Pigment–Structure Leaf Syndromes in Poinsettia ( Euphorbia pulcherrima Willd. ex Klotzsch) Alter Chloroplast Ultrastructure, Biochemical Profiling, and Photosynthetic Quantum Yields

High Resolution Image Download MS PowerPoint Slide Colored bracts and leaves are widespread in plants; however, how their pigments and structures jointly control the fate of absorbed light is poorly understood. We used contrasting albino and red Poinsettia ( Euphorbia pulcherrima Willd. ex Klotzsch) phenotypes to test how selection for extreme color morphs reshapes chloroplast ultrastructure, photosynthetic quantum yield, and the spectral signatures of colored canopies. We combined hyperspectral and thermal imaging, pigment, biochemical and antioxidant profiling, gas exchange and chlorophyll a fluorescence, and light and electron microscopy across four tissues: albino bracts, green leaves of albino plants, red bracts, and green leaves of red plants. These tissues form four distinct “pigment–structure leaf syndromes” that decouple light capture from carbon assimilation. Albino and anthocyanin-rich red bracts retained functional photosystem II (PSII) but contained very few, weakly stacked chloroplasts, showed much lower stomatal and mesophyll conductance and carboxylative capacity, and behaved as photoprotective, antioxidant sinks with almost zero net CO 2 uptake. By contrast, the companion green leaves─especially those of red plants, developed a thick mesophyll with large intercellular airspaces and numerous grana-rich chloroplasts, reached the highest maximum Rubisco carboxylation, electron transport, and triose-phosphate-use capacities, and achieved the highest absorbed-light quantum yield of CO 2 assimilation, thereby compensating for albino and red bracts at the module and whole-plant scale. Across tissues, absorptance and PSII quantum yield alone failed to predict CO 2 -assimilation quantum yield, which instead tracked chloroplast number, thylakoid investment, and CO 2 conductance. Full-range ultraviolet-to-shortwave-infrared spectra and multivariate analyses captured these syndromes as distinct optical fingerprints, providing a mechanistic framework for interpreting hyperspectral signals from canopies containing nongreen or variegated organs.