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This study was conducted under Ahvaz, Iran environmental condition during 2012 and 2013 growing seasons in order to investigate the influence of foliar application of potassium on some physiological and biochemical characteristics of three olive cultivars including ‘Mission’, ‘Koroneiki’ and ‘Dezfuli’. Potassium sulfate in different concentrations of 0, 1, and 2 g l^-1 was sprayed twice on selected mature 10 year old trees; at 50 and 65 days after full bloom. Potassium sprays increased leaf chlorophyll content of all cultivars, leaf potassium content in ‘Mission’ and ‘Koroneiki’ cvs., fruit anthocyanin concentration of ‘Dezfuli’ in two crop seasons. However, K treatments had no significant effect on leaf N and P content, fruit K and P content in all studied cultivars. Fruit soluble carbohydrates increased by foliar application of potassium in ‘Koroneiki’ and ‘Dezfuli’ cultivars in the second year of study. Stem water potential and leaf stomatal conductance were significantly affected by cultivar and K treatments during the two years. Our findings showed that foliar application of potassium resulted in the decrease of stomatal conductance of ‘Koroneiki’ and ‘Dezfuli’ in two crop seasons. Based on the results, it can be concluded that the studied cultivars differently respond to K treatments during the two crop seasons and foliar potassium application could have a positive impact on leaf chlorophyll, leaf potassium, fruit soluble carbohydrates and fruit anthocyanins in olive cultivars.

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Silicon (Si) and its derivatives have beneficial effects on a wide variety of plant species, especially under both biotic and abiotic stresses. Yet, their effects on wheat (Triticum aestivum L.) plants under drought stress are not well known. Therefore, in order to evaluate the effects of SiO₂ NanoParticles (NPs) under drought stress, wheat seeds were separately sown in pots. Then, the SiO₂ NPs were added to them through soil and foliar application at three stages of plant growth. Results indicated that drought stress significantly decreased majority of the studied traits compared to the normal irrigation. Soil application of NPs, under drought stress, significantly increased leaf greenness (SPAD) and Relative Water Content (RWC) by 12.54 and 84.04%, respectively, compared to the control (NPs= 0 ppm). Moreover, under drought stress, wheat yield also increased by 25.35 and 17.81%, respectively, by foliar and soil application of NPs. Under the same irrigation regimes, soil application of NPs significantly increased plant height and biomass compared to the foliar application of NPs. Finally, our results highlight that usage of the SiO₂ NPs, especially at rates of 30 and 60 ppm, can mitigate adverse effects of drought stress in wheat plants.
 

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The objectives of this study were to determine if Selenium (Se) in the forms of Se (IV) and Se (VI) interact during uptake and assimilation by spinach plants (Spinacia oleracea L.), when they are applied together. That might affect selected physiological and morphological characteristics, and crop yield. Plants were foliar sprayed with different concentrations of Se as selenite and selenate, separately (each at the rate of 5, 10, 15 mg Se L^-1), and simultaneously with selenite plus selenate (each at the rate of 5 mg Se L^-1). Se accumulation in the spinach leaves was monitored, along with selected physiological and morphological characteristics. These foliar Se treatments had little or no effects on crop yield, content of photosynthetic pigments and UVA and UVB absorbing compounds, respiratory potential and plant biomass, and potential efficiency of photosystem II. This demonstrated the good conditions of the spinach plants under these foliar Se treatments. The spinach plants readily accumulated both forms of Se into the leaves. Direct comparison of their combined application (5+5 mg L^-1) with their individual applications (10 mg L^-1) showed that in the combined application, the plants accumulated Se more than in selenite alone treatment, but less Se than in the selenate alone treatment. Foliar spraying with all tested concentrations of selenite, selenate, or their combination ensured that spinach leaves were safe for use in human nutrition. According to our results, exogenous treatment with selenate in concentration of 15 mg L^-1 was the most efficient treatment for production of Se enriched spinach.