The use of different LEDs wavelength and light intensities for in vitro proliferation of cherry rootstock: influence on photosynthesis and photomorphogenesis

Plant growth and development are strongly influenced by light quality conditions in their environment. In this study, in vitro shoot proliferation, photosynthetic pigments, leaf anatomy and photosystem II photochemistry of Gisela 6 cherry rootstock (Prunus cerasus x Prunus canescens) were investigated. The culture medium used was the MS (Murashige and Skoog) containing 4.4 μΜ 6-benzyladenine (BA), 0.05 μΜ α-naphthalene acetic acid (NAA) and 0.3 μM gibberellic acid (GA) (30 days, 16 h photoperiod, 22 ± 2 °C). Initially, two different light wavelength absorption spectra: 400–700 nm provided by white fluorescent light lamps (mainly blue–green, BG at equal ratio 1:1; WFL-40) and, 430–690 nm provided by two Light Emitting Diodes (LED) types, differing in the spectral ratio of multiple light emitting wavelengths [LED2-40 (blue–red, BR) and LED3-40 (blue–green–yellow–orange–red, BGYOR)] were studied, under 40 μmol m s of light intensity. Following that, three LED intensities-20 (LED1-20), 40 (LED2-40), and 120 μmol m s (LED4-120) were investigated under BR spectrum. WFL-40 exhibited non-significant differences with LED2-40 (shoot number 4.25, proliferation rate 4.30, shoot height 0.91 cm). LED2-40 displayed higher fresh and dry shoot biomass, better PSII functionality, increased Chl a/b, Chl b and carotenoids content as well as decreased number of stressed explants. Leaf anatomy under LED2-40 and WFL-40 was similar. LED4-120 presented the highest rate of stressed explants, with their leaf anatomy being severely affected, as leaves had a reduced mesophyll cell density. In LED4-120, the proportion of the absorbed energy used in photochemistry (Φ) was decreased whereas the increased quantum yield of non-regulated energy loss in PSII (Φ) could not be compensated by the increased photoprotective energy dissipation (Φ). Therefore, LED2-40 is proposed as the most beneficial for growing cherry rootstock Gisela 6 plantlets in vitro.