Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/1995
Publication Date: N/A
Interpretive Summary: During normal growth conditions, all plants and animal produce toxic levels of chemicals known as oxygen free radicals. When barley (and other plants) are grown under high intensity light conditions, such as normally occurs in the field, higher levels of free radicals are produced. Plants survive because certain chemicals and enzymes neutralize the free radicals. Barley contains two forms of one of these enzymes, catalase-1 and catalase-2. The enzymes are encoded by the Cat1 and Cat2 genes. We found that the Cat1 gene is active in leaves of dark-grown barley seedlings, while the Cat2 gene is inactive. The opposite is true when seedlings are grown in the light. A mutant of barley was examined to determine why it appears damaged and has a poor seed yield when grown under normal light. It was found that its Cat2 gene is never turned on or expressed in the light, so it does not produce the catalase-2 enzyme. It is known that various stress and disease conditions can decrease the amount of catalase in leaves. This suggests that, at catalase levels below a certain threshold, normal light levels could contribute to existing stress conditions and become a key factor limiting production during stress periods. Our studies provide further insight into the mechanism of stress in cereal plants. With further study, this could lead to a method for preserving catalase activity during stress and therefore allow producers to have greater yields under marginal growth conditions.
Technical Abstract: DNA-RNA hybridization on northern blots was utilized to determine which of the two barley catalase genes is more active in etiolated leaves vs. light grown (greened) leaves. Etiolated leaves had high amounts of the catalase-1 messenger RNA (Cat1 mRNA) and very little Cat2 mRNA. Upon exposure to light, the level of Cat1 declined rapidly, while Cat2 mRNA increased and predominated by 17 hours. These changes correlated with changes in catalase enzyme activity in the leaves. The ability of barley to survive stresses associated with growth under normal light conditions may be partially due to catalase enzyme activity. This was tested by analyzing the low-catalase barley mutant RPr 79/4. This mutant grows poorly under natural light and has a large number of necrotic lesions and high head sterility. It was found that RPr 79/4 does not produce the Cat2 mRNA, which encodes the CAT-2 catalase isozyme. Thus, this isozyme is potentially critical to the optimal growth of barley in the field. DNA sequencing and DNA homology searches determined that the barley catalase genes are homologous to the light- and dark-specific catalase genes in maize.