UVB Stress Induced Changes in Germination and Carbohydrate Mobilization in Chenopodium Quinoa Willd. Seeds

Chenopodium quinoa Willd. (quinoa) is a very promising crop due to its nutraceutical properties and strong tolerance to extreme conditions, including high UVB. However, the physiological mechanisms underlying its adaptation to high UVB are still unclear, especially during germination as its traditional sowing consists of either broadcasting or continuous stream distribution in furrows. We evaluated the response of germinating quinoa seeds to acute UVB radiation, looking at the mobilization of starch reserves as well as the utilization of starch and free sugars. Biometric and physiological traits were evaluated in control (0 W m−2) and UVB (3.4 W m−2)-exposed seeds during a 24 h treatment starting with seed imbibition. Quinoa exposed to UVB showed a delay in germination and strong reduction in root elongation. Although the negative effect of UVB on germination was fully recovered at 48 h of imbibition, that on root elongation was irreversible, especially with a longer exposure time. Further analysis showed low differences in the concentration of free sugars, except at 2 and 24 h of treatment. Furthermore, starch mobilization in UVB-treated seeds was strongly reduced compared to control. This was associated with the amylolytic activity analysis, which showed strong reductions in both α- and β-amylase activities during the whole treatment, indicating that UVB strongly reduced enzyme activation for the mobilization and use of starch reserves. Overall, these data suggest that quinoa seeds can regulate the expression of genes encoding enzymes involved in reserve mobilization, in order to resist to acute UVB radiation and maintain seed viability.