Pulses of low-intensity red light inhibit the expression of chlorophyll degradation genes during postharvest senescence of kale leaves.

BACKGROUND

Kale is a leafy vegetable rich in phytochemicals that promote health. After harvest, leaf senescence is induced, and kale turns yellow due to the degradation of chlorophyll. Previous studies have shown that low-intensity red light pulses delay postharvest senescence in kale. This effect may be mediated by phytochromes activated by red light. The effect of low-intensity red-light LED treatment on the expression of genes involved in chlorophyll degradation (NYC1, NOL, SGR, PPH, and PAO) and genes encoding senescence-associated transcription factors related to the phytochrome signaling cascade (PIF4, ORE1, and WRKY6) was examined in this work.

METHODS AND RESULTS

Kale leaves were treated daily with red-light-LED (22 ± 3 µmol m s) for 1 h and then were stored in the dark together with untreated leaves. Samples were taken during storage to perform biochemical and gene analysis. A close correlation was found between chlorophyll degradation and the gene expression of NYC1, SGR, and PAO in control leaves. Red light treatment caused a strong inhibition of these gene expressions, which explains the retention of chlorophylls. PIF4 and WRKY6 were not upregulated at the expression level in the dark, while red light induced that expression only for a short time. ORE1 expression increased in darkness and was inhibited by red treatment.

CONCLUSION

Red light treatment preserved chlorophyll by the strong inhibition of NYC1, SGR, and PAO expression in irradiated leaves. The expression of ORE1 increased in darkness and was inhibited by red treatment, as was expected in the red light-activated phytochrome signaling cascade.