Occurrence and stress response of N-methylproline compounds in Tamarix species.

A number of N-methylproline analogues have been found to accumulate in different species of Tamarix. These include N-methyl-L-proline (MP), trans-4-hydroxy-N-methyl-L-proline (M4HP) and trans-3-hydroxy-N-methyl-L-proline (M3HP). The three compounds appeared in all species but their relative and absolute levels depend upon species, ecotype and level of applied salt stress. A salt-conditioned ecotype of T. jordanis (Sodom) dramatically increased its accumulation of all proline analogues when subject to salt stress whereas a non-saline ecotype (Gilboa) showed little effect. The levels of M4HP and M3HP in T. meyeri increased with increasing salt stress whereas MP levels remained almost constant.