Page 24 - IPCoSME 2021

1 INTERNATIONAL POSTGRADUATE CONFERENCE ON SCIENCE AND MARINE ENVIRONMENT 2021
st
(IPCoSME 2021)
“Environmental Sustainability Enhancement Through the Collaboration of Sciences”

RB-01

PHOTOSYNTHETIC RESPONSE AND OXIDATIVE STRESS IN THE
SEAGRASSES, Halophila ovalis AND Thalassia hemprichii EXPOSED TO

COMBINED HEAT AND HIGH LIGHT STRESS

1
CHANIDA SAEWONG , PIMCHANOK BUAPET 2*

1,2 Biology, Faculty of Science, Prince of SongKla University

*Corresponding author email: pimchanok.b@psu.ac.th

Abstract: Thalassia hemprichii and Halophila ovalis are seagrasses living in the intertidal
zone. When the tide is low during the day, they are exposed to high-intensity light and heat.

These conditions generate reactive oxygen species (ROS) and consequently initiate the water-
water cycle (WWC). In the WWC step, superoxide dismutase (SOD) is the first enzyme to

eliminate ROS. If ROS are not detoxified, they will destroy various components of plant cells,
including the photosynthesis mechanism. We compared the photosynthetic response and

oxidative stress caused by the multifactorial factor (light and heat). Divided seagrasses into 4

-2 -1
groups (control: 30°C, 150 µmol photon m s , high light stress: 30°C, 1000 µmol photon m -
2 -1 -2 -1
s , thermal stress: 42°C, 150 µmol photon m s , combined stress: 42 °C, 1000 µmol photon
-2 -1
m s ), and the experiment lasts for 3 hours. We assessed the effect on photosynthesis by
determining the maximum quantum yield of PSII (Fv/Fm) and the effective quantum yield of

PSII (PSII), as well as oxidative stress-related parameters such as ROS and SOD activity. The
result showed that heat stress had a more significant effect on Fv/Fm than high light stress and

there was an interactive effect of heat and high light. H. ovalis was more sensitive than T.

hemprichii, indicating more severe photodamage. On the other hand, ΦPSII was affected by
high light and heat stress to a similar extent and interactive effects of heat and high light were

also detected. Reduction of ΦPSII in heat-stressed seagrass could be related to a decline in CO2

assimilation, a process susceptible to heat stress. No difference in ROS nor SOD activity was
detected among treatments. Hence, we assumed that these seagrasses might have another

enzyme to exterminate ROS and the decline in Fv/Fm and yield was unrelated to oxidative
stress.

Keywords: chlorophyll fluorescence, high light stress, heat stress, intertidal seagrasses,
oxidative stress

24