Red Light-emitting Diode Light Irradiation Improves Root and Leaf Formation in Difficult-to-propagate Protea cynaroides L. Plantlets In Vitro

Abstract

<jats:p>The effects of light quality emitted by light-emitting diodes (LEDs) on the growth and morphogenesis, and concentrations of endogenous phenolic compounds of <jats:italic>Protea cynaroides</jats:italic> L. plantlets in vitro, were investigated. Plantlets were cultured under four light treatments: conventional fluorescent lamps (control), red LEDs (630 nm), blue LEDs (460 nm), and red + blue LEDs (1:1 photosynthetic photon flux). Four phenolic compounds extracted from the plantlets were analyzed: 3,4-dihydroxybenzoic acid, gallic acid, caffeic acid, and ferulic acid. The highest rooting percentage was observed in plantlets cultured under red LEDs (67%) compared with 7% under conventional white fluorescent light, 13% under blue LEDs, and 13% under red + blue LEDs. The highest number of roots per plantlet was also found under red LEDs, whereas a significantly lower number of roots per plantlet was obtained under the other light treatments. Furthermore, red light promoted the formation of new leaves in <jats:italic>P. cynaroides</jats:italic> plantlets. However, the highest leaf dry weight (53.8 mg per plantlet) was found in plantlets irradiated by the combination of red and blue LEDs. Phenolic analyses showed that the lowest concentrations of 3,4-dihydroxybenzoic acid (4.3 mg·g<jats:sup>−1</jats:sup>), gallic acid (7.0 mg·g<jats:sup>−1</jats:sup>), and ferulic acid (7.4 mg·g<jats:sup>−1</jats:sup>) were detected in plantlets exposed to red light, whereas those irradiated by white fluorescent light contained the highest concentration. A significant inverse correlation (<jats:italic>r</jats:italic> = –0.419) was established between 3,4-dihydroxybenzoic acid and rooting percentage. Strong inverse correlations were also established between 3,4-dihydroxybenzoic acid and number of roots per plantlet (<jats:italic>r</jats:italic> = –0.768) as well as between ferulic acid and number of roots per plantlet (<jats:italic>r</jats:italic> = –0.732). These results indicate that the stimulation of root formation in <jats:italic>P. cynaroides</jats:italic> plantlets under red LEDs is the result of the low endogenous concentrations of 3,4-dihydroxybenzoic acid and ferulic acid.</jats:p>

Effects of Light Quality on Vegetative Cutting and In Vitro Propagation of Coleus (Plectranthus scutellarioides)

“…homeostasis, transport, and signaling were controlled in a light-dependent manner in Arabidopsis Sorin et al, 2005). Red light was reported to enhance rooting of Jatropha curcas, allowing 80% survival rate after acclimatization (Daud et al, 2013) and improve lateral root formation rate up to 67% in Protea cynaroides from 7% of white fluorescent light due to reduced endogenous 3,4-dihydroxybenzoic acid and ferulic acid (Wu and Lin, 2012). Low intensity of red light (45 mmol · m -2 · s -1 ) also signifi-cantly increased root number and shoot weight in strawberry propagated in vitro (Nhut et al, 2003).…”

“…Red light (650-660 nm) has been reported to enhance adventitious root formation in grapes (Poudel et al, 2008), Ficus benjamina (Gabryszewska and Rudnicki, 1994), and Protea cynariodes (Wu and Lin, 2012). In Arabidopsis, phytochrome A and B (PHY A and PHY B) mediate the positive phototropic responses to red light, and these two photoreceptors are involved in the modification of local endogenous auxin levels .…”

Photobiology in protected horticulture

“…). When Wu and Lin () propagated Protea cynarodies plantlets under red LED light, 67% rooted compared to 7% under conventional fluorescent tubes, and 13% rooted under blue light or a red:blue (50:50%) LED light combination. Root development was also found to be more extensive under the red light treatments.…”

Effect of Light Quality and Quantity on the Accumulation of Flavonoid in Plant Species

“…Red net and 100% irradiance yield the lowest flavonoid content while the highest accumulation of flavonoid was observed under blue net [52]. This is also true for Prutea cynaroides [61] but not true for Zingiber officinale [14]. The quality and quantity of irradiance is important for accumulation of flavonoid [52].…”