Abstract
Arabidopsis thaliana possesses three types of hemoglobin (Hb) gene. The ΔAtGLB3 is a T-DNA insertion mutant that lacks the functional gene of trHb, a homologue of bacterial truncated Hb. We compared non-photochemical quenching (NPQ) of photosynthesis between the wild type and ΔAtGLB3. There is no phenotypic difference between the wild type and ΔAtGLB3. We have found that NPQ of ΔAtGLB3 is severely inhibited at 35 °C where that of wild type is tolerant. Interestingly, there was no substantial difference in NPQ between the wild type and ΔAtGLB3 at 25 °C. Since NPQ mechanism can be inhibited by thiol reagents through the modification of functional SH groups of a NPQ enzyme, we consider that NO may inhibit NPQ mechanism in ΔAtGLB3 due to the absence of trHb, an NO scavenging protein. The results strongly suggest that trHb is required to protect NPQ from heat stress.
