LED lighting affects the biomass accumulation and leaf stomatal characteristics of raspberry (Rubus idaeus L.) in vitro

Light-emitting diodes (LEDs) have become an alternative light source to the fluorescent lamp (FL) for the maintenance of plant tissue cultures due to their low heat emission, low power consumption and the ability to fine-tune the light spectrum. In this study, the effect of LEDs on the growth and leaf stomata features of in vitro cultivated raspberries (Rubus idaeus L. 'Lloyd George') was examined. The plantlets were grown in vitro under a lighting system based on the Philips GreenPower LED research module. Four groups of LEDs emitting white (W), red (R), blue (B), and mixed (W:R:B: far red = 1:1:1:1) lights and FL (control) were used. As a second control (marked as EV), plants grown in the multiplication and rooting stage under fluorescent lamps and then acclimatized ex vitro in a greenhouse for 90 days in natural light were included. Relative growth rate (RGR), protein content as well as stomata morphology and density of the plantlets were analysed after three passages under corresponding light treatment. The results show that different LEDs specifically affect the growth and size of leaf stomata and density of in vitro cultured raspberry plants and can be applied as an effective modulator of morphogenesis during micropropagation. The combination of white, blue, red and far red LED stimulated the accumulation of biomass and proteins, as well as the formation of a higher number of stomata on the lower surface of the leaves, which would be a prerequisite for more effective control of water loss from plantlets during the ex vitro acclimatization.