The paramount influence of nitrate in increasing apoplastic pH of young sunflower leaves to induce Fe deficiency chlorosis,and the re-greening effect brought about by acidic foliar sprays

The main objective of the present work was to clarify the causal relationship between leaf apoplastic pH increase and Fe chlorosis under alkaline growth conditions. It has been shown that nitrate supply in contrast to ammonium supply induced a pH increase in the apoplast of young green leaves of Helianthus annuus which was followed within 12 hours by leaf yellowing. Hence nitrate nutrition is the primary cause of a high leaf apoplastic pH which induces Fe deficiency chlorosis and not the impaired provision of ATP for plasmalemma H⁺ pumps in yellow leaves. Supply of bicarbonate in physiological concentrations had virtually no influence on leaf apoplastic pH. Spraying leaves with diluted acids (citric acid, sulphuric acid) resulted in a decrease of apoplastic pH followed by leaf re-greening. Interestingly, the Fe concentrations remained the same in the yellow control leaves and in the sprayed green leaves. From this it follows that Fe efficiency in leaves is mainly related to the Fe distribution between apoplast and symplast. It was demonstrated that Fe chlorosis induced by nitrate nutrition begins from the base of the youngest leaves, presumably from growing interveinal microsites showing high nitrate uptake rates. Leaf yellowing spread gradually from the leaf base to the tip and after seven days of nitrate supply the leaf was almost completely yellow (98%). Leaf yellowing was measured by means of a video imaging technique. Leaf apoplastic pH recordings were conducted after loading the fluorescent dye FITC-Dextran (4000 D) into the leaf apoplast of intact plants thus simulating in vivo conditions. It was also shown using the new loading technique that the fluorescent dye did not penetrate the leaf symplast.     

INFLUENCE OF CHEMICAL FORM AND CONCENTRATION OF NITROGEN ON APOPLASTIC pH OF LEAVES

The objective of this study was to investigate the effects of various forms of nitrogen (NO^? ₃, NH⁺ ₄) supplied to the roots via a nutrient solution on the apoplastic pH in intact leaves determined by fluorescence ratio imaging. In contrast to NH⁺ ₄, higher apoplastic pH values in leaves of Phaseolus vulgaris and Helianthus annuus were measured with NO^? ₃ nutrition. In this context no significant differences were found in leaves of Vicia faba and Zea mays supplied with the various forms of N. Comparative studies on apoplastic pH in leaves of Vicia faba, Zea mays and Helianthus annuus demonstrated that NO^? ₃ reductase activity in roots was responsible for the differences in NO^? ₃ concentration and pH in the leaf apoplast. Light-induced pH changes in the leaf apoplast also occur and may overlap the effects of various forms of N. Increasing concentrations of NO^? ₃ supply to the roots did not significantly affect apoplastic pH in leaves of Helianthus annuus. Depletion of NO^? ₃ in the nutrient solution led to lower apoplastic pH in leaves of Zea mays. Leaf fertilization with NH⁺ ₄ led to a decline in apoplastic pH of leaves whereas NH₃ gas exposure caused a biphasic response in apoplastic pH.     

High K+ supply avoids Na+ toxicity and improves photosynthesis by allowing favorable K+ : Na+ ratios through the inhibition of Na+ uptake and transport to the shoots of Jatropha curcas plants

This study assessed the relationships between external K⁺ supply and K⁺ : Na⁺ ratios associated with Na⁺ toxicity in Jatropha curcas. Plants were exposed to increasing external K⁺ concentrations (6.25, 12.5, 25, 37.5, and 50 mM), combined with 50 mM NaCl in a nutrient solution. Photosynthesis progressively increased as the external K⁺ : Na⁺ ratios increased up to 0.75. The increase of photosynthesis and plant dry matter correlated positively with K⁺ : Na⁺ in xylem and leaves. The transport rates of K⁺ and Na⁺ from roots to xylem and leaves were inversely correlated. These ions presented an antagonistic pattern of accumulation in all organs. Maximum rates of photosynthesis and plant growth occurred with leaf K⁺ : Na⁺ ratios that ranged from 1.0 to 2.0, indicating that this parameter in leaves might be a good indicator for a favorable K⁺ homeostasis under salinity conditions. The higher K⁺ affinity and selectivity compared with Na⁺ in all organs associated with higher xylem flux and transport to shoots are essential for maintaining adequate K⁺ : Na⁺ ratios at the whole‐plant level. These characteristics, combined with adequate K⁺ concentrations, allow J. curcas to sustain high rates of photosynthesis and growth even under toxic NaCl levels.     

Physiology of manganese toxicity and tolerance in Vigna unguiculata (L.) Walp.

In cowpea (Vigna unguiculata (L.) Walp.) tolerance of manganese (Mn) excess depends on genotype, silicon (Si) nutrition, form of nitrogen (N) supply, and leaf age. The physiological mechanisms for improved Mn leaf-tissue tolerance are still poorly understood. On the basis of the density of brown spots per unit of leaf area and the callose content which are sensitive indicators of Mn toxicity, it was confirmed that cultivar (cv.) TVu 1987 was more Mn-tolerant than cv. TVu 91, young leaves were more Mn-tolerant, Si improved Mn tolerance, and NO₃^—-grown plants were more Mn-tolerant than NH₄⁺-grown plants. A close positive relationship existed between the bulk-leaf Mn content and the vacuolar Mn concentration from the same leaves. Since no clear and consistent differences existed between leaf tissues differing in Mn tolerance, the results suggest that accumulation of Mn in the vacuoles and its complexation by organic anions do not play a role in Mn leaf-tissue tolerance in cowpea. A near linear relationship was found between leaf Mn contents and concentrations of free (H₂O-soluble) and exchangeable-bound (BaCl₂-extractable) Mn in the apoplastic washing fluid (AWF) extracted from whole leaves by an infiltration and centrifugation technique. There were no differences in apoplastic Mn concentrations owing to genotype and form of nitrogen nutrition. However, Si decreased the Mn concentration in the AWF. With increasing bulk-leaf Mn contents, concentrations of organic anions in the AWF also increased. The results suggest that complexation of Mn by organic anions in the leaf apoplast contribute to Mn tolerance due to genotype and more clearly due to NO₃-N nutrition. Cell wall-bound peroxidase activity increased with leaf age and was higher in the Mn-sensitive cv. TVu 91 than in cv. TVu 1987. This was in agreement with a higher H₂O₂ production rate in cv. TVu 91. Also, a lower ratio of reduced to oxidized ascorbic acid in the AWF revealed that in Mn-sensitive leaf tissue, the apoplastic reduction capacity was lower than in Mn-tolerant leaf tissue when genotypes and leaves of different age were compared. We interpret our results as strong circumstantial evidence that Mn tolerance depends on the control of the free Mn²⁺concentration and of Mn²⁺-mediated oxidation/reduction reactions in the leaf apoplast.     

Study of K+ uptake kinetics of flue-cured tobacco in K+-enriched and conventional tobacco genotypes

Screening of potassium efficient genotypes will be one of the best ways to solve the low potassium content of flue-cured tobacco. The study was conducted to determine whether the potassium efficient genotypes could be screening with high K⁺ uptake efficiency. The K⁺ uptake characteristics of a high K⁺ content line (GK8) and the conventional cultivated variety (K326) of flue-cured tobacco were compared at the seedling stage. K_m, C_min, and I_max values were higher in young seedlings (4?～?5 versus 6?～?7 leaf stage) and cultures with high initial K⁺ concentration (0.35 versus 0.25?mmol?L^?1). Culture solutions with a high K⁺ concentration (2.0 versus 0.6?mmol?L^?1) showed a high K_m, and C_min, but the I_max was lower as compared with the young seedlings and the solution with high initial K⁺ concentration. In conclusion, the GK8?line had a stronger ability for limited K⁺ uptake than K.     

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.     

Puccinellia tenuiflora Exhibits Stronger Selectivity for K+ over Na+ than Wheat

Abstract

The characteristics of selectivity for K⁺ over Na⁺ by the roots of the halophyte Puccinellia tenuiflora were investigated in comparison with the glycophyte wheat (Triticum aestivum). Under various NaCl concentrations, the concentrations of K⁺ in the shoots of P. tenuiflora were 16–24% lower than those of wheat, whereas the concentrations of K⁺ in Puccinellia roots were 2.8–4.0 times higher than those of wheat. In 200 mM NaCl, the concentrations of Na⁺ in shoots of P. tenuiflora and wheat were similar under high K⁺ levels, but the concentrations of Na⁺ in wheat were 1.6 times higher than those in Puccinellia under low K⁺ levels. The concentrations of K⁺ in roots of P. tenuiflora were 1.5–2.0 times higher than those of wheat under low K⁺ levels. Formulas are given for calculating net selective absorption (SA) capacity and selective transport (ST) capacity by roots for K⁺ over Na⁺. We interpret SA as the net capacity of selectively absorbing K⁺ over Na⁺ by epidermal and cortical cells of whole plant roots into the root symplast. ST could reflect the net capacity of selection for K⁺ over Na⁺ transport from whole root stelar symplast to the xylem vessels. The lower ST value of P. tenuiflora might be the reason for accumulation of K⁺ in its roots. The SA values of P. tenuiflora and wheat were approximately equivalent in the low-affinity K⁺ uptake range. The SA values of the former were about two times higher than that of the latter in the high-affinity K⁺ uptake range, showing the root high-affinity K⁺ uptake system of the halophyte P. tenuiflora has a stronger capacity for K⁺ uptake.     

Ammonia exchange between rice leaf blades and the atmosphere: Effect of broadcast urea and changes in xylem sap and leaf apoplastic ammonium concentrations

Abstract

To elucidate the effects of broadcast urea on ammonia (NH₃) exchange between the atmosphere and rice, we investigated the NH₃ exchange flux between rice leaf blades and the atmosphere, xylem sap ammonium (NH⁺ ₄) concentration, leaf apoplastic NH⁺ ₄ concentration and pH, and determined the stomatal NH₃ compensation point. Paddy rice (Oryza sativa L. cv. Nipponbare) cultivation using experimental pots was conducted in the open air. Three treatments, no nitrogen (NN), standard nitrogen (SN) and high nitrogen (HN), were prepared for two supplemental fertilizations. Urea with 0, 30 and 60 kg N ha^?1 for the NN, SN and HN treatments, respectively, was broadcast at panicle initiation, and urea with 0, 20 and 40 kg N ha^?1 for the NN, SN and HN treatments, respectively, was broadcast at heading. The NH₃ exchange fluxes between the rice leaf blades and the atmosphere (SN treatment) measured using a dynamic chamber technique showed net deposition in general; however, net emission from the old leaves occurred 1 day after the application at heading. In contrast, the xylem sap NH⁺ ₄ concentrations increased markedly 1 day after both applications, which suggests direct transportation of NH⁺ ₄ from the rice roots to the above-ground parts. The applications resulted in no obvious increase in the leaf apoplastic NH⁺ ₄ concentrations. The relationship between the NH⁺ ₄ concentration in the xylem sap and that in the leaf apoplast was uncertain, although the NH⁺ ₄ in the xylem sap came from the roots and the NH⁺ ₄ in the apoplast might be affected by the stomatal deposition of NH₃. The stomatal NH₃ compensation point of rice was estimated to be 0.1–4.1 nmol mol^?1 air (20°C). The direction and intensity of the exchange flux through the stomata, interpreted on the basis of the temperature-corrected NH₃ compensation point, agreed with the observed exchange flux between the rice leaf blades and the atmosphere.     

Common reed absorbs K+ more selectively than rice against high Na+/K+ ratio in nutrient solution

The introduction of an active Na⁺ excretion system from salt-tolerant plants in salt-sensitive crop plants might necessitate enhancement of the robustness of K⁺ homeostasis and lead to improved plant growth under salt stress. To address this issue, we compared the acquisition and retention of K⁺ under excess Na⁺ concentrations in the common reed, which possesses excellent Na⁺ excretion ability, and low-Na⁺ excreting rice. Under excess Na⁺ concentrations, common reed maintained constant K⁺ content in all plant parts, whereas K⁺ content in rice decreased with increasing Na⁺ concentration. Preferential uptake of K⁺ against high Na⁺/K⁺ ratio in nutrient solution was approximately 10 times higher in common reed than in rice. The impact of excess Na⁺ on net K⁺ absorption rate of common reed was small. On the other hand, the net K⁺ absorption rate of rice was decreased by excess Na⁺ concentration. However, after the Na⁺ concentration in the nutrient solution was decreased from 50 to 1 mM, K⁺ absorption in rice recovered immediately. Thus, selectivity of K⁺ transporters or channels for K⁺ over Na⁺ in roots could be involved in the differences in K⁺ accumulation in rice and common reed.     

RESPONSE OF LISIANTHUS TO IRRIGATION WITH SALINE WATER: ION RELATIONS

Eustoma grandiflorum (Raf.) Shinn. (lisianthus) is a moderately salt tolerant species that can be produced commercially under irrigation with saline wastewaters prevalent in two salt-affected areas of California. The objective of the present studies was to determine the effect of irrigation with saline waters of two different compositions on the ion accumulation and ion relations of lisianthus ‘Pure White’ and ‘Echo Blue’. The ionic composition of irrigation waters simulated the compositions typical of i) seawater dilutions (SWD) and ii) concentrations of Colorado River water (CCRW). Electrical conductivities (EC) of SWD and CCRW were between 2 and 12 dS · m^?1. Plants irrigated with CCRW were higher in Ca²⁺ compared to plants irrigated with SWD water. Calcium was also higher in ‘Pure White’ than in ‘Echo Blue’. Increasing EC of irrigation water caused a significant decrease in shoot and leaf Ca²⁺ concentration in ‘Echo Blue’, but had no effect on Ca²⁺ content of ‘Pure White’ shoots and leaves. Magnesium concentration in ‘Echo Blue’ was higher than in ‘Pure White’. Electrical conductivity did not significantly affect Mg²⁺ concentration of either cultivar, despite the increasingly higher external concentration. Potassium concentration of young and mature leaves of ‘Echo Blue’ increased as EC increased from 2 to 8 dS · m^?1, then decreased significantly once EC exceeded 8 dS · m^?1. Potassium concentration of ‘Pure White’ leaves decreased over the range of salinity treatments tested, suggesting that the reduced potassium ion (K⁺) activity at EC levels of 8 dS · m^?1, or less, that resulted in lower leaf?K⁺ in ‘Pure White’ did not cause a decrease in K⁺ uptake in ‘Echo Blue’. Increases in external Na⁺ caused a significant increase in Na⁺ in ‘Pure White’ leaves and these plants exhibited the best growth even when levels of Na⁺ were high enough to be considered detrimental for growth.     

SOME DELETERIOUS EFFECTS OF LONG-TERM SALT STRESS ON GROWTH,NUTRITION, AND PHYSIOLOGY OF GERBERA (GERBERA JAMESONII L.) AND POTENTIAL INDICATORS OF ITS SALT TOLERANCE

Tolerance of gerbera (Gerbera jamesonii L.) to long-term sodium chloride (NaCl) salt stress was evaluated by subjecting plants to 0, 10, 20, 30 and 40 mM NaCl levels for ten weeks. Increased NaCl led to a significant decrease in leaf and stem biomass. Salt stress significantly affected sodium (Na⁺), potassium (K⁺) concentrations in leaves, stems and roots leading to sharp declines in K⁺/Na⁺ ratios. Magnesium concentrations in stems and roots also showed significant declines. Adverse effect of salt stress on chlorophyll content was also significant. Proline seemed less effective in osmotic adjustment under long-term high salt stress. Switching from vegetative to reproductive growth phase was crucial for certain physiological functions. Leaf Na⁺ concentration showed significant correlation with important traits. These data suggest that NaCl threshold level in irrigation water for gerbera is around 10 mM. Leaf fresh weight, chlorophyll content and leaf K⁺/Na⁺ ratio are promising indicators of salt-sensitivity of gerbera.     

Effect of Various Nitrogen Forms on the pH in Leaf Apoplast and on Iron Chlorosis of Glycine max L.

The effect of NH₄NO₃ (control) and increasing NO₃- levels in nutrient solutions containing no and 100 μM Fe respectively on iron chlorosis of Glycine max was investigated. After two weeks of growth apoplastic pH in excised leaves was measured by means of fluorescence. In plants growing without Fe supply increasing concentrations of NO₃- in the nutrient solution which also was applied to the cut end of the petiole, resulted in a pH increase in the leaf apoplast from 5.34 (NH₄NO₃) to 5.50 (NO₃-) associated with chlorosis observed with intact plants. A close negative correlation was found between chlorophyll concentration and pH in the apoplast (r = ?0.97). While leaves in the treatment exclusively fed with NO₃- were strongly chlorotic, those in the NH₄NO₃ treatment were green. With exception of the plants only fed with NO₃- the Fe concentration in the leaves was not affected by the type of N nutrition. It is therefore assumed that some Fe is immobilized in the leaf tissue by high apoplast pH induced by an increase in the proportion of nitrate in the nutrient solution. Plants fed with Fe (100 μM) showed no chlorosis, regardless of the form of N nutrition and hence regardless of apoplast pH. The Fe concentration in leaves of Fe fed plants was approximately twice those in the leaves not supplied with Fe.     

Growth,ion accumulation,and lipid composition of two olive genotypes under salinity 1

Olive (Olea europaea L cv. Leccino and cv. Frantoio) plants grown in aeroponic cultivation system were supplied with Hoagland solutions containing 0 and 150 mM NaCl for 4 weeks. Sodium (Na⁺), chloride (Cl^‐), and potassium (K⁺) concentration was measued on 15‐day‐old leaves and K⁺/Na⁺ selectivity ratio was calculated. Plant water relations were estimated on the same leaves by measuring leaf bulk water and osmotic potentials, and by calculating leaf turgor pressure. Root and leaf tissues were also analysed for lipid composition, estimating free sterol (FS), glycolipid (GL) and phospholipd (PL) content. The salt‐sensitive Leccino accumulated more Na⁺ and Cl^‐ in the leaves and showed a lower K⁺/Na⁺ selectivity ratio than the salt‐tolerant Frantoio. The FS/PL ratio and the content of GL (namely mono‐galactosyldiglyceride, MGDG) in the roots were related to the salt accumulation in the shoot. Salinity‐induced changes on root lipids were more important in Frantoio than in Leccino, indicating the specific role of the roots in salt exclusion mechanisms. Conversely the effect of salinity on leaf lipid composition was more important in the leaves of the salt‐sensitive Leccino.     

Negative correlation between the ratio of K+ to Na+ and proline accumulation in tobacco suspension cells

Abstract

The concentrations of K⁺, Na⁺, and proline and the ratio of K⁺ to Na⁺ (K⁺ / Na⁺) were analyzed in NaCl-unadapted and NaCl-adapted tobacco (Nicotiana tabacum) cells in suspension culture. At 3 to 5 d after inoculation, the NaCl-unadapted cells cultured in 100 mmol L^?1 NaCl saline culture medium (Na100 medium) accumulated 28.7 mmol L^?1 proline with a low ratio of K⁺ to Na⁺ (= 2.8) and the NaCl-adapted cells cultured in the Na100 medium contained 6.28 mmol L^?1 proline with a high K⁺ / Na⁺ ratio (≧ 7.5). The contents of amino acids for the NaCl-adapted cells in the Na100 medium were similar to those for the NaCl-unadapted cells in a modified LS medium (standard medium). At 14 d after inoculation, the NaCl-unadapted cells in the Na100 medium contained 4.77 mmol L^?1 proline and restored the K⁺ / Na⁺ ratio from 2.8 to 6.2. These results indicate the presence of a negative correlation between the K⁺ / Na⁺ ratio and proline accumulation and suggest that a balance between the K⁺ / Na⁺ ratio and proline accumulation may be the factor involved in determining the salt tolerance of plant cells.     

Effects of different forms of nitrogen supply on the gas exchange of young pedunculate oaks (Quercus robur L.)

The effects of different forms and concentrations of N in the rooting medium on the CO₂/H₂O gas exchange of leaves of the pedunculate oak (Quercus robur L.) were investigated. Two-year-old seedlings were grown in nutrient solutions containing low (1.8 mM) or high (4.8 mM) concentrations of NH₄⁺, 3.6 mM NO₃^?, or both NH₄⁺ and NO₃^? (1.8 mM + 1.8 mM). In various sets of plants subjected to these N treatments, the following parameters were determined: biomasses of leaves and fine roots, leaf area-related net photosynthesis at light saturation (A) and leaf conductance (g), foliar concentrations of chlorophylls, N, Ca²⁺, Mg²⁺ and K⁺ and the ash alkalinity of the leaves (as a measure of the carboxylate content). In all treatments, the leaves were equally well supplied with nutrients. Oaks grown in high NH₄⁺ concentrations produced significantly smaller leaf and root biomasses. Compared to oaks cultivated with both N forms or with low NH₄⁺ concentration, oaks grown with high NH₄⁺ supply showed lower values of A and g, but no significant differences in ash alkalinity and leaf area-related chlorophyll concentrations. Oaks fed with NO₃^? as the only N form had an intermediate biomass production, but low values of A and g. The time courses of A in the different treatments closely followed the patterns of g. In all N treatments, the same linear relationship was found between A and g, indicating that, within a rather wide range, the variation in the form and amount of supplied N does not affect the instantaneous water use efficiency of young pedunculate oaks.     

Response of potted anthurium (Anthurium andreanum Lind.) to the K+: Ca+2: Mg+2 balance in the nutrient solution

The climatic conditions of the humid tropical areas of México allow the year-round production of cut flowers and potted plants of anthurium. However, the scarce basic and applied research on tropical ornamental species limits the development of technology to increase productivity and quality. In this article, we are reporting the information as to the effect of the proportions of potassium (K⁺), calcium (Ca⁺²), magnesium (Mg⁺²) in the nutrient solution on anthurium growth using mixture analysis and response surface methodology. The sum of all the three cations was 20 meq L^?1 and each one is expressed as a fraction of this total concentration. Response surface analysis detected that spathe and leaf areas decreased in plants fed with solutions of high proportions of Mg⁺². Total shoot and root fresh weight, as well as total dry weight and root volume, also demonstrated the deleterious effects of high Mg⁺². In general, the best growth occurred in two areas of the explored space; a) an area of high Ca⁺², with optimum proportions ranging from 0.24–0.44 for K⁺, 0.54–0.68 for Ca⁺², and 0.01–0.08 for Mg⁺², and b) another area of high K⁺, on which the optimum proportions ranged 0.54–0.65 for K⁺, 0.25–0.29 for Ca⁺², and 0.10–0.21 for Mg⁺². Shoot and root K⁺, Ca⁺², and Mg⁺² concentration was significantly affected by the cation balances in the external solution, however, there was not a clear tendency as to the effect of each cation in the mixture; nonetheless, the internal K⁺: Ca⁺²: Mg⁺² balances were affected by the balances in the nutrient solution, as in the shoot they were located in a very specific area of the explored space, indicating that anthurium plants accumulated more Mg⁺² compared to what it is in the external solution, whereas Ca⁺² was lower than that of the external solution. Plants accumulated K⁺ at high rates regardless of the external balance. In conclusion, the optimum nutrient solutions for anthurium may contain very wide ratios of K⁺ as long Ca⁺² and Mg⁺² are maintained at low proportion in the nutrient solution.     

A Correlation of Rapid Cardy Meter Sap Test and ICP Spectrometry of Dry Tissue for Measuring Potassium (K+) Concentrations in Pak Choi (Brassica Rapa Chinensis Group)

Nutritional status of vegetable crops is often monitored by analysis of dried plant tissues, which is costly and often time consuming. Two greenhouse trials were conducted, at the University of Hawaii at Manoa, Magoon facilities, to evaluate the portable cardy ion meter (CIM) in determining potassium (K⁺) status in fresh petiole sap of pak choi as compared with standard laboratory methods. In the first greenhouse trial, three algae species (Gracilaria salicornia, Kappaphycus alvarezii, and Eucheuma denticulatum) were used to apply five rates of K⁺ (0, 84, 168,252, and 336 kg.ha^?1). The pak choi was directly seeded into 4 L pots and was grown in peat moss. In the second greenhouse trial, K+ was provided through Eucheuma denticulatum and potassium nitrate (KNO₃) at five rates (0,112, 168, 224, 280, and 336 kg.ha^?1) in peat moss and soil media. At harvest, K⁺ concentrations in fresh petiole sap were analyzed immediately with CIM and the dried samples were analyzed by inductively coupled plasma spectroscopy (ICP) measurement. The results showed increase in leaf K+ content at higher rates and the maximum concentration of leaf K⁺ at 4500–5300 mg/L for sap and 8–9% for tissue was obtained when K⁺ was provided between 224 and 284 kg.ha^?1. There was a close correlation between the CIM readings and the ICP method (r = 0.8048 and 0.8314) from the first and second GH results, respectively. The results suggest that the CIM could be used for the rapid monitoring of the relative K⁺ status of plants. The data further suggested 4500–5000 mg K/L for fresh petiole sap and 7.5% K⁺ in tissue as critical levels for K⁺ concentration in pak choi.     

High monosilicic acid supply rapidly increases Na accumulation in maize roots by decreasing external Ca2+ activity

Both calcium (Ca²⁺) and silicon (Si) improve plant performance under salt (NaCl) stress. Although these two mineral elements share numerous similarities, the information on how their extracellular interactions in the root apoplast affect uptake of sodium (Na⁺) is still lacking. Here, we investigated the effect of high Si supply in the bioavailable form of monosilicic acid (H₄SiO₄) on the activity of Ca²⁺ in the external root solution, and subsequent root uptake and compartmentation of Na in maize (Zea mays L.). In the short‐term experiments (6 h), 14‐d‐old maize plants were exposed to various concentrations of Ca²⁺ at three different pH‐values (6.5, 7.5, and 8.5) and two Si concentrations, i.e., low (1 mM) and high (4 mM) supply of H₄SiO₄. The activity of Ca²⁺ and Na⁺ in the external solution as well as the root concentrations of total and cell sap and BaCl₂‐exchangeble apoplastic fractions of both elements were analyzed. The pH of the nutrient solution affected neither the ion activities nor the root accumulation of both Ca²⁺ and Na⁺. At higher pH values (7.5 and 8.5) the interactions of Ca²⁺ and Si at high Si supply led to a decrease of Ca²⁺ activity and, hence, an increase of Na⁺ : Ca²⁺ activity ratio in the external root solution. Concomitantly, despite the elevated exchangeable apoplastic fraction of both Ca²⁺ and Na⁺, the total and cell sap concentrations were remarkably decreased for Ca²⁺ and increased for Na⁺ by the addition of 4 mM H₄SiO₄. This work demonstrates that at high Si supply extracellular Ca‐Si interactions leading to lowered activity of Ca²⁺ might rapidly compromise the ameliorative effect of Ca²⁺ on Na⁺ accumulation in roots. Practically, Si over‐fertilization of saline and, in particular, sodic soils may further promote the accumulation of Na⁺ in root tissues hours after Si application and, hence, increase a potential risk of Na⁺ toxicity.     

Influence of the Modification of Nutritional Parameters in Aglaonema commutatum: K+, Ca2+, Mg2+ and Na+

Abstract

This trial was carried out to establish an appropriate nutrient solution for Aglaonema commutatum and to investigate the nutritional effects generated by modifications in the solution. Six treatments were tested: control (T₀; pH 6.5, E.C. 1.5 dS m^?1, 6 mmol L^?1 NO₃ ^?‐N, and 6 mmol L^?1 K⁺); high nitrogen (N) level (T₁; 9 mmol L^?1 6:3 NO₃ ^?–NH₄ ⁺); N form (T₂; 6 mmol L^?1 N‐NH₄ ⁺); high K⁺ level (T₃; 12 mmol L^?1 K⁺); high electrical conductivity (T₄; E.C. 4 dS m^?1, 25 mmol L^?1 NaCl), and basic pH (T₅; pH 8). At the end of the cultivation, leaf, shoot, and root dry weights and elemental concentrations were determined. Nutrient contents and total plant uptake were calculated from the dry weights and nutrient concentrations. Plant K⁺ uptake increased with application of K⁺ or basic nutrient solution. The uptake and transport of calcium (Ca) were enhanced by the use of NO₃ ^?‐N and inhibited by the presence of other cations in the medium (NH₄ ⁺, K⁺, Na⁺) and by basic pH. Magnesium (Mg) uptake increased with NO₃ ^?‐N application and with pH. Sodium (Na) uptake was the highest in the saline treatment (T₄), followed by the basic pH treatment. Sodium accumulation was detected in the roots (natrophobic plant), where the plant generated a physiological barrier to avoid damage. Dry weight did not differ significantly (p<0.05) among treatments except in the NaCl treatment. These results may help in the formulation of nutrient solutions that take into account the ionic composition of irrigation water and the physiological requirements of plants.     

小麦不同品种吸收钾离子的动力学研究

小麦不同品种吸收钾离子(K+)的动力学参数不同。米氏常数(Km)以绵阳11最大,红矮1最小;最大吸收速率(1max)繁6最高,红芒22最低。供试小麦各品种吸收K+的补偿点(Cmin)3.44.mol/L,远低于一般土壤溶液中的K+浓度,说明土壤溶液中K+浓度与小麦吸收K+的需要相适应。此外,硝酸根(NO3)、吲哚乙酸(IAA)和稀土显著促进小麦吸收K+;但铵离子(NH4+)显著抑制K+吸收;尿素对小麦吸收K+无显著影响。动力学参数的测定表明,NH4+抑制K+吸收的原因是提高了小麦吸收K+的Km;而NO3和稀土产生促进作用的原因分别是吸收K+的Imax增加和Km减少。IAA能促进H+分泌,导致小麦吸收K+的速率提高。