MANIPULATION OF CATALASE LEVELS PRODUCES ALTERED PHOTOSYNTHESIS IN TRANSGENIC TOBACCO PLANTS

Constructs containing the cDNAs encoding the primary leaf catalase in Nicotiana or subunit 1 of cottonseed (Gossypium hirsutum) catalase wer e introduced in the sense and antisense orientation into the Nicotiana tabacum genome. The N. tabacum leaf cDNA specifically overexpressed C AT-1, the high catalytic form, activity. Antisense constructs reduced leaf catalase specific activities from 0.20 to 0.75 times those of wil d type (WT), and overexpression constructs increased catalase specific activities from 1.25 to more than 2.0 times those of WT. The NADH-hyd roxypyruvate reductase specific activity in transgenic plants was simi lar to that in WT. The effect of antisense constructs on photorespirat ion was studied in transgenic plants by measuring the CO2 compensation point (Gamma) at a leaf temperature of 38 degrees C. A significant li near increase was observed in Gamma with decreasing catalase (at 50% l ower catalase activity Gamma increased 39%). There was a significant t emperature-dependent linear decrease in Gamma in transgenic leaves wit h elevated catalase compared with WT leaves (at 50% higher catalase Ga mma decreased 17%). At 29 degrees C, Gamma also decreased with increas ing catalase in transgenic leaves compared with WT leaves, but the tre nd was not statistically significant. Rates of dark respiration were t he same in WT and transgenic leaves. Thus, photorespiratory losses of CO2 were significantly reduced with increasing catalase activities at 38 degrees C, indicating that the stoichiometry of photorespiratory CO 2 formation per glycolate oxidized normally increases at higher temper atures because of enhanced peroxidation.