فصلنامه زیست شناسی گیاهی ایران
سال سوم شماره 3 (پیاپی 9، پاییز 1390)

Low temperature stress is an important environmental factor that limits citrus cultivation and yields. In this study, the effect of low temperature stress on physiological and biochemical responses of Page mandarin on citrange rootstock (on two year old plants), in incubator condition (with 65±5 relative humidity and 15000 lux Light intensity) has been investigated. Experiment was conducted using randomized design including low temperature (9, 6, 3, 0, -3 and -6°C) and control treatments (25±2°C). The comparison of treatment means showed that the lowest total chlorophyll (1.513 mg/gr leaf FW), green color (61.25%) and leaf water content (33.55% leaf FW) were related to -6°C temperature treatment. The highest accumulation of proline (48 mg/gr leaf FW) was related to -3°C temperature and maximum amount of carbohydrate (55.3 mg/gr leaf FW), was obtained with 0°C temperature treatment. Also, the highest amount of water soaking (51-75%) and electrolyte leakage (75.66%) in -6°C temperature, lipid peroxidation (2.643 MDA μgr/gr leaf FW), antioxidant capacity (63.5%) and phenol (2.863 mg/gr leaf FW) in -3°C temperature, were observed. The highest SOD enzyme activity (8.44×104 IU/gr leaf FW) was related to 0°C temperature. It could be concluded that Page mandarin (on citrange rootstock) could tolerate the freezing stress up to -3°C by increasing of proline, carbohydrate (osmotic adjustment) and antioxidant capacity.

Salinity is one of the most important factor that limits plant growth and production in the whole world. Identification of salt tolerant cultivars and improving tolerance of plants is the most effective method for increasing yield. To evaluate the response of growth and pigment contents in canola genotypes to salinity, a factorial complete randomized design with four replications was conducted. Sodium chloride salinity at three levels 0, 175 and 350 mM on two genotypes, Brassica napus L. cv.Sarigol and Brassica napus L. cv.Hyola308 was applied in stages 3-4 leaves. Dry weight of shoots and roots, chlorophyll a and b, carotenes and xanthophylls, anthocyanins, flavonoids and finally UV absorbing compounds contents were studied in the leaves. The results showed root dry weights reduced in both genotypes during high salinity conditions. The exposure of Sarigol plants to 175 mM NaCl induced a significant increase in shoot dry weight, but salinity had no significant effect on Hyola308 plants. Only in Sarigol cultivar Chlorophyll a contents increased during low salinity but Chlorophyll b contents decreased with high salinity. Increasing carotenoids in Hyola308 could be a reason of resistance to salinity and stability in photosynthetic structures. Under high salinity, there was not a significant trend in decreasing non-photosynthetic pigments in both genotypes. So it could be concluded that in canola plants, one of the most important factors for salinity tolerance could be unimpairing the main photosynthetic pigments.

Shoot apical meristem (SAM) culture is known as an effective method for the production of virus free plants. Detection and then dissection of SAM are the first two steps in establishment of successful culture. Providing of leaf primordium-free meristem is a very difficult operation due to the small size and colorless appearance of the SAM. Amongst the commercial plants, grapevine demonstrates specific and complex developmental pattern at which the SAM plays a crucial role. In this research, the live meristems were stained using novel procedure and then they were stained by water solution of FDA (0.1%) and fuchsine acid (0.05%), simultaneously. The prepared meristems were then detected and excised under a fluorescence stereomicroscope (510 nm) and afterwards they were immediately cultured on the half strength MS medium. Microscopic studies were shown that the size of SAM in the grapevine was fluctuated in terms of its developmental course. The higher organogenesis ability of SAM, the more viability of the explants that were achieved during the meristem culture. On the other hand, viability of meristem containing leaf and uncommitted primordium was higher than that of organ-free meristem.

This research was done to study the effects of lead and salicylic acid on content of photosynthetic pigments (chlorophylls a, b and a+b), and changes of soluble and insoluble sugars (starch) in roots and shoots of Brassica napus L.. One-week old seedlings of Brassica napus L. were grown in nutrient solution consisting Pb(NO3)2 (0.25, 0.5, 0.75, 1, 1.5 and 2 mmol) and salicylic acid (5 and 10 μmol) for 20 days. The fulfillments were in triplicate and data were statistically analyzed by using full randomize plots, SPSS and Duncan test. Based on the results by increasing the concentrations of Pb (NO3)2 in hydroponic cultures; the plants could not tolerate high concentrations of lead (1.5 and 2 mmol). Other lead treated plants showed significant decrease in the amount of chlorophyll a, b and a+b and content of soluble and insoluble sugars in roots and shoot compared to control plants, in the meantime, the activities of catalase and peroxidase enzymes were significantly increased. Decreasing of the amount of chlorophyll a was higher than chlorophyll b in all treatments. There were considerable increases in chlorophyll a, soluble and insoluble sugars in both roots and shoot under lead and salicylic acid treatments. But application of salicylic acid did not show significant effect on the amount of chlorophyll b and a+b, whereas using of salicylic acid under lead treatments decreased activities of catalase and peroxidase enzymes, but salicylic acid did not have significant effect on average of catalase activities in root. On the other hand, an increase of soluble and insoluble sugars and oxidative enzymes could show the role of salicylic acid in increasing tolerance of plants under lead stress. Therefore, salicylic acid had a role in mitigation of damaged caused by oxidative stress.

Heavy metal pollution in air and agricultural soils is one of the most important ecological problems in the whole world. According to the environmental protection agency (EPA), Pb is the most common heavy metal contaminant in the environment. M.chamomilla is one of the most important and the most frequently cultivated medicinal herbs. In this study, effects of Pb toxicity on M. chamomilla in the first stage of development and also in shooting and flowering stages were investigated. In doing so, seeds of M. chamomilla were grown in greenhouse, then plants in first stage of development were transplanted to hydroponic culture design five treatments of 0, 60, 120, 180, 240 µM Pb. No morphological change was observed during the treatment process in the different stages, but in all different stages reduction of total biomass was observed, compared to the control plants. The results indicated Pb accumulation in roots and aerial parts and an increasing trend with increasing Pb supply up to 180 µM. The results also showed that Pb concentration was higher in root than aerial parts especially in the first stage of development. Indeed, the results confirmed that chamomile had the ability to accumulate Pb in the roots so that preferential Pb accumulation prevented Pb toxicity symptom.

Drought stress is one of the main stresses that inhibit the growth of plants due to mainly disturbance of the balance between production of ROS and antioxidant defense mechanism and causing oxidative stress. Sodium nitroprusside (SNP) commonly was used as nitric oxide (NO) donor in plants. In this study, the effect of different concentrations of SNP on alleviation of oxidative stress induced by drought was investigated. Results of the measurements of lipid peroxidation and photosynthetic pigments content showed that low concentration of SNP could protect plants against oxidative stress because under SNP treatment, lipid peroxidation decreased and pigment loss was ameliorated. In this study, the relationship between this defense mechanisms and activity of antioxidant enzymes was investigated. Results showed that drought stress increased the activity of ascorbate peroxidase, guaiacol peroxidase and catalase. Concentration of 100 and 200 µM of SNP increased the activity of APX had no effect on activity of GPX and decreased the activity of CAT in plant under drought stress. In plants which were under drought stress the activity of PAL also increased but the concentration of 100 and 200 µM of SNP had no effect on activity of these enzymes under drought stress. The concentration of 500 µM of SNP decreased the activity of PAL in drought stressed plants. Drought stress and 100 µM SNP treatments had no significant effects on phenol content and 100 and 200 µM of SNP decreased the amount of these compounds under drought stress. In conclusion, in tomato plants, pretreatment with concentration of 100 µM of SNP or below could protect the plants under drought stress, probably through the contracts with ROS and or induction of anti-oxidative enzymes.

In this study, the flora of the Chadegan region, in 115 Km of the west of Isfahan investigated. This region is a mountainous area with some small plains and short hills that cover a surface of ca. 10000 hectares. The annual precipitation in the region is about 324.3 mm and its elevation varies from 1950 to 3915 meter above of the sea level (mean is 2932 m). The results showed that there were 339 plant species belonging to 204 genera and 54 families of higher vascular plants (49 families were dicotyledones, 5 families were monocotyledons, 1 family was gymnosperme and 1 family was cryptogame). The family Asteraceae with 27 genera and 49 species was the largest family and the genus Astragalus (Fabaceae) with 25 species was the largest genus in the region, respectively. The genera Centaurea with 9 species, Cousinia and Salvia each with 6 species, and Polygonum, Stachys and Allium each with 5 species are the other large genera in the flora of Cahdegan region. Furthermore, 3 species were parasitic or semi- parasitic plants. Survey of the life form of the plants showed that 5% of the species were phanerophytes, 11% were chamaephytes, 44% were hemicryptophytes, 13% were geophytes and 27% were therophytes. The dominance of hemicryptophytes and therophytes (totally, 71%), indicates the severe conditions of the area which is characteristics of the mountainous regions. Phytogeographically, 64.6% of the species belonged to the Irano-Turanian region, 9.7% were pluriregional and 25.7% belonged to the other regions. Also, 29 species were endemic for the flora of Iran, 3 species were endangered, 3 species were rare, and 15 species were vulnerable.