Response of the photosynthetic apparatus in the tropical fern Platycerium bifurcatum to increased ozone concentration

A rapid increase of ozone concentration up to the phytotoxic level is currently observed in the tropical forests. However, the effect of elevated concentration of O3 on tropical ferns and epiphytes has not yet been described and mechanisms of tolerance remain unknown. The aim of this study was to determine the physiological response of the epiphytic fern Platycerium bifurcatum to a high concentration of ozone (150 ppb). In particular, changes in the course of photosynthesis and the pigment composition of sporotrophophyll leaves were taken into account. P. bifurcatum showed high resistance to the 4-week ozone stress. The effect of ozone was an initial decrease in net photosynthesis and reduction in transpiration. Ozone tolerance mechanisms are associated with the closure of stomata and the synthesis of carotenoids and flavonoids. We found that brassinosteroids play an important role in the resistance of P. bifurcatum to ozone. In response to ozone stress an increase in 28-homocastasterone content was observed.