Analysis technique for determination of Chlorophyll Fluorescence, Photosynthetic Pigments / Gas Exchange and Carbohydrates of 3 Vegetables under different combination of Red and Blue-LED


Analysis technique for determination of Chlorophyll Fluorescence, Photosynthetic Pigments / Gas Exchange and Carbohydrates of 3 Vegetables under different combination of Red and Blue-LED


This practical was carried out to investigate the different combinations of red- and blue LED on chlorophyll fluorescence, photosynthetic pigments, photosynthetic gas exchange and carbohydrate in Lettuce (Lactuca sativa), Kai Lan (Brassica albograblac) and the green Chinese Basil (Perillafrutescen). Secondly, this was done to learn the analysis technique for determination of chlorophyll fluorescence, photosynthetic pigments, photosynthetic gas exchange and carbohydrate. After germination, all plants were grown under natural sunlight for two weeks with half strength of complete nutrition solution for the first week followed by full strength of complete nutrition solution for the second week. The plants were then exposed to different red- and blue-LED lighting at fluctuating ambient temperatures of between 260C and 360C. The root zone temperature was set at 250C throughout the experimental period and all plants were cultured with a 16-h photoperiod of light.

In recent, times the use of chlorophyll as a tool for analysis in plant physiology is making researchers to make informed decisions on factors that affect growth and plant processes. Chlorophyll fluorescence analysis has been applied as a rapid non-destructive tool to obtain information about the state of photosynthetic apparatus and especially photosystemII (PSII) [ CITATION Oso04 l 1033 ]. It can be used as a probe of photosynthetic activity since the intensity of chlorophyll fluorescence varies with changes in photosynthetic metabolism that underlies photosynthesis. For autotrophic plants, some of the factors that affect growth are photosynthetic active radiation (PAR) and Photosynthetic Photon Flux Density (PPFD). PAR between 400nm and 700nm is the major environmental factor controlling growth in autotrophic plants [ CITATION Bul08 l 1033 ]. The use of light emitting diodes (LED’s) in research in plant physiology is increasingly being used in lighting for tissue culture and supplementing photoperiod lighting in greenhouse [ CITATION Mor08 l 1033 ]. The LED’s are designed to produce radiation in the red region of the spectrum that coincides with the maximum absorption of chlorophyll [ CITATION Bul08 l 1033 ]. On the other hand, blue light strongly affects growth and development of higher plants. Studies have shown that an increase of blue light enhanced accumulation of sugars and that fluorescent light mixed with R or B LED resulted in improved morphology, greater biomass and higher pigment content of Lettuce plant [ CITATION Xia14 l 1033 ]. Consequently, LED’s provide a unique flexibility for composing the optimal spectrum for plant cultivation thereby stimulating a wide variety of physiological processes [ CITATION Tam04 l 1033 ]. Photosynthetic rate also tends to increase with an increase in blue light [ CITATION Ryo07 l 1033 ]. Plants grown under blue light showed a higher rate of leaf photosynthesis than plants grown under red light. In determining chlorophyll fluorescence in this study, the parameters considered in determining chlorophyll fluorescence include Electron Transfer Rate (ETR), Photochemical quenching qP, non photochemical quenching NPQ, CO2 assimilation rate, Stomatal conductance, and internal CO2 concentration. It has been established that stomatal regulation of gas exchange by leaves is of great importance to the plants. Light affects stomatal movements just as much as water and CO2 concentration does. Bright light and low CO2 concentration cause the stomata to open and high concentration of CO2 causes the stomata to close [ CITATION Hye04 l 1033 ]. Blue light between 430nm and 460nm was nearly ten times more effective than red light between 630nm and 680nm in producing a conductance of 0.15µmol-2s-1 [ CITATION Hye04 l 1033 ]. Studies also indicate that CO2 assimilation rate, stomatal conductance, and rate of stomatal opening optimize CO2 photosynthetic uptake and minimize tranpirational water loss from leaves [ CITATION Bar08 l 1033 ]. It has also been shown that blue light helps to boost the acclimation responses of energy partitioning in PSII and CO2 assimilation to high irradiance [ CITATION Mat08 l 1033 ]. In this study, different blue light photon flux densities of 10B, 20B, 30B, and 40B were used with the spectral treatments expressed as the blue light percentage [ CITATION Hog10 l 1033 ].

Methods and material


Data collected from the experiment was tabulated and recorded as in the tables in appendices. The figures below give a presentation of the data in graphical form drawn to determine chlorophyll fluorescence in the three plants mentioned using the parameters indicated.

Chlorophyll Fluorescence in Kai Lan.

Figure 1: ETR graph for Kai Lan

Figure 2: NPQ graph for Kai Lan plant

Figure 3: qP graph for Kai Lan plant

Figure 4: Chlorophyll fluorescence chart for Kai Lan

Chlorophyll Fluorescence in Basil

Figure 5: ETR graph for Basil plant

Figure 6: qP graph for Basil plant

Figure 7: NPQ graph for Basil plant

Figure 8: Chlorophyll fluorescence chart for Basil plant.

Chlorophyll Fluorescence in Lettuce plant.

Figure 9: ETR graph for Lettuce plant.

Figure 10: qP graph for Lettuce plant.

Figure 11: NPQ graph for Lettuce plant.

Figure 12: Chlorophyll fluorescence chart in Lettuce plant.


Studies have shown that Lettuce plants have high soluble sugar content under RBW LED’s [ CITATION The13 l 1033 ]. Studies have also shown that spectral quality (red and a combination of red and blue LED’s) of light influences the morphogenesis and diverse physiological response of plants thereby improving development and increasing carbohydrate accumulation [ CITATION Sam10 l 1033 ],and that Implementation of LED based illumination for plant cultivation relies on improving the performance and lowering the prices of high power LED’s [ CITATION Tam05 l 1033 ]. Based on photosynthetic active radiation ranging from 1 to 1585, the electron transfer rates increase with an increase in PAR but gradually drops after reaching PAR levels beyond 715. In the graphs for photochemical quenching, an increase in PAR results in a sharp drop which eases at PAR 205 but gradually drops to its lowest points at PAR 1585. The non photochemical quenching graphs are more or less hyperbolic rising as the PAR is increased from 1 to 1585. An increase in the electron transfer rate realized in this study confirms an increase in carbon fixation or photosynthesis to optimized levels even with varying percentages of Blue light exposures. This conforms to results obtained on exposure to RBW LED’s. The results obtained in this study also indicate that optimal levels of photosynthesis can be achieved by reducing photochemical quenching and increasing non photochemical quenching. In lettuce plants, the study indicated that as the treatments varied from 10B to 40B, the amount of free sugars dropped from 0.15 to 0 implying that the soluble sugars were converted fully to insoluble sugars. This was not the case in Basil and Kai Lan plants. In Basil plants, the treatment at 30B greatly increased stomatal conductance resulting in a higher transpiration rate (6.17) and increased CO2 assimilation (0.52). Interestingly in Kai Lan plants, treatment at 30B exhibited the highest level of free sugars (1.04) against the lowest levels of stomatal conductance (0.56) and CO2 assimilation (20.37). There were more of soluble sugars than insoluble sugars, a quality that was not shown in Lettuce and Basil plants. But, in all the three plants, the total amount of chlorophyll a and b was highest at a treatment of 30B indicating a higher level of photosynthetic activity. These results confirm that varying the levels or percentage of blue light will affect photosynthesis in plants and in this case a 30% combination of blue light accumulates more chlorophyll in the leaves of the three plants.


Chlorophyll fluorescence is important in determining, and analyzing photosynthetic activities and processes in plants. When photochemical quenching is reduced to negligible levels, maximum fluorescence is achieved and consequently optimizing photosynthetic activities and processes of the plant. Electron transport is therefore closely related to photosynthesis as a process which ultimately results in carbon fixation. However, much more should be done to establish a standard analytical tool from chlorophyll fluorescence. It is also evident from this study that varying percentage of blue light in a given radiation increases chlorophyll fluorescence and photosynthetic activity in the leaves of a plant.


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