In recent years, light emitting diodes (LEDs), due to their low energy consumption, low heat emission and specific wavelength irradiation, have become an alternative to fluorescent lamps (FLs) in plant tissue culture. The aim of this study was to investigate the effects of various LED light sources on the in vitro growth and rooting of plum rootstock Saint Julien (Prunus domestica subsp. insititia). The test plantlets were cultivated under a Philips GreenPower LEDs research module illumination system with four spectral regions: white (W), red (R), blue (B) and mixed (W:R:B:far-red = 1:1:1:1). The control plantlets were cultivated under fluorescent lamps (FL) and the photosynthetic photon flux density (PPFD) of all treatments was set at 87 ± 7.5 μmol m⁻² s⁻¹. The effect of light source on the selected physiological, biochemical and growth parameters of plantlets was monitored. Additionally, microscopic observations of leaf anatomy, leaf morphometric parameters and stomata characteristics were carried out. The results showed that the multiplication index (MI) varied from 8.3 (B) to 16.3 (R). The MI of plantlets grown under mixed light (WBR) was 9, lower compared to the control (FL) and white light (W), being 12.7 and 10.7, respectively. In addition, a mixed light (WBR) favored plantlets’ stem growth and biomass accumulation at the multiplication stage. Considering these three indicators, we could conclude that under the mixed light, the microplants were of better quality and therefore mixed light (WBR) was more suitable during the multiplication phase. A reduction in both net photosynthesis rate and stomatal conductance in the leaves of plants grown under B were observed. The quantum yield (Yield = F_V/F_M), which represents the potential photochemical activity of PS II, ranged from 0.805 to 0.831 and corresponded to the typical photochemical activity (0.750–0.830) in the leaves of unstressed healthy plants. The red light had a beneficial effect on the rooting of plum plants; the rooting was over 98%, significantly higher than for the control (FL, 68%) and the mixed light (WBR, 19%). In conclusion, the mixed light (WBR) turned out to be the best choice during the multiplication phase and the red LED light was more suitable during the rooting stage.

Light quality and duration profoundly influence the growth and productivity of plant species. This study investigated the effects of a blue–red LED light combination, known to induce flowering, on the physiological state and content of biologically active substances in catmint (Nepeta nuda L.) grown under controlled in vitro conditions. White light (W) was used as a control and compared with two blue–red intensities: BR (high-intensity blue–red light) and BRS (low-intensity blue–red light or “BR with shadow”). BR-treated plants showed increased leaf area, mesophyll thickness, biomass and starch content but reduced levels of plastid pigments. BR also modified the oxidative state of plants by inducing lipid peroxidation while simultaneously activating ROS scavenging mechanisms and enhancing phenolic antioxidants. Interestingly, BR decreased the accumulation of the Nepeta sp.-specific iridoid, nepetalactone. These effects appear to be regulated by the phytohormones auxin, abscisic acid and jasmonates. BRS treatment produced effects similar to the W control but led to increased plant height and reduced leaf area and thickness. Both BR and BRS regimes induced the accumulation of proteins and amino acids. We conclude that blue–red light can enhance the survival capacity of micropropagated N. nuda during subsequent soil adaptation, suggesting that similar light pre-treatment could improve plant performance under stress conditions.

The leaf anatomy and chloroplast ultrastructure of Nepeta nuda L. plantlets regenerated in vitro from cryopreserved shoot apical meristem and in vitro-micropropagated plantlets were studied comparatively to assess whether cryoprocedure affected leaf morphogenesis. Both postcryo and in vitro plantlets failed to develop a distinguishable palisade layer, making the mesophyll appear homogeneous. Significant damage to the chloroplast envelope and substantial thylakoid ruptures were also observed. We assumed that the specific in vitro conditions more likely affected the structures than the cryotreatment itself. Light and transmission electron microscopy observations were also carried out on newly formed leaves of ex vitro-adapted plants. The examined leaf features were similar to those in the in situ plants – bifacial leaf lamina, double-layered palisade parenchyma, loosely arranged spongy parenchyma cells, and chloroplasts with intact envelope and evenly distributed throughout the stroma internal membrane system. The obtained histological and ultrastructural results revealed the retained morphogenetic potential of N. nuda plants and proved cryopreservation as a suitable method for long-term storage. The leaf anatomy and chloroplast ultrastructure of Nepeta nuda L. plantlets regenerated in vitro from cryopreserved shoot apical meristem and in vitro-micropropagated plantlets were studied comparatively to assess whether cryoprocedure affected leaf morphogenesis. Both postcryo and in vitro plantlets failed to develop a distinguishable palisade layer, making the mesophyll appear homogeneous. Significant damage to the chloroplast envelope and substantial thylakoid ruptures were also observed. We assumed that the specific in vitro conditions more likely affected the structures than the cryotreatment itself. Light and transmission electron microscopy observations were also carried out on newly formed leaves of ex vitro-adapted plants. The examined leaf features were similar to those in the in situ plants – bifacial leaf lamina, double-layered palisade parenchyma, loosely arranged spongy parenchyma cells, and chloroplasts with intact envelope and evenly distributed throughout the stroma internal membrane system. The obtained histological and ultrastructural results revealed the retained morphogenetic potential of N. nuda plants and proved cryopreservation as a suitable method for long-term storage.