Effects of drought stress on phytosterols content and expression of key genes involved in Beta sitosterol biosysthesis pathway in medicinal plant pumpkin (Cucurbita pepo L.)

Biological stresses such as drought affect the production of secondary metabolites, especially plant sterols (phytosterols). Among the phytoestrols found in pumpkin seeds, betasitosterol is one of the most important components which also have many medicinal properties. In this study, the effect of five levels of drought stress on seed oil production and its phytosterols was studied in three genotypes and Styriaca variety of pumpkin (Cucurbita pepo L.). Analysis of phytosterols using GC/MS showed that increasing drought stress had a negative effect on oil production from pumpkin ripe seeds, but oil phytosterols, especially betasitosterol, increased and this increase was higher in Styriaca than other genotypes. To confirm these results, the seeds were harvested 15-30 days after flowering and the expression of SQS, PP2A, SMT2, ERG26 and Cycloartenol synthase genes involved in the phytosterol biosynthesis pathway was investigated. The results indicated that, among the different levels of drought stress and genes studied, highest expression level was observed at the rainfed level and at that time, betasitosterol and stigmasterol pathway had the main activity in steroid biosynthesis pathway in pumpkin.