weight. Photosynthetic pigment levels were lower under LED light compared to control lamps. Phenolic acids and flavonoids were identified in M. communis leaf extracts. Myricetin was the major constituent with highest concentration under red LEDs and highest BA level. Keywords Myrtle · Light quality · Photosynthetic pigments · Secondary metabolites · HPLC Abbreviations LED Light emitting diode B 100% blue LED RB 70% red and 30% blue LED R 100% red LED C Control fluorescent light BA 6-Benzyladenine NAA 1-Naphthaleneacetic acid MS Murashige and Skoog medium HPLC High performance liquid chromatography PPFD Photosynthetic photon flux density Communicated by Sergio J. Ochatt.
A mixture of red and blue light-emitting diodes (LEDs; at a ratio of 7:3, respectively) were used to analyze the effects of different photosynthetic photon flux densities (PPFDs) (40, 80, and 120 µmol m−2 s−1 hereafter known as LED 40, 80, and 120, respectively) on the micropropagation of Gerbera jamesonii Bolus shoots. The experiment also examined the effect of 6-benzyladenine (BA) in 1, 2.5, and 5 µM concentrations in the media. Biometrical observations and analyses of leaf morphometry and photosynthetic pigment content were conducted. Shoot multiplication increased with an increasing BA concentration. A PPFD of 80 µmol m−2 s−1 and 5 µM BA is suggested as efficient for shoot propagation and economically viable. LED 120 increased the leaf blade area and its width, and circularity and elongation ratios. The intensity of light did not affect the fresh weight, which increased at higher BA concentrations (2.5 and 5 μM). The dry weight content decreased with increasing cytokinin concentration; the greatest content was observed on media with 1 µM BA under PPFD 120 µmol m−2 s−1. LED 80 increased the photosynthetic pigments content in the leaves in comparison to the standard intensity of LED 40. Increased BA concentration raises the content of chlorophyll a.
The experiment was carried out in the winter and autumn of 2011 using lamb's lettuce (Valerianella locusta Laterr. Em Betce) as a test plant under greenhouse growing conditions. The aim of the study was to evaluate the effect of a prolonged day with modern SSL LED (Solid State Lighting Light Emitting Diodes) technology on photosynthetic parameters and plant yield. Two kinds of LED lamps with different spectral properties were used. The first emitted a white light and the second a mixture of red and blue light. Measurements of chlorophyll fluorescence and gas exchange were taken in natural and artificial light. Control plants were not treated with additional lighting. During the day with natural light in March (winter growing), photosynthesis intensity, stomatal conductance and transpiration of lamb's lettuce leaves were higher than in November (autumn growing). In the evening hours of March and November, during artificial plant lighting, similar photosynthesis intensity was observed. This intensity was significantly higher than in the afternoon hours (by natural light) in the autumn. The highest content of chlorophyll a, b and carotenoids was found in the treatment with red+blue LEDs in winter growing. Supplemental lighting with red+blue LED light stimulated the high efficiency of the photosynthetic apparatus, which was manifested by the highest Performance Index (PI). The highest weight of the rosettes was noted in the autumn growing period in plants that were under the influence of the red+blue supplemental lighting followed by the white LED. This could be the result of a significant stimulation of photosynthesis during supplemental lighting with the LED lamps during this period.
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