The response of the date palm cultivars studied was determined by measuring photosynthetic pigments (chlorophyll 'a', 'b' and total chlorophyll, carotenoids), biochemical content (proline, protein, amino acid), proline glutamyl kinase activity, proline oxidase activity analyze. , non-enzymatic antioxidants (total phenols, -tocopherol, reduced glutathione content) and antioxidant enzyme activities (polyphenoloxidase, peroxidase, superoxide dismutase, catalase, ascorbate peroxidase) were analyzed. However, more biotic stress and yield parameters are needed for the identification of biotic stress tolerant date palm cultivars.
Introduction
Overview
- Climate Change
- Elevated Level of CO 2 (eCO 2 )
- Enhanced UVB
- Soil Salinity
- Date Palm Varieties
- Date Palm in the UAE
Date palm production faces serious problems such as low yields as well as marketing constraints. However, the research on the evaluation of the impact of climate change on the date palm has received little attention.
Hypothesis
To identify date palm cultivars that are tolerant to environmental stresses and best suited to the current and future growing conditions in the UAE. iv). To identify agronomic and physiological traits that warrant greater date palm growth and improved tolerance to environmental stress.
Literature Review
Effect of Elevated Level CO 2 on Plants
The results showed that the stomatal conductance and biomass of the plants were greatly increased at eCO2. The authors also noted that the eCO2 treatment yields higher plant biomass (67%), plant height (22%), stem thickness (24%) and photosynthesis rate (55%) compared to the CO2 concentration in the environment.
Effect of UVB on Plants
It may be due to stimulation of photosynthesis by carbon uptake below eCO2. Whereas, PSII efficiency, peroxidase and malondialdehyde protective capacity, osmotic regulation such as proline and soluble sugar content did not significantly affect eCO2. Gossypium hirsutum grown in controlled environment chambers was exposed to 2-11 kJ m-2 d-1 of UV-B radiation to detect changes in plant height, leaf area, branch and internode length, number of the main trunk. node, area and length of petals and bracts, number of anthers per flower.
Also, leaf thickness, epidermal cell and stomatal density and index of the stomata, thickness of palisade, epidermal mesophyll tissue were measured. Moreover, epicuticular wax content and stomatal index were increased in both abaxial and adaxial leaf tissues. The high level UV-B radiation affects the vegetative parameters, but the reproductive parameters are reduced in ambient and high UV-B levels (Kakani et al., 2003).
Based on the response to UV-B, the genotypes were classified as sensitive, intermediate and tolerant to UV-B radiation (Singh et al., 2008). Two barley cultivars were exposed to high level UV-B and leaf tissue structure, pollen fertility, seedling viability, embryo root viability and statolytic starch were analyzed. Also, genetic analysis based on the ISSR marker showed that the polymorphic level increased (80%) in somatic tissue and decreased (33%) in reproductive tissue under UV-B radiation (Kravets et al., 2012).
Combined Effects of eCO 2 and UV-B on Plants
It has also been found that the effect of the studied climate change factors on broad bean growth was time-dependent and developmental stages. In addition, with shorter tube lengths, these flowers had less pollen and pollen germination was poor. Also, CO2 enrichment increased plant height, dry matter, leaf area, photosynthetic pigments and net photosynthesis.
The results of the study showed that plants treated with CO2 increased the growth of the plants. Understanding the impact of multiple stressors is especially important when their combined effect cannot be predicted from evidence from studies of individual stressors (Breitburg et al., 1998). Most of our knowledge about the effect of abiotic stress on crop productivity is based entirely on the experiments with individual abiotic stress.
Which is understandable because many abiotic stress research programs are complex in nature, require state-of-the-art facilities, and are financially prohibitive. 2010) reported that the multiple stresses had the greatest impact on the growth and development of crop plants compared to a single stressor. Therefore, the combined effect of two or more stress factors such as heat and drought should be treated as if it is a new state of abiotic stress and not simply the sum of two different stress factors (Breitburg et al., 1998; Singh et al., 2010 ). Therefore, an understanding of the response of plants to several environmental factors that mimic weather variability under current and future climate change scenarios will be one of the primary focuses of the research program.
Material and Methods
- Experimental Site
- Date Palm Cultivars
- Open Top Chambers Facility
- Salinity Stress
- Growth Parameters
- Plant Height
- Fresh and Dry Weight of Root and Shoot
- eCO 2 and UV-B Treatments
- Photosynthetic Pigments
- Determination of Chlorophyll and Carotenoids Contents
- Biochemical Contents
- Estimation of Proline Content
- Estimation of Protein
- Estimation of Amino Acid
- Proline Metabolizing Enzymes
- Estimation of Proline Oxidase Activity
- Non Enzymatic Antioxidants
- Estimation of Total Phenols
- Determination of -Toczopherol Activity
- Reduced Glutathione Activity
- Antioxidant Enzymes
- Polyphenol Oxidase Activity
- Peroxidase Activity
- Superoxide Dismutase Activity
- Catalase Activity
- Ascorbate Peroxidase Activity
- Statistical Analysis
Fresh leaf material (500 mg) was ground with pestle and mortar with 10 ml of 80 % acetone and the extract was centrifuged for 10 minutes at 2500 rpm. Then the extract was transferred to a graduated tube and 10 ml of 80% was used to make up to 10 ml. 500 mg of leaf samples were homogenized with 10 ml of 3% aqueous sulfosalicylic acid using a pestle and mortar.
Briefly, 20 ml of 20% trichloroacetic acid (TCA) was added to 1 g of plant sample and ground using a mortar and pestle. A standard curve was plotted with absorbance values obtained to determine the soluble protein content of the samples, and the values are expressed in mg/g fresh weight. 1 g of plant sample was homogenized in a pre-chilled pestle and mortar using 5 ml of homogenizing medium and it was filtered using two layers of muslin cloth.
The test tubes were placed in a water bath after the addition of 0.5 ml of Folin-Ciocalteau reagent and the absorbance was read at 660 nm. To neutralize the extract for estimation, 0.6 ml (10%) sodium citrate buffer was added to 0.9 ml of the extract. The H2O2 decomposition was monitored by reading the absorbance at 240 nm and the results are expressed in mg-1 protein.
Results
Effect of Salinity on Grown Parameters
The results on the shoot fresh weight of all the studied date palm cultivars are. Similar to plant height, salinity affected the shoot fresh weight of Chichi, Kalas and Nabt Saif date palm cultivars. The results on the shoot dry weight of date palm cultivars after the salinity treatment are given in Figure 7.
The dry weight results of control cultivars and salinity-treated date palm cultivars are given in Figure 9. Chichi, Kalas and Nabt saif cultivars showed a significant decrease in root dry weight after salinity treatment compared to the control plant. Date palm seedling cultivars Sultana and Zamli had less effect against salinity compared to the control.
Based on the morphological responses such as plant height, shoot fresh and dry weight, root fresh and dry weight, Sultana and Zamli varieties were characterized as salinity tolerant varieties selected to find out the response to future climatic scenarios such as high atmospheric CO2 and.
- Photosynthetic Pigments
- Biochemical Contents
- Proline Metabolizing Enzymes
- Non Enzymatic Antioxidants
- Enzymatic Antioxidants
The total chlorophyll content of Sultana and Zamli date palm cultivars after eCO2, UVB treatment is given in Figure 12. A similar trend was observed in carotenoid content as in the chlorophyll content of leaves of Sultana and Zamli date palm cultivars after eCO2 and UVB treatment (Fig. 13). The effect of UVB, eCO2 and combined treatment on biochemical contents in leaves of Sultana and Zamli date palm cultivars is presented in Figures 14-16.
The results on proline oxidase activity recorded in the leaves of Sultana and Zamli date palm cultivars are shown graphically in Figure 18. The total phenolic content of the studied date cultivars after UVB and eCO2 treatments is given in Figure 19. In both cultivars of the date. Reduced glutathione activity increased in the UVB treatment, then decreased in the eCO2 treatment and increased again in the combined treatment when compared to the control (Figure 21).
The results of the peroxidase activity of UVB- and eCO2-treated date palm plants are given in Figure 23. The highest level of dismutase activity was also recorded in the leaves of Sultana date palm cultivars treated with UVB. As observed with other antioxidant enzymes, ascorbate peroxidase activity also increased in both date palm cultivars treated with UVB irradiation (Figure 26).
Discussion
Hormonal imbalance and inhibition are also responsible for the reduction in apical growth of date palm cultivars induced by salinity stress (Younis et al., 2003). The content of photosynthetic pigments of date palm plant was reduced under UVB radiation and then gradually increased under the combined eCO2+UVB treatment in a controlled environment (Karthishwaran et al., 2020). Furthermore, it was reported that carotenoids in barley were significantly reduced (Cicek et al., 2012) when the plant was treated with UVB radiation.
This was similar to the results obtained by Balouchi et al. reported that the plants accumulate the proline when treated with UV radiation and that it could protect the cells against peroxidative processes caused by the UV radiation. The results obtained in the current protein content study are similar to the previous report published by (Salama et al., 2011). Bandurska et al., on the other hand. 2012) found a reduced amino acid content in the shoots and roots of barley seedlings treated with UVB+ water deficiency.
Various reports have shown that increased enzyme activities are associated with better tolerance to environmental stress (Zaefyzadeh et al., 2009; Chen et al., 2011). In addition, multiple enzymes with immediate expression had a greater potential for stress tolerance than single/dual expression (Lee et al., 2007). For example, UVB increased the antioxidant defense efficiency of Picea asperata seedlings via antioxidant enzymes (Han et al., 2009).
Conclusion
Effects of extreme high temperature, drought, and elevated CO2 on photosynthesis of the Mojave desert evergreen shrub, Larrea tridentata. Short-term effects of experimental heating and extended ultraviolet-B radiation on photosynthesis and antioxidant defense of Picea asperata seedlings. Effects of CO2 concentration and UV-B radiation on date palm (Phoenix dactylifera) grown in open-top chambers.
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Interactive effects of ultraviolet radiation and elevated CO2 concentration on photosynthetic characteristics of European beech seedlings during the growing season. Combined effects of high levels of CO2 and UV-B radiation on growth characteristics of Elymus athericus (E. pycnanathus). Combined effects of CO2 concentration and solar UV-B radiation on broad bean grown in open-top chambers.
