Medicinal Plants
Mehdi Rastegar; Hassan Mumivand; Alireza Shayganfar; Abdolhossein Rezaei Nejad
Abstract
Introduction: In the last decades, human activities have had adverse effects on the atmosphere and the stratospheric ozone layer, resulting in an increase in the ultraviolet radiation on the ground, especially in highlands. Among living organisms, plants are the most exposed to ultraviolet rays due to ...
Read More
Introduction: In the last decades, human activities have had adverse effects on the atmosphere and the stratospheric ozone layer, resulting in an increase in the ultraviolet radiation on the ground, especially in highlands. Among living organisms, plants are the most exposed to ultraviolet rays due to their high and unavoidable need to light for photosynthesis, and are therefore more vulnerable to them. Plants show different responses to ambient UV radiation. The response of plants to ultraviolet light is manifested in two general ways, including tolerating the destructive effects of this radiation or/and avoiding it. The present study was conducted to evaluate the effect of ultraviolet light on growth, morphological and phenological characteristics of three cornflower cultivars under greenhouse conditions in 2018.
Materials and Methods: The experiment was performed as a split plot in a completely randomized design. Ultraviolet light was considered as the first factor in four levels (including: control, ultraviolet –A radiation, ultraviolet -B radiation and ultraviolet A + B radiations) and three cornflower cultivars (including: ‘Kornblume pink’, ‘Kornblume rot’ and ‘Kornblume blau’) as the second factor. The UV treatment was applied by lamps made by Q-Lab Co, USA. It should be noted that the 40-watt lamps used in this study were broadband and had the highest compliance with ultraviolet B (in the case of UV-B lamps) and ultraviolet A (in the case of UV-A lamps) received from the sun on the ground. So they provided the best possible simulation. During the growth period of plants, phenological traits were recorded and morphological traits and biomass traits were measured at the end of the experiment.
Results and Discussion: The results showed that UV-B radiation and simultaneous application of UV-A and UV-B radiations resulted in the reduction of the most morphological traits and yield traits including plant height, internode length, leaf width, leaf area, flowering stem length, plant fresh and dry weight, leaf dry weight, flower dry weight and number of flowers. However, flower yield was not affected by ultraviolet radiations. UV-A treatment reduced the flowering stem length and fresh and dry weight of plant in compared to the control treatment, but it had no significant effect on plant height, leaf width, leaf dry weight, flower dry weight and number of flowers. Plants response to ultraviolet radiation is very different. In many species, it has been observed that UV-A does not have a negative effect on plant growth, while, UV-B reduced the growth and yield of plants. It seems that the main reason for the reduction of plant growth and production is prevention of cell division caused by ultraviolet radiation. Degradation of plant pigments (chlorophyll) is also one of the main reason of photosynthesis decrease led to plant growth and yield reduction. The results of the present study showed that the application of UV-A reduced the number of days until the emersion of the first flower bud and the number of days until the opening of the first flower in cornflower cultivars compared to the control. UV-B treatment forced cornflowers to earlier flowering than UV-A. However, the fastest entry into the reproductive and flowering phase of cornflower cultivars was observed with the simultaneous application of UV-A and B radiations. Plants mechanisms against environmental stresses mainly depend on their origin and genetic factors. These mechanisms include three main strategies including “avoidance”, “tolerance” and “escaping”. One of the most important ways to reduce the life cycle is early flowering. It seems that the process of early flowering and completing the growth in cornflower species is a kind of stress escaping under ultraviolet radiation stress.
Conclusion: In this study, ultraviolet radiation reduced the growth and development of all three species of cornflowers. However, UV-A treatment showed the least negative effect on flower yield of plants. On the contrary, UV-B radiation and simultaneous application of UV-A and UV-B radiations reduced the growth and development of cornflowers, but did not have any significant negative effect on the flower yield (as the main useable organ of plant). Therefore, it seems that the ultraviolet radiation can be considered as a positive factor due to its positive effects on the production of secondary metabolites and early flowering and lack of significant negative effects on plant flower yield. Finally, ‘Kornblume pink’ cultivar, with higher flower yield and earlier flowering, is more suitable for cultivation than other cultivars.
Atiyeh Oraee; Ali Tehranifar; Ahmad Nezami; Mahmood Shoor
Abstract
Introduction: Climate change is expected to have impacts on ecosystems worldwide. During the last 50 years, the greatest warming trends have been observed in winter months and significant increases in both the occurrence and duration of winter warming have already been reported. In general, predicted ...
Read More
Introduction: Climate change is expected to have impacts on ecosystems worldwide. During the last 50 years, the greatest warming trends have been observed in winter months and significant increases in both the occurrence and duration of winter warming have already been reported. In general, predicted future climate change scenarios will result in less than optimal cold acclimation conditions, leading to decreases in freezing tolerance and predisposition of plants to winter injury. Nonetheless, it is not clear whether water stress induced during cold hardening is of high importance in inducing freezing tolerance in plants or it is an integral part of typical cold hardening process. Since rapid and effective assessment of plant cold tolerance is important for researchers and also field trials have no regular process and have high error, different kinds of artificial freeze tests such as survival percentage test and regrowth after imposing stress have been developed.
Materials and Methods: In order to evaluate the effect of drought stress on plant freezing tolerance of viola, a factorial experiment was conducted based on completely randomized design with three replications in faculty of Agriculture, Ferdowsi University of Mashhad. Experimental factors include three water treatments (80% FC, 60 % FC and 40% FC) and 10 temperature levels (Control, from zero to -24 with 3 °C intervals). Pansy seeds sown in a nursery in the summer of 2015 and after reaching the five-leaf stage in the fall plants were transferred to the pots. After the potted plants spend cold acclimation in nature conditions, plants were subjected to water stress including control (80% FC), 60% and 40% FC for two weeks. After drought stress, whole plants were sampled for freezing tolerance assessment and they were transferred to the freezer thermos-gradient. After applying the stress, electrolyte leakage, lethal temperature 50 according to the electrolyte leakage percentage (LT50el) were measured. One months later, survival percentage, lethal temperature 50% of plant according to the survival percentage (LT50su), leaf area, number of flower and bud, dry weight (dry weight of vegetative, reproductive, root and total) and reduced dry matter temperature 50 (RDMT50) were evaluated.
Results and Discussion: Electrolyte leakage percentage (EL %) and survival (%) were significantly (p ≤ 0.01) affected by irrigation treatments in the freezing conditions. By lowering the temperature from 20 to -24 °C, the EL% significantly increased in three irrigation treatments and it increased in 80% FC compared to 60% (by 16%) at -24°C. plants under 60% FC treatment exhibited higher baseline freezing tolerance (LT50 of −18.4 °C) compared to 80% FC (LT50 of −11.8 °C).Treated plants (except 80% FC) were able to tolerate lowering the temperature to -21°C. Lowering the temperature to -24°C caused the total mortality. According to the LT50su index, 60% FC treatment was less than compared to other treatments. Leaf area significantly increased by 16%, respectively, when plants were under water deficit (60% FC) compared to 80% FC at 0 °C. The maximum number of flower were seen in 60% FC at – 3 °C and the maximum number of bud were observed at 0 °C. The results showed that dry weight was significantly (p ≤ 0.01) increased by drought stress in the freezing conditions. Plants under 60% FC at 0 °C had the highest increase (55, 62 and 64%, respectively) dry weight of vegetative, reproductive and total growth, respectively compared to control. By lowering the temperature to -18 °C in 80% FC vegetative, reproductive and root growth decreased (36, 38 and 42%, respectively) compared to control plants. RDMT50 significantly affected by drought stress. There were significantly correlation between EL with LT50el and RDMT50 (r =0.25* and r = 0.72**, respectively). In total, plants under 60% FC showed highest freezing tolerance compared to the other treatments.
Conclusions: In the current study, we found that the greatest gain in freezing tolerance was associated with cold and that the effect of drought stress on freezing tolerance varied with temperature. Drought stress resulted in an improvement in freezing tolerance of viola (lower LT50). Among the different parameters evaluated, 60% FC treatment at 0 °C most consistently induced increases in survival percentage, reproductive and vegetative growth which suggested a synergistic effect between drought exposure and low temperature. Higher dry weight of viola plants may contribute to better plant overwintering capacity. In addition, future research should explore the effect of repeated mild drought events on freezing tolerance of acclimated plants, by using strategies such as wilt-based irrigation scheduling, partial root zone drying, and deficit irrigation.
