Caracterização da escotomorfogênese em plântulas de araucaria angustifolia (araucariaceae)

Abstract

Depending on light availability, plants may adopt two antagonistic developmental patterns: photomorphogenesis in the light and skotomorphogenesis in the darkness. Skotomorphogenesis is characterized by the use of the reserves to promote mostly stem elongation in order to seek light, while delaying leaf production and development of the photosynthetic apparatus. Despite being well described in angiosperms, it is poorly addressed in gymnosperms. This study aims to characterize this process in Araucaria angustifolia, an endangered conifer from South America, by imposing darkness to their aerial environments and forcing shoots to initially develop belowground. Seeds were either sown close to the soil surface or deep into the soil. Half of these seeds had access to light and half remained in the darkness. These plants were grown for 147 days, and then measured for several growth parameters. There was an increased investment on stem elongation at the expenses of leaf production when light was not available. Leaves that developed in the dark were smaller, lighter, and more widely spaced than those that developed in the light. Photomorphogenic shoots were greener and accumulated much more chlorophylls than the whitish skotomorphogenic ones. Darkness had no effect in the rate of consumption of seed reserves and on total dry mass accumulation. True leaves were not produced when shoots developed belowground, and these shoots were colorless, wider and invested more in dry mass in order to elongate when compared to shoots that extended aboveground. Skotomorphogenesis in A. angustifolia was characterized by a developmental pattern that increases the chances of plants reaching for light while saving as much carbon as possible. Darkness imposed by seed burial was also associated to the physical resistance offered by the soil, thus altering some aspects of the skotomorphogenesis.