Anthocyanin Content of Red Leaf Lettuce Cv. Firecracker Grown Under Led's Is Enhanced with Ultraviolet Light

Future space missions beyond Low Earth orbit will expose crew members to higher doses of cosmic radiation than currently received onboard Space Shuttle or the International Space Station. A diet rich in bioactive phytochemicals is a potential radiation countermeasure to both reduce the effective radiation dose and induce in situ repair of radiation damage during these long-duration space missions. It has been shown that light quality can be use to increase the anthocyanins content, and thus, anti-oxidant value, of the salad crops. A series of experiments were conducted to determine the effect of UV-A (315-400 nm) and UV-B (285-315 nm) on the induction of anthocyanin in Lactuca sativa cv.  Firecracker (a red loose-leaf type).  Lettuce was grown in controlled environment chambers (EGC M-12 or EGC M-36, Environmental Growth Chambers, Chagrin Falls, OH) at 23^oC, 65% RH and 1200 mmol mol^-1 CO₂. An 18 h light/ 6 hr dark photoperiod was maintained at 300 μmol m^-2 s^-1. Three control treatments, red LEDs only (640 nm) ,  270 μmol m^-2 s^-1 red (640 nm) / 30 μmol m^-2 s^-1 blue (440 nm), and 300 μmol triphosphor fluorescent (TPF) were used.  UV-A treatments were applied with F8T5/BLB 130V 8W fluorescent lamp (385 nm max).  UV-B treatments were applied with F9BX/827/ECO 9W fluorescent lamp.   Treatments consisted of application of ~0.5 W m^-2 UV-A or UV-B either continuously through development , or during 14-21 days.  Lettuce was harvested at 21 DAP and dry mass, leaf area, plant height, anthocyanin content and oxygen radical absorbance capacity (ORAC) value determined.  The results clearly showed that blue light was required for the induction of anthocyanin formation in Firecracker.  This is consistent with previous research with cv. Outredgeous.   The addition of UV-A resulted in a slight increase in anthocyanin formation under TFP lamps, but not under red LED’s.  The addition of blue (440nn) to the LED treatments induced anthocyanin, but no additional response to UV-A was observed.  In marked contrast, all UV-B treatments induced additional anthocyanin formation in the red LED, red + blue LED, and TPF treatments.    The addition of UV-B during 14-21 DAP was more effective at inducing pigmentation than continuous exposure. These data suggest the bioprotective and nutraceutical value can be enhanced by selective management of UV applications under spectral conditions to optimize plant performance of cropping efficiency.