Cold Stress-induced Seed Germination and Biosynthesis of Polyphenolics Content in Medicinally Important Brassica rapa

Background: : Brassica rapa is an annual to biennial herb, cultivated worldwide, and mostly adapted to temperate climates. It is commonly cultivated in many countries as edible vegetable and for the production of vegetable oil for growing population. However, the fluctuation in temperature greatly affect the plant growth and development and the production of bioactive compounds. Thus the current study aim to investigate the effect of cold stress on seed germination, biomass gain, and biosynthesis of polyphenolics content in medicinally important Brassica rapa. Methods: : In order to investigate cold stress on seed germination, biomass gain, and biosynthesis of polyphenolics content, the authenticated seeds of Brassica rapa were collected from PCSIR Labs Complex, Peshawar-Pakistan. The surface sterilized seeds were keep under control temperature to germinate and then the geminated seeds were treated with cold stress of 72 hours (3 days), 144 hours (6 days), 216 hours (9 days) and 288 hours (12 days). Results: : In this study, 72 hours (T1=3 Days) of cold stress was found to be the best treatment for radicle development (152 mm) as compared to control (95 mm). However, 144 hours of cold stress (T2=6 Days) suppressed radicle development (69 mm) compared to the control. The cold treatments (T3=216 and T4=288 hours) also reduced radicle development. The radicle length in the dark was very elongated (105 mm) compared to control. Furthermore, the minimum cold stress of 72 hours promoted plumule development (55 mm) compared to the control (42 mm). However, other cold treatments reduced the growth of plumule. The seeds placed in dark incubation produced maximum plumule length (115 mm) compared to control and other treatments. The increasing doses of cold stress gradually reduced biomass accumulation. Currently, 72 hours and dark incubation improved biomass accumulation. The cold treatment of 72 hours induced maximum production of phenolics content (2.61 mg/g-DW). However, cold stress of 216 hours produced 0.892 mg/g-DW flavonoids content. Conclusion: : Our study found that duration of cold stress is inversely proportional to the radicle and the plumule length of the plantlets. Also we found that cold stress of 72 hours (3 days) promoted seed germination while 288 hours of cold stress reduced germination in Brassica rapa. Finally our study suggests further improvement of Brassica species and its use as medicinal herb and need to understand the molecular mechanism involve during cold stress to protect plants from such abiotic stresses.