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A laboratory experiment was conducted to determine the effect of ultrasound (US) exposure time on germination behavior of sesame seeds. All tests were carried out at 20 kHz in a water bath ultrasonic device varying two factors, treatment duration (10, 20 and 30 min) and germination temperature (15, 20 and 25 ºC). Parallel tests were run in which seeds were soaked in water without sonication in order to eliminate the effect of water from US test results. US treatments enhanced seeds water uptake. At mild exposure time it improved sesame seed germination performance and seedling growth at suboptimal temperatures as indicated by higher germination percentage and germination rate. US applying for 20 min had relatively high superoxide dismutase activity; however, had not significant differences with control and US duration for 10 min. The catalase activity was strongly increased by applying the US for a 10 and 20 min. Among the treatments, application of US vibration for 10 and 20 min reduced both of malondialdehyde and H 2 O 2 contents, however high US duration (30 min) increased both of the traits. In general, ultrasonic priming technique can be useful for early planting the sesame seeds, and lead to higher yields.

The objective of this study was to determine the effects of foliar application of polyamines (PAs) on antioxidant defence and essential oil production of valerian (<em>Valeriana officinalis</em> L.) grown under different drought stress treatments (100, 70, 50 and 30% available water content). This study was carried out using pots in greenhouse condition. Drought–stressed valerian seedlings were sprayed with 1 mM concentration of each putrescine (Put), spermidine (Spd) and spermine (Spm). The results showed that drought stress significantly affected most biochemical characteristics of valerian plants. Characteristics including leaf relative water content, chlorophyll a and b contents were decreased, while carotenoids and electrolyte leakage were increased with the increase of water stress. In this research, defensive characteristics comprising proline content, soluble sugars, catalase, and ascorbate peroxidase were increased followed by drought stress to ameliorate the adverse effect of it.  Results revealed that foliar application of Spd and Spm provoked the antioxidant enzymes activity as well as proline accumulation in valerian which alleviate the membrane damages. Consequently, Spd and Spm increased photosynthetic pigments which act as energy supply for plant growth and production. Here, putrescine had detrimental effects on CAT activity and Chl a content. Albeit, PAs presented remarkable effects under moderate drought stress condition but it showed reverse trends in severe drought stress condition.  In terms of quantity and quality yield, drought stress reduced root growth but increased the concentration of essential oils. PAs are able to alleviate water deficit-induced diminish root growth. These results suggest that in moderate drought stress, growers can use PAs to increase productivity valerian.

Volumen 33, Nº 4. Páginas 5-13 IDESIA (Chile) Septiembre-Noviembre, 2015 Effect of paclobutrazol and salicylic acid on antioxidants enzyme activity in drought stress in wheat ABSTRACTIn this study wheat plants were treated with paclobutrazol (PBZ) and salicylic acid (SA) to analyze the enzyme activity and chlorophyll content under two drought stresses (-6 and -12 bar). The Bahar cultivar was grown in a hydroponic system and drought stress was applied using PEG-6000 (-6 and -12 bar potential). Plants were kept under stress conditions for 10 days. Treatments with 5 mg L -1 paclobutrazol and 0.1 mm salicylic acid were carried out simultaneously with drought stress. The effects of PBZ and SA treatments on wheat were monitored by measuring the changes in CAT, APX, SOD, GPX, MDA, H 2 O 2 and chlorophyll under drought stress. Both PBZ and SA increased antioxidant enzyme activity and showed significant differences (p< 0.001 and 0.05). APX, SOD and CAT activity decreased under the drought condition but PBZ treatment resulted in increased APX activity in the drought stress treatment. However, seedlings supplemented under drought stress showed a profound increase in GPX activity (100% and 53% higher at -6 and -12 bar PEG on 3D) compared to stressed seedlings without SA spray. The results showed that paclobutrazol minimizes the negative effects of drought stress with evidence of enhancing chlorophyll content and antioxidant enzymes such as APX, CAT and GPX that reduces H 2 O 2 and lipid peroxidation (MDA) content.. Key words: paclobutrazol, salicylic acid, antioxidant enzyme, drought stress, wheat. RESUMENEn este estudio, las plantas de trigo fueron tratadas con paclobutrazol (PBZ) y ácido salicílico (SA) para analizar la actividad enzimática y el contenido de clorofila en dos tensiones de humedad (-6 y -12 bar). El trigo variedad Bahar se cultivó en un sistema hidropónico y se sometió a estrés hídrico mediante el uso de PEG-6000 (-6 y -12 bar potencial). Las plantas se mantuvieron bajo condiciones de estrés durante 10 días. Los tratamientos fueron la aplicación de 5 mg L -1 de paclobutrazol y 0,1 mm de ácido salicílico y se aplicaron simultáneamente con el estrés hídrico. Los efectos de los tratamientos de PBZ y SA en trigo fueron monitoreados por medio de la medición de los cambios en el CAT, APX, SOD, GPX, MDA, H 2 O 2 y clorofila en condiciones de sequía. En ambos tratamientos aumentó la actividad de la enzima antioxidante con diferencias significativas (p <0,001 y 0,05). La actividad de APX, SOD y CAT disminuyó bajo condiciones de sequía, pero el tratamiento PBZ aumentó la actividad de APX en el tratamiento de estrés por sequía. Las plantas del semillero bajo estrés hídrico aumentaron significativamente la actividad de GPX (100 y 53% más altos en -6 y -12bar PEG en 3D) respecto de las plantas del semillero estresadas sin SA. Los resultados sugieren que la aplicación de paclobutrazol minimiza los efectos negativos del estrés hídrico aumentando la concentración de clorofila y enzimas antioxidantes como APX, CAT y GPX...