The effects of epiphytes on light harvesting and antioxidant responses in the s...

• Author(s): Costa, Monya ; Silva, João ; Olivé, Irene ; Barrote, Isabel ; Alexandre, A. ; Albano, Sílvia ; Santos, Rui
• Date: 2013
• Persistent ID: http://hdl.handle.net/10400.1/3328
• Origin: Sapientia - Universidade do Algarve
• Subject(s): Epiphytes; Light harvesting; Antioxidants; Seagrass; Posidonia oceanica; Oxygen reactive species; Oxidative stress; Photosynthetic pigments; Xanthophyll cycle; Antioxidant enzymes
• Document Type: Conference Object
• Language: English

Description

Posidonia oceanica (L.) Delile is a subtidal seagrass whose leaves are commonly colonized by epiphytes. Epiphytes pose physical barriers to light penetration within the leaves, with possible significant impacts on photosynthesis. Furthermore, epiphytes can indirectly be responsible for leaf chlorosis, necrosis and senescence which are known to be related with the increase of oxygen reactive species (ROS) levels, potentially leading to oxidative stress. The aim of this work was to investigate in situ (i) the effect of epiphytes on the composition and balance of light harvesting pigments in leaves of the naturally growing seagrass P. oceanica, and (ii) evaluate differences in antioxidant responses. Epiphytized and non-epiphytized plants were analyzed to establish potential photosynthetic pigment roleshift between light harvesting and photoprotection functions. The experiments were carried out in Cabo de Gata Natural Park, southern Spain, where epiphytized and non-epiphytized plants can be found at identical depths and light exposure. The results showed that both O2 evolution rate along the day and chlorophyll a/b ratio were higher in non-epiphytized plants, indicating a negative effect of epiphytes on photosynthesis and light harvesting. Although under high irradiance (at solar noon) the xanthophyll cycle was activated in both epiphytized and non-epiphytized leaves, the de-epoxidation-ratio (AZ/VAZ) was lower in epiphytized leaves, due to light attenuation by epiphytes. The antioxidant capacity (TEAC and ORAC essays) and the activity of the antioxidant enzymes ascorbate peroxidase and dehydroascorbate were higher in epiphytized plants, showing that epiphytes can also be a potential source of oxidative stress to P. oceanica. Our results show that despite the light attenuation effect, leaf colonization by epiphytes can also be potentially stressful and reduces plant productivity.