Effect of Leaf Position on Levels of the Chloroplast and Cytosolic Phosphofructoaldolase Isozymes in the Pea Leaf Nucleus

Immunocytolocalization experiments indicate that nuclear levels of the pea leaf cytosolic aldolase (EC 4.1.2.13) isozyme are higher in leaves located near the base of the plant and lower in leaves at the apex. In contrast, nuclear levels of the chloroplastic isozyme are highest in the apical leaf. Analysis of doubleimmunolabeling experiments indicates that both isozymes are distributed nonrandomly with respect to DNA in the nucleus, and therefore are colocalized with DNA, and that the isozyme in the chloroplast is distributed nonrandomly with respect to DNA, and therefore is colocalized with plastid DNA. It seems possible that the chloroplast and cytosolic aldolase isozymes in the nucleus might function as sensors that link sugar metabolism in the cytoplasm to gene expression.