Functional Quality, Antioxidant Capacity and Essential Oil Percentage in Different Mint Species Affected by Salinity Stress

Saline stress is responsible for significant reductions in the growth of plants, and it globally leads to limitations in the performance of crops, especially in drought-affected areas. However, a better understanding of the mechanisms involved in the resistance of plants to environmental stress can lead to a better plant breeding and selection of cultivars. Mint is one of the most important medicinal plants, and it has important properties for industry, and for the medicinal and pharmacy fields. The effects of salinity on the biochemical and enzymatic properties of 18 ecotypes of mint from six different species, that is, Mentha piperita, Mentha mozafariani, Mentha rotundifolia, Mentha spicata, Mentha pulegium and Mentha longifolia, have been examined in this study. The experimental results showed that salinity increased with increasing in stress integrity influenced the enzymatic properties, proline content, electrolyte leakage, and the hydrogen peroxide, malondialdehyde, and essential oil contents. Cluster analysis and principal component analysis were conducted, and they grouped the studied species on the basis of their biochemical characteristics. According to the obtained biplot results, M. piperita and M. rotundifolia showed better stress tolerance than the other varieties, and M. longifolia was identified as being salt sensitive. Generally, the results showed that H₂ O₂ and malondialdehyde had a positive connection with each other and showed a reverse relationship with all the enzymatic and non-enzymatic antioxidants. Finally, it was found that the M. spicata, M. rotundifolia and M. piperita ecotypes could be used for future breeding projects to improve the salinity tolerance of other ecotypes.

The Potential of the Synthetic Strigolactone Analogue GR24 for the Maintenance of Photosynthesis and Yield in Winter Wheat under Drought: Investigations on the Mechanisms of Action and Delivery Modes

Strigolactones (SLs) have been implicated in many plant biological and physiological processes, including the responses to abiotic stresses such as drought, in concert with other phytohormones. While it is now clear that exogenous SLs may help plants to survive in harsh environmental condition, the best, most effective protocols for treatment have not been defined yet, and the mechanisms of action are far from being fully understood. In the set of experiments reported here, we contrasted two application methods for treatment with a synthetic analog of SL, GR24. A number of morphometric, physiological and biochemical parameters were measured following foliar application of GR24 or application in the residual irrigation water in winter wheat plants under irrigated and drought stress conditions. Depending on the concentration and the method of GR24 application, differentiated photosynthesis and transpiration rate, stomatal conductance, leaf water potential, antioxidant enzyme activities and yield in drought conditions were observed. We present evidence that different methods of GR24 application led to increased photosynthesis and yield under stress by a combination of drought tolerance and escape factors, which should be considered for future research exploring the potential of this new family of bioactive molecules for practical applications.

Effect of Drought Stress on Certain Morphological and Physiological Characteristics of a Resistant and a Sensitive Canola Cultivar

Water stress is one of the main abiotic factors that reduces plant growth, mainly due to high evaporative demand and low water availability. In order to evaluate the effects of drought stress on certain morphological and physiological characteristics of two canola cultivars, we conducted a factorial experiment based on a completely randomized design. The findings show that drought stress exacerbations result in the plant's response to stress due to increased canola resistance caused by changes in plant pigments, proline, catalase, ascorbate peroxidase, peroxidase, superoxide dismutase and malondialdehyde, glucose, galactose, rhamnose and xylose. These in turn ultimately influence the morphological characteristics of canola. Drought stress reduces the concentration of carotenoids, chlorophyll a, chlorophyll b, total chlorophylls; however, glucose, galactose, rhamnose, xylose, proline, catalase, ascorbate peroxidase, peroxidase, superoxide dismutase, malondialdehyde (in leaves and roots) and the chlorophyll a and b ratios were increased. Reduction of plant height, stem height, root length, fresh and dry weight of canola treated with 300 g/l PEG compared to non-treatment were 0.264, 0.236, 0.394, 0.183 and 0.395, respectively. From the two canola cultivars, the morphological characteristics of the NIMA increased compared to the Ks7 cultivar. Interaction effects of cultivar and drought stress showed that NIMA cultivar without treatment had the highest number of morphological characteristics such as carotenoid concentration, chlorophyll a, chlorophyll b, total chlorophylls a and b, whereas the cultivar with 300 g/l PEG (drought stress) had the highest amount of proline, malondialdehyde, soluble sugars and enzymes in leaves and roots. Increasing activity of oxidative enzymes and soluble sugars in canola under drought stress could be a sign of their relative tolerance to drought stress.

How to change the ratio of unsaturated (omega 3, 6, 7 and 9) to saturated fatty acids in Oenothera biennis L. oil under water deficit stress, fertilizers and geographical zones

The 2015-2020 dietary guidelines for Americans advise substituting total unsaturated fatty acids (∑UFA) for total saturated fatty acids (∑SFA). Thus, field experiments were carried out to verify the influence of irrigation regime (well-irrigated and water deficit) and fertilizers (chemical and biological) on the ratio of ∑UFA to ∑SFA of evening primrose seed oil. Therefore, two experiments were conducted at the experimental stations (arid and semi-arid) of Iran in 2014 and 2015. Experiments were conducted in a split factorial layout within a randomized complete block design with three replications. Water deficit significantly reduced UFA (omega 3, 6, 7 and 9), ∑UFA and ratio of ∑UFA to ∑SFA (especially in the arid region), but it increased SFA and ∑SFA (especially in the arid region). In fact, fatty acid quality (increased ratio of ∑UFA to ∑SFA) of evening primrose seed oil was significantly increased in well-irrigated compared to water deficit stress (especially in the semi-arid region). Bio-fertilizers (Azospirillum lipoferum and Glomus mosseae) and chemical fertilizers (urea + triple superphosphate) increased the ratio of ∑UFA to ∑SFA of evening primrose seed oil (especially in the semi-arid region), but fatty acid quality of evening primrose oil was significantly increased in bio-fertilizers compared to the chemical fertilizers (especially in the arid region).

Physiological and antioxidant responses of winter wheat cultivars to strigolactone and salicylic acid in drought

Strigolactones are considered as important regulators of plant growth and development. Recently positive regulatory influence of strigolactones in plant in response to drought and salt stress has been revealed. Salicylic acid, a phytohormone, has reported to be involved in a number of stress responses such as pathogen infection, UV irradiation, salinity and drought. Considering the concealed role of strigolactones in agronomic crops drought tolerance and possible interaction among salicylic acid and strigolactone, we investigated the effects of exogenous application of GR24 and salicylic acid on two winter wheat cultivars under drought conditions. Foliar GR24 and salicylic acid were applied on drought sensitive and drought tolerant winter wheat cultivars at tillering and anthesis stages in 40% and 80% of field capacity moisture levels. Strigolactones and salicylic acid treated plants showed higher tolerance to drought stress with regard to lower electrolyte leakage and higher relative water content, leaf stomatal limitation, membrane stability index and antioxidant enzyme activities. Salicylic acid application dampened malondialdehyde content in wheat plants. Drought tolerance of wheat plants were intensified in most of the cases when theses phytohormones were used together, suggesting a possible interaction between salicylic acid and strigolactones in drought situations.

Effects of water stress and light intensity on chlorophyll fluorescence parameters and pigments of Aloe vera L

Aloe vera L. is one of the most important medicinal plants in the world. In order to determine the effects of light intensity and water deficit stress on chlorophyll (Chl) fluorescence and pigments of A. vera, a split-plot in time experiment was laid out in a randomized complete block design with four replications in a research greenhouse. The factorial combination of three light intensities (50, 75 and 100% of sunlight) and four irrigation regimes (irrigation after depleting 20, 40, 60 and 80% of soil water content) were considered as main factors. Sampling time was considered as sub factor. The first, second and third samplings were performed 90, 180 and 270 days after imposing the treatments, respectively. The results demonstrated that the highest light intensity and the severe water stress decreased maximum fluorescence (Fm), variable fluorescence (Fv)/Fm, quantum yield of PSII photochemistry (ФPSII), Chl and photochemical quenching (qP) but increased non-photochemical quenching (NPQ), minimum fluorescence (F0) and Anthocyanin (Anth). Additionally, the highest Fm, Fv/Fm, ФPSII and qP and the lowest NPQ and F0 were observed when 50% of sunlight was blocked and irrigation was done after 40% soil water depletion. Irradiance of full sunlight and water deficit stress let to the photoinhibition of photosynthesis, as indicated by a reduced quantum yield of PSII, ФPSII, and qP, as well as higher NPQ. Thus, chlorophyll florescence measurements provide valuable physiological data. Close to half of total solar radiation and irrigation after depleting 40% of soil water content were selected as the most efficient treatments.