QUANTIFYING PHOTOPIGMENTS VIA HIGH PERFORMANCE LIQUID CHROMATOGRAPHY AND SPECTROSCOPY

Matthew Adner, Anna Testorf

Overview

Plant pigment biochemistry is known to change during environmental stress. This work investigates the influence of artificial light-induced stress by exposure to light sources of varying wavelength and irradiance. Receiving too much or too little light energy at certain wavelengths changes the concentration of plant pigments, including chlorophylls and carotenoids. Broad-leafed bean plants, Phaseolus vulgaris, were exposed to different artificial light sources including: broad spectrum grow-lights (420nm-480nm and 590nm-700nm), fluorescent lights (sporadic spectrum between 400nm and 850nm), colored LEDs (blue:415nm-500nm, green:470nm-600nm, red:590nm-660nm), and UV lights (370nm-450nm). Plants were grown under the following conditions: a grow-light, a grow-light with UV light, a red-blue LED with equal intensity spectral components, a red-blue LED with UV light, a UV light, a florescent light, a green LED, and no light. Measurement of pigment concentration following light exposure was done using High Performance Liquid Chromatography (HPLC) and UV-Vis spectroscopy. UV-Visspectroscopy measured initial critical increase of light absorbance of an intact leaf. HPLC found the highest concentration of pigments in plants exposed to red-blue LED light. Grow-lights, with and without UV light, produced lower pigment concentrations than red-blue LED light. Adding UV light to the red-blue LED showed the lowest pigment concentration. A slightly higher pigment concentration was seen with only UV light than the combinations of red-blue LEDs with UV light. The UV-Vis absorption spectra of leaf pigments showed a distinct absorption edge with a cut-off wavelength dependent on the light condition. Leaves that measured lower concentration of pigments from the HPLC generally showed the absorption edge at a lower wavelength (425nm-435nm) as compared to leaves with a high pigment concentration (435nm-441nm). Our results demonstrate the importance of blue and red light for a high pigment concentration, which we interpret as an indicator for good plant health. UV light was identified as an important stressor, which inhibits the production of pigments at least similar to the absence of red or blue light. This has important implications for plants as indicators for UV exposure. The absorption spectra recorded alongside the HPLC analysis indicate the possibility to assess plant health directly from spectroscopic measurements of the light reflected or transmitted by foliage.

Video

Anna Testorf (photo 1)

I was born in Hanover, NH and have lived there all my life. I started doing research in the New Hampshire Academy of Science in 6th grade, however due to the natural complexity of EEG it didn't go very far. I was able to complete my first research project in 8th grade using C. elegans and aspartame. In the following summers I had shifted my focus to other life goals, primarily athletic ones. I had thoughts about continuing research with my previous research partner, however we never ended up actually continuing out research. It wasn't till the winter of 2021 where I decided on a whim to try my hand at another research project. Boi was it the best decision I made that year. I found a project that I really liked, I saw old friends and made new ones, and I was allowed to feel like a crazy scientist using volumetric flask while creating colorful concoctions.

Matthew Adner (photo 2)

I first attended AJAS with my research in 8th grade studying the effects of roundup on C. elegans. Having experienced the unpleasantness of counting C. elegans worms firsthand, I wanted to avoid that, so in following years, I worked towards the development of a computer vision system to automate population data collection for C. elegans. This past year I was able to shift from computer science towards biology, studying plant stress. Not only was the research itself interesting, but also background reading. Beyond science, I enjoy skiing, ski instructing, reading, consuming media, and spending time with my cat and dog.