Image changes in chlorophyll fluorescence of cucumber leaves in response to iron deficiency and resupply

Iron (Fe) is an essential element for plants and its deficiency causes decrease not only in the photosynthetic rate but also in the actual photosystem II efficiency at steady‐state photosynthesis. The aim of this work was to determine the effect of Fe deficiency in plants of Cucumis sativus (L.) in two different experimental conditions. In the first experiment, plants were grown with or without Fe for 7 d. After 7 d, Fe‐deficient plants were resupplied with Fe and sampled after 12 h and 48 h. In the second experiment, plants were grown with Fe in the nutrient solution for 3 d and after this period, Fe was withdrawn and plants sampled after 3 and 6 d. Iron and chlorophyll (Chl) concentration and Chl‐fluorescence imaging were measured. In cucumber leaves subjected to Fe deficiency, fluorescence imaging of Chl a evidenced spatial changes on leaf lamina. Following Fe deficiency both after 7 d (Exp. 1) or 6 d (Exp. 2) leaves showed a slight, nonsignificant decrease in F_v/F_m ratio. However Chl‐fluorescence parameters determined in light conditions showed significant changes which indicate an alteration in the photosynthetic process. Surprisingly, the effect of Fe deficiency was more pronounced in leaves of plant of Exp. 2 as compared to those that had grown in complete absence of Fe (Exp. 1). In the latter case down‐regulated mechanisms preserved leaves from irreversible photoinhibition leading to complete recovery when plants were resupplied with the microelement.     

Leaf Responses to Reduced Iron Availability in Two Tomato Genotypes: T3238FER (Iron Efficient) and T3238fer (Iron Inefficient)

Abstract

The present work is aimed at evaluating some effects induced by different levels of iron availability in the growth medium for two different tomato (Lycopersicon esculentum Mill.) genotypes, the T3238fer (Tfer), unable to activate mechanisms for iron mobilization and uptake known as “strategy I,” and its correspondent wild‐type T3238FER (TFER). By using different iron concentration in the growth solution, the most suitable iron level to induce phenotypic differences between the two genotypes without being lethal for the mutant was found to be 40 µM Fe‐Na‐EDTA. The analyses were carried out also on plants grown with 80 µM Fe‐Na‐EDTA, an iron concentration at which the two genotypes showed no phenotypic differences. A significant decrease in total leaf iron and chlorophyll content was detected in both genotypes following reduction of iron concentration in the nutrient solution, and was particularly evident in Tfer40, which showed symptoms of chlorosis. The photo‐electron transport rate of the whole chain was significantly affected by growth conditions as well as by genotype, the lowest activity being detected in Tfer40 plants. Chlorophyll a fluorescence analysis revealed an increase in non‐photochemical quenching (q _NP) of Tfer plants grown at both iron concentrations, indicating the activation of photoprotective mechanisms, which, however, were not sufficient to prevent photoinhibition when plants were grown at 40 µM iron, as indicated by significant reduction in PSII photochemistry (F _v/F _m) and photochemical quenching (q _P). The actual quantum yield of PSII (Φ_PSII) and the intrinsic PSII efficiency (Φ_EXC) showed the same behavior of q _P and F _v/F _m ratio. A significant effect of mutation and iron supply on all the pigments was detected, and was particularly evident in the mutant grown at 40 µM iron. A different behavior was shown by the three pigments involved in the xantophyll cycle, violaxanthin being less affected than chlorophylls and the other carotenoids, and zeaxanthin even increasing, due to the xanthophyll cycle activation. In conclusion, the interaction between iron deprivation and fer mutation induced functional alterations to the photosynthetic apparatus. Anyway, as far as concerns the photo‐electron transport activity, the influence of fer mutation seemed to occur independently from iron supply.     

Amelioration of copper toxicity by iron on Spinach physiology

The effect of excess copper (Cu) on young spinach (Spinacia oleraced) as well as the role of iron (Fe) for amelioration of toxicity on growth and photosynthesis in Cu‐treated plants was evaluated. Plants treated with 160 μM Cu showed symptoms of heavy metal toxicity, while addition of Fe (40 μM) ameliorates to a certain extent toxic effects of Cu, due to antagonistic action between Cu and Fe. Root length and biomass revealed a lower decrease under Cu+Fe than under Cu treatment. Copper accumulation in plant tissues increased, while Fe, sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg) declined under Cu treatment. The significant increase in chlorophyll fluorescence (F_o) under 160 μM Cu, possibly reflects the more severe damages suffered at the membrane level with respect to Cu+Fe treatment. Copper decreased the efficiency of excitation energy capture by PSH reaction centers and negatively affected the effective antenna size of PSH. Changes in the rate of carbon dioxide (CO₂) assimilation were associated with changes in both stomatal conductance (gs) and mesophyll capacity for photochemistry as well as with lower pigment content. Net CO₂ assimilation, transpiration rate, and stomatal conductance were reduced. These changes at PSII are characteristic of a saturation of photosynthetic metabolic activity. The results suggest a tight linkage between PSII activity and CO₂ fixation under Cu treatment. Amelioration of Cu toxicity was obvious under Fe application.     

DIFFERENTIAL RESPONSE OF TWO OLIVE CULTIVARS TO EXCESS MANGANESE

The response of three-month-old rooted cuttings of the olive cultivars ‘Picual’ and ‘Koroneiki’ grown in black plastic bags containing perlite as a substrate to excess manganese (Mn) (640 μM) was studied. The rooted cuttings were irrigated with 50% modified Hoagland nutrient solution. At the end of the experimental period, which lasted 130 days, the total fresh and dry weights, as well as the shoot elongation of ‘Picual’ plants were significantly reduced under excess Mn (640 μM), compared to the control plants (2 μM), whereas the growth of ‘Koroneiki’ plants was similar in both Mn treatments. The tolerance index, which is derived from the ratios between the plant growth data of different treatments and the control one, of ‘Picual’ plants to excess Mn was about half of this of ‘Koroneiki’ plants. In both cultivars, the concentrations of Mn in various plant parts (root, basal stem, top stem, basal leaves, top leaves) were significantly increased as Mn concentration in the nutrient solution increased. Furthermore, in the 640 μM Mn treatment, 2 to 2.5-fold greater Mn concentrations were recorded in almost all plant parts of ‘Koroneiki’, than those of ‘Picual’. Similar results were recorded with regard to the total Mn content per plant (‘Koroneiki’ absorbed much more Mn from the nutrient solution than ‘Picual’). On the other hand, excess Mn negatively affected the absorption of iron (Fe), calcium (Ca), magnesium (Mg), phosphorus (P), zinc (Zn), and boron (B), depending on the olive cultivar. In both cultivars, while the Mn use efficiency was significantly decreased under excess Mn conditions, the nutrient use efficiencies of P, Ca, and Fe were significantly increased, compared to the control plants (2 μM Mn). It was also found that excess Mn resulted in a significant increase of stomatal conductance and transpiration rate of both cultivars, whereas the photosynthetic rate was significantly increased only in ‘Koroneiki’. In ‘Picual’, similar photosynthetic rates were recorded in both Mn treatments. The measurement of the various chlorophyll fluorescence parameters, F_v/F_m and F_v/F₀ ratios, revealed that the functional integrity of photosystem II (PSII) of photosynthesis was not affected due to excess Mn, irrespectively of the cultivar. In conclusion, although ‘Koroneiki’ tissues had much higher Mn concentrations than those of ‘Picual’, the parameters related to the growth and photosynthetic performance of plants indicates that the internal tolerance of ‘Koroneiki’ tissues to excess Mn was higher than this of ‘Picual’.     

Alleviation of photoinhibition in heliconia grown under tropical natural conditions after release from nutrient stress

We have previously reported that full sun‐grown Heliconia "Golden Torch”; leaves exhibited sustained decreased in PS II efficiency as compared to those grown under shade conditions. In this study, full sunlight plus low level of fertilization caused a further reduction of photosynthesis, chlorophyll content and F_v/F_m ratio while plants grown at high level of nutrient showed higher values of all these parameters. When plants grown under intermediate and deep shade, there was no significant difference in all parameters irrespective of nutrient supply. In the recovery experiments, plants without fertilizer were re‐fertilized weekly. Maximal photosynthetic rates, chlorophyll content, and F_v/F_m ratio increased gradually after re‐fertilizing the plants grown under full sunlight. However, no significant changes of these parameters were observed in plants grown under intermediate and deep shade over the same period. Total leaf nitrogen (N) was measured parallel with all the parameters. Photosynthetic rates, chlorophyll content, and F_v/F_m ratio showed a clear linear correlation with total leaf N in plants grown under full sunlight while there was no clear relationship observed in those plants grown under intermediate and deep shade. These results suggest that acclimation of Heliconia under full sunlight could be achieved by high level of nutrient fertilization.     

Genotypic variation in foliar nutrient concentrations, δ13C,and chlorophyll fluorescence in relation to tree growth of radiata pine clones in a serpentine soil

This study investigated the genotypic variation in foliar nutrient concentrations, isotopic signature (δ¹³C), and chlorophyll fluorescence (F_v/F_m) and tree growth of 40 radiata pine clones grown on a New Zealand serpentine soil, and the relationships between growth and physiological traits of these clones from improved and unimproved groups. Genotypic variation in growth and physiological traits existed within (i.e., clonal) and between groups, with larger variation among clones. The clonal repeatabilities were greater for foliar nitrogen (N), calcium (Ca), magnesium (Mg), boron (B) concentrations, δ¹³C, and Ca : Mg ratio (0.35–0.64) than for growth traits (0.14–0.27) and other physiological traits (0.08–0.24). Significant phenotypic correlations were found between growth traits and foliar phosphorus (P), potassium (K), sulfur (S), iron (Fe), and K : Mg and Ca : Mg ratios and F_v/F_m (positive), and foliar Mg (negative). This study indicates that the trees on this serpentine soil generally suffered from multiple nutrient deficiencies and imbalances and the clonal variation in growth performance was more related to their capabilities of acclimation to nutrient than water stresses. Overall, the clones that absorbed more P, K, S, and Fe and less Mg from the soil grew better on this serpentine soil. For unimproved clones, the most limiting nutrients for tree growth were foliar K and Fe, while for improved clones it was foliar K.     

Nitrate/ammonium ratio effects on mineral element uptake by sorghum 1

Abstract

Experiments were conducted using different NO₃ ^–/NH₄ ⁺ ratios to determine the effects of these sources of N on mineral element uptake by sorghum [Sorghum bicolor (L.) Moench] plants grown in nutrient solution. The NO₃ ^–/NH₄ ⁺ ratios in nutrient solution were 200/0, 195/5, 190/10, and 160/40 mg N L^–1. Nutrient solutions were sampled daily and plants harvested every other day during the 12‐day treatment period.

Moderately severe Fe deficiencies were observed on leaves of plants grown with 200/0 NO₃ ^–/NH₄ ⁺ solutions, but not on the leaves of plants grown with the other NO₃ ^–/NH₄ ⁺ ratios. As plants aged, less Fe, Mn, and Cu were translocated from the roots to leaves and leaf/root ratios of these elements decreased dramatically in plants grown with 200/0 NO₃ ^–/NH₄ ⁺ solutions. Extensive amounts of Fe, Mn, and Cu accumulated in or on the roots of plants grown with 200/0 NO₃ ^–/NH₄ ⁺ solutions. Manganese and Cu may have interacted strongly with Fe to inhibit Fe translocation to leaves and to induce Fe deficiency. As the proportion of NH₄ ⁺ in solution increased, K, Ca, Mg, Mn, and Zn concentrations decreased in the leaves, and Ca, Mg, Mn, and Cu concentrations decreased in roots. Potassium and Zn tended to increase in roots as NH₄ ⁺ in solution increased.     

Effect of rain shelters and drought on leaf water status and photosynthetic parameters in tomato

The present study explored the effect of rain shelter and drought on photosynthetic activity and changes in leaf water status. Tomatoes were grown in the trial plot located at Hohai University, China, in 2011 and 2012, and allotted to five treatments [80% field capacity under open field (T1, control) and rain shelter (T2), 70%, 60%, and 50% of T2 (T3, T4, and T5)]. The lowest sap flow rate and relative water content and the highest values for specific leaf area were obtained from plants in T5. T2 decreased the average net photosynthetic rate (P_N) by 5.35% compared to the control, although there was no reduction in intercellular CO₂ concentration and stomatal conductance. The average reduction of transpiration rate registered under rain shelters was only around 10.2% in both the years. The P_N, maximum quantum yield of PSII photochemistry (Fv/Fm) and activity of the water-splitting complex on the donor side of the PSII (Fv/Fo) decreased with irrigation volume. Quenching analyses showed the development of a lower photochemical quenching (qP) in plants under rain shelters, accompanied by the development of a higher nonphotochemical quenching (qN). Drought-stressed tomato exhibited a decrease in qP parallel to an increase in qN.     

Responses of photosynthesis,chlorophyll fluorescence,and grain yield of maize to controlled‐release urea and irrigation after anthesis

Controlled‐release urea (CRU) is a new type of urea, which may increase crop nitrogen (N)‐use efficiency compared with conventional urea (CU), but the conditions where it outperforms urea are not well defined. A field experiment assessing responses of plant growth and grain yield of maize to CRU and irrigation was conducted on a typical agricultural farm in Shandong, China. Five treatments of the two types of urea (75, 150 kg N ha^–1, 0 kg N ha^–1) were applied as basal fertilizer when sowing maize, and two water treatments (W₀ and W₁) were used 23 d after anthesis. Net photosynthetic rate (P_N) and chlorophyll concentration as well as leaf‐area index (LAI) increased significantly by both CRU and CU application, with the increases being larger in CRU‐treated plants than in CU‐treated plants at grain filling and maturing stages. CRU significantly enhanced the maximum photochemical efficiency (F_v / F_m), PSII coefficient of photochemical fluorescence quenching (q_P), and actual quantum yield of PSII electron transformation (Φ_PSII) but decreased the nonphotochemical quenching (NPQ). Cob‐leaf N concentration of CRU‐treated plants was significantly higher than that of CU‐treated plants under no irrigation, but not in the irrigation treatment 30 d after anthesis. Significant positive correlations were found between cob‐leaf N concentration and P_N both with and without irrigation. Grain yield of maize was significantly higher in the CRU treatment than in the CU treatment under both irrigation conditions. In conclusion, CRU as a basal application appeared to increase the N‐use efficiency for maize relative to CU especially by maintaining N supply after anthesis.     

Effects of Foliar Spray of K on Mint,Radish, Parsley and Coriander Plants in Aquaponic System

An aquaponic system was designed to investigate the effects of foliar applications of potassium (K) on mint, radish, parsley, and coriander growth and physiological characteristics. Plants were sprayed with 100 mL pot^?1 of 0.5 g L^?1 potassium sulfate (K₂SO₄) twice a week. Fresh and dry masses of shoot in all species were higher in K-treated plants. Potassium concentration increased with K spray in the shoots of all species. K-sprayed parsley accumulated a greater amount of Fe and chlorophyll in shoots. Values of SPAD index in all species decreased significantly in untreated plants. The highest Quantum Photosynthetic Yield (F_v/F_m) values were observed in coriander plants treated with K, which was attributed to higher SPAD value in these plants. Potassium application had a negative effect on sodium (Na) and positive effect on magnesium (Mg), manganese (Mn), and zinc (Zn) concentrations in plants. These results indicated that foliar spray of K can effectively alleviate nutrient deficiencies in leafy and root vegetables grown in aquaponics.     

Magnesium deficiency–induced impairment of photosynthesis in leaves of fruiting Citrus reticulata trees accompanied by up‐regulation of antioxidant metabolism to avoid photo‐oxidative damage

Limited data are available on the physiological responses of leaves from fruiting trees to magnesium (Mg) deficiency. Magnesium deficiency–induced effects on photosystem II (PSII) photochemistry in leaves of fruiting (Citrus reticulate cv. Ponkan) trees were assessed by the chlorophyll a fluorescence (OJIP) transient. Magnesium deficiency decreased leaf CO₂ assimilation and carbohydrates, but had no effect on intercellular CO₂ concentration. Activity of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) and concentrations of Chlorophyll (Chl) and carotenoids (Car) decreased to a lesser extent than CO₂ assimilation. Chlorophyll a fluorescence transient from Mg‐deficient leaves had increased O step and decreased P step, accompanied by positive ΔL, ΔK, ΔJ, and ΔI bands. Magnesium deficiency decreased maximum quantum yield of primary photochemistry (F_v/F_m), quantum yield of electron transport from Q<$>_A^‐<$> to the photosystem I (PSI) end electron acceptors (φ_R0), maximum amplitude of IP phase and total performance index (PI_{tot, abs}), but increased deactiviation of oxygen‐evolving complex (OEC) and energy dissipation. Magnesium‐deficient leaves had higher or similar activities of antioxidant enzymes except for lower catalase (CAT) activity, higher or similar concentrations of antioxidant metabolites, and a higher ratio of Car : Chl. Magnesium‐deficiency did not affect concentration of malondialdehyde (MDA) and ratios of ascorbate (ASC) to ASC + dehydroascorbate (DHA) and reduced glutathione (GSH) to GSH + oxidized glutathione (GSSG). In conclusion, Mg deficiency–induced impairment of the whole photosynthetic electron transport chain may be the main factor contributing to decreased CO₂ assimilation. Enhanced energy dissipation and antioxidant metabolism provide sufficient protection to Mg‐deficient leaves against photo‐oxidative damage.     

Influence of calcium on vegetative and reproductive development of Pelargonium

Cloned stem cuttings of geranium (Pelargonium peltatum) were maintained in control and mineral deficient solutions for five weeks. Hydroponic solutions were formulated to be deficient in a single mineral; e.g., ‐Ca, ‐Fe, ‐Mg, ‐N, and ‐P. Positive control solutions contained all macro and micronutrients, while negative controls consisted of double distilled water. Weights and numbers of all organs of the shoot were determined, as was an analysis of adventitious roots. Plants grown in ‐Ca solutions characteristically manifested reduced organ weights and numbers as compared to plants grown in other mineral deficiencies and both controls. Examples of reduced values recorded in ‐Ca plants, as compared to the negative control plants, were: (i) a 60% decrease in overall plant weight, (ii) a 40% reduction in the total weight of leaves per plant, (iii) a 50% reduction in stem weight, (iv) a 60% drop in the weight of the stem base and associated adventitious roots, (v) a 30% decline in inflorescence weight, (vi) a 20% reduction in the number of leaves produced per plant, and (vii) a 20% decrease in the weight of individual leaves. Perhaps the most striking developmental distinction was the absence of adventitious roots in ‐Ca plants. Cuttings in distilled water produced an average of nearly 30 roots near the stem base. Anatomical examination of stem bases from plants grown in Ca‐deficient nutrient solutions revealed a few initiated roots in only one instance, but all roots were poorly developed and few in number. Most stem bases in ‐Ca did not have any initiated root primordia. It is believed that Ca has the capability of ameliorating mineral toxicity induced by other elements in the nutrient solution.     

The response of okra to molybdenum in sandculture

Abstract

The role of molybdenum in plant growth was examined by growing ‘Emerald’ okra (Abelmoschus esculentus L. Moench) to fruiting in sand‐culture.

Molybdenum treatment lower than 1 ppm, resulted in leaves that were generally pale yellow and curled upwards. At 1 ppm and 4 ppm Mo, plants were generally healthy with deep green leaves, while Mo application at 6 and 16 ppm resulted in stunted plant growth, deep green leaves, and dark brownish coating on the roots. Shoot/root ratio decreased with increasing rates of Mo. Total chlorophyll was unaffected by Mo application, whereas plant dry matter production and fruit yield were depressed at the 16 ppm Mo treatment.

Leaves of plants receiving less than 1 ppm Mo had higher concentrations of NO₃‐N, P, K, Ca and Mg than plants receiving above 1 ppm Mo treatments. The reverse was the case with the micronutrient levels. Specifically, Mo treatments higher than 1 ppm increased leaf‐Mo, ‐Fe, Mn and Zn and root‐Mo and Mn. The highest percentage of Fe and Mn, accumulated in the leaves, followed by the root and least in the wood, whereas the roots had the highest percentage of accumulated Mo, Cu and Zn. Leaf‐Mo was positively correlated with leaf‐Fe and Mn and root‐Mo and Mn. Molybdenum deficiency symptoms appeared in plants with leaf‐Mo of 5 ppm and treated with less than 1 ppm Mo. The 2 ppm Mo treatment with leaf‐Mo of 18 ppm produced normal and healthy plants, whereas. Mo application from 8 to 16 ppm with corresponding leaf‐Mo of 42 and 90 ppm Ho respectively produced plants that were severely stunted and had generally poor growth. The relatively high Ho concentration observed suggests that the okra plant is a Mo accumulator.     

Effect of pH of ammonium oxalate extracting solutions on prediction of plant available molybdenum in soil

Abstract

Molybdenum (Mo) is an essential element of plants and animals and is of concern from human nutrition and environmental standpoints. Rational applications to soil of Mo in fertilizers, sewage sludges, or other soil amendments requires information of the concentrations of Mo in soils and plants. Two greenhouse experiments were conducted at Lexington, Kentucky, using surface samples of 12 soils (11 soil types) derived from diverse parent materials in Kentucky with soil pH ranging from 5.18 to 7.46. Molybdenum (Na₂MoO₄.2H₂O) was added at rates equivalent to 0, 0.3, and 0.6 mg Mo kg^‐1 soil. Tobacco (Nicotiana tabacum L., cv. Ky14) and soybean [Glycine max. (L.) Merrill cv. McCall] were grown to provide plant Mo data for Mo soil test correlations and comparisons. The primary purpose of these investigations was to determine the effect of pH of NH₄‐oxalate extractant solution on the relationship of soil Mo and Mo uptake by tobacco and soybeans, and to evaluate the automated KI‐H₂O₂ procedure for use in determining Mo in soil extracting solutions. The mean dry weight and Mo concentration of tobacco and soybean were increased by applications of Mo fertilizer to soil in the greenhouse. Dry matter of tobacco was increased 11 to 25% and concentration of Mo from 40 to 82% by each increment of added Mo fertilizer. The results of this study suggest that many soils in Kentucky are not meeting the requirements for Mo sufficiency for tobacco and soybean plants. The average amount of soil Mo extracted by NH₄‐oxalate decreased with increasing pH of extractant. Regression estimates for the relationship of Mo uptake by tobacco or soybean and extractable soil Mo show that the slope and the coefficients of determination increased with pH of NH₄‐oxalate solution from pH 3.3 to 6.0 and then decreased again at pH 6.4. The greatest amounts of variation in Mo uptake by plants (67% and 20%, respectively, for tobacco and soybean) were accounted for by the soil Mo data at pH 6.0. Soil Mo values for the NH₄‐oxalate extractant (pH 6.0) were related to values for anion exchange resin extractant (r² = 0.61**), but not soil pH. However, values for anion exchange resin were more closely related to Mo uptake by tobacco (r² = 0.86**) and soybean (r² = 0.60**) than were values for NH₄‐oxalate (r² = 0.65** and r² = 0.27**, respectively). Results of this study indicate that the automated KI‐H₂O₂ method used previously in analysis for plant Mo can be used to analyze Mo in soil extracts. Other instrumentation such as GFAAS and ICP may be effective in the analysis of extracts obtained by the NH₄‐oxalate (pH 6.0) or by anion exchange resin procedures when the Mo concentration of extracts falls within the detection limits of the instrument.     

Effects of phosphate,nitrate and chloride on calcium,magnesium and manganese content of cigar‐wrapper tobacco

Abstract

Nutrient solutions containing three levels of phosphate, nitrate, and chloride were applied to cigar‐wrapper tobacco (Nicotiana tabacum L.) plants growing in sand culture for a period of 18 days. Concentrations of other nutrient elements in the nutrient solutions were held constant and the solutions were applied to pots as needed to maintain favorable moisture conditions for plant growth. Plants were in the two leaf stage when transplanted and were maintained on a single nutrient solution for 38 days before treatments were started. At the end of an eight weeks growing period, plant leaves were harvested and analyzed for Ca, Mg, and Mn. Dry matter yield was significantly (P=0.01) increased when 2 mM/1 of Ca(NO₃)₂ replaced an equivalent amount of Ca(H₂PO₄)₂ or CaCl₂ in the nutrient solution. Nitrate significantly (P=0.05) increased Ca and Mg content and decreased Mn concentration in leaf tissue in comparison to chloride. Calcium and Mg content were significantly (P=0.05) decreased and Mn content of tobacco leaves was increased by phosphate in comparison to nitrate and chloride.     

Impact of Boron Deficiency on Changes in Biochemical Attributes,Yield, and Seed Reserves in Chickpea

To determine the effect of boron (B) deficiency on biomass, reproductive yield, metabolism, and alterations in seed reserves of chickpea (Cicer arietinum L.) cv. ‘13.G‐256,’ plants were grown in refined sand until maturity at deficient (0.033 mg L^?1) and adequate (0.33 mg L^?1) B, supplied as boric acid (H₃BO₃). Boron‐deficient plants exhibited visible deficiency symptoms in addition to reduced number of pods and seeds, resulting in lowered biomass and economic yield. Boron deficiency lowered the concentration of B in leaves and seeds, photosynthetic pigments (leaves), Hill reaction activity, starch (in leaves and seeds), and proteins and protein N (in seeds), whereas phenols, sugars (in leaves and seeds), and nonprotein N (in seeds) were elevated. Specific activity of peroxidase (POX) increased in leaves and pod wall and decreased in seeds, while activity of acid phosphate and ribonuclease were stimulated in leaves, seeds, and pod wall in B‐deficient chickpea.     

Mitigation of alkaline stress by arbuscular mycorrhiza in zucchini plants grown under mineral and organic fertilization

A greenhouse experiment was carried out during the spring–summer 2009 to test the hypotheses that: (1) arbuscular‐mycorrhizal (AM) inoculation with a biofertilizer containing Glomus intraradices gives an advantage to overcome alkalinity problems, (2) mineral fertilization is more detrimental to AM development than organic fertilization on an equivalent nutrient basis. Arbuscular mycorrhizal (AM) and non‐AM of zucchini (Cucurbita pepo L.) plants were grown in sand culture with two pH levels in the nutrient solution (6.0 or 8.1) and two fertilization regimes (organic or mineral). The high‐pH nutrient solution had the same basic composition as the low‐pH solution, plus an additional 10 mM NaHCO₃ and 0.5 g L^–1 CaCO₃. Increasing the concentration of NaHCO₃ from 0 to 10 mM in the nutrient solution significantly decreased yield, plant growth, SPAD index, net assimilation of CO₂ (A_CO2), N, P, Ca, Mg, Fe, Mn, and Zn concentration in leaf tissue. The +AM plants under alkaline conditions had higher total, marketable yield and total biomass compared to –AM plants. The higher yield and biomass production in +AM plants seems to be related to the capacity of maintaining higher SPAD index, net A_CO2, and to a better nutritional status (high P, K, Fe, Mn, and Zn and low Na accumulation) in response to bicarbonate stress with respect to –AM plants. The percentage root colonization was significantly higher in organic‐fertilized (35.7%) than in mineral‐fertilized plants (11.7%). Even though the AM root colonization was higher in organic‐fertilized plants, the highest yield and biomass production were observed in mineral‐fertilized plants due to the better nutritional status (higher N, P, Ca, and Mg), higher leaf area, SPAD index, and A_CO2.     

Effects of Calcium Chloride on Growth,Membrane Permeability and Root Hydraulic Conductivity in Two Atriplex Species Grown at High (Sodium Chloride) Salinity

Calcium (Ca) has an important role in plant physiology, including involvement in the responses to salt stress, and controls numerous processes. To overcome the negative impact of high salinity, the addition of supplemental Ca to the growth medium as an ameliorative agent could be necessary. Atriplex halimus subsp. schweinfurthii and Atriplex canescens subsp. linearis were grown in hydroponic conditions to investigate the effectiveness of supplementary calcium chloride (CaCl₂) applied into nutrient solution on plants grown at high (400 mM) sodium chloride (NaCl) concentration. Treatments were: 1) nutrient solution alone [control (C)]; 2) nutrient solution plus 400 mM sodium chloride (NaCl); and 3) nutrient solution and 400 mM NaCl plus supplementary 40 mM CaCl₂ supplied in nutrient solution (NaCl + CaCl₂). The experiment was set up as a completely randomized design, consisting of two species (A. halimus and A. canescens), three treatments (control, NaCl, and NaCl + CaCl₂), and five replicates. Dry weight and chlorophyll content of plants grown at high NaCl were lower than those at normal nutrient solution. Supplementary CaCl₂ ameliorated the negative effects of salinity on plant growth in both species. Root hydraulic conductivity (L ₀) decreased with elevated NaCl and increased with supplementary CaCl₂ compared to the stressed plants. Membrane permeability increased with high NaCl application and these increases in root membrane permeability decreased with supplementary CaCl₂ compared to the NaCl treatment. Sodium (Na) concentration in plant tissues increased in both species in high NaCl level. Application of supplementary CaCl₂ lowered Na concentration. Concentrations of calcium (Ca) and potassium (K) were at deficient ranges in the plants grown at high NaCl levels and these deficiencies were corrected by supplementary CaCl₂.     

Nutrient disorders of Dianthus ‘Bouquet Purple’

‘Bouquet Purple’ pinks (Dianthus sp.) were grown in silica-sand culture to induce and photograph symptoms of nutritional disorders. Plants received a complete modified Hoagland's all-nitrate (NO₃) solution. Nutrient-deficient treatments were induced with a complete nutrient formula minus one of the nutrients, and a boron (B)-toxicity treatment was induced by increasing B 10-fold in the complete nutrient formula. Plants were monitored daily to document sequential series of symptoms as they developed. Typical symptomology of nutrient disorders and corresponding tissue concentrations were determined. All treatments exhibited deficiency symptomology. Disorders for nitrogen (N), iron (Fe), calcium (Ca), and sulfur (S) were the first to manifest in pinks. Unique symptomology was observed for plants grown under potassium- (K), B-, copper- (Cu), and molybdenum- (Mo) deficient conditions, which supported the need for a species-specific approach when characterizing nutrient disorders of floriculture crops.     

The role of potassium in alleviating detrimental effects of abiotic stresses in plants

Plants exposed to environmental stress factors, such as drought, chilling, high light intensity, heat, and nutrient limitations, suffer from oxidative damage catalyzed by reactive oxygen species (ROS), e.g., superoxide radical (O₂equation/tex2gif-sup-1.gif^–), hydrogen peroxide (H₂O₂) and hydroxyl radical (OHequation/tex2gif-sup-4.gif). Reactive O₂ species are known to be primarily responsible for impairment of cellular function and growth depression under stress conditions. In plants, ROS are predominantly produced during the photosynthetic electron transport and activation of membrane‐bound NAD(P)H oxidases. Increasing evidence suggests that improvement of potassium (K)‐nutritional status of plants can greatly lower the ROS production by reducing activity of NAD(P)H oxidases and maintaining photosynthetic electron transport. Potassium deficiency causes severe reduction in photosynthetic CO₂ fixation and impairment in partitioning and utilization of photosynthates. Such disturbances result in excess of photosynthetically produced electrons and thus stimulation of ROS production by intensified transfer of electrons to O₂. Recently, it was shown that there is an impressive increase in capacity of bean root cells to oxidize NADPH when exposed to K deficiency. An increase in NADPH oxidation was up to 8‐fold higher in plants with low K supply than in K‐sufficient plants. Accordingly, K deficiency also caused an increase in NADPH‐dependent O₂equation/tex2gif-sup-6.gif^– generation in root cells. The results indicate that increases in ROS production during both photosynthetic electron transport and NADPH‐oxidizing enzyme reactions may be involved in membrane damage and chlorophyll degradation in K‐deficient plants. In good agreement with this suggestion, increases in severity of K deficiency were associated with enhanced activity of enzymes involved in detoxification of H₂O₂ (ascorbate peroxidase) and utilization of H₂O₂ in oxidative processes (guaiacol peroxidase). Moreover, K‐deficient plants are highly light‐sensitive and very rapidly become chlorotic and necrotic when exposed to high light intensity. In view of the fact that ROS production by photosynthetic electron transport and NADPH oxidases is especially high when plants are exposed to environmental stress conditions, it seems reasonable to suggest that the improvement of K‐nutritional status of plants might be of great importance for the survival of crop plants under environmental stress conditions, such as drought, chilling, and high light intensity. Several examples are presented here emphasizing the roles of K in alleviating adverse effects of different abiotic stress factors on crop production.