فصلنامه فرآیند و کارکرد گیاهی
سال ششم شماره 4 (پیاپی 22، زمستان 1396)

The effects of magnetic fields (MF) on germination and early growth parameters, redox state and the activity of antioxidant system were investigated in soybean (Glycine max L. Merrill) seedlings. The seeds were imbibed in water and then were exposed to a 30 mT static magnetic field (SMF) and a 10 kHz electromagnetic field (EMF) for 4 days, each 5 h. Water uptake of seeds increased after 40 and 120 minutes of the treatment with MF. In comparison with the control group, exposure to EMF significantly increased germination percent of the seeds and vigor index I, II of seedlings while SMF significantly increased vigor index II but had no effect on seed germination. The ratio of fresh weight to dry weight and ferritin content of both MF-treated groups was significantly higher than those of the control group. Treatment with EMF improved radical scavenging capacity of seedlings and reduced membrane leakages. Exposure to MF also protected seedlings from the risk of increase of internal calcium content. The results provide us with a new approach for application of magnetic fields in order for growth promotion of strategic crops.

A field experiment was conducted to evaluate the effect of planting pattern and irrigation system on antioxidant activity of wheat and Persian clover. The experiment was carried out as a two-factor factorial with three replications. The first factor was irrigation system (conventional and partial root-zone irrigation) and the second was planting pattern (sole wheat, sole Persian clover, alternate-row intercropping and within-row intercropping). Results indicated that RWC of wheat and clover leaves decreased with lowering water supply. Both crops had higher RWC in intercropping. At the stage of before irrigation, wheat and clover had lower proline in intercropping systems (15% and 9% lower for wheat and clover, respectively). SOD in wheat and Persian clover increased with the severity of water deficit. Under partial root-zone irrigation, SOD of wheat and Persian clover was increased 10% and 46% compared with conventional irrigation. The MDA content of wheat and Persian clover leaves under partial root-zone irrigation was more than that of conventional irrigation. Regarding MDA wheat experienced a higher stress under sole cropping. Grain yield of wheat and Persian clover reduced 27 and 36 percent in partial root-zone irrigation, respectively. Land equivalent ratio of intercropping in partial root-zone irrigation was significantly (P≤0.01) than that of conventional irrigation, suggesting that intercropping reduced the negative effect of lower water supply. Generally, partial root-zone irrigation induced higher antioxidant activity of wheat and Persian clover. However, partial root-zone irrigation may have a good potential for reducing water consumption in intercropping systems.

A field experiment was conducted to evaluate the crop water stress index (CWSI), grain yield and canopy temperature of triticale under two irrigation regimes at Research Station of College of Agriculture and Natural Resources of Darab, Shiraz University, in 2013. A split plot design was used with three triticale cultivars (Sanabad, ET-83-3, and ET-84-5), as sub-plots and four levels of irrigation regimes including well watered, cutting off irrigation at flowering, milk development, and dough development stages as main plots replicated three times. Results showed that Sanabad (6.31 °C) and ET-83-3 (6.89 °C ) cultivars had the higher canopy-air temperature differences, while in ET-84-5 this difference reached to 2.66 °C. In all cultivars, high amount of variation (0.18 to 0.91) was observed for monthly CWSI and decreased by cutting off irrigation from flowering to dough development. Under cutting off irrigation at flowering, ET-83-3 with 0.67 had the highest mean seasonal CWSI, while in ET-84-5 reached to 0.50. In cutting off irrigation at flowering, the highest triticale grain yield was obtained in Et-84-5 (354.3 g) and it might be attributed to higher grain number per spike and spike number per square meter compared to Sanabad and ET-83-3. Polynomial regression showed that with increasing CWSI, triticale grain yield decreased and the slope of regression between 237 to 284 g/m2 grain yield was more than the other spots (R2=0.79). The highest grain yield (476.2 g/m2) was obtained in ET-84-5 under well watered and CWSI in this cultivar ranged from 0.18 to 0.33. By cutting off irrigation at flowering and increasing CWSI compared to cutting off irrigation at milk and dough development stages, grain yield decreased especially in Sanabad and ET-83-3, significantly. Overall, ET-84-5 with lower canopy and air temperature differences (Tc-Ta) and mean CWSI, had better performance when exposed to cutting off irrigation.

Sapodilla is one of the important fruit crops in tropical area which has problem with seed germination. So Manilkara hexandra (kherol) is generally used as a rootstock for sapodilla. This experiment was performed to assess the morphological changes and antioxidant enzymatic activity of Manilkara hexandra seedling under salinity condition. A pot experiment was carried out in a greenhouse using different concentrations of seawater (3, 6, 9, 12 ds/m) on the one-old age seedling and fresh water used as control. The experimental design was a Completely Randomized Design (CRD) experiment. Result showed that seawater irrigation had no significant effect on length and volume of root. However, fresh weight of leaf, stem and root decreased significantly by increasing seawater concentration. POD and CAT antioxidant enzymes showed the similar trend under stress and their activities increased strongly. However, APX activities increased gradually by increasing salinity level.This dramatic increase might show that POD and CAT are a major enzyme among antioxidant enzymes examined in Manilkara hexandra (kherol) under salt stress. Thus, antioxidant defense system induced by salinity plays important role in this plant under salinity stress.

In order to investigate the seasonal changes and the possible role of the free polyamines in the leaves and stems on the alternate bearing habit of the ‘Kinnow’ mandarin (Citrus reticulata Blanco) trees, a comparative study was conducted to analyze the levels of free polyamines (putrescine, spermidine and spermine) in the leaves and stems tissues of “on” and “off” trees during the flower bud formation period. Samples were taken from trees in one month interval period in a commercial orchard in the City of Darab, Fars Province from Nov. 2010 till Mar. 2011 according to the stages of flower bud phenology in citrus. The experiments were designed as a randomized complete block with three replications and two trees per each replication. The experiments were designed as a randomized complete block with three replications and two trees per each replication. Total polyamines (putrescine, spermidine and spermine) levels in leaves were higher in “off” trees than in “on” trees throughout the experimental period but only the differences of spermine contents were significant during the most of season. The contents of spermidine and spermine in the stems of “off” trees were significantly higher than in “on” trees most of the season. Putrescine levels and polyamine ratio (putrescine/spermidine늗ꮚ⧞) in the stems were significantly higher in “on” trees than in “off” ones. Time of sampling had no significant effect on the stem total polyamines, putrescine and polyamine ratio in “off” trees. Results could not show a relationship between polyamine fluctuations in stems and leaves with processes of flower bud formation in mandarin trees.

Drought stress is the major problem in arid and semi-arid regions of the world. Investigating the response of different cultivars of crop plants to drought stress can help to select the tolerant ones for agriculture in arid lands. In this study, a greenhouse experiment was conducted as a factorial experiment based on completely randomized design with two common bean cultivars (Phaseolus vulgaris L.) including Derakhshan and Goli, and four moisture levels of 25, 50, 75 and 100% field capacity. When the true leaves were emerged (10 days after planting), the seedlings were exposed to the different levels of drought stress until the end of the flowering stage. Based on the morphological (stem length, leaf and root area, dry weight of shoot and root, and the root/shoot ratio), physiological (leaf relative water content, membrane stability index, photosystem II photochemical efficiency, stomatal resistance, chlorophyll index, and water use efficiency), and biochemical (proline content, soluble protein content, and the activity of antioxidant enzymes including superoxide dismutase, polyphenol oxidase, and peroxidase) characteristics, both cultivars showed a relatively good tolerance to the low and intermediate drought stress, while both were sensitive to the highest level of drought condition (25% field capacity). The main characteristics which indicated the tolerance of common bean cultivars to drought stress was an increase in the root/shoot ratio, stomatal resistance, water use efficiency, proline content, and antioxidant enzyme activity. Regarding these characteristics, the responses of Derakhshan cultivar was more associated with drought tolerance, compared with Goli cultivar.

In order to investigate the effect of seed inoculation with Plant Growth Promoting Rhizobactria (PGPR) on germination and some biochemical and physiological indices of Cumin (Cuminum cyminum L.) under salinity stress, an experiment was conducted. Experimental factors were included in seed priming in five levels (seed inoculation with three strains of Pf2, Pf25 and CHA0 of Pseudomonas fluorescens, and one strain of Bacillus subtilis and hydration in distilled water (as priming control)) and three levels of salinity stress (0, -4 and -8 bar imposed by NaCl). Salt stress reduced germination percentage, catalase (CAT) and ascorbate peroxidase (APX) activities and seedling potassium content and increased sodium content. Priming not only mitigated the inhibitory effect of salt stress on studied characteristics but also in most cases induced a stimulatory effect on seed physiological quality in both stressed and non-stressed seeds. The highest germination percentage, APX activity and K content were achieved in the seeds inoculated with CHA0 strain of P. fluorescens. The effect of this treatment was more obvious under salinity potentials of -4 and -8 bar. The results indicated that salinity can affect cumin seed germination and the beneficial effect of PGPR could be used for improving its salt tolerance.

The aim of the present study was to investigate the effects of SA on UV-A, UV-B, and UV-C stressed plants. Data showed that SA counteracted the UV harmful effects on pepper. Pepper (Capsicum annuum L.) seedlings sprayed with salicylic acid (SA) and treated with UV-A (320-390 nm), UV-B (312 nm), and UV-C (254 nm) of 6.1, 5.8, and 5.7 W m-2, respectively. UV significantly increased contents of ascorbate, dehydro ascorbate, total ascorbate, proline, aldehyde, quercetin, electrolyte leakage and total ethylene. SA treatment moderated ascorbate, dehydro ascorbate, total ascorbate, aldehyde, electrolyte leakage and total ethylene increase in plants treated with UV. The quantity of proline and quercetin in plants that treated with UV and SA were significantly increased. Exogenous application (foliar spray) of SA counteracted the UV effects on pepper.

An experiment was carried out to evaluate the effect of various concentrations of Mg (0, 1, 2, 3 and 4 mM) in the nutrient solution and shading (0 and 50%) on growth, yield, fruit quality and physiological properties in hydroponically grown cucumber (Cucumis sativus L. cv. Nagen 792). With increased Mg concentration in both shaded and unshaded plants, the total plant leaf area and dry weight of leaves increased, whereas specific leaf weight decreased. The highest yield in terms of fruit weight and number per plant in both shaded and unshaded plants were obtained in 3 mM Mg treatment; however yield in shaded plants was 57% that of in unshaded plants. Increased Mg concentration drastically increased Mg content and reduced K and Ca content in the leaves and fruits, particular in shaded plants. Leaf and fruit concentration of Mg increased drastically while K and Ca decreased with increasing Mg in the nutrient solution. The activity of ascorbate peroxidase (APX) and peroxidase (POX) in the leaves was decreased by increasing of Mg concentration. The highest activity of APX and POX was observed in Mg deficiency plants and it becomes more pronounced in unshaded plants. Leaf soluble sugars and starch content were decreased with increasing Mg concentration in the solution, especially in shaded plants. Low Mg concentration in the nutrient solution significantly increased total free amino acids (FAA) in the leaves. In conclusion, Mg requirement of cucumber plants likely increases with light intensity. Thus, higher concentration of Mg (3 mM) in the nutrient solution was the most favorable for cucumber plant growth and function grown in hydroponics.