Short-Term Ultraviolet (UV)-A Light-Emitting Diode (LED) Radiation Improves Biomass and Bioactive Compounds of Kale

Abstract

The aim of this study was to determine the influence of two types of UV-A LEDs on the growth and accumulation of phytochemicals in kale ( Brassica oleracea var. acephala ). Fourteen-day-old kale seedlings were transferred to a growth chamber and cultivated for 3 weeks. The kale plants were subsequently subjected to two types of UV-A LEDs (370 and 385 nm) of 30 W/m 2 for 5 days. Growth characteristics were all significantly increased in plants exposed to UV-A LEDs, especially at the 385 nm level, for which dry weight of shoots and roots were significantly increased by 2.22 and 2.5 times, respectively, at 5 days of treatment. Maximum quantum efficiency of photosystem II photochemistry (Fv/Fm ratio) began to decrease after 3 h of treatment compared to the control. The total phenolic content of plants exposed to the two types of UV-A LEDs increased by 25% at 370 nm and 42% at 385 nm at 5 days of treatment, and antioxidant capacity also increased. The two types of UV-A LEDs also induced increasing contents of caffeic acid, ferulic acid, and kaempferol. The reactive oxygen species (ROS) temporarily increased in plants exposed to the two types of UV-A LEDs after 3 h of treatment. Moreover, transcript levels of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), and flavanone 3-hydroxylase (F3H) genes and PAL enzyme activity were higher in plants treated with UV-A LEDs. Our results suggested that short-term UV-A LEDs were effective in increasing growth and improving antioxidant phenolic compounds in kale, thereby representing a potentially effective strategy for enhancing the production of phytochemicals.

Quantitative Analysis of UV-B Radiation Interception in 3D Plant Structures and Intraindividual Distribution of Phenolic Contents

“…Uneven UV-B irradiation and leaf developmental age could result in spatial heterogeneity of plant stress levels and responses within a whole plant. The photochemical activity of PSII, which is sensitive to UV-B exposure, has been measured by chlorophyll fluorescence and is considered to quantify the stress level on plants by various stressors, such as low temperature, drought, UV-A, and UV-B radiation [ 4 , 18 , 36 , 37 , 38 , 39 ]. Our previous study found that even within an individual plant, leaves more exposed to UV-B showed lower F v / F m values and higher contents of total flavonoid compounds [ 40 ].…”

Physiological and Metabolomic Responses of Kale to Combined Chilling and UV-A Treatment

“…Verdaguer et al [19] reported that UV-A radiation was absorbed directly into light-harvesting pigments such as chlorophylls and carotenoids; therefore, UV-A could promote plant growth under low-light intensities that did not reach the saturation point. In our previous study, the shoot fresh-weight of kale subjected to UV-A LED light with 370- and 385-nm peak wavelengths increased by 32% and 58%, respectively, when cultivated under a light intensity below the light saturation point [20]. In this study, it is likely that UV-A radiation contributed to the photosynthetic photon flux density (PPFD) by functioning as a supplemental light source and enhanced plant growth, as the PPFD supplied by plant growth light was 132 μmol m −2 s −1 , which was far below the light saturation point.…”

Elicitation of Chilling Tolerance of Pepper Seedlings Using UV-A LED

“…따라서, 높은 항산화능력을 보유한 식물은 불량한 환경스트레스에 대한 저 항성이 높다. 식물 생장에 해를 주지 않는 에너지 수준의 UV-A 조사는 식물의 환경 저항성을 증대시킬 수 있는 재배 기술로 활용될 수 있고, 식물의 파이토케미컬을 증대시키기 위한 UV-A와 관련된 많은 연구들이 진행되고 있다 [8,9,[13][14][15][16]. 실제로 UV-A 조사는 식물 세포벽 강화와 관련된 페 놀화합물, 프롤린, 수베린, 리그닌을 증가시키며 이러한 화합 물들은 저온 스트레스에 대한 내성을 증대시킨다고 보고되었 다 [14,17,18].…”

“…저온 처리 직 후, 두 UV-A 광 처리구의 항산화도는 대조구보다 유의적으로 높았 고 회복 기간 동안 두 UV-A 광 처리구와 대조구 모두 감소 하였다. [14,19,25,26]. 본 실험의 결과 UV-A 광 조사는 고추 묘의 Fv/Fm 값 을 0.8 이하로 감소시켰고 특히, 상대적으로 광양자 당 에너 지가 더 큰 370 nm UV-A에 의해 Fv/Fm 값이 유의적으로 감소되었다 (Fig.…”

“…기존 연구 [4] [4,26]. 따 라서 식물은 저온 저항성과 관련된 2차대사산물을 생성해 저 온에 의한 손상을 방어한다 [14,25]. 저온 처리 후 저온 스트 레스에 의해 대조구의 총 페놀화합물과 항산화도가 증가한 반면UV-A 광에 조사된 고추 묘의 총 페놀화합물은 증가하지 않았다 (Fig.…”