Fardin Ghanbari; Saadollah Akbari
Abstract
Introduction: Melon, like other members of cucurbitaceae family, is sensitive to cold stress. Applying different cultivation techniques in the nursery can provide some degree of tolerance to environmental stresses in the plants. In the other words, applying stress conditions on plants may cause them ...
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Introduction: Melon, like other members of cucurbitaceae family, is sensitive to cold stress. Applying different cultivation techniques in the nursery can provide some degree of tolerance to environmental stresses in the plants. In the other words, applying stress conditions on plants may cause them to withstand subsequent stresses, this is so called a cross-adaptation or cross-tolerance. For example, Whitaker (1994) showed that cold stress damage can be mitigated by temperature pretreatment. This technique was then used to improve stress tolerance in different plants. In this regard, heat treatment has been used to increase the chilling tolerance in fruits and vegetables. Therefore, in this study, the possibility of increasing cold stress tolerance in melon seedlings using heat shock was investigated. Materials and Methods: The experiment was conducted in a completely randomized design (CRD) with three replications and five treatments (including control and spraying with water at temperatures of 20, 45, 50 and 55 °C for 90 seconds) in Faculty of Agriculture of Ilam University in 2019. Heat treatments where used as foliar spray by heated water. After applying different levels of heat treatment and recovery at 24 hours, seedlings were exposed to chilling stress at 3 °C for 6 h in 6 consecutive days. All seedlings were transferred to greenhouse and after 72 hours, the related traits were measured. Results and Discussion: Results showed that pre-treated seedlings had higher growth rate than control seedlings at the end of chilling period. Heat shock pretreatment significantly increased the content of chlorophyll, proline and hydrogen peroxide and reduced the amount of malondialdehyde compared to the control. The lowest amount of malondialdehyde (1.14 nmol g-1 fresh weight) was observed in the 50 °C treatment, which was 50% lower than the control. Similar to other environmental stresses, low temperature usually leads ROS production and oxidative stress. Malondialdehyde content is an index to measure membrane lipid peroxidation and its measurement is a criterion of damage to plants in stress conditions. Reduction of malondialdehyde has been reported to increase cell membrane stability and increase stress tolerance in plants. In the present study, heat shock reduced the accumulation of malondialdehyde compared to the control, indicating a decrease in cold effects on the plant. Mei and Song (2010) investigated the effect of heat pretreatment on increasing high temperature tolerance in barley, and reported that using this method by stimulating the synthesis of antioxidant enzymes prevented the increase of malondialdehyde in the plant under heat stress. Therefore, maintaining the membrane structure and decreasing the accumulation of malondialdehyde in melon seedlings under cold conditions indicates an improvement of plant defense responses induced by heat shock. Environmental stresses including cold stress by producing hydrogen peroxide and other free radicals lead to oxidative stress and damage plant cells. Hydrogen peroxide is converted to water by ascorbate peroxidase, peroxide redoxin, glutathione peroxidase and guaiacol peroxidase groups. Therefore, increasing the activity of antioxidant enzymes in plants is one of the most important mechanisms of the plant to cope with stress conditions. In the present study, heat shock pretreatment significantly increased peroxidase (POD) and poly phenol oxidase (PPO) activity and increased the amount of proline and hydrogen peroxide. In this regard, it has been reported that hydrogen peroxide has a dual role in plants and its increase in stress conditions by regulating the production of antioxidant enzymes helps plants to enhance their tolerance to the stress conditions. Our results is in consistent with Ao et al. (2013) report that stated hardening pretreatment of Jatropha curcas seedlings caused to increase the antioxidant enzymes activity, plant glutathione and ascorbate content. The increases in antioxidant enzymes activity by heat shock might be a positive mechanism, which facilitate the scavenging of ROS and induce plant growth and development under chilling stress. These results indicate that antioxidant defense system has a specific role in enhancing plant tolerance to stress conditions and hydrogen peroxide play an important signaling role in plant adaptive responses. Conclusion: In general, the results showed that heat shock (especially at 50 and 55 oC) caused positive physiological changes in melon seedlings and could increase their tolerance to cold stress conditions.
Seyyedeh Fatemeh Rasouli; Manoucher Gholipoor; Kambiz Jahanbin; Hamid Reza Asghari
Abstract
Introduction: Salicylic acid and jasmonates (chemical elicitors) are considered as key signaling compounds in induction process, which leads to accumulate of secondary metabolites. External uses of these compounds cause to induce pseudo stress in plants and excites defensive replies in plants, in response ...
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Introduction: Salicylic acid and jasmonates (chemical elicitors) are considered as key signaling compounds in induction process, which leads to accumulate of secondary metabolites. External uses of these compounds cause to induce pseudo stress in plants and excites defensive replies in plants, in response to induction of oxidative stress, the plant increases amount of antioxidant genes expression and increase enzymatic activity and non-enzymatic antioxidants concentration (they often have a medicinal aspect).
Material and methods: The present study investigated the effects of jasmonic acid and salicylic acid on hydrogen peroxide content, electrical lockage, GPX, GST and PAL activity, total phenol, flavonoid and anthocyanin changing in Stevia rebaudiana bertoni under field conditions. The experiment arranged as a randomized complete block design with 12 treatments and three replications in 2015-2016 at Amol city in Mazandaran Province in Iran. Experimental treatments were spraying by different concentration of jasmonic acid, salicylic acid and components of jasmonic acid- salicylic acid. Foliar application started after plant establishment in vegetative phase. Each experimental plot was 2 m× 3 m consisting 10 rows with 30 cm row spaces and seedling transplanted on 15 May. At the end of foliar application, sampling was done for the measuring. Sampling for biochemical analyses from second fully developed leaf was done and freezed in liquid nitrogen, then quickly carried out to laboratory.
Results and Discussion: The analysis of variance showed that different concentration of jasmonic acid and salicylic acid and spraying both of them in 7-day intervals appeared to be effective (with 99% confidence) on studied traits (data not shown). Spraying with jasmonic and salicylic acid increased hydrogen peroxide content in 9 treatments compared to the control. The highest amount of hydrogen peroxide content in compounds treatment 20 ????M JA -1 mM SA with mean of 5.46 ????mol in fresh weight observed. Plant in response to jasmonic and salicylic acid spraying increased GPX activity in 10 treatments and GST activity in 7 treatments compared to the control and follow them electrical lockage in most treatments (10) was lower than control. The highest amount of GPX activity in treatments 5 ????MJA and 5 ????MJA with average of 0.11 ????molmin-1g-1 FW observed. The highest amount of GST activity was obtained from treatments of 0.5 mM SA -5 ????M JA and 1 mM SA with average of 0.35 ????molmin-1g-1 FW. The PAL enzyme activity (the first enzyme in phenyl proponed compounds biosynthesis pathway) in 10 treatment increased. The highest amount of PAL activity was in compounds treatment of 50 ????M JA -1 mM SA with average of 1140 ????mol cynamic acid mg-1 protein min-1. The PAL enzyme activity had correlation with hydrogen peroxide concentration and GST activity. The PAL enzyme initiates a phenylpropanoid route that converts L-phenylalanine to trans-cyanamide acid deamination. The PAL enzyme can consider as an antioxidant enzyme because it has the role of depositing oxygen radicals through phenolic compounds. Spraying increased total phenol content in 8 treatments compared to the control. The highest amount of total phenol content was observed in compounds treatment of 20 ????M JA -1 mM SA with mean of 423.7 mgg-1 FW. Spraying with jasmonic acid and salicylic acid increased flavonoid concentration in 9 treatments compared to the control. The highest amount of flavonoid content was in treatment of 20 ????M JA -1 mM SA with mean of 110 mgg-1 FW. Spraying increased anthocyanin concentration in 6 treatments compared to the control. Anthocyanins are the most important group of natural pigments after chlorophyll that are involved in light protection. The noticeable point is that in most treatment PAL enzyme activity, total phenol, flavonoid and anthocyanin content in compound treatment increased.
Conclusion: The highest amount of total phenol and flavonoid content observed in compounds treatment of 20 ????M JA -1 mM SA and anthocyanin increased in total compounds treatment and using PAL enzyme activity had correlation and significant effect (data not shown). Stevia has anti–cancer effect, anti-blood glucose effect and anti-cardiovascular effect. This effects for the existence phenolic compounds in stevia such that had the ability to remove ROS, so increasing phenolic component by jasmonic acid and salicylic acid spraying in stevia was useful.
