UVR regulation of photoprotection in Phaeodactylum tricornutum (Bacillariophyceae): roles of light energy doses.

Abstract

The ability of diatoms to adapt to variable light conditions such as photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) is crucial for their survival and ecological role. The study aimed to investigate how different doses of UVR regulate the photoprotection mechanism in Phaeodactylum tricornutum. Five treatments were established: Control (PAR only), PAR + UVR D_6h (17.5 W m^- 2, 6 h, 378 KJ m^- 2), PAR + UVR 2D_6h (35 W m^- 2, 6 h, 756 KJ m^- 2), PAR + UVR 2D_12h (17.5 W m^- 2, 12 h, 756 KJ m^- 2), and PAR + UVR 4D_12h (35 W m^- 2, 12 h, 1.512 KJ m^- 2). The growth of P. tricornutum was significantly affected by UVR doses, with a growth pattern of 42-55% below the control (PAR only). Increasing the UVR dose also had negative effects on photosynthesis parameters and the levels of chlorophyll-a and fucoxanthin. The de-epoxidation state showed a high rate in treatments subjected to higher UVR doses, promoting an attempt to activate cellular protection mechanisms. In the transcriptional genes related to the xanthophyll cycle, a reduction in transcript levels of ZEP1 and ZEP2 genes was observed in PAR + UVR treatments, including a reduction up to 75% at 72 h of exposure. Also, an increase in transcript levels of VDE and VDL1 genes was observed for treatments with the same UVR dose, reaching about 9-fold increase for the 2D_12h dose and 10-fold increase for the 2D_6h dose, both at 72 h, suggesting a modification in the cell's ability to respond to UVR light stress.