Salicylic acid (SA) acts as a potential non-enzymatic antioxidant and a plant growth regulator, which plays a major role in regulating
various plant physiological mechanisms. The effects of salicylic acid (SA; 0.05 mM) on physiological parameters, antioxidative capacity and phenolic
metabolism, lignin, alkaloid accumulation in salt stressed Catharanthus roseus
Materials and Methods: Catharanthus roseus
seeds were grown for two months in a glass house at 27–30°C in sunlight, and then divided into four
different groups and transplanted with each group with the following solutions for one month: group I (non-saline control), group II, 100 mM NaCl,
group III, 0.05 mM SA, group IV, 100 mM NaCl+0.05 mM SA and to determine the physiological parameters (DW, FW, WC), chlorophyll contents,
carotenoid contents, lipid peroxidation, phenolics, lignin, alkaloid and enzymatic assays in each leaf pairs and roots.
SA exhibited growth-promoting property, which correlated with the increase of dry weight, water content, photosynthetic pigments and
soluble proteins. SA has additive effect on the significant increase in phenylalanine ammonia-lyase (PAL) activity, which is followed by an increase in
total soluble phenolics and lignin contents in all leaf pairs and root of C. roseus
. SA enhances malondialdehyde content in all leaf pairs and root. The
antioxidant enzymes (catalase, glutathione reductase, glutathione-S-tranferase, superoxide dismutase, peroxidase) as well as alkaloid accumulation
increased in all treatments over that of non-saline control but the magnitude of increase was found more in root. Further, the magnitude of increase of
alkaloid accumulation was significantly higher in 100 mM NaCl, but highly significant was found in presence of 0.05 mM SA and intermediate in
presence of both 0.05 mM SA+100 mM NaCl.
We concluded that applied SA to salt stress, antioxidant and phenolic metabolism, and alkaloid accumulation were significantly altered
and the extent of alteration varied between the SA and salt stress.