نشریه فیزیولوژی محیطی گیاهی
پیاپی 56 (زمستان 1398)

Salt stress is one of the most important environmental threats that adversely affects the growth, development, and productivity of plants; therefore, suitable approaches are needed to mitigate its negative effects on plants. For this purpose, a pot experiment was carried out in a completely randomized design with two treatments include salinity (0, 25, 50, and 75 mM) and foliar application of selenium (0, 5 and 10 µM Na2SeO4), and the possible role of selenium in regulating Moldavian balm salt tolerance was investigated. Foliar applications of selenium were applied after seedlings establishment at three stages, simultaneously with the application of salinity stress, and then at weekly intervals. Results indicated that growth indices, photosynthetic pigments, and relative water content of leaves in Moldavian balm plants were decreased significantly by various levels of salinity stress. Foliar application of selenium especially at the low concentration increased all the mentioned traits in stress conditions. In contrast, high level of selenium magnified the negative effect of salinity, so that the highest value of malondialdehyde, electrolyte leakage, and water potential were obtained by 10 µM selenium under 75 mM NaCl and caused the accumulation of proline and soluble sugars. This study indicates that selenium at low concentration plays a significant role in alleviating the harmful effects of salinity through photosynthetic pigments, maintaining membrane integrity, reducing water potential, accumulation of compatible solutes, and consequently, improved the performance in Moldavian balm plants growing under salt stress.

Cold tolerance is one of the important factors in the distribution of plant species. The aim of this study was to investigate the survival and gas exchange responses of olive (Olea europaea L.) seedlings to low temperature and freezing stress. For this purpose, 144 two-years-old potted seedlings of olive (cultivar yellow) with averaged height of 30 cm were examined as factorial in a completely random design (CRD) with 3 replications. Seedlings were exposed to six temperature levels (+2, -5, -7, -10, -16, and -20° C) for 1 and 3 hours. Gas exchange parameters such as net photosynthesis rate, transpiration, and stomatal conductance were measured for each treatment in three steps: before stress, immediately after stress, and 12 days after stress. Results showed that in each temperature level net photosynthesis rates, stomatal conductance, and transpiration reduced in both 1 and 3 hours chilling and this reduction was higher in seedlings subjected to 3 hours chilling. Olive seedlings exposed to -10, -16 and -20 °C temperatures were dead while in seedlings subjected to -7 °C and higher temperature (under both 1 and 3 hours chilling) gas exchange variables were recovered on day 12 after the stress. In general, this research revealed that olive seedlings (cultivar yellow) are able to tolerate low temperature up to -7°C for 3 hours.

Salicylic acid and chitosan improve the plants’ resistance against drought stress through various mechanisms. To date, no information is available about the simultaneous effect of drought stress, chitosan, and salicylic acid onthe biochemical and physiological responses of burdock (Arctium lappa L.) plant. Therefore, a field experiment was conducted in a split plot form based on randomized complete block design with four replicates at the experimental farm of the Agriculture Faculty of Payame Noor University in Isfahan, during two successive years (2017-2018). Treatments included irrigation as the main factor at three levels (40%, 60%, and 80% hereafter called I1, I2 and I3, respectively), based on a predefined level of maximum allowable depletion of the threshold of available soil water, and four levels of foliar applications as the subplots (control, 5 g/liter of chitosan, 1 mg/liter of salicylic acid, and combined application of salicylic acid and chitosan hereafter called S1, S2, S3, and S4, respectively). Results indicated that the reduction of irrigation water, I2 and I3 treatments, compared to I1 treatment increased the activity of antioxidant enzymes, the content of reactive oxygen species, and content of mucilage in burdock plant. The mucilage content in root showed an increase by 61%, and 110% in I2 and I3, respectively, in comparison with I1 regardless of foliar applications. Also, application of chitosan and salicylic acid led to improved chlorophyll content, gas exchange parameters, plant water status, and the uptake of nutrients. Burdock photosynthesis rate was higher in S2-S4 than S1 regardless of irrigation levels (on the average 1.9, 2.9, and 2.4 μmol CO2 m-2 s-1, respectively). It is therefore suggested that application of chitosan and salicylic acid could be effective in growing burdock under drought stress.

Salinity stress is one of the main factors limiting the growth and production of plants. Zinc is one of the essential elements in the plant growth and metabolic processes whose application causes the plants to withstand environmental stresses. On the other hand, application of nano-material has been considered recently for the ease of uptake. In order to investigate the effect of foliar application of ZnO nanoparticles under salinity stress, a factorial experiment was conducted based on a completely randomized design with three replications. Treatments consisted of two levels of ZnO solution at concentrations of 2 and 4 mg.l-1 and NaCl salinity at five levels of 0 (control), 50, 100, 150, and 200 mM. Results showed that stem length, plant fresh weight, leaf number, leaf area, and photosynthetic pigments content, as well as soluble carbohydrate content were significantly decreased compared to control especially at 200 mM salinity level. On the other hand, foliar application of 4 mgr/l nano zinc oxide through positive effects on parameters such growth parameters, chlorophyll stability index, chlorophylls, carotenoids, proline and soluble sugars content of leaf and root. Also, analysis of the interaction of effects of the treatments showed that maximum root length and total fresh weight at 50 mM NaCl and maximum proline and chlorophyll at 100 mM NaCl were observed in spraying nano zinc oxide with a concentration of 4 mg/l. In general, the results of the study showed that the application of 4 mg/l nano-zinc oxide resulted in an increase in the growth and compatible osmolytes of Salvia leriifolia Benth., improving its response to salinity stress.

An experiment was conducted as split-split plot based on randomized complete block design (RCBD) with three replications during cultivation season 2017-2018 in Darreh-Shahr, Ilam Province. The experimental factors were four levels of irrigation as main plots including normal irrigation, cut of irrigation at stem elongation stage, cut of irrigation at the beginning stage of flowering, and cut of Irrigation at the beginning of the pod. Sub-factors included two levels of spraying and non-spraying of gibberellin hormone (100ppm) and salicylic acid (150 ppm), respectively. The comparison of mean effects of gibberellin showed that application of gibberellin resulted in highest saturated fatty acid while the plants receiving no gibberellin contained the lowest saturated fatty acid. The later drought stress occurred, the more significant was reduction in the oil percentage. The effect of drought stress on saturated fatty acid was significant but it had no significant impact on the unsaturated fatty acid. Both applications of gibberellin and salicylic acid increased the oil percentage and saturated fatty acid content. Results showed that normal irrigation with both uses of gibberellin hormone and salicylic acid produced the highest biological yield and the lowest dry matter was obtained in irrigation cutting at the beginning of podding stage without any spraying . The combined application of these two hormones increased seed oil content significantly. Finally, the findings indicated that the spraying of gibberellin and salicylic acid under drought stress significantly affected the yield in canola and when these hormones are applied at a suitable time they decrease the adverse effects of drought stress and increases oil yield.

Deterioration of seed is one of the vigor reducing factors limiting seed germination. Determination of factors affecting seed deterioration is important. In order to determine the effect of plant hormones on germination characteristics and antioxidant enzymes activities of deteriorated corn seeds an experiment was carried out at seed and biotechnology laboratories of College of Agriculture, Tehran University in 2019. The study was designed with a factorial experiment based on completely randomized design (CRD) with four replications. The experiment treatments included varieties at 2 levels (704 single cross hybrid and 260 single cross hybrid), accelerated aging at 4 levels (0, 5, 10, and 15 day), and hormones at 2 levels (gibberellin and cytokinin). Seed deterioration reduced germination indexes and peroxidase and catalase enzymes activity. Treatment of deteriorated seeds with cytokinin and gibberellin increased antioxidant enzymes activities. Cytokinin was more effective than gibberellin in increasing the activities of antioxidant enzymes in deteriorated seeds. Results indicated that low seed vigor decreased the activity of enzymes and plant hormones as an agronomy solution compensated for the loss in low vigor seeds. Also, cultivar 704, with a higher vigor indicated amore enzyme activity than cultivar260.