Fahimeh Dezhabad; Maryam Haghighi
Abstract
Introduction: Most plants, especially those that are native to hot areas, show signs of injury when exposed to low temperatures. Damages caused by cold stress occurs at the cell and organs level, which reflects it at the plant surface. Color change, chlorosis, general reduction of growth, cellular tissue ...
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Introduction: Most plants, especially those that are native to hot areas, show signs of injury when exposed to low temperatures. Damages caused by cold stress occurs at the cell and organs level, which reflects it at the plant surface. Color change, chlorosis, general reduction of growth, cellular tissue destruction, non-absorption of nutrients, reduction of photosynthesis, non-transferring photosynthetic materials are from early effects of cold stress. Cellular responses to colds including loss of thoracic pressure, vacuolization, collapse of cytoplasmic membrane balance, cytoplasmic flow loss, and general organ dysfunction. The susceptibility of the plant to frost is different depending on the type of plant, variety, tissue morphology and other cellular characteristics, as well as the cold conditions of the period, time and cold intensity. In addition, it seems that organs of the plant have different degrees of cold tolerance. If the temperature of the aerial part is favorable, the low temperature of the root zone can be one of the factors limiting the root system and plant growth. The consumption of balanced boron content by neutralizing the negative effects of cold stress and mechanisms such as maintaining the structure of the membrane, improving and increasing root growth, increasing the synthesis of proteins needed for the plant, adjustment of stomatal movements and improved stomatal conductance, increased cell division, increased nitrogen metabolism and chlorophyll production, and its consequence was increased photosynthesis and dry matter production, increased activity of antioxidants, calcium / potassium ratio adjustment, optimizing the transfer of calcium in the plant, adjusting the amount of water and conducting it in the cell, increasing the moisture content and relative content of leaf water, transferring soluble materials and increasing water use efficiency creates a relative resistance to low temperature stress. Although the root temperature is very effective in plant growth, it has been less attractive. Therefore, the aim of this study was to investigate the effect of low temperature of root and shoot on the ability to restore plant growth and physiological activity in the presence and absence of boron.
Materials and Methods: In order to compare the impact of sudden low temperature stress of root and shoot on recovery of vegetative and physiological traits of tomato, a research was conducted in two separate experiments under controlled conditions in the greenhouse of Faculty of Agriculture, Isfahan University of Technology. Two experiments were factorial based on completely randomized design with 10 replications including two concentrations of boron (0, 0.5, 1 and 1.5 in ppm) and two temperature levels of shoot and root sections (10 degrees’ Celsius temperature, and 11 rootstock temperatures and 22 ° C optimum and control temperatures). Indicators included photosynthesis rate, respiration rate, stomatal carbon dioxide, stomatal conductance, chlorophyll fluorescence, chlorophyll index, water use efficiency, proline, antioxidant, phenol secretion from root and leaf extracts, leaf relative water content, soluble protein concentration, ion leakage, leaf water potential, root and shoot dry weights and starch content. Finally, the analysis of the results was done by statistical software statistic and comparing the meanings by LSD test at 5% level.
Result and discussion: The results showed that the highest amount of photosynthesis, root dry weight and dry weight of the aerial part were in the consumption of 0.5 ppm of boron during abrupt stresses of low temperature on the root after the recovery period. The highest amount of stem proline and electrolyte leakage were also obtained from 0.5-1.5 ppm of boron consumption during abrupt low temperature on the shoot part. According to the results, it was found that when stress has entered from the root zone to the aerial part of the plant, the plant was in the better conditions after the recovery period. It seems that when a cold stress occurred on the roots, the plant can produced more antioxidant substances, including phenol and proline, while counteracting the relative water content of the leaves were more effective with radical agents. Thus, in normal conditions, the roots of the plant operated at a lower temperature than the airspace. They also exhibited more adaptations to the lower air at the lower temperature than the air section and the plant is less damaged. At levels above the boron element due to the effect of boron toxicity and the production of excess free oxygen radicals, the plant probably suffered more severe damage than cold damage.
Conclusions: Sudden low temperatures stresses on the root and shoot had negative effects on the recovery of the vegetative and physiological traits of tomatoes. When lower temperatures were imposed on the shoot, the plant suffered much more damages. Consumption of 0.5 ppm of boron during cold stress by creating optimal conditions for growth also caused the relative neutralization.
Golnar GhazianTafrishi; Hossein Arouiee; Majid Azizi; Hamidreza Khazaie; Saeid Reza Vessal
Abstract
Introduction: Plants native to tropical and subtropical climates which grown in the temperate climate zone, suffer chilling injury when exposed to non-freezing temperatures for a certain period of time. The optimum growth temperature for cucumber (a tropical plant) is 20 to 25°C. Cucumber is sensitive ...
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Introduction: Plants native to tropical and subtropical climates which grown in the temperate climate zone, suffer chilling injury when exposed to non-freezing temperatures for a certain period of time. The optimum growth temperature for cucumber (a tropical plant) is 20 to 25°C. Cucumber is sensitive to temperatures lower than 10 °C. Cucumber area of production exposes to late spring and early autumn cold weather in Khorasan-e-Razavai, Iran. Studies showed that chilling leads to an alteration in fatty acid composition of membrane lipids and its permeability, changes in photosynthetic pigments content and decrease in photosynthesis. Many researchers pointed to a possible role of polyamine compounds in plant defense against environmental stresses. Exog enous application Spd could prevent the electrolyte and amino acid leakage or recovering the plasma membrane damage in rice and cucumber in response to salinity, chilling and water stressed conditions.
Materials and methods: A factorial experiment, based on completely randomized design was conducted to investigate the effect of short-term chilling on cucumber plantlets which was earlier treated with spermidine. Factors were included two levels of temperature (6 and 12°C) and four levels of spermidine (0, 0.25, 0.5 and .0.75 mg/L). The studied cultivar was ‘Super-Dominus’. In order to determine the extent of chilling injury, plants of each treatment were rated based on visual symptoms. By assigning values of 1, 2, 3, 4, and 5 while 1: no visible symptoms 2:5% of leaf area necrotic, 3: 5-25% of leaf area necrotic, 4: 26-50% of leaf area necrotic but plant still alive, 5: lost, entire plant necrotic and collapsed. Measured traits were root and shoot length, root and shoot dry weight, root and leaf electrical leakage, and leaf chlorophyll content.
Results and discussion: Plants which exposed to low temperature showed chilling injury symptoms (5-25% leaf area necrotic). The symptoms reduced (less than 5% leaf area necrotic) by using 0.25 and 0.5 mg/L spermidine. The symptoms enhanced by 50% by applying 0.75 mg/L spermidine at 6°C. Analysis of variance showed that there was significant difference between temperature levels, spermidine levels and interaction between them in respect to root length, shoot length, shoot dry weight and root and leaf electrical leakage. Root dry weight, root to shoot ratio and chlorophyll content just affected by temperature and spermidines levels but not by interaction between them. Root and shoot length and dry weight decreased by low temperature. At cold stress condition growth decreased due to a reduction in photosynthesis and carbohydrate metabolism .Root and shoot length decreased more than 79% at 6°C compare with 12°. Root to shoot ratio increased at cold condition which was the result of lower root weight loss in response to cold temperature compared with shoot weight losses. Electrical leakage (EL) enhanced in leaf and root cells at chilling temperature, but the enhancement was significantly more at root cells. Electrical leakage enhanced more than 52% in root cells at 6°C compared with 35% in leaf cells. EL suppressed, using 0.25 and 0.5 mg/L spermidine while an increase observed in El at 0.75 mg/L spermidine. The lowest EL percentage observed for leaf samples treated with 0.25 and 0.5 mg/L spermidine at 12°C. The highest EL percentage belonged to root samples treated with 0.75 mg/L Spd at 6°C .Chlorophyll content (ChlC) decreased at cold condition. ChlC was 52% at12°C compared with 37% at 6°C. High significant correlation observed between chlorophyll content and shoot dry matter (r2= 0.96**). Root and shoot length and dry weight and leaf chlorophyll content enhanced using 0.25 and 0.5 mg/L spermidine at both chilling and control temperatures. A decrease observed in measured traits applying 0.75mg/L spermidine. There was no significant difference between 0.25 and 0.5 mg/L spermidine levels in respect of measured traits expect for shoot dry weight. Spermidine enhances chilling tolerance in cucumber by prohibiting the activity of NADPH oxidase. The capacity of PAs to enhance the tolerance of cucumber to chilling injury is attributed to the scavenging of H2O2 production under chilling condition.
Conclusion: Results showed that root and shoot length and weight, root and leaf electrical leakage and chlorophyll content of leaf adversely affected by chilling stress. Using 0.25 mg/L spermidine modulates plant responses to chilling stress. There was no significant difference between 0.25 and 0.5 mg/L spermidine in respect of measured traits. But all measured traits adversely affected using 0.75 mg/L spermidine at both 6 and 12°C.
