فصلنامه فرآیند و کارکرد گیاهی
سال هفتم شماره 3 (پیاپی 25، Aug and Sep 2018)

Arabinogalactan proteins (AGP) are a class of cell surface plant peptidoglycans which have been implicated in root elongation and signal transduction pathways. AGPs function not only as markers of cellular identity but also as signaling molecules, which might initiate signal transduction. Aluminum promotes the elongation of tea (Camellia sinensis L.) roots. Although some mechanisms by which Al induced root elongation in tea have been reported, there is no direct evidence on the signaling molecules affected by aluminum and triggering signaling.  In this study the possible involvement of AGP in regulation of auxin, gibberellin, and callose contents after exposure of tea seedlings to 400 μM Al was evaluated.  The results show that the Al-induced elongation of tea roots was accompanied by significant increment of the AGP. The maximum content of endogenous GA3 in the tea root was found after 6 h of the Al treatment. The content of IAA, rapidly (6 h of the treatment) and remarkably declined due to Al to 50% of the control. In addition Al exposure for 6 and 24h decreased the callose content of tea seedlings by 20% and 50% of that of the control cells, respectively. However, Al treatment for 6h increased the gene expression (167% of the control), and the activity of β-1,3-glucanase (150% of the control). The findings suggest a cross-talk between AGP, callose, and the two main growth hormones auxin and gibberellin in tea seedling which was started by Al exposure and resulted in elongation of root.

The detrimental drought effects could be listed as the loss in dry weight and silicon is known to enhance crop tolerance to drought by increasing seedling growth and hydraulic conductivity. To investigate the effects of silicon priming (0, 1 and 2 mM as sodium silicate), on seedling growth and root anatomy of three barley cultivars (Khatam, Rihane, and Nimrooz) a laboratory experiment was conducted under drought stress induced by 3.6 mM polyethylene glycol (PEG). Under 3.6 mM PEG, the highest root length was observed in Nimrooz barley cultivar (7.86 mm) at 2 mM silicon. In Nimrooz, seedling dry weight increased from 0.19 mg plant-1 in control to 0.27 mg plant-1 at 2 mM silicon (29.6% increase). At 2 mM silicon, Nimrooz with highest root surface area had the highest hydraulic conductivity (6.29×10 -9 m s-1 MPa-1) while in Rihane and Khatam was low as 5.38 and 5.19×10-9 m s-1 MPa-1 under 3.6 mM PEG, respectively. In Nimrooz, positive relationship was observed between application of 2 mM silicon and increasing the mean diameter of peripheral metaxylem vessels under drought. In all barely cultivars, drought stress affected the diameter of the vessels more than the number of the vessels. Also, under 3.6 mM PEG, K+ and Ca2+content increased from 0 mM silicon to 2 mM. Overall, silicon priming at 2 mM, especially in Nimrooz appears to be a promising and cost-effective procedure to alleviate the drought stress.

This study was performed to investigate the effect of storage conditions on seed germination performance of faba bean (cv. Shami). For this purpose, a three factors factorial experiment was conducted in laboratory of Seed Science and Technology, Faculty of Agriculture, Yasouj University, in 2013-2014, based on CRD design with five replications. The experimental factors were storage temperature (15, 25, 35 and 45 °C), seed moisture content (6, 10, 14, 18 and 22 percent) and storage duration (0, 30, 60, 90, 120, 150, 180, 210, 240 and 270 days). Also, in order to study some biochemical characteristics, 5 storage durations (0, 30, 90, 180 and 270 days of storage) were selected. Results showed that during storage, germination percentage, seedling length, seedling dry weight and seedling vigor index responded to temperature and seed moisture content (SMC), that is by increasing the moisture content of seeds at each temperature, germination percentage reduced (5-100%) and electrolyte leakage (60 to 370%) increased. At temperatures of 15 and 25 °C at moisture contents of 6, 10 and 14%, the seed deterioration rate was low while was fast (more than twice) at moisture levels of 18 and 22%. However, at 35 and 45 °C, the rate of seed deterioration, increased storage moisture content of 10 %, so that at SMC of 22 %, germination and seedling growth dropped to the lowest levels (zero) after 30 days of storage. Soluble protein content and catalase activity also decreased with during storage period. Reduction of antioxidant enzymes activity and increase of free radical damage were found as main reasons for the decline of faba bean seed viability during storage at high temperatures and high seed moisture content. Seed moisture contents of 6, 10 and 14% at temperatures of 15 °C and 25 °C are recommended for long-term storage of faba bean seeds.

This study was conducted in two phases: 1) to investigate the effect of drought stress on relative water content and proline of leaf and 2) to evaluate the effect of drought stress and potassium concentrations in nutrient solution on the lily (Lilium longifolium × Asiatic cv. Termoli). Based on a completely randomized design in mixture of sand and perlite medium and in three levels of potassium (0, 6 and 12 mM), the growth indices, vase life of flowers, potassium concentration and antioxidant enzymes activity were measured. The results showed that the proline concentration increased about 7 times in the medium containing the moisture content of one third of field capacity (FC) compared to the FC treatment after 3 months in plant leaves. Lily vase life at 6 mM potassium increased 5.7 days relative to potassium-free conditions. Peroxidase activity in the nutrient solution with 12 mM potassium was significantly lower than the potassium-free conditions.

In this study we have demonstrated the variations of carbohydrates and phenolic compounds present in the leaves and stems of ‘Kinnow’ mandarin (Citrus reticulata Blanco) trees in alternate bearing cycle and the possible involvement of these compounds to flower bud formation process. The amounts of these compounds were determined in the leaves and stems of “on” and “off” trees monthly from Nov. 2010 until Mar. 2011 coinciding with citrus trees floral bud induction and differentiation in northern hemisphere. The experiments were designed as a randomized complete block with three replications and two trees per each replication. Results showed that the presence of fruits on “on” trees inhibited flower bud formation, decreased total sprouted buds and resulted in the reduction of vegetative growth of these trees. The endogenous levels of soluble sugars and total non-structural carbohydrates in leaves and the starch contents of stems were affected by fruiting state of trees. Variations of total phenol contents in the leaves and stems related to presence or absence of fruits on trees. The phenolic contents of the stems were significantly lower in non-bearing trees than in fruit-bearing ones. Among the five phenolic compounds analyzed, the pattern of changes in the contents of chlorogenic acid, caffeic acid and naringin were different in two types of trees. Similar trend was observed for the amounts of all phenolic compounds in the stems of bearing and non-bearing tress.

In present study, growth, arsenic accumulation, and antioxidant responses in root of Isatis cappadocica were investigated in response to application of arsenate and phosphate. Reduction in root dry weights was significant with 1200 µM arsenate and 5 µM phosphate treatments. Phosphate had a steady effect on root dry weight improvement, especially in high arsenate treatments ≥ 200 μM. As concentrations in roots increased with increasing arsenate supply levels, and decreased markedly with increasing phosphate in each arsenate treatment.. Applied arsenate induced oxidative stress, which caused increasing the concentrations of hydrogen peroxide (H2O2) and malondialdehyde (MDA). The activities of antioxidant enzyme such as catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) in Isatis cappadocica roots increased significantly from 200-800 µM arsenate and 5 µM phosphate treatments while their activities were decreased at 1200 µM arsenate and 5 µM phosphate, compared with control plants. The phosphate mediated decline of CAT, POD and APX activities, which could be an important factor in regulating As-induced oxidative stress in roots. Our results concluded that, I. cappadocica has a great capability to tolerance and accumulate the As . Also, application of phosphate has a clearly vital role in oxidative stress reduction in roots of exposed I. cappadocica to arsenate.

Methyl jasmonate and Epi-brassinolide as plant growth regulators have significant biological effects on plant growth, including increased tolerance to salt stress in plants. In this study, the effects of salinity stress and its interaction with methyl jasmonate and Epi-brassinolide on chlorophyll concentration, rate of photosynthesis, transpiration, stomatal conductance and resistance and chlorophyll fluorescence in medical plant of black mustard (Brassica nigra L.) in hydroponic conditions, were evaluated based on a factorial design in completely randomized design with four replications. So that four weeks after germination plants were treated with various concentrations of sodium chloride (80, 40, 0 mM), methyl jasmonate (0 and 75 mM) and Epi-brassinolide (0, 5.1, 3 mM). The plants treated with salinity, with increasing concentration of sodium chloride, their chlorophyll concentrations, Hill reaction rate, transpiration and stomatal conductance decreased but the stomatal resistance, the initial fluorescence (F0) and maximum fluorescence (Fm) increased. At the same amounts of NaCl, with increasing concentrations of methyl jasmonate and Epi-brassinolide all tested traits were improved, such that by spraying 75 mM of methyl jasmonate, stomatal conductance (90.23 m2s mol-1) reached its highest level. With increasing levels of Epi-brassinolide in the same condition, the salinity of maximum fluorescence (Fm) reached to (559.21). The results of this experiment showed that the application of methyl jasmonate and Epi-brassinolide can improve the efficiency of photosynthesis and thereby improves the growth of black mustard (Brassica nigra L.) under salinity stress.