Proline Analogues in Melaleuca Species: Response of Melaleuca lanceolata and M. uncinata to Water Stress and Salinity

Abstract

Fifteen species of Melaleuca and two species of Callistemon from the field were examined to determine whether they accumulated nitrogen-containing compatible solutes and, if so, which. In addition to L-proline, N-methyl-L-proline (MP) (isolated for the first time from plants), trans-4-hydroxy-N-methyl- L-proline (MHP), and N, N'-dimethyl-trans-4-hydroxy-L-proline (DHP) were found in various combinations in the 15 Melaleuca species. M. lanceolata seedlings were subjected to water or salinity stress and M. uncinata to water stress under laboratory conditions. In both species significant reductions in leaf water potential (Ψw), osmotic potential (Ψs), turgor potential (Ψp), and relative water content (RWC) were observed in response to water stress. Salinised M. lanceolata plants showed considerable osmotic adjustment and maintained Ψp comparable to that of control plants; salinity, however, decreased RWC. In response to the imposed stresses under laboratory conditions, proline and MHP levels in M. lanceolata, and MHP and DHP levels in M. uncinata, increased. In addition to possible protective or osmotic roles in vivo, these proline analogues may be useful in chemotaxonomic investigations of Melaleuca species.

Salt tolerance in Eucalyptus spp.: identity and response of putative osmolytes

“…various betaines in Melaleuca spp. ; Naidu et al . 1987, 2000), we found no such evidence for the species studied here.…”

Betaines of Alfalfa

“…Determination of the levels ofthe putative intermediates involved in the synthesis ofthese imino acid betaines (e.g. N-methylproline, N-methylpipecolic acid, and N-methylhydroxyproline) (11), and their rates of labeling from supplied isotopically labeled amino acid precursors are now required to elucidate these pathways. Presumably, the pathway ofhydroxyprolinebetaine synthesis in alfalfa could be explored by supplying isotopically labeled proline, hydroxyproline, N-methylproline, and N-methylhydroxyproline to high-and low-hydroxyprolinebetaine genotypes to determine if hydroxyprolinebetaine deficiency results from a lesion in the capacity to metabolize hydroxyproline to N-methyhydroxyproline, a lesion in the capacity to metabolize N-methylhydroxyproline to hydroxyprolinebetaine, and/or a lesion in the capacity to metabolize N-methylproline to Nmethylhydroxyproline.…”

Variable tolerance of wetland tree species to combined salinity and waterlogging is related to regulation of ion uptake and production of organic solutes

“…For ion compartmentation to take place, osmotic balance must be achieved between the vacuole and cytoplasm, which can occur through the production of compatible organic solutes in the cytosol and organelles (Hall et al ., 1978). The compatible organic solute methyl proline has been found in leaves of M. cuticularis in the field (Naidu et al ., 1987, 2000; Poljakoff‐Mayber et al ., 1987; Carter, 2004), but in these studies the concentration was not found to increase with drought or osmotic stress. Similarly, proline was measured in the cladodes (modified photosynthetic stems) of C. obesa in the field, but despite marked seasonal changes in root‐zone salinity the concentrations were relatively constant (Carter, 2004).…”