Journal of Plant Process and Function

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Abstract
In order to study the effect of water deficit stress on some physiological characteristics including leaf water osmotic and turgor potentials and osmolytes including sugars, proline and invertase activity of Persian melon (Cucumis melo Group. cantaloupensis cv. samsoury), an experiment was conducted in complete randomized design. Treatments including three irrigation levels (start of irrigation at -50 (control), -65 (moderate stress) and -75 kPa (severe stress) of matric potentials. Severe decrease of osmotic potential even less than predicted value (about -23 bar) was happened in severe water deficit stress (start of irrigation at -75 kPa of matric potential). Results indicate that water deficit levels in this experiment were cause to changes in sugars content and invertase activity. Water deficit stress decreased invertase activity to 2.01 at 35th days after start of stress, while the activity of this enzyme at this stage was measured about 4.14, for control (start of irrigation at -75 kPa of matric potential). Severe level of water deficit (start of irrigation at -75 kPa of matric potential) increased fruit sucrose content (0.32 mg/g FW) and glucose content (0.08 mg/g FW), leaves proline content (0.35 µmol/ g FW) at 35th days after start of stress. Also, an osmotic regulation was happened in this plant by sucrose and proline aggregation under water deficit stress and according to the leaf osmotic potential has decresed even more than expected value.

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Water deficiency is an important factor for plant growth in arid environments. Foliar application of methanol in C3 plants is believed to be more important in water stress tolerance. In order to evaluate the effects of foliar application of methanol on photosynthetic features, chlorophyll fluorescence and chlorophyll content of lentil under water deficit stress, a factorial experiment in completely randomized design was conducted with three replications. Methanol foliar application factor had 5 levels including control (without foliar application), 5, 15, 25 and 35 volumetric percentage (v/v). Foliar application was applied 3 times during the growing season (seedling, flowering and podding) at 10-days intervals. Water deficit factors were included severe water stress (25% of field capacity), moderate water stress (75% of field capacity) and non water stress (100% field capacity). The results of methanol and water stress interaction showed that in non water stress condition, methanol levels at the seedling, flowering and podding stage significantly enhanced in all traits except transpiration rate compared with the control level. Methanol levels at three stages significantly decreased the transpiration rate compared with the control. In modrate and severe water stress treatments at seedling stage, methanol levels had significant effect regarding photosynthetic features but at flowering and podding stages, the application of methanol except some features did not reduce the negative effects of water stress.

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  Water deficit can be considered as one of the most important abiotic factors limiting plant function, which has also adverse affects on growth and production of medicinal plants. In this research, in order to evaluate the effects of water deficit stress on of Artemisia dracunculus plant, a completely randomized design with three replications was performed in greenhouse conditions. The experimental treatments were different levels of irrigation based on control (90% of field capacity), T1: 60% of field capacity and T2: 40% of field capacity. Four weeks after treatment, physiological and biochemical indices were measured. Results showed that, water deficit stress had significant effects on measured traits and the average value of some traits such as: fresh and dry weight, leaf area, relative water content and shoot length were decreased under stress in both A. dracunculus collections in compare to control plants. The least average value of these traits was observed in T2 plants. Analysis of biochemical data also showed that, enzyme activity of peroxidase, proline and soluble sugars contents and the specific activity of peroxidase were increased in both A. dracunculus collections under water stress condition. However, enzyme activity of catalase, content of photosynthetic pigments (chl a, chl b and carotenoides), soluble protein content and the specific activity of catalase were decreased under stress. As a conclusion, Irrigation level at 40% of field capacity can be considered as stress level for this plant. Furthermore, A. dracunculus can respond to water deficit stress by increasing of the contents of proline and soluble sugars and the activity of peroxidase as one of antioxidant enzymes.

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Drought is one of the most frequent abiotic stresses. Use of chemical fertilizers resulted in pollution of soil, water and air. For this reason today again considered organic fertilizers. Vermicompost is an organic fertilizer which has a potential influence on plant growth as well as stress tolerance. Deficiency irrigation water, severely reduce the yield of crops, especially olives. Thus, a greenhouse experiment was coducted in 2015 to study the effect of vermicompost on growth and drought tolerance of olive cuttings cultivar Zard. The experiment was set up as factorial experiment in completely randomized design with two factors, including vermicompost application at four levels (0%, 12.5%, 25% or 50% ) and drought stress at two levels (full irrigation or non-irrigation) and 4 replications. The results showed that drought stress decreased and addition of vermicompost increased vegetative growth parameters significantly compared to plants cultivated in unamended soil. Water stress treatment decreased the total chlorophyll and increased ion leakage, ascorbat peroxidase and catalase activity and proline content and application of vermicompost significantly decreased ion leakage. Although, all vermicompost levels of 12.5, 25 or 50%  continued to be positive effects, 25% vermicompost treatment was numerically superior to others, increased chlorophyll and proline contents and antioxidant enzyme activity and decreased ion leakage from leaves.

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The negative effects of water stress, reduced water use and nutritional disorders in plants. So in order to study the effects of foliar application of iron and manganese on some morphological and physiological characteristics of Mungbean (cultivar beam) under water deficit stress, this experiment was conducted in the Faculty of Agriculture of Tarbiat Modares University as randomized complete block design arrangement in split plot with three replications. Treatment of water difficit stress, is irrigation regims in three levels: [optimal irrigation, withholding irrigation from vegetative growth (stage of Primary growth to the fast formation of leaves) and withholding irrigation from flowering stage to the first pod formation stage] As main plot and and foliar application of micronutrients included were (no foliar application, water foliar application, iron sulfate 1%, iron sulfate 1.5%, manganese sulfate 0.5%, manganese sulfate 1%, iron sulfate 1%+ manganese sulfate 0.5% and iron sulfate 1.5%+ manganese sulfate 1%) Were considered as sub plot. The results showed that foliar application of iron and manganese could prevent the devastating effects of drought stress And the effect of combined treatment of iron and manganese were higher than other treatments of foliar application. Foliar application of 1.5% Fe+ 1% Mn Reduced proline content in the vegetative and reproductive stress conditions, respectively 62 and 64 percent and total chlorophyll content in the vegetative and reproductive stage increased  respectively 43.5 and 45.8 percent.

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             Drought stress is one of the major environmental concerns associated with various defects in plant growth and development. Environmental stressors trigger a wide range of reactions in plants, ranging from changes in gene expression level and cell metabolism to alteration in growth rate and plant function. Application of certain chemicals, such as gamma amino butyric acid (GABA), is suggested to minimize the detrimental effects of drought stress. To investigate the effect of GABA in vegetative characteristics and resistance indices of saffron (Crocus sativus L.) plants under water deficit condition, current experiment was conducted in research greenhouse at Tehran University of Sciences. The experiment was performed in factorial pattern based on the completely randomized block design. In this experiment GABA was applied on plants at three concentrations of 0, 25 and 50 μM under three levels of polyethylene glycol (PEG)(0%, 10% and 15%) as drought stress inducer. The results showed that water deficit conditions decreased fresh and dry weight of shoot and root, leaf number, leaf area, photosynthetic pigments and protein content. Besides, physiological parameters such as proline content and antioxidant enzyme activity increased under drought stress conditions. Application of GABA in this experiment generally improved the morphological characteristics (including leaf number and leaf area, fresh and dry weight of leaves and roots), photosynthetic pigments and soluble protein content. GABA application improved qualitative and biochemical properties including anthocyanin, total phenol and flavonoid content under drought stress conditions. GABA exposure resulted in decreased MDA activity and increased antioxidant superoxide dismutase (SOD) functionality. GABA increased the plant's resistance to water deficit stress by affecting the activity of catalase enzyme activity in stressed plants compared to those of control. This effect was very significant under 15% PEG and 50 μM GABA treatments. Our findings indicate that GABA application can increase plant yield under drought stress conditions. According to these results and positive effect of the GABA application on induction of drought resistance in saffron, it is recommended to use GABA as an effective compound to diminish the detrimental effects of drought stress in saffron plants.
 

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It is very important to find ways to increase the tolerance of plants under drought stress conditions. In order to study the effect of drought stress levels and types of humic fertilizers, amino acid and organic supplements on quantitative and qualitative traits of safflower (Goldasht cultivar), an experiment was conducted as split plots base on randomized complete block design with three replications at the research farm of Zabol University (Chah Nimeh). The main factor of irrigation cut-off levels based on plant growth stages: control (full irrigation), irrigation up to the main stem formation stage and irrigation up to the stage of flowering completion and the secondary factor of five levels of fertilizer treatment: Control (not applicable), amino micropower fertilizer, humic acid, humica and organic supplements in amounts of two per thousand. Maximum plant height (69.76 cm), number of leaves per plant (78.43), number of branches (6.2), oil content (34.2), chlorophyll a, b and carotenoids (11.51, 3.37, 2.40 mg/g fresh weight respectively) was obtained from foliar application treatment with humic acid and complete irrigation. Percentage of changes in plant height (27.7), number of leaves (19.5), number of branches (35.5), petal weight (50), oil content (48), chlorophyll a, b, carotenoids (respectively 33, 38 and 27) under complete irrigation and foliar application of humic acid due to severe stress and non-application of fertilizers. Catalase enzyme activity (97%), peroxidase (99%) and Protein content (62%) increased due to stress and foliar application of humic acid. In general, it seems that foliar application of humic acid compared to other organic fertilizers used in this study can achieve better results under drought stress conditions.

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This research was conducted in order to investigate the application of melatonin and potassium sulfate on the quantitative and qualitative characteristics of broccoli (Brassica oleracea var. italica) under water stress. A factorial experiment was performed in a completely randomized design with three replications. The experimental factors included irrigation conditions at two levels (50 and 100% FC), melatonin at three levels (0, 150 and 300 µM) and potassium sulfate at three levels (0, 2 and 5 mM). The results showed that in the treatment of 300 µM melatonin and control irrigation (100% FC), the leaf area was twofold greater than in the treatment of 50% FC without the use of melatonin. The highest activity of the catalase enzyme was observed in the interaction of 50% irrigation level and 150 µM melatonin and the highest amount of malondialdehyde was observed in the same field capacity without the use of melatonin. The highest amounts of chlorophyll a and b were obtained in the interaction of 100% FC, 150 μM melatonin and 5 mM potassium sulfate. The highest amount of head yield was achieved in the interaction of 100% FC with the use of 300 µM melatonin and 5 mM potassium sulfate, and in this treatment, the highest nitrate reductase enzyme activity and the lowest nitrate accumulation in the crop head were observed. The highest content of proline and activity of the peroxidase enzyme were observed under conditions of 50% FC without the use of melatonin and potassium sulfate. The best treatment in most of the interaction traits was melatonin 300 µM, potassium sulfate 5 mM under control irrigation conditions (100% FC). Therefore, the use of these compounds is recommended to improve the physiological characteristics, yield and quality of broccoli.

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In order to evaluate the reaction of the peppermint plant (Mentha piperita L.) to water deficit stress and the use of growth-promoting bacteria, a factorial experiment was conducted in the form of a completely randomized design with four replications in the research greenhouses of the Faculty of Agriculture of Lorestan University in 2022. The first factor included water deficit stress (80, 50, and 20% available water content (AWC)), and the second factor included growth-promoting bacteria (without the use of bacteria (control), Pseudomonas putida strain, and Curtobacterium sp. strain wlu). The results of the present experiment show the water deficit stress had a significant effect on the morphophysiological and biochemical indicators, so that at the level of 20% AWC, it increased electrolyte leakage (219%), malondialdehyde concentration (50%) and the activity of antioxidant enzymes such as catalase (1174%), peroxidase (308%) and ascorbate peroxidase (82.7%) compared to the control treatment, but growth components such as plant height, stem number, total fresh and dry weight (29.3%, 37.2%, 56.1% and 55.5%, respectively), relative leaf water content (36.1%), essential oil percentage and yield (38.8% and 71.6%, respectively) decreased compared to the control treatment. Photosynthesis rate, intracellular carbon dioxide concentration, stomatal conductance, and mesophyllic conductance also decreased by 76.5%, 61.8%, 40%, and 38.5%, respectively, under water deficit stress conditions of 20% AWC. The application of growth-promoting bacteria in stress and non-stress conditions improved the growth components by increasing water absorption through root growth, increasing the activity of antioxidant enzymes, and increasing the rate of photosynthesis and stomatal conductance. Also, the percentage of essential oil and the yield of essential oil increased under the influence of the use of growth-promoting bacteria. In general, the results showed that the treatment of growth-promoting bacteria, especially the Pseudomonas putida strain, improved the water balance through increasing water absorption, increased biomass due to increasing the rate of photosynthesis, and also increased the activity of antioxidant enzymes to reduce the negative effects of water deficit stress in peppermint.