Poster: Oxidative stress

Abs # 86: Photosynthetic performance of Arabidopsis APX3 knockout mutants under heat stress conditions

Presenter:	Narendra, Savitha , SNARENDR@TTACS.TTU.EDU
Authors	Narendra, Savitha  (A)
Affiliations:	(A): Texas Tech University

Photosynthetic performance of Arabidopsis APX3 knockout mutants under heat stress conditions Savitha Narendra¹, Dmytro Kornyeyev^{1, 2}, Juqiang Yan¹, Scott Holaday¹ and Hong Zhang^{1 1}Department of Biological sciences, Texas Tech University, Lubbock, TX 79409-3131 ² Institute of plant physiology and genetics, Kyiv, Ukraine Enzymatic activities of superoxide dismutase, catalase and ascorbate peroxidase (APX) remove reactive oxygen species in plant cells and therefore protect plants from the harmful effects of these substances. APX is an H₂O₂-scavenging enzyme that exists in five isoforms in Arabidopsis, and we have been studying the peroxisomal membrane-bound isoform (i.e. APX3). To study the in vivo function of APX3, we analyzed the photosynthetic performance of APX3 knockout mutants under various stress conditions, particularly during heat treatment. Chlorophyll fluorescence analysis was used to study energy partitioning in Photosystem II (PSII) complex. After light acclimation at 350 μmol m^-2s^-1 and 25 ^oC, the leaf temperature was quickly elevated to 40 ^oC. The temperature shift led to short-term increase in effective quantum yield of PSII photochemistry, the portion of light energy absorbed by PSII antennae that was used for linear electron transport. The value of this parameter declined after about half an hour under heat stress for both wild type and APX3 knockout plants. However, the decrease in electron transport occurred earlier in APX3 knockout mutants than in wild type plants. APX3 is likely involved in scavenging H₂O₂ generated through photorespiration, because loss of APX3 gene apparently leads to a modified response of photosynthetic electron transport to elevated leaf temperature.