Effect of NaCl and Phenylalanine on the Production of some Secondary Metabolites in In Vitro Cultures of Mentha longifolia

Ola A. EL-Shennawy, Mohamed G. El-Torky, Hoda E. El-Mokadem and Basem I. Abass

The present study was conducted at the Tissue Culture and Plant Micropropagation Laboratory of Floriculture, Ornamental Horticulture and Landscape Gardening Department, Faculty of Agriculture, Alexandria University, during 2014 and 2015, to study the effect of five different concentrations of phenylalanine (0, 0.5, 5, 10, and 15 mg/l) and four different concentrations of sodium chloride (0, 2000, 4000 and 6000 mg/l) on the production of some secondary metabolites in in vitro cultures of Mentha longifolia using shoot tips and leaves.

Leaf segments about 1 cm2 and shoot tips consisting of 3-4 cm long stem segments containing three auxiliary buds (as explants) were planted on MS medium supplemented with NAA (0.25 mg/l) + BAP(2.5 mg/l ) + 30 g/liter sucrose + 7 g/liter agar for shoot regeneration from shoot tips, while MS medium contained 2,4-D (4 mg/l) + BAP (0.5 mg/l ) for callus induction from leaf segments, the pH was adjusted to 5.8±0.02. Plantlets were subjected to 16 hours light and 8 hours darkness (2000- 2500 lux for 16 h/d provided by fluorescent tubes), the temperature was adjusted at 25º C ± 2 and 60-70% humidity. The cultures were incubated for 60 days in case of shoot tips and 100 days in case of leaves for callus induction. Chemical analysis was performed on callus tissues after 60 and 100 days from planting and shoot tissues after 60 days from planting which were produced under salinity levels, phenylalanine levels and their interaction to determine the contents of total chlorophyll, total phenolic, rosmarinic acid and proline in both tissues.

From the obtained results in this study, using shoot tips for the production of phenolic acid and rosmarinic acid was superior than the callus. Low concentration of sodium chloride (2000 mg /l) enhanced the production of some secondary metabolites. However high concentrations of sodium chloride (6000 mg /l) leads to slow growth, yellowing of cells and sometimes the deterioration of plants. Uses of intermediate concentrations of phenylalanine (5 and 10 mg /l) enhanced the production of chlorophyll and some secondary metabolites where as high concentration (15 mg /l) does not stop growth and cell division.

Key words: Mentha longifolia – Amino acids – In vitro – Secondary metabolites – Salt stress – Lamiaceae.