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 photosynthesis). 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 determine the extent to which individual maize chromosomes contribute to C4 photosynthesis and for the identification 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 pyruvate orthophosphate dikinase (PPDK) mRNA expression in oat-maize addition lines containing chromosome 6 and 6 + 9. Protein immunoblotting with polyclonal antibodies against PEPc and PPDK in leaf protein extracts further showed the translation of the detected mRNA. Indirect immunocytological tests on microtomed tissue using monoclonal 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 chromosome 9 and 6 lines, respectively. The CO ₂ compensation 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 responded more like C3 and C4 photosynthesis with the difference possibly due to oat genotype background effects.