Modification in the ascorbate-glutathione cycle leads to a better acclimation to high light in the rose Bengal resistant mutant of Nannochloropsis oceanica

Tsung Yu Tsai, Yi Lin Chien, Yu Yun Zheng, Yu Chia Li, Jen Chih Chen, Ruey Chih Su, Avraham Ben-Sheleg, Inna Khozin-Goldberg, Avigad Vonshak, Tse Min Lee

Research output: Contribution to journalArticlepeer-review

Abstract

Understanding how to adapt outdoor cultures of Nannochloropsis oceanica to high light (HL) is vital for boosting productivity. The N. oceanica RB2 mutant, obtained via ethyl methanesulfonate mutagenesis, was chosen for its tolerance to Rose Bengal (RB), a singlet oxygen (1O2) generator. Compared to the wild type (WT), the RB2 mutant showed higher resilience to excess light conditions. Analyzing the ascorbate-glutathione cycle (AGC), involving ascorbate peroxidases (APX, EC 1.11.1.11), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GR, EC 1.8.1.7), in the RB2 mutant under HL stress provided valuable insights. At 250 μmol photon m−2 s−1 (HL), the WT strain displayed superoxide anion radicals (O2▪-) and hydrogen peroxide (H2O2) accumulation, increased lipid peroxidation, and cell death compared to normal light (NL) conditions (50 μmol photon m−2 s−1). The RB2 mutant didn't accumulate O2▪- and H2O2 after HL exposure, and exhibited increased APX, DHAR, and GR activities and transcript levels compared to WT and remained consistent after HL treatment. Although the RB2 mutant had a smaller ascorbate (AsA) pool than the WT, its ability to regenerate dehydroascorbate (DHA) increased post HL exposure, indicated by a higher AsA/DHA ratio. Additionally, under HL conditions, the RB2 mutant displayed an improved glutathione (GSH) regeneration rate (GSH/GSSG ratio) without changing the GSH pool size. Remarkably, H2O2 or menadione (a O2▪- donor) treatment induced cell death in the WT strain but not in the RB2 mutant. These findings emphasize the essential role of AGC in the RB2 mutant of Nannochloropsis in handling photo-oxidative stress.

Original languageEnglish
Article number108326
JournalPlant Physiology and Biochemistry
Volume207
DOIs
StatePublished - 1 Feb 2024

Keywords

  • Antioxidant defense system
  • Ascorbate peroxidase
  • Dehydroascorbate reductase
  • Glutathione reductase
  • High light
  • Nannochloropsis

ASJC Scopus subject areas

  • Genetics
  • Physiology
  • Plant Science

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