Effect of Silicic Acid on some Anatomical and Biochemical Characteristics of Pelargonium graveolens L. under Salinity Stress

Intruduction Scented geranium (Pelargonium graveolens L.) is a perennial plant of the family Geranium (Geraniaceae). Although CaCl2 at higher concentrations than NaCl in the soils and groundwater in many areas of the word (Marschner, 1995), Most studies have been based on experiments that NaCl is the predominant salt. Relatively few studies have focused on the effects of CaCl2 on plant growth and physiology (Tas et al, 2005; Trajkova and Papadantonakis, 2006; Yokas et al, 2008). Silicon (Si) is considered as an essential element in several crops enhancing growth and alleviating different biotic and abiotic stresses. In this study, the role of Si in alleviation the deleterious effects of salinity on geranium (Pelargonium graveolens L.) have been studied.
Materials and Methods This experiment was conducted in spring-summer 2014 in research greenhouse situated on the Faculty of Agriculture, Lorestan University, Khorramabad, Iran. The greenhouse conditions were temperature 16.5–37.5 ◦C, relative humidity 30–80%. Terminal stem cuttings with five nodes were obtained from mother plants in the same greenhouse and placed in a sand substrate for rooting in April. Uniform rooted cuttings were then transplanted into plastic pots (22 cm diameter and height) filled with sand substrates and grown hydroponically. Transplanting was done in May and one plant per pot was cultivated. Plants cultivated were irrigated with Hoagland’s medium electrical conductivity (EC) 1.8 dS/m, (pH) 5.8 twice a day. Experiment was laid out factorially based on a completely randomized design with five replications. Factors consisted of daily application of 1.8, 4 and 6 ds/m CaCl2 and weekly application of 0, 0.5 and 1 mM silicic acid in nutrient solution. Plants were harvested in November. In this research some characteristics include Number of leaf, leaf area, photosynthetic pigments (chla, chlb. Totall chl, carotenoids), MDA, EL, RWC, Proline, Number of stomata in surface unit of leaf, density of stomata and stomata index and antioxidant enzyme include CAT and POD measured.
Results and Discussion In current study salinity decreased the number of leaf and leaf area and Si increased these characteristics. In general, decrease in the leaf area can result in a reduction in size of individual leaves of plants, decrease in the production of leaves and fall the old leaves. Reduce in growth rate of leaf in Salinity which causes osmotic effect around the roots (rhizosphere). Over time, the rate of cell division and elongation decreased, and finally this changes leads to decrease in the final size of leaf (Munns, 2002). In this study, salinity increased electrolyte leakage and the use of Silicic acid prevents electrolyte leakage. Probably saturation of Phospholipids with increasing salinity increased, as a result the fluidity of membrane decreased and finally increased the electrolyte leakage, Silicic acid absorbed in plant and deposited in the cell membrane, causing the silica hardened. This causes in stress condition, cell membrane maintains stability and significantly reduced the amount of electrolyte leakage (Zhu et al, 2004). In this study application Si in various concentrations under salinity stress brought a significant decrease in MDA compared with salinity alone (Table 2). salinity increase the MDA and EL so that application of 1 mM silicic acid decrease EL to 16.7 and 11.9 percent plants grown in 4 and 6 dS/m EC, respectively, compared with controls. Application of 1 mM silicic acid decrease the MDA to 23.6 and 35 percent plants grown in 4 and 6 dS/m EC, respectively, compared with controls. Therefore, the present results indicate that Si can effectively ameliorate membrane lipid peroxidation, thus protecting plants from oxidative stress. Salinity affected on leaf anatomy and chloroplast ultrastructure, therefore photosynthesis also affected by these factors (Parida and Das, 2005). Reduction in chlorophyll in height salinity levels due to chloroplast destructive. The results showed that Salinity decreased the density and stomatal index in plants and silicic acid increased these characteristics. Salinity decreased the RWC and antioxidant enzymes and application silicic acid improved them. Increase in salinity increased the leaf proline and application silicic acid alone in plant on stress decreased it.
Conclusions Overall, the results of present research showed that high EC induced by CaCl2 negatively affected geranium growth, and weekly application of 1 mM silicic acid alleviated the destructive effects of stress and in high salinity the positive effect of silicic acid is more than in low salinity.