The impact of cold stress on genes expression pattern of mono- and sesquiterpene biosynthesis and their contents in Ocimum basilicum L.

Basil (Ocimum basilicum L.) contains valuable monoterpene and sesquiterpene compounds used for medical purposes. Environmental stresses are suggested to change the essential oil composition in medicinal plants. In the current investigation, an experiment was arranged in greenhouse to study the effect of cold stress on genes expression patterns of linalool synthase (LIS), beta-myrcene synthase (MYS), gamma-cadinene synthase (CDS), germacrene D synthase (GDS) and geraniol synthase (GES) which is involved in monoterpenes and sesquiterpenes biosynthesis in O. basilicum. The monoterpenes and sesquiterpenes composition and content were also investigated. Plants were exposed to temperatures 22 (control), 4 and 10 degrees C at 6 to 8 leaf stage for 12, 24 and 48 h. The genes expression levels were determined by real time PCR in plant leaves. Essential oil was extracted at flowering stage by distillation using Clevenger apparatus and its compounds were identified using gas chromatography/mass spectrometry (GC-MS). The results revealed that the LIS expression increasingly occurred to 4.86 fold at 10 degrees C after 12 h while that of GES reached to 5.7 fold at 10 degrees C after 48 h. Temperature 4 degrees C for 12 h increased the expression levels of MYS and GDS genes to 41.5 and 14.2 fold, respectively, while the expression level of CDS increased to 25.5 fold at 4 degrees C for 48 h. Significant differences (P <= 0.01) were observed among treatments with respect to all compounds except alpha-pinene and camphene. The maximum proportion of geraniol and gamma-cadinene were observed at 4 degrees C for 24 h, while the maximum proportion of germacrene D and alpha-bergamotene obtained at 10 degrees C for 12 h. The highest proportion of 1, 8-cineole was achieved at 4 degrees C for 48 h. Positive associations between germacrene D content and GDS expression (r = 0.8, P <= 0.05) and gamma-cadinene and CDS expression (r = 0.78, P <= 0.05) proposed that the content of terpenoid compounds in basil can be enhanced through increasing the expression levels of genes involved in their biosynthesis.