Effects Of Exogenous Nitric Oxide On Seed Germination And Physiological Characteristics Of Pepper Seedlings Under Salt Stress

The effects of sodium nitropprusside (SNP, an exogenous nitric oxide donor) on pepper seed germination and growth, chlorophyll fluorescence parameters, oxidative damage, osmotic adjustment, endogenous phytohormones contents in pepper seedlings under 100mmol/L NaCl stress were investigated, in order to clarify the possible mechanisms of enhancing salt-tolerance in plants. Pepper cultivar(Longjiao NO.2) was selected as a testing material .The main results were presented as follows:1.Under 100mmol/L NaCl stress condition, the effects of SNP at the concentrations of 0.1-2mmol/L on seed germination and physiological characteristics of pepper seedlings were investigated. The results showed that germination of pepper seeds were limited under salt stress. 0.1-0.7mmol/L SNP treatments could increase pepper seed germination force, germination index, activity index and decrease MDA content, accelerate the accumulation of proline under salt stress. The effects of 0.1-0.3mmol/L SNP treatments on the alleviation of NaCl stress damage were the most obvious. Furthermore, the treatment of 0.1mmol/L SNP could also alleviate the rise of membrane permeability in pepper seedlings under salt stress. Except for 0.5 mmol/L SNP treatment, 0.1-0.7mmol/L SNP treatments could increase the root activity of pepper seedlings under salt stress.2. The growth of pepper seedlings were limited under 100mmol/L NaCl stress. 0.1mmol/LSNP treatment could increase height, fresh weight and dry weight of pepper seedlings under salt stress. Meanwhile, relative water content in leaves and root activity of pepper seedlings were increased under salt stress. The above results indicated that exogenous nitric oxide could significantly improve the growth of pepper seedlings. As a result, alleviate the growth inhibition of pepper seedlings under salt stress .3. NaCl stress could significantly decrease content of chlorophyll, Fv/Fm, Fv/Fo,ФPSII, qP and Fv′/Fm′in leaves of pepper seedlings under salt stress. 0.1mmol/LSNP treatment could apparently increase content of chlorophyll, Fv/Fm, Fv/Fo,ФPSII, qP和Fv′/Fm′in leaves of pepper seedlings under salt stress. And there was a relation between the increase of salt tolerance and the change of chlorophyll fluorescence parameters in pepper seedlings.4. 0.1mmol/LSNP treatment could apparently alleviate the accumulation of malondialdehyde (MDA) and decrease membrane permeability in leaves of pepper seedlings under salt stress. Meanwhile, the activities of protective enzymes(including SOD, POD and CAT) and contents of proline, soluble sugar and soluble protein in leaves of pepper seedlings were significantly increased under salt stress. It could be concluded that lower membrane permeability, MDA content and higher protective enzyme activieties, osmotic adjustment substances contents in salt-stressed leaves induced by NO addition in relation to the increase of salt tolerance of pepper seedlings. NO may protect the plant tissues from membrane oxidative damage under salt stress, thus mitigating salt toxicity and improving the osmotic adjustment of pepper plants.5. NaCl stress could increase contents of ABA and IAA, but decrease GA content in leaves of pepper seedlings under salt stress. 0.1mmol/LSNP treatment could apparently increase contents of ABA, GA and IAA in leaves of pepper seedlings under salt stress. And there was a certain relation between the increase of salt tolerance and the change of three endogenous phytohormones contents in pepper seedlings.6.1mg/ml hemoglobin (specific NO scavenger) treatment completely reverted above SNP actions under NaCl stress, it can decrease osmotic adjustment substances and endogenous phytohormone contents. whereas, using NaNO2 and K3[Fe(CN)6] as control further confirmed the specific role of NO confering the salt tolerance to pepper seedlings.