Development of the Epidermal Cells of the Pinnules of Adiantum raddianum C.Presl (Pteridaceae): Environmental Adaptive Plastidial Characteristics

Abstract

Plants have different strategies for adapting to environmental conditions, such as characteristics that allow them to be more efficient in shady or sunny environments. Those that grow in dimly lit environments often have a photosynthetic epidermis. However, Adiantum raddianum, known as the maidenhair fern, is a species found in sunny environments that has this characteristic. Within the abaxial and adaxial epidermal cells of the leaf pinnules of this species, there are arm-like projections where chloroplasts agglomerate. The goal of this study was to describe the development of the epidermal cells of A. raddianum, describe the morphological characteristics of the chloroplasts in these cells, and interpret any cytological characteristics that this species might have as a result of an adaptive survival strategy. The study found that the arm-like projections within the epidermis develop when the leaves are young and still exhibit circinate vernation. Cytological observations revealed a plastidial dimorphism, where there was variation in the arrangement of the thylakoid system, and the presence of stromules, which may help establish a connection among chloroplasts and between these organelles and mitochondria and peroxisomes. Descriptions of the stromules and plastidial dimorphism, made in this study, can be included with other known epidermal adaptive strategies (e.g., plastidial movement and mucilage secretion), which help this plant to survive under different environmental conditions.