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Development and Growth Regulation

Effect of Ear Removal on CO₂ Exchange and Activities of Ribulose Bisphosphate Carboxylase/Oxygenase and Phosphoenolpyruvate Carboxylase of Maize Hybrids and Inbred Lines ¹

United States Department of Agriculture, Agricultural Research Service, University of Kentucky, Lexington, Kentucky 40546, Department of Agronomy, University of Kentucky, Lexington, Kentucky 40546

The effects of ear removal on gas exchange traits, chlorophyll, and leaf N profiles, and activities of ribulose 1,5-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase were examined using four maize hybrids (B73 x Mo17, B73 x LH38, FS854, and CB59G x LH38) and four inbred lines (B73, Mo17, LH38, and CB59G) as experimental material. A diverse genotypic response to ear removal was observed which was generally typified by (a) greatly accelerated loss of chlorophyll, leaf N, enzyme activities, and CO₂ exchange relative to controls for B73, B73 x Mo17, and B73 x LH38, (b) intermediate rate of decline for leaf constituents for FS854, LH38, and Mo17, or (c) loss of leaf constituents at similar or slower rates than for control plants for CB59G and CB59G x LH38. For all genotypes which had accelerated senescence relative to controls, loss of CO₂ exchange activity was correlated with increased internal CO₂ concentrations. Thus, it was concluded that metabolic factors and not stomatal effects were responsible for loss of CO₂ exchange activity. Loss of chlorophyll, leaf N, and enzyme activities correlated well with loss of CO₂ exchange activity only for some of the genotypes. Accelerated leaf senescence in response to ear removal for the inbred line B73 and the hybrids B73 x Mo17 and B73 x LH38, as well as the apparent delayed leaf senescence for the inbred line CB59G and the hybrid CB59G x LH38 show that the contrasting responses to ear removal, rapid versus delayed senescence, can be transmitted as dominant traits to F₁ hybrids. The intermediate response by some genotypes, and the dominance of contrasting senescence traits, suggested a relatively complex inheritance for expression of the ear removal response.

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