Growth characteristics and phytochemicals of canola (Brassica napus) grown under UV radiation and low root zone temperature in a controlled environment

Abstract

We determined the effects of UV radiation and low root zone temperature on growth characteristics and phytochemicals of Brassica napus (canola) cultivated in a controlled environment (25/20 degrees C 16/8 [light/dark]; 70% relative humidity; 1000 mu mol mol(-1) CO2 with photosynthetic photon flux density of 100 and 200 mu mol m(-2) s(-1) for 7 and 18 days, respectively). The 18-day-old B. napus plants were treated for 5 days with two nutrient solution-temperature regimes (normal temperature [NT] and low-temperature [10 degrees C; LT]) and three levels of UV radiation (0, 0.3, and 0.6 W m(-2)). Treatment with 0.6 W m(-2) UV decreased quantum efficiency of photosystem II the most. Most growth characteristics decreased under LT + UV treatments. Treatments with 0.6 W m(-2) UV, compared to those without UV, significantly inhibited shoot height. LT + 0.3 and +0.6 UV decreased shoot height the most. Temperature (T) x UV interaction did not affect most growth characteristics except leaf area, specific leaf weight, and shoot water content. Antioxidant capacity (total ORAC) resembled lipophilic ORAC and showed the highest value in the LT + 0.6 UV treatment. T x UV interaction did not affect ORAC values, although LT + 0.3 UV and LT + 0.6 UV treatments produced the highest values. Both LT and UV radiation enhanced the total phenolic content, and in the combined treatments, it was two times that of the control. UV intensities (0.3 and 0.6 W m(-2)) remained constant regardless of variation in root zone temperature. UV radiation enhanced total flavonoid content equally across different intensities; LT + 0.6 W m(-2) UV treatment produced a relatively high value. Thus, LT and UV negatively affected plant growth parameters, except total dry weight, whereas LT, UV, or LT + UV positively affected antioxidant properties, total phenolics, and flavonoids, suggesting the potential of using an LT treatment in a hydroponic system as well as UV radiation to enhance growth performance of greenhouse and factory plants.