Our research aimed to study the correlation between the SPAD-502 readings and the color space CIE L*a*b* values in two cultivars of Alstroemeria sp. during leaf senescence and to evaluate the statistical criteria used in the selection of the best fit calibration functions. We demonstrate the importance of the Akaike information criterion and the parsimonious function besides the coefficient of determination. The reliability of the functions was tested by Student's t-test comparison between the chlorophyll (Chl) estimated from SPAD readings and their chemical concentrations. Polynomial and Hoerl function described well the changes in Chl a and total Chl (a+b) during senescence, but calibration functions are required to perform for each cultivar. We demonstrated that CIE L*a*b* system is reliable to estimate SPAD reading at stages of leaf senescence of Alstroemeria sp. and can be used instead of SPAD-502.
The content of chlorophylls (Chl) (a+b), total carotenoids (x+c), and the pigment ratios of Chl a/b and Chls to carotenoids (a+b)/(x+c) of green leaves of five C4 plants were determined and compared to those of C3 plants. The C4 plants were: Pacific and Chinese silvergrass (Miscanthus floridulus and Miscanthus sinensis), sugar cane (Saccharum officinarum) as well as feed and sugar maize (Zea mays). The three C3 plants were beech, ginkgo, and oak. C4 plants possess higher values for the ratio Chl a/b (3.4-4.5) as compared to the C3 plants (2.6-3.3). Sugar maize had the highest values for Chl a/b (4.04-4.70) and exceptionally high contents of total carotenoids and consequently lower values for the ratio of (a+b)/(x+c) (mean: 3.75 ± 0.6). During autumnal senescence also C4 plants showed a faster decline of Chl b as compared to Chl a yielding high values for Chl a/b of 6 to 8. Chlorophylls declined faster than carotenoids yielding low (a+b)/(x+c) values below 1.0.
Oxygenic photosynthesis takes place in thylakoid membranes (TM) of cyanobacteria, algae, and higher plants. It begins with light absorption by pigments in large (modular) assemblies of pigment-binding proteins, which then transfer excitation energy to the photosynthetic reaction centers of photosystem (PS) I and PSII. In green algae and plants, these light-harvesting protein complexes contain chlorophylls (Chls) and carotenoids (Cars). However, cyanobacteria, red algae, and glaucophytes contain, in addition, phycobiliproteins in phycobilisomes that are attached to the stromal surface of TM, and transfer excitation energy to the reaction centers via the Chl a molecules in the inner antennas of PSI and PSII. The color and the intensity of the light to which these photosynthetic organisms are exposed in their environment have a great influence on the composition and the structure of the light-harvesting complexes (the antenna) as well as the rest of the photosynthetic apparatus, thus affecting the photosynthetic process and even the entire organism. We present here a perspective on 'Light Quality and Oxygenic Photosynthesis', in memory of George Christos Papageorgiou (9 May 1933-21 November 2020; see notes a and b). Our review includes (1) the influence of the solar spectrum on the antenna composition, and the special significance of Chl a; (2) the effects of light quality on photosynthesis, measured using Chl a fluorescence; and (3) the importance of light quality, intensity, and its duration for the optimal growth of photosynthetic organisms.