Albinism in plants: far beyond the loss of chlorophyll. Structural and physiological aspects of wild-type and albino royal poinciana (Delonix regia) seedlings

• The partial or complete loss of chlorophylls, or albinism, is a rare phenomenon in plants. In the present study, we first report the occurrence of albino Delonix regia seedlings and describe the morpho-physiological changes associated with albinism. • Wild-type and albino seedlings were characterized. Leaflets samples were processed following usual procedures for analysis in light, scanning and transmission electron microscopies. The chlorophyll a fluorescence parameters and the carbohydrate, lipid and soluble protein contents were also determined in leaf and cotyledon samples of both albino and wild-type seedlings. • Albino seedlings showed reduced growth. They also showed lower chlorophyll and protein contents in foliar tissues than did wild-type seedlings, in addition to lower concentrations of lipids and carbohydrates stored in cotyledons. The chloroplasts of albino seedlings were poorly developed, with an undefined internal membrane system and the presence of plastoglobules. Wild-type seedlings had a uniseriate and hypoestomatic epidermis. The mesophyll was dorsiventral, consisting of a layer of palisade parenchyma and two to four layers of spongy parenchyma. In albino seedlings, the spongy parenchyma was compact with few intercellular spaces and the thickness of the mesophyll was greater, resulting in a greater thickness of the leaf blade. Albino seedlings showed higher stomatal density and number of pavement cells, although the stomata had smaller dimensions. • In addition to the partial loss of chlorophylls, albino D. regia showed changes at the physiological and structural levels, demonstrating the crucial nature of photosynthetic pigments during the development and differentiation of plant leaf tissues/cells.

Keywords: Albino seedlings; chlorophyll deficiency; chloroplast; flamboyant; mesophyll; stomata development.