Response of Brassica napus L grains to the interactive effect of salinity and salicylic acid

and carotenoids content in maize plants. SA is also known as an important signal molecule for modulating plant responses to environmental stress. (Senaratna et al. 2000). t is now clear that SA provide protection against a number of abiotic stress as heat stress in mustard seedlings (Dat et al. 1998), chilling damage in different plants (Tasgı´n et al.2003), heavy metal stress in barley (Metwally et al. 2003) and drought stress on wheat plants (Singh and Usha, 2003). The present investigation was carried out to study the effect of grain soaking presowing with salicylic acid on the salt stress responses of Brassica napus .

MATERIALS AND METHODS

Grains were sterilized with sodium hypochlorite solution (5%) for 5 min, washed 3 times with sterilized distilled water. Salicylic acid was dissolved in distilled water and the pH was adjusted at 6.5 with KOH (1 N). Preliminary screening the grains were soaked for 12 h in the dark at 220C, either in concentrations (0.5, 1, 1.5, 2 and 5 mM SA) or in distilled water as control. Then many pretreated grains were putted in Petri dishes (9 cm diameter) provided with two filter paper saturated with 20 ml Nacl in concentrations (0, 4, 8 and 12 dsm-1). The final GP and Average velocity of germination (AVG) was recorded after a period of 5 days in grains. n this stage the optimum response of germination in concentration of 1 mM SA was selected. The next stage many pretreated grains in 1mM SA content were putted in Petri dishes saturated with 7 ml Nacl in concentrations (0, 4, 8 and 12 dsm-1) and 20 ml of 50% strength Hoagland’s nutrient solution (Hoagland and Arnon 1950). The pH of the nutrient solution was maintained at pH 6.5 three replicates were prepared for each treatment. The final fresh weights of shoot and root, RWC, Electrolyte leakage and MDA content was recorded after a period of 15 days in seedling. The comparison of mean was done with

LSD test to SPSS 14.o software in probability level of 1٪ for drawing graph, we use Excel 2003 software.

Leaf relative water contents (%):

The leaf relative water contents (RWC) were calculated at the time harvest according to Beadle et al. (1993) using the equation: RWC (%) = [(FW -DW)/ (TW - DW)] 100 Where FW is fresh weight, DW is dry weight, and TW is turgid weight.

Electrolyte leakage measurements:

Approximately 0.2 g of fresh leaves was cut into about 1-cm segments and placed in 5 ml of deionized water at room temperature. After 45 min, the conductivity (C 1 ) was measured and then the samples were incubated in a boiling water bath for 15 min to achieve 100% electrolyte leakage (C 2 ). The results were calculated according to the formula: (%)=(C 1 C 2 )100 ( Dua at el; 2006).

Lipid peroxidation measurements:

Lipid peroxidation in leaves was evaluated by the malondialdehyde (MDA) content. Approximately 0.5 g of fresh leaves was homogenized in 5 ml of 5% (w/v) TCA in an ice bath. Then the homogenates were transferred into a tube and centrifuged at 1000g for 10 min at 4°C . Aliquots of the supernatant and 0.5% (w/v) thiobarbituric acid in 20% (w/v) TCA were added into a new tube. This mixture was incubated at 98°C for 40 min, then cooled to room temperature and centrifuged at 8000g for 5 min. The supernatant was subjected to spectrophotometric analysis. MDA content was calculated from the absorbance (A535– A600)using the extinction coefficient of 155/(mM cm). Karabal at el;(2003).

RESULTS AND DISCUSSION

The results of germination percentage(GP) and Average velocity of germination (AVG) Brassica napus grains under SA and salinity treatments has brought at figure (1). n the study, ncreasing of

NaCl levels reduced germination percent in brassica napus. These results are consistent with those of Steppuhn et al;(2001) who showed reduced germination percent in brassica and wheat plants. The seeds pretreated with (0.5, 1, 1.5, 2 and 5 mM) SA solution exhibited lower germination percentage than those of untreated(control) seeds. These results are consistent with those of (Zea mays) (Guan Senaratna et al., 2000). Exogenously applications of salicylic acid helped to increase plant growth significantly in saline conditions (Setevens et al., 2007). Gutieґrrez-Coronado et al. (1998) also reported a similar increase in the growth of shoots and roots of soybean plants under normal conditions in response to salicylic acid treatment. salt stress with oxin and cytokinin reduced growth in wheat seedling. Shakirova, F.rn; et al (2003). SA treatment increased oxin and cytokinin contents in wheat under salt stress. Sakabutdinova at el; (2003). (Singh et al., 2003)found that SA application increased the dry mass of wheat seedlings under water stress. Khodary (2004) has reported that SA increased the fresh and dry weight of shoots and roots of stressed maize plants, which is consistent with our results in brassica plants. The results of RWC, MDA content and electrolyte leakage Brassica napus seedlings under SA and salinity treatments has brought at figure (3).

Figure 1 Effect of SA on germination percentage and germination speed mean

SA treatment (niM)                                controls           ImM

SA treatment {mM)

Figure 2 Effect of SA on shoot and root weight in Brassica.

n general, the RWC of leaves declined under salt stress. SA treatments induced an increase in RWC of the stressed seedlings, These observations are consistent with those of Barskosky and Einhellig (1993) who showed a consistently higher leaf diffusive resistance and lower transpiration and water potential in soybean plants with SA application. Because salinity stress enhanced free radicals levels in plants. peroxidation and electrolyte leakage in the stressed seedlings. The data showed that electrolyte leakage and lipid peroxidation increased as the stress level raised. These results agree with those of Bor et al. (2003) who found salt stress increases the lipid peroxidation in the leaves of two beet species. Grains soaking presowing with SA led to a significant decrease in the level of lipid peroxidation.

Figure 3 . Effect of SA on relative water content (%) and level leaf Brassic

Figure 4. Effect of SA on relative Electrolyte leakage (%) and MDA content Brassica