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’.     

IS CHLOROPHYLL FLUORESCENCE TECHNIQUE A USEFUL TOOL TO ASSESS MANGANESE DEFICIENCY AND TOXICITY STRESS IN OLIVE PLANTS?

A 130-day hydroponic experiment was carried out in a glasshouse to examine whether manganese (Mn) concentration in the nutrient solution affects the nutritional status of olive plants and to find out whether the chlorophyll fluorescence technique is suitable to assess Mn toxicity and/or deficiency stress in olive plants prior to the appearance of these two nutritional disorders. For this purpose, chlorophyll fluorescence parameters (F_v/F_m and F_v/F₀ ratios) were recorded every 40 days in the leaves of ‘Kothreiki’ and ‘FS-17’ olive cultivars, which were irrigated with Hoagland's nutrient solutions containing various Mn concentrations. In parallel the elongation of the main shoot of all experimental plants, as well as the concentrations of Mn, iron (Fe), zinc (Zn), boron (B), phosphorus (P), calcium (Ca), magnesium (Mg), and potassium (K) in their leaves were recorded. The following Mn treatments were applied: 0 μM Mn (to induce Mn deficiency), 40 μM Mn (to promote normal growth), and 640 μM Mn (to induce Mn toxicity). Our results indicated that not only the rate of shoot elongation but also the fluctuation with time of the leaf concentrations of all determined mineral elements (except for Mn) was not significantly affected by the Mn concentration in the nutrient solution, irrespectively of the cultivar. This was not observed with regard to the time variation of the F_v/F_m and F_v/F₀ ratios, where the values of these parameters were significantly reduced in the 640 μM Mn treatment at the 80th and 130th day of the experiment in both olive cultivars, compared to the relevant previous ones (those of the days 0 and 40th), something which did not happen in the other two Mn treatments (0 and 40 μM). However, in none of the two cultivars tested and in any of the three Mn treatments (0, 40 and 640μM) the F_v/F_m and F_v/F₀ ratios did not drop below the critical values of 0.8 and 4, respectively, even at the end of the experiment, where high Mn concentrations were found in the leaves of both cultivars treated with 640 μM Mn (616 μg g^?1 d.w. in ‘FS-17’ and 734 μg g^?1 d.w. in ‘Kothreiki’). Symptoms of Mn toxicity (curling and brown speckles) were observed in the top leaves of both cultivars, after the 90th day of the experiment. At the same time, the final leaf Mn concentrations (those of the 130th day of the experiment) in plants grown under 0 μM Mn were 23 μg g^?1 d.w. in ‘FS-17’ and 20 μg g^?1 d.w. in ‘Kothreiki’, i.e., a little above of the deficiency range (<20 μg g^?1 d.w.). At the 130th day, Mn concentration in nutrient solution, as well as Mn concentration in the leaves of both olive cultivars was negatively correlated with the leaf concentration of Fe and the values of the F_v/F_m and F_v/F₀ ratios, and positively with the concentrations of Zn and P in the leaves. Finally, the periodical measurement of the F_v/F_m and F_v/F₀ ratios was proved to be a non-reliable means to predict the appearance of the visible symptoms of Mn toxicity in olive leaves (although their values declined significantly at the 80th and 130th day of the experiment in both olive cultivars).     

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.     

PHYSIOLOGICAL RESPONSE OF SPRING DURUM WHEAT GENOTYPES TO SALINITY

Soil salinity is a serious threat in many parts of Iran, which negatively affects plant production. In order to investigate response of durum wheat to salinity, two genotypes, ‘Turkey 506’ (salt tolerant) and ‘Egypt 557’ (salt sensitive), were grown in hydroponic conditions, exposed to various salt levels (0, 50, 100, 150 and 200 mmol NaCl) in a split split plot based on randomized complete block design with three replications of each treatment. Salinity stress decreased relative water content (RWC), potassium content, potassium/sodium ratio, chlorophyll a (chla), chlorophyll b (chlb), and total chlorophyll contents, efficiency of photosystem II (F_v/F_m) and membrane stability index (MSI), and increased sodium, proline and soluble sugars concentrations and ratio of chla/chlb in both genotypes. The decrease in RWC, chla, chlb, F_v/F_m, and MSI were significantly higher in ‘Egypt 557’ than ‘Turkey 506’. ‘Turkey 506’ showed higher content of potassium, potassium/sodium ratio, proline, and soluble sugar concentrations as well as lower sodium content as compared with ‘Egypt 557’. The salinity tolerance of ‘Turkey 506’ is associated with higher RWC, potassium content, osmolyte concentrations, chlorophyll contents, F_v/F_m ratio, and maybe more vacuole sequestration of sodium.     

Foliar application of zinc alleviates the heat stress of pakchoi (Brassica chinensis L.)

Abstract

Experiments were conducted to examine whether the foliar application of zinc (Zn) could mitigate the adverse effects of heat stress on pakchoi plants. Two varieties of pakchoi (Aikangqing and Wuyueman) were foliar applied with ZnSO₄·7H₂O (0%, 0.02%, 0.05%, 0.10%, 0.20%, 0.40%, 0.60%, and 0.80%), and then subjected to two temperature levels (22°C/16°C, day/night; 40°C/30°C, day/night). Heat stress decreased the net photosynthetic rate (P_n) (50.65% and 62.14% for Aikangqing and Wuyueman, respectively), chlorophyll content, chlorophyll fluorescence ratio (F_v/F_m), and effective quantum yield of PSII photochemistry (ΦPSII) of the leaves. Foliar application of ZnSO₄·7H₂O (0.02%–0.40%) effectively alleviated the heat stress in pakchoi by enhancing shoot Zn concentration, superoxide dismutase (SOD) activity, chlorophyll content, F_v/F_m, and ΦPSII. P_n increased by 12.61%–46.19% and 45.73%–119.01% in Aikangqing and Wuyueman compared with those without Zn treatments, respectively. Fuzzy comprehensive evaluation and the extreme model showed that Aikangqing and Wuyueman treated with 0.1218%–0.1220% ZnSO₄·7H₂O (approximately 0.004?M Zn²⁺) and 0.2178%–0.2744% ZnSO₄·7H₂O (approximately 0.008?M Zn²⁺) exhibited the most heat resistance, respectively. Furthermore, Zn (0.02%–0.80% ZnSO₄·7H₂O) application had no significant effect on most physicochemical parameters under normal temperature, which only increased shoot Zn and SOD. The results suggest that additional Zn would be required to fully protect plant growth from heat stress. Foliar application enhanced Zn concentration in leaves, thereby maintaining the SOD activity and membrane stability and protecting photosynthesis against heat damage.     

Effects of Zinc Application on Growth,Absorption and Distribution of Mineral Nutrients Under Salinity Stress in Soybean (Glycine Max L.)

The purpose of the present work was to evaluate effects of zinc application on growth and uptake and distribution of mineral nutrients under salinity stress [0, 33, 66, and 99 mM sodium chloride (NaCl)] in soybean plants. Results showed that, salinity levels caused a significant decrease in shoot dry and fresh weight in non-zinc application plants. Whereas, zinc application on plants exposed to salinity stress improved the shoot dry and fresh weight. Potassium (K) concentration, K/sodium (Na) and calcium (Ca)/Na ratios significantly decreased, while sodium (Na) concentration increased in root, shoot, and seed as soil salinity increased. Phosphorus (P) concentration significantly decreased in shoot under salinity stress. Moreover, calcium (Ca) significantly decreased in root, but increased in seed with increased salinization. Iron (Fe) concentration significantly decreased in all organs of plant (root, shoot, and seed) in response to salinity levels. Zinc (Zn) concentration of plant was not significantly affected by salinity stress. Copper (Cu) concentration significantly decreased by salinity in root. Nonetheless, manganese (Mn) concentration of root, shoot, and seed was not affected by experimental treatments. Zinc application increased Ca/Na (shoot and seed) ratio and K (shoot and seed), P (shoot), Ca (root and seed), Zn (root, shoot, and seed) and Fe (root and shoot) concentration in soybean plants under salinity stress. Zinc application decreased Na concentration in shoot tissue.     

Silicon: a beneficial nutrient for maize crop to enhance photochemical efficiency of photosystem II under salt stress

Soil salinity imposes an unprecedented risk to the soil fertility and availability of plant nutrients. The present proposal is designed to address the effect of salt stress on photosynthetic apparatus of maize including chlorophyll a fluorescence and how silicon nutrition helps to overcome this issue. In a sand culture experiment, two maize cultivars were sown in small pots with two levels of silicon (0 and 2 mM H₂SiO₃) and two levels of salinity stress (0 and 60 mM NaCl). Salinity stress reduced dry matter yield and potassium (K) concentration in both maize cultivars and also induced inefficient working of photosynthetic apparatus including photochemical efficiency of photosystem II. Silicon addition alleviated NaCl stress on maize crop by improving the dry matter yield and water use efficiency (WUE). It decreased shoot Na concentration by increasing root and shoot K concentration of maize plants. It enhanced maximum quantum yield of primary photochemistry which leads to smooth electron transport chain. It also significantly enhanced shoot silicon concentration and has a significant positive correlation with WUE. Therefore, silicon-treated maize plants have better chance to survive under salt stress conditions as their photosynthetic apparatus is working far better than non-silicon-treated plants.     

Cadmium Effects on Sunflower Growth and Photosynthesis

The objective of this work was to evaluate the effects of cadmium (Cd) exposure on sunflower (Helianthus annuus L.) plant growth, chlorophyll content, and fluorescence. Sunflower plants were exposed to different concentrations of Cd (0, 5, 50, and 500 μ M) for 21 d. Growth parameters (organ length, fresh and dry weights) were determined and results compared with two parameters associated with photosynthesis degradation: chlorophyll content and fluorescence (an easy and non-destructive method). Exposure to Cd significantly decreased growth by decreasing shoot and root lengths and their fresh and dry weight. Cadmium also decreased significantly chlorophyll content and fluorescence efficiency in all treatments. Chlorophyll a (chl a) and chl b contents showed a significant correlation with chlorophyll fluorescence (F_v/F_m ratio). The EC₅₀ values showed that the roots' length was the most sensitive endpoint in this study, followed by the roots' and shoots' weight endpoints. Also, chl b showed higher sensitivity to Cd contamination than chl a. These data show that in complement to growth parameters, the use of photosynthetic parameters provides helpful information on plant response to Cd exposure.     

Alleviation of Alkalinity-Induced Fe Deficiency in Eggplant (Solanum melongena L.) by Foliar Application of Different Fe Sources in Recirculating System

This study was carried out to investigate the effects of foliar sprays of different iron (Fe) sources on eggplant grown in alkaline aquaponic solutions. Four treatments were used, untreated control, foliar application of iron sulfate (FeSO₄), ferric ethylenediaminetetraacetic acid (Fe-EDTA) and ferric ethylenediamine bis(2-hydroxyphenyl)acetic acid (Fe-EDDHA). The results showed that overall growth was significantly increased by foliar Fe application, and the highest values of vegetative growth parameters were recorded in plants treated with FeSO₄. The Fe treatment led to a significant increase of shoot Fe concentration, and the highest Fe was observed in plants sprayed with FeSO₄, compared to Fe-EDTA and Fe-EDDHA. The lowest chlorophyll content was observed in untreated plants. The highest SPAD index, maximal quantum yield of photosystem (PS II) photochemistry (F_v/F_m) and performance index (PI) values of young and old leaves were found with FeSO₄ treatment. It is concluded that application of foliar Fe must be performed in the aquaponic system, to overcome Fe deficiencies in alkaline conditions.     

不同水分状况下施锌对玉米生长和锌吸收的影响

选择潮土(砂壤)和土(粘壤)两种质地不同的土壤,进行盆栽试验,研究不同土壤水分条件下施锌对玉米生长和锌吸收的影响。结果表明,施锌显著增加了玉米植株根、茎、叶以及整株干物质重;缺锌条件下玉米植株根冠比、根叶比和根茎比趋向增大。施锌显著提高了玉米植株各器官中锌的浓度和吸收量,并明显促进锌向地上部运移。干旱胁迫抑制了玉米植株生长,根冠比、根茎比、根叶比增大;随着土壤水分供应增加,植株生长加快,各器官生物量以茎和叶增加大于根。水分胁迫下,在潮土上玉米叶片中锌浓度上升;在土上叶片中锌浓度下降。但增施锌后,根和茎锌浓度增加幅度较大,叶片增加幅度较小;施锌和水分胁迫对根和茎锌浓度的交互作用极显著。水分胁迫下,玉米植株对锌的吸收总量减少。水分胁迫和锌肥施用对玉米叶片、茎锌吸收量的交互作用十分显著,但对根锌吸收量的交互影响不显著。     

Growth,Mineral Composition,and Biochemical Changes of Broad Bean as Affected by Sodium Chloride and Zinc Levels and Sources

Plants grown in salt‐affected soils may suffer from limited available water, ion toxicity, and essential plant nutrient deficiency, leading to reduced growth. The present experiment was initiated to evaluate how salinity and soil zinc (Zn) fertilization would affects growth and chemical and biochemical composition of broad bean grown in a calcareous soil low in available Zn. The broad bean was subjected to five sodium chloride (NaCl) levels (0, 10, 20, 30, and 40 m mol kg^?1 soil) and three Zn rates [0, 5, and 10 mg kg^?1 as Zn sulfate (ZnSO₄) or Zn ethylenediaminetetraaceticacid (EDTA)] under greenhouse conditions. The experiment was arranged in a factorial manner in a completely randomized design with three replications. Sodium chloride significantly decreased shoot dry weight, leaf area, and chlorophyll concentration, whereas Zn treatment strongly increased these plant growth parameters. The suppressing effect of soil salinity on the shoot dry weight and leaf area were alleviated by soil Zn fertilization, but the stimulating effect became less pronounced at higher NaCl levels. Moreover, rice seedlings treated with ZnSO₄ produced more shoot dry weight and had greater leaf area and chlorophyll concentration than those treated with Zn EDTA. In the present study, plant chloride and sodium accumulations were significantly increased and those of potassium (K), calcium (Ca), and magnesium (Mg) strongly decreased as NaCl concentrations in the soil were increased. Moreover, changes in rice shoot Cl^?, Na⁺, and K⁺ concentrations were primarily affected by the changes in NaCl rate and to a lesser degree were related to Zn levels. The concentrations of Cl^? and Na⁺ associated with 50% shoot growth suppression were greater with Zn‐treated plants than untreated ones, suggesting that Zn fertilization might increase the plant tolerance to high Cl^? and Na⁺ accumulations in rice shoot. Zinc application markedly increased Zn concentration of broad bean shoots, whereas plants grown on NaCl‐treated soil contained significantly less Zn than those grown on NaCl‐untreated soil. Our study showed a consistent increase in praline content and a significant decrease in reducing sugar concentration with increasing salinity and Zn rates. However, Zn‐treated broad bean contained less proline and reducing sugars than Zn‐untreated plants, and the depressing impact of applied Zn as Zn EDTA on reducing sugar concentration was greater than that of ZnSO₄. In conclusion, it appears that when broad bean is to be grown in salt‐affected soils, it is highly advisable to supply plants with adequate available Zn.     

Effect of cadmium on growth and the uptake of cadmium and other elements by durum wheat

A solution culture study was conducted to determine the effects of cadmium (Cd) application on the uptake of Cd, potassium (K), zinc (Zn), manganese (Mn), copper (Cu), iron (Fe) and on the growth of seedlings of three wheat (Triticum turgidum L. var Durum) cultivars, Kyle, Nile, and SC84–994. Cadmium application decreased shoot and root biomass, root length, and leaf area. Cadmium application did not produce any differences among cultivars in these growth parameters. There were differential cultivar responses in the uptake of Cd and K but not for Zn, Mn, Cu, and Fe uptake. A solution Cd concentration of 0.1 μM did not affect the concentration of Cd and K compared to zero Cd but at and above 0.5 μM Cd, Nile had a higher concentration and contents of Cd and K in root and shoot than SC84–994 and Kyle. Kyle and SC84–994 were not different in any of the elements tested except K concentration in shoot where the order was SC84–994<Kyle<Nile. Cadmium application increased the Cd concentration but decreased the concentration of K, Zn, and Mn in root and shoot, while the Fe and Cu concentrations in shoot and root were not affected. Cultivar differences were observed in the translocation of Cd from root to shoot. In SC84–994 and Kyle, 0.5 μmole Cd/L decreased the total Cd translocated to shoot, Further addition of Cd did not affect Cd translocation, whereas in Nile, increased Cd concentration in solution did not affect Cd translocation to the shoot. A modified version of Weibull frequency distribution [y = a exp.(b.Cd^c)] was applied to explain the effect of Cd on plant growth parameters and on the uptake of K, Mn, Zn, and Cu in plants.     

GROWTH ENHANCEMENT BY SUPPLEMENTARY PHOSPHORUS AND IRON IN TOMATO CULTIVARS GROWN HYDROPONICALLY AT HIGH ZINC

A short term experiment with tomato (Lycopersicon esculentum) cvs. Blizzard, Liberto, and Calypso was carried out in a controlled temperature room to investigate the effectiveness of phosphorus (P) and iron (Fe) supplemented in nutrient solution on plant growth at high zinc (Zn) (77.0 μmol L^?1). Zinc concentrations in complete nutrient solution were either 7.7 or 77.0 μmol L^?1. One week after application of high Zn, supplementary P and Fe at 1 and 0.05 mmol L^?1respectively were added into nutrient solution for three weeks. There were significant reductions in both dry weights and chlorophyll contents in the plants grown at high (77.0 μmol L^?1) Zn compared with those in the control treatment for all three cultivars. Application of supplementary P and Fe resulted in marked increases in both dry weight and chlorophyll concentrations for all three cultivars achieving values not significantly different to the control. Zinc concentration in plant tissues increased to toxic levels for all three cultivars in the high Zn treatment. Application of supplementary P and Fe decreased Zn concentration in the leaves and roots of plants grown at high Zn, but Zn concentrations were still at toxic levels. Phosphorus and Fe concentration in leaves declined to a deficient level in the high Zn treatment, but was markedly increased in the roots. Application of supplementary P and Fe corrected both P and Fe deficiencies in leaves of plants grown at high Zn and reduced root P and Fe concentrations.     

RESPONSES OF “NEWHALL” ORANGE TREES TO IRON DEFICIENCY IN HYDROPONICS: EFFECTS ON LEAF CHLOROPHYLL,PHOTOSYNTHETIC EFFICIENCY,AND ROOT FERRIC CHELATE REDUCTASE ACTIVITY

Orange (Citrus sinensis L. Osb. cv. ‘Newhall’) plants grafted on Citrange troyer rootstock were grown in nutrient solution with 0, 5, 10, or 20 μM iron (Fe), with and without calcium carbonate. Calcium carbonate was added in order to mimic the natural conditions in calcareous soils. Leaf chlorophyll concentration was estimated every 3–4 days using the portable instrument SPAD-502 meter. Chlorophyll fluorescence parameters, photosynthetic capacity estimated from oxygen evolution, leaf Fe concentrations, and root tip ferric chelate reductase activity were measured at the end of the experiment. Plants from the 0 and 5 μM Fe treatments showed leaf chlorosis and had decreased leaf chlorophyll concentrations. Leaves of plants grown in the absence of Fe in the solution had smaller rates of oxygen evolution both in the presence and absence of calcium carbonate, compared with plants grown in the presence of 10 μM Fe. In the absence of calcium carbonate the photosystem II efficiency, estimated from fluorescence parameters, was similar in all treatments. A slight decrease in photosystem II efficiency was observed in plants grown without Fe and in the presence of calcium carbonate. A 2.5-fold increase in root tip ferric chelate reductase activity over the control values was found only when plants were grown with low levels of Fe and in the presence of calcium carbonate.     

Supra‐optimal growth temperature exacerbates adverse effects of low Zn supply in wheat

Rising temperatures are a major threat to global wheat production, particularly when accompanied by other abiotic stressors such as mineral nutrient deficiencies. This study aimed to quantify the effects of supra‐optimal temperature on growth, photosynthetic performance, and antioxidative responses in bread wheat cultivars grown under varied zinc (Zn) supply. Two bread wheat cultivars (Triticum aestivum L., cvs. Lasani‐2008 and Faisalabad‐2008) with varied responsiveness to Zn supply and drought tolerance were cultured in nutrient solution with low (0.1 µM) or adequate (1.0 µM) Zn under optimal (25/20°C day/night) or supra‐optimal (36/28°C day/night) temperature regimes. Supra‐optimal temperature severely reduced root but not shoot biomass, whereas low Zn reduced shoot as well as root biomass. Shoot‐to‐root biomass ratio was reduced under low Zn but increased under supra‐optimal temperature. Supra‐optimal temperature inhibited root elongation and volume particularly in plants supplied with low Zn. In both cultivars, Zn efficiency index was reduced by supra‐optimal temperature, whereas heat tolerance index was reduced by low Zn supply. Supra‐optimal temperature decreased photosynthesis, quantum yield, and chlorophyll density in low‐Zn but not in adequate‐Zn plants. In comparison, low Zn decreased specific activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) and increased glutathione reductase (GR), where supra‐optimal temperature increased SOD, decreased GR and did not change APX activity in leaves and roots. Moreover, supra‐optimal temperature severely reduced shoot Zn concentration and Zn uptake per plant specifically under adequate Zn supply. Overall, supra‐optimal temperature exacerbated adverse effects of low Zn supply, resulting in severe reductions in growth traits viz. shoot and root biomass, root length and volume, and consequently impeded Zn uptake, enhanced oxidative stress and impaired photosynthetic performance. Adequate Zn nutrition is crucial to prevent yield loss in wheat cultivated under supra‐optimal temperatures.     

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.     

Zinc-Induced Changes in Growth Characters,Foliar Properties,and Zn-Accumulation Capacity of Pigeon Pea at Different Stages of Plant Growth

Application of zinc (Zn) [50, 100, 200, 300, and 400 μ g zinc sulfate (ZnSO₄)/g of soil] reduced the foliage and the total growth of pigeon pea [Cajanus cajan (Linn.) Huth]. The root-shoot length ratio, varying little with age, was relatively low in the treated plants. Decrease in dry weights of stem and root was more pronounced in the late stages of plant development. The root-shoot dry weight ratio, maximum in the flowering stage, was lower in treated plants than in the control. Number of pods per plant declined, showing a positive correlation with Zn concentration. Net photosynthetic rate, declining with plant age, was significantly low in the treated plants. Density and size of stomata and trichomes, stomatal conductance, intercellular carbon dioxide concentration, quantity of green pigments, nitrate reductase activity, and the nitrate and protein contents in the leaves also declined significantly. Proportion of vascular tissues both in stems and roots increased with plant age with a concomitant reduction of pith and cortex. Under zinc stress, the relative proportion of tissues varied inconsistently. Dimensions of vessel elements and fibers in stems and roots, increasing with the plant age, were always smaller in the treated plants. The vulnerability factor and mesomorphic ratio of treated plants declined, suggesting induction of water stress due to zinc treatments. Accumulation of Zn^{2 +} in different plant parts was considerably high at each developmental stage of the treated plants, and showed a positive correlation with Zn in the soil.     

Foliar manganese,zinc and boron application effects on mineral nutrition of an experimental olive grove (cv. “Chondrolia Chalkidikis”)

A 6-month field experiment (from October to March) was conducted in a 20-year-old experimental grove of the Aristotle University of Thessaloniki in order to enhance its micronutrient levels and assess the effect of micronutrient foliar application manganese, zinc and boron (Mn, Zn and B) on mineral nutrition, chlorophyll concentration and chlorophyll fluorescence parameters (F_v/F_m, F_v/F₀ and Performance index, PI) of the olive trees (cv. “Chondrolia Chalkidikis”). The experiment consisted of four treatments (Control-C: trees sprayed with deionized water, T50: trees sprayed with 50 mg/L Mn, Zn and B, T100: trees sprayed with 100 mg/L Mn, Zn and B, T200: trees sprayed with 200 mg/L Mn, Zn and B); the three micronutrients were applied in the forms of manganese sulfate (MnSO₄), zinc sulfate (ZnSO₄) and boric acid (H₃BO₃), respectively. The results showed that the most effective treatment for the enhancement of foliar Mn and B levels was T200, while for the increase of Zn levels was T100. In addition, significant differences among the treatments were recorded for most leaf nutrient concentrations (with the exception of potassium (K), which was not influenced by foliar treatment, the other macronutrients, such as calcium (Ca), magnesium (Mg), phosphorus (P) and nitrogen (N), as well as iron (Fe), obtained their maximum concentrations, at the end of the experiment, in C or T50 treatment). Chlorophyll concentrations were not influenced by foliar treatment. Concerning chlorophyll fluorescence parameters (F_v/F_m, F_v/F₀ and P index), significantly lower values were found in the control (C) trees, compared to the other three treatments, so it seems that a chlorophyll fluorescence technique may be used to detect micronutrient deficiencies in olive groves. However, from all the leaf nutrient concentrations determined, it was found that with the exceptions of: 1) Mn concentrations in the C, T50 and T100 treatments, which were marginal, or slightly deficient; 2) B and Zn concentrations in the C and T50 treatments, which were slightly deficient and marginal, respectively; 3) some K concentrations during the early spring period, which were slightly deficient, all the other concentrations were within the normal levels of sufficiency or within the optimum range, so no serious nutrient deficiency was detected.     

Exogenous succinate increases resistance of maize plants to copper stress

The effect of copper (Cu) excess (1.5, 4.7, 31, 78, 156 μM) and exogenously supplied succinate on plant growth, chlorophyll content, chlorophyll fluorescence, and isoenzym profiles of some antioxidant enzymes in maize plants was studied. Excessive Cu supply led to a reduction in the relative growth rate (RGR), tolerance index (TI), chlorophyll a and chlorophyll b contents, and the quantum yield of PSII electron transport in the light‐adapted state (ΦPSII). Copper treatment induced several changes in the anionic and cationic peroxidases (PODs), as well as superoxide dismutase (SOD) isoenzyme profiles. After 8 d of 78 μM–Cu treatment, two new anionic and two new cationic peroxidase isoenzymes in the roots were registered. Copper applied at concentrations above 31 μM resulted in higher levels of manganese superoxide dismutase (Mn‐SOD) in the roots and Cu,Zn‐superoxide dismutase (Cu,Zn‐SOD) in the leaves. However, the addition of Na‐succinate (200 μM) to the root medium prior to Cu treatment increased the capacity of the plants to partially overcome Cu toxicity.     

ROOT ZONE TEMPERATURE INFLUENCES ZINC REQUIREMENT OF MAIZE CULTIVARS ON A CALCAREOUS LOAM SOIL

The zinc (Zn) requirement of a maize (Zea mays L.) hybrid (‘FHY-396’) and an indigenous variety (‘EV-7004’) was measured at low (22.4 ± 5°C) and high (28.8 ± 5°C) root-zone temperatures (RZT). Four Zn rates (0, 3, 9 and 27 mg kg^?1 soil) were applied to a calcareous loam soil in pots for the glasshouse study. Shoot and root dry matter yields were significantly more at the higher RZT. Regardless the RZT, maximum relative shoot dry matter yield in hybrid and variety was produced, respectively, at 9 and 3 mg Zn kg^?1 soil. Zinc concentration in roots and shoots of both the cultivars increased with Zn rates and it was significantly more at the higher RZT. Cultivars differed in critical Zn concentration (C_ZnC) required for maximum shoot dry matter yield. The C_ZnC ranged from 25 to 39 μg Zn g^?1 plant tissue for optimum growth of both the cultivars at low and high RZT.