Light-Induced Adaptive Responses under Greenhouse and Controlled Conditions in the Fern Pteris cretica var. ouvrardii

The influence of different growth irradiance conditions on plant development and foliar features were assessed in a shade-adapted fern variety, Pteris cretica var. ouvrardii. A comparison of frond morphology, anatomy, chloroplast infrastructure and chlorophyll content of plants cultivated in both greenhouse and in controlled growth chambers under moderate light, low light (control) and extreme shade revealed pronounced phenotypic modifications. Moderate light induced decreased frond surfaces, thicker leaves, lower chlorophyll content per surface unit, and a markedly reduced density of intraplastidial membranes. In contrast, morphological responses to extreme shade included the formation of larger, thinner fronds, increased chlorophyll content; and a higher membrane density in chrloplasts. A dorsi-ventral distribution of starch-gorged chlroplasts (lower mesophyll cell layers) and essentially starch-free chloroplasts (upper cell layer) characterizes low-light and moderate light fronds, while homogenous starch-free chloroplasts are present in all cell layers of extreme shade fronds. The light-induced modifications are discussed as adaptive responses.