2018 ASHS Annual Conference

Previous studies have demonstrated the impact of light quantity and quality on anthocyanin accumulation in red leaf lettuce. In this experiment we studied the effect of a 48-hr spectral shift on the temporal dynamics of pigment concentrations and expression of genes in the anthocyanin pathway. Seedlings of lettuce (Lactuca sativa) ‘Rouxai’ were grown for 18 days from seeding under white (broad spectrum) light emitting diodes under sole source light in environment controlled growth chambers. Growth chamber temperature was 23 °C and a light intensity of 185-200 µmol·m^-2·s^-1 with a 24 hr photoperiod was provided. At 18 days, the light source was switched to cool white fluorescent (CWF) fixtures providing continuous light at 185-200 µmol·m^-2·s^-1 for 48 hr. Anthocyanin and chlorophyll concentration, and expression of anthocyanin pathway genes were measured. Following shift to CWF, leaf color gradually became darker red over time. The CWF spectrum stimulated the biosynthesis of total anthocyanin and chlorophyll a and b. For all pigments measured, highest concentrations were observed in plants which were shifted from white LEDs to the CWF spectrum for 42h. To determine the molecular regulation of pigment biosynthesis by the light spectrum, we examined the expression of anthocyanin and chlorophyll a/b-binding proteins genes using real-time PCR. Anthocyanin biosynthesis genes (CHS, DFR, ANS and UFGT) and chlorophyll a/b-binding proteins genes (Lhca1-4 and Lhcb1) exhibited increased expression in response to CWF. While pigment accumulation, also tended to increased over time, response lagged several hours behind gene expression. Interestingly, while the experiment was conducted with continuous lighting, a pattern of 24 hr oscillations in gene expression were evident suggesting that genes responsible for pigment accumulation were regulated by both light treatment as well as circadian rhythm. Our findings help elucidate the role of the chlorophyll and anthocyanin pathway genes in response to light spectrum and suggest further study to understand the involvement of circadian clock genes in the regulation of anthocyanin and chlorophyll pathways.