organic solutes in mungbean (Vigna radiata L.) cultivars differing in salinity tolerance

A pot experiment was conducted to appraise the inhibitory effects of salt stress on biochemical attributes in the three mungbean cultivars (NCM-209, NCM-89 and NM-92). Salt stress caused a significant decrease in plant height, shoot relative water contents, photosynthetic pigments, endogenous levels of K⁺ and K⁺/Na⁺ ratios and increase in cellular levels of H₂O₂, MDA, Na⁺ and Cl^?. However, cv. NCM-209 was found to be tolerant in terms of lower salt-induced decline in K⁺, K⁺/Na⁺ ratio and photosynthetic pigments. The endogenous levels of H₂O₂ and MDA were also lower in cv. NCM-209. Salt stress markedly also affected different yield attributes in all mungbean cultivars. Again cultivar NCM-209 exhibited less inhibitory effects of salt stress on different growth attributes. Salt stress resulted in a marked increase in the activities of antioxidant enzymes (superoxide dismutase, peroxidase, catalase and ascorbate peroxidase) in mungbean cultivars. Activity of peroxidase was maximal in cv. NCM-209 and catalase activity was maximal in cv. NCM-89, whereas cvs. NCM-89 and NM-92 showed higher activities of superoxide dismutase. Similarly activity of ascorbate peroxidase was higher in cv. NM-92. It could be inferred from data of antioxidant enzymes that mungbean cultivars cannot be categorized as salt tolerant or sensitive on the basis of a single antioxidant enzyme.     

Effects of zinc activity in nutrient solution on uptake,translocation, and root export of cadmium and zinc in three wheat genotypes with different zinc efficiencies

The interactions of zinc (Zn) and cadmium (Cd) in uptake and translocation are common but not consistent. We hypothesized that Cd²⁺ and Zn²⁺ activity in the apoplasmic solution bathing root-cells could affect Zn accumulation in plants dependent on the wheat genotype. This hypothesis was tested using seedlings of two bread wheat genotypes (Triticum aestivum L. cvs. Rushan and Cross) and one durum wheat genotype (Triticum durum L. cv. Arya) with different Zn efficiencies grown in chelate-buffered nutrient solutions with three Zn²⁺ (10^?11.11, 10^?9.11, and 10^?8.81?µM) and two Cd²⁺ (10^?11.21 and 10^?10.2?µM) activity levels. Increasing Zn²⁺ activity in the nutrient solution significantly increased Zn concentration in root and shoots of all three wheat genotypes, although the magnitude of this increase was dependent on the genotype. Cadmium decreased Zn concentration in roots of “Cross” while it had no significant effect on root Zn concentration in “Rushan.” At Zn^2+?=?10^?11.11?µM, Cd decreased shoot Zn concentration in “Arya” whereas it increased shoot Zn concentration at Zn^2+?=?10^?8.81?µM. Cadmium increased shoot Zn concentration of “Rushan” and “Cross” at Zn^2+?=?10^?8.81?µM but it had no significant effect on shoot Zn concentration of these genotypes at Zn^2+?=?10^?11.11?µM. The zinc-inefficient genotype “Arya” accumulated significantly more Cd in its root in comparison with “Cross” and “Rushan.” Cadmium concentration in roots of “Arya” was decreased significantly with increasing Zn activity. The effect of Zn on accumulation of Cd in roots of “Cross” and “Rushan” was dependent on the dose provided, and therefore, both synergistic (at Zn^2+?=?10^?9.11?µM) and antagonistic (at Zn^2+?=?10^?8.81?µM) interactive effects were found in these genotypes. Zinc supply increased the Zn concentration of xylem sap in “Cross” and “Rushan” whereas Zn content in xylem sap of “Arya” was decreased at Zn^2+?=?10^?9.11?µM and thereafter increased at Zn^2+?=?10^?8.81?µM. Cadmium treatment reduced Zn concentration in xylem sap of “Arya,” while it tended to increase Zn content in xylem sap of “Cross.” At Zn-deficient conditions, greater retention of Zn in root cell walls of Zn-inefficient “Arya” resulted in lower root-to-shoot transport of Zn in this genotype. Results revealed that the effect of Cd on the root-to-shoot translocation of Zn via the xylem is dependent on wheat genotype and Zn activity in the nutrient solution.     

Interactions Between Cadmium Uptake and Phytotoxic Levels of Zinc in Hard Red Spring Wheat

Abstract

Wheat grown on cadmium (Cd)‐uncontaminated soils can still potentially translocate unacceptable levels of Cd to grain. The effect of zinc (Zn) and Cd levels on Cd uptake and translocation in “Grandin” hard red spring wheat (HRS‐wheat) (Triticum aestivum L.) was investigated using a double chelator‐buffered nutrient solution [EGTA used to buffer Cd, Zn, copper (Cu), manganese (Mn), and nickel (Ni); and Ferrozine (FZ) used to buffer Fe²⁺]. In the Zn level series of treatments, Cd²⁺ activity was held constant at 10^?10.7 M, and the Zn²⁺ activity was varied from 10^?7.6 to 10^?5.2 M. As Zn²⁺ activity increased, the translocation of Cd to the shoots decreased. The shoot : root Cd concentration ratio decreased from 0.20 to 0.03 as pZn²⁺ went from 7.6 to 5.2, indicating that adequate to high levels of Zn are effective in reducing Cd translocation to the shoots of “Grandin” HRS‐wheat. In the Cd series, the Zn activity was at 10^?6.6 M, while Cd activity was increased from 10^?10.7 to 10^?9.2 M. High levels of Cd did not significantly affect the uptake and translocation of Zn in the roots and shoots. While at pCd²⁺ of 9.2, the root and shoot Cd concentrations significantly increased, there was not a significant increase in the shoot : root Cd ratio. This would indicate that even at high Cd²⁺ activities, Zn is effective in regulating Cd uptake and translocation in “Grandin” HRS‐wheat.