Influence of colorful light-emitting diodes on growth, biochemistry, and production of volatile organic compounds in vitro of Lippia filifolia (Verbenaceae).

Lippia filifolia Mart. & Schauer belongs to the Verbenaceae family and it is endemic from the rupestrian fields of the Espinhaço mountain range, located in Minas Gerais, Brazil. It is an aromatic species with medicinal potential due to the production of volatile compounds that constitute its essential oil. The objective of this work was to evaluate the effects of light quality using light-emitting diodes (LEDs) over the growth of L. filifolia grown in vitro after 45 days of culture, analyzing its volatile organic compounds (VOCs), biochemical, and biometric traits. This study had four treatments according to the wavelength of LED lamps: (i) white (control), (ii) blue, (iii) red, and (iv) a combination of red + blue (mix). The light quality influenced the growth, metabolism, and VOCs production of plantlets. The specimens showed higher height under red and white treatments and higher biomass accumulation, nodal segments, and shoot numbers under the mix treatment. Higher total carbohydrate content was also observed on the mix treatment, while the white LED provided higher chlorophylls and carotenoids contents. In addition, the lipid peroxidation was more pronounced in mix and white LEDs treatments, and it was also observed significant but not quite changes in VOCs profiles due to light quality. Eucalyptol was the compound found in a higher concentration among the VOCs of L. filifolia grown in vitro at all light quality treatments studied.

Alternating temperature combined with darkness resets base temperature for germination (Tb ) in photoblastic seeds of Lippia and Aloysia (Verbenaceae).

Thermal time models for seed germination assume a continuum of rate responses in the sub-optimal temperature range. Generally, the models describe germination performance in non-dormant seeds at constant temperatures, yet alternating temperature (AT) is a feature of many natural environments. We studied the possible interacting effects of AT on germination progress in photoblastic seeds of three aromatic-medicinal Verbenaceae species in the genera Lippia and Aloysia. For Lippia turbinata f. turbinata and L. turbinata f. magnifolia seed, germination only occurred in light conditions, while for L. integrifolia and Aloysia citriodora it was significantly higher in the light than in darkness. Although relative light germination (RLG) was not different between constant and AT in the sub-optimal range, AT raised the base temperature for germination progress (Tb ) from ca. 3-6 °C in constant temperature to 7-12 °C in AT. Among the species, thermal time for 50% seed germination [θT(50) ] was 55-100 °Cd at constant temperature. Although AT resulted in slight modifications to θT(50) , the germination rate at comparable average temperatures in the sub-optimal range was slower than under constant temperatures. For all species, the proportion of germinated seeds was similar for constant and AT. Our results suggest that an interaction between cool temperature and darkness during AT treatment limits the temperature range permissive for germination in these positively photoblastic seed, reflecting both close adaptation to the natural ecology and niche requirements of the species.