فصلنامه زیست شناسی گیاهی ایران
سال چهارم شماره 4 (پیاپی 14، زمستان 1391)

Sunflower seeds were planted under field conditions in order to investigate the behavioral pattern of photooxidation tolerance in plants in response to leaf aging. During pollination stage, the leaves were theoretically divided into three sections including young, middle aged and senescent leaves, so that the cell defense potential would change with leaf aging, and then modeling of different intensities of light and its effects on light oxidation of biological materials in the leaves of different ages was investigated. The results from the first series of experiments showed that despite of no change of chlorophyll content in leaves due to leaf aging, total protein content and membrane stability index were declined. Furthermore, lipid peroxidation and hydrogen peroxide were increased in respond to leaf aging. Meanwhile, the activity of hydrogen peroxide scavenging enzymes and glutathione S-transferase in senescent leaves were higher than that of young leaves. Overall, the results showed that with any increase in leaf age, defense potential of cells slowed down and the production of oxidants exceeded the scavenging potential of the cells. The results of modeling of different intensities of light revealed that in senescent leaves under high light intensities, hydrogen peroxide reached to its highest levels. However, under those light condition, hydrogen peroxide scavenging enzymes and glutathione S-transferse activities were recorded at amounts lower than that of low light intensities. The outcome of the above mentioned factors lead to oxidation of chlorophyll and subsequently its content reduction under highlight intensities in aged leaves. In total, under high light intensities, the damage of oxidation stress on aged leaves was more intensified compared to young leaves mainly due to diminished defense potential of stress faced cells.

The flower structure in Amorpha fruticosa L. is unique among legumes because it possesses only one petal. In order to clarify the ontogenetic basis for missing petals, the initiation and development of floral organs were examined using epi-illumination light microscopy. First, the flower buds of different ages were collected and fixed in FAA. After a fixation period of 24 h, the samples were rinsed, dissected in 70% ethanol and further dehydrated in 95% ethanol prior to staining with 0.5% nigrosin black in ethanol. The most distinctive features of Amorpha flower ontogeny were the abaxial-adaxial unidirectional initiation of organ primordia within each floral whorl, high overlap in the time of initiation of whorls and early carpel primordium initiation. Based on our results, although five petals were first initiated in the flower buds, the abaxial and lateral ones failed to enlarge and thus disappeared completely by midstage.

Salt stress causes ionic, osmotic and oxidative stresses in plants. Salicylic acid (SA) is a plant-produced phenolic compound that can function as growth regulator. In this study, the role of SA pretreatment in inducing tolerance to oxidative stress induced by salt in maize plants was investigated. In this research, effects of SA in three levels (control, soaked in water and soaked in solution of 0.1 mM salicylic acid) and also salt stress (0 and 80 mM NaCl) were studied. Salinity decreased growth parameters but increased lipid peroxidasion and electrolyt leakage. In addition, salt stress decreased the content of ascorbate pool and phenolic compounds and increased the activity of antioxidant enzymes including ascorbate peroxidase (APX), catalase (CAT) and peroxidase (GPOD). Meanwhile, SA pretreatment reduced lipid preoxidation and electrolyte leakage by increasing the nonenzymatic antioxidants such as ascorbate pool and phenolic compounds but the activity of ascorbate peroxidase (APX), catalase (CAT) and peroxidase (GPOD) which were reflected in improving the plants growth. However, it was concluded that SA was able to induce protective reactions via increasing quantity and activity of these antioxidants under salt stress conditions.

Cold stress is a major environmental factor that limits the agricultural products. Plants can increase their cold and freezing tolerance by being exposed to short days and cold, non freezing temperatures, a process known as cold acclimation. In the period of cold acclimation that causes dehydration of cells, dehydrin proteins accumulate inside the cells and protect the membranes and macromolecules structure. Pistachio (Pistacia vera L.) is a tree species characteristic of arid zone, which is exposed to extreme temperatures. In this study, the effects of cold and short day treatments on dehydrin gene expression were investigated in seedlings and regenerated shoots of pistachio cultivar Badami. The results showed that cold treatment increased the gene expression meaningfully compaired to the control. The short day treatments had no effect on dehydrin gene expression. Because the regenerated plants may encounter somaclonal variations and thus show different responses to stresses, a comparison was made between in vivo and in vitro grown plants with respect to the rate of gene expression, under similar cold treatment. Comparison of the plants grown in vivo and in vitro showed that dehydrin gene expression was lower in regenerated shoots under natural condition and after cold treatment.

Rice (Oryza sativa L.) which is the main food for more than half of the world’s population, is often considered as one of the most drought, salt and cold-sensitive crop plants particularly at early stages of post germination. Plants monitor the environmental status during a post-germination growth arrest and this prevents them to grow under unfavourable conditions which ultimately helps them to survive. In Arabidopsis, this response is mediated by abscisic acid and requires the ABI5 and ABI3 transcription factors. In this research, we investigated whether a similar abiotic stress induced growth arrest mechanism was operating in rice seedlings through the expression analysis of OsVP1 and OsABI5 (rice orthologues of the Arabidopsis transcription factors ABI3 and ABI5) in two rice cultivars, FL478 and IR29, which were salt tolerant and sensitive respectively. For exposing to salt, drought or cold stresses, the two-day seedlings were transferred to MS media complemented with iso-osmotic concentrations of NaCl (0, 50, 100 and 150 mM) or mannitol (0, 100, 180 and 275 mM) at 25°C or MS media at 4 and 15°C for 10 days. In both cultivars, stresses decreased shoot growth and increased the transcript level of OsABI5 and OsVP1 genes. Therefore, based on the achieved results, probably, OsABI5 and OsVP1 transcription factors either directly or indirectly regulated the expression of other genes involved in abiotic stress-induced growth arrest in rice.

Iron is an essential element in all plants and its deficiency causes drastic growth retardation. Silicon is also an essential element in Poaceae family including rice that may reduce biotic and abiotic stresses in plants. In this research, the interactions of silicon and iron nutrition were studied in rice (Oryza sativa L. cv. Tarem). The plants cultivated in greenhouse under iron treatments of 0, 2 and 10 mg l-1 as a Fe-EDTA and silicon treatments of 0 and 1.5 mM as a sodium silicate. The expeiment was teriminated after 3 weeks of iron treatments and then the plants were harvested for assying growth and biochemical factors. Iron deficiency resulted in reduction of fresh mass, contents of chlorophyll, carotenoides and iron in shoots. In addition, the activity of catalase, cell wall and soluble guaiacol peroxidase, and polyphenol oxidase in shoots decreased under iron deficiency. As a result, the amount of hydrogen peroxide in roots and lipide peroxidation in shoots increased due to iron deficiency. Silicon nutrition, however, increased the iron content and recovered the fresh mass, chlorophyll and carotenoides contents as well. The effects of silicon application and optimal iron nutrition on plant growth were synergetic. Silicon nutrition caused significant increase in the cell wall and soluble guaiacol peroxidase activity in both roots and shoots and the catalytic activity in shoots. Consequently, the hydrogen peroxide in roots and the lipide peroxidation in shoots decreased following silicon application. The results indicated that silicon application could alivatie the harmful effects of iron deficiency in vegetative growth stage in rice.

In this study, the role of salicylic acid in cadmium induced physiological changes was investigated in solid hydroponic culture in soybean plantlets. After presoaking soybean sterilized seeds in 0.5 mM SA solution for 6 hrs, seeds were transferred to pots containing perlite and then they were irrigated with Hoagland nutrient solution (full strength) containing 200 µM CdCl2 for 20 days. After harvesting the plantlets and calculation of growth parameters (root and shoot dry and fresh weight and length), photosynthetic pigments contents (chl a and b), electrolyte leakage in leaves, and cadmium content (in the roots and the shoots) as well as Ca and K content in shoots, it came to our knowledge that salicylic acid had little effect on this parameters in the absence of cadmium, but in the presence of cadmium, SA increased growth parameters, photosynthetic pigments contents, Ca and K content in shoots, against decreased electrolyte leakage in leaves and cadmium content in arial parts of plant. Therefore, SA could reduce cadmium toxicity and protect growth potential of plant by changing plant strategy in translocation of elements to aerial parts of plant and inhibition of electrolyte leakage and protection of photosynthetic pigments.

Salvia leriifolia (Lamiaceae) is endemic of Khorasan and Semnan provinces and is an endangered plant. In this research, for the first time, micropropagation of this plant was studied through shoot tip proliferation. Plantlets were obtained via embryo culture in 1/2 MS culture medium supplemented with 1 mg/L BAP and 1 mg/L NAA. For micropropagation, shoot tips of the plantlet were cultured on MS medium supplemented with different concentration of BAP and KIN alone or in combination with IBA. For rooting, MS medium containing different concentration of IBA, NAA and 2,4-D was used. Statistical analysis was performed according to the JMP and MSTAT-C software. The results showed that combination of BAP and IBA was appropriate for shoot proliferation and MS medium containing 2 mg/L BAP and 0.5 mg/L IBA was optimum for proliferation. Also, auxin was necessary for root formation and the best treatment for rooting was MS medium supplemented with 1 mg/L IBA. It could be concluded that, this treatment might be recommended for micropropagation of Salvia leriifolia via shoot tip culture.

Physalis alkekengi (Solanaceae) is a rich source of different antioxidants, which has been advised for the treatment of various diseases such as inflammation and rheumatism. In this paper, antioxidant properties of different parts of P. alkekengi including leave, calyx, green and orange fruits randomly collected from around the Tonekabon-Iran were studied. Antioxidant activity of extract was measured with DPPH radical scavenging activity, inhibition of fatty acid oxidation and ferric-reducing antioxidant power. Also, the total phenol, flavonoid, quercetin, luteolin, anthocyanin and carotenoid contents of samples were determined. The tests were conducted in a completely randomized design with 4 replications. The leaves of P. alkekengi contained the most content of the total phenol, flavonoid and ferric-reducing antioxidant power. The maximum of DPPH radical scavenging activity (1.81±0.214 g/gFW), peroxidation fatty acid inhibition (75.53±5.35 %), and total carotenoids content (10.05±1.45 mg/gFw) were observed in orange fruit of P. alkekengi. The highest value of luteolin was measured in the leaves of green fruit stage, and it was 0.198±0.001 mg/gDW. Querccetin was found only in the leaves of vegetative and flowering stages, 9.2±0.05 and 9±0.53 μg/gDw respectively.