Expression of C4 photosynthetic enzymes in oat-maize chromosome addition lines

Oat-maize addition lines are plants of oat (Avena sativa L.) (C3 photosynthesis) that include one or more chromosomes from maize (Zea mays L.) (C4 photo- synthesis). Addition lines are available for every maize chromosome 1 through 10. These oat-maize addition lines and derivative radiation hybrid lines may be useful to de- termine the extent to which individual maize chromo- somes contribute to C4 photosynthesis and for the identi- fication of the precise chromosomal regions involved in C4 photosynthesis. Investigations have been conducted that focused on the expression of two C4 enzymes in these oat-maize addition lines. RNA blot analysis showed C4-associated phosphoenolpyruvate carboxylase (PEPc) mRNA expression in oat-maize addition lines containing maize chromosome 9 and 6 + 9, and C4-associated pyru- vate orthophosphate dikinase (PPDK) mRNA expression in oat-maize addition lines containing chromosome 6 and 6 + 9. Protein immunoblotting with poly clo nal antibodies against PEPc and PPDK in leaf protein extracts further showed the translation of the detected mRNA. Indirect immunocytological tests on microtomed tissue using mon- oclonal antibodies against PEPc and PPDK showed gene expression for PEPc in mesophyll cells of OMA 9 and not in oat, and PPDK in mesophyll cells of OMA 6 and not in oat. Assays with leaf protein extracts showed elevated PEPc and PPDK enzyme activities in the oat-maize chro- mosome 9 and 6 lines, respectively. The CO 2 compensa- tion point of oat-maize addition line 9 was comparable to normal oat (C3). The CO 2 compensation points of oat- maize addition lines 6 and the 6 + 9 combination were significantly lower than normal oat, but the lines still re- sponded more like C3 than C4 photosynthesis with the difference possibly due to oat genotype background ef- fects.