The ameliorating effects of polyamine supplement on physiological and biochemical parameters of Stevia rebaudiana Bertoni under cold stress

Stevia rebaudiana Bertoni is a perennial medicinal herb indigenous to tropical regions of South America. The present study evaluated some physiological changes of the plant under cold in the absence and the presence of polyamine conditions. The results showed photosynthetic pigments and photochemical efficiency of PSII reduced in cold treatment conditions than control, significantly. However, a considerable increase in the parameters was observed in all of polyamine treated goups. Leaf compatible solutes such as proline and glycine betaine that were not shown significantly increasing at cold treatment groups, elevated in the 2 days cold-polyamine-treated group. The similar results were seen for free amino acid and total protein contents of the treated plants. It was also revealed that specific activity of some antioxidant enzymes such as catalase and ascorbate peroxidase increased in cold-treated or cold + polyamine-treated groups than related controls. It caused a significant decrease in H₂O₂ and malondialdehyde contents of the treated plants. The results indicated an increasing in saturated long chain fatty acids after 4 days of cold at 4 °C. It was concluded that the polyamine supplement can induced a considerable tolerance in stevia plants at cold condition.     

Impact of drought stress on yield,photosynthesis rate,and sugar alcohols contents in wheat after anthesis in semiarid region of Iran

Owing to the importance of after anthesis water deficit in Mediterranean regions (such as Iran), this study has focused on harmful impact of after anthesis drought stress on grain yield (GY), photosynthesis, and some physiological characteristics of wheat. To this aim, a factorial experiment based on randomized complete block design with three replications was used in greenhouse conditions in Razi University in Kermanshah city of Iran, during 2010–2011 growing season. Two bread wheat genotypes, “Zagros” (tolerant to drought) and “Marvdasht” (sensitive to drought) were grown in normal water supply condition (100% of field capacity) and drought stress from anthesis until maturity (50% of field capacity). The results indicated that after anthesis water deficit considerably reduced grain and biological yields, thousand grain weight (TGW) and a number of grains per spike (NGS) among different traits in genotypes. Under well-watered and drought-treated conditions, genotypes in terms of all evaluated traits had considerable variations. Water deficit caused more reduction of net photosynthesis rate (Pn), stomatal conductance (gs), relative water content (RWC) of leaf, chlorophyll a, b (Chl), and soluble proteins content in sensitive genotype; values were respectively 66.3, 73.2, 14.6, 32.1, 46.2, and 25.6%. Better performance of tolerant genotype under water deficit was associated with a great ability in production of some osmoprotectants as inositol, glycerol, and erythritol sugars. Rather adaptation of tolerant genotype to water deficit may be attributable to having maximum soluble protein, sugar alcohols, Chl content, RWC, gs and Pn in drought stress, and with respect to the results, wheat might not be able to synthesize mannitol. Transfer of gene(s) producing mannitol may cause more improvement of growth performance of wheat under stresses.     

The response of Stevia (Stevia rebaudiana Bertoni) to nitrogen supply under greenhouse condition

Stevia (Stevia rebaudiana Bertoni) is a perennial plant producing some natural sweeteners. Stevia is considered as a new crop in some countries. This study was conducted to find the stevia response to nitrogen fertilizer supply. Different levels of nitrogen (0, 30, 60, 90, 120, and 150 kg/ha from urea source) were used in a greenhouse condition and then the stevia growth and metabolites were assessed under different availability of nitrogen. Results showed that the optimum growth of stevia was obtained by 60 kg/ha nitrogen and more nitrogen supply did not enhance the stevia growth. It was observed that the total steviol glycosides (SVglys) content of Stevia was significantly increased by nitrogen fertilizer application just up to 30 kg/ha, while it decreased by more rates of nitrogen fertilizer. Our result clearly showed that SVglys yield reached to maximum value by application of 60 kg/ha of nitrogen fertilizer. Since the variation of SVglys content and shoot growth of the stevia were compromised by 60 kg/ha nitrogen, it can be concluded that 60 kg/ha of nitrogen fertilizer could be considered as an optimum rate of nitrogen for stevia and could also be recommended for greenhouse conditions.