Proline and glycinebetaine accumulation by Spartina alterniflora Loisel. in response to NaCl and nitrogen in a controlled environment

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Abstract
The interaction of salinity and nitrogen availability on the growth and accumulation of proline and glycinebetaine by Spartina alterniflora Loisel. grown in hydroponic solution in controlled environements was investigated. Growth of shoots was reduced by increasing salinity and enhanced at higher nitrogen levels. Proline was accumulated when a threshold salinity was reached. At higher nitrogen levels, the threshold salinity to induce proline accumulation was lowered and the amount of proline accumulated was enhanced. Glycinebetaine content was higher in plants grown at higher nitrogen levels, but was less affected by salinity and nitrogen levels than proline. Glycinebetaine contents were approximately 10 times higher than proline contents. When plants that were non-stressed for 1 month were exposed to salinity stress, proline and glycinebetaine increased immediately and reached a plateau in 1–2 days. After the removal of salinity stress, proline disappeared rapidly but glycinebetaine content remained unchanged. Unlike NaCl, neither proline nor glycinebetaine had a significant effect on the in vitro activity of malate dehydrogenase activity from leaves.