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Tobacco shoots were grown in vitro for 35 d, in MS culture mediummodified to include various sources (nitrate-N, ammonium-N ora mixture) and levels (0120 mM) of N, and in the presenceof 0180 mM NaCI or iso-osmotic concentrations of mannitol.Growth of control plantlets was significantly inhibited whenNH4+-N was the sole N source, and at high (120 mM) NO3-N supply. Under conditions of salt stress (90 and 180 mM NaCI)growth was repressed, with roots being more severely affectedthan shoots. Salinity also inhibited root emergence in vitro.The only alleviation of the salt stress by nitrate nutritionobserved in this study was on shoot growth parameters of plantletsgrown on 60 mM NO3-N and 90 mM NaCI. Although both weresignificantly inhibited by NaCI, nitrate reduc-tase activitywas more severely affected than nitrate uptake. When mannitolreplaced NaCI in the culture medium, similar Inhibition of growth,nutrient uptake and enzyme activity were recorded. These observations,together with the relatively low recorded values for Na+ andCI uptake, indicate that under in vitro salt stress conditionsthe negative effects of NaCI are primarily osmotic. Key words: Growth, nitrogen metabolism, osmotic stress, salinity 相似文献
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