Nuclear genes and chloroplast modifications in maize : (Zea mays, iojap , cytoplasmic inheritance, nucleus-cytoplasm interaction, sorting-out, morphological modifications)
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The recessive nuclear genes (ij) and chloroplast mutator (cm) in maize have been studied as examples of genes whose roles affect the continuity of the plastid and its genetic machinery. The phenotypic expression of cm is mostly straight forward, clonal striping in homozygous plants, while that of iojap is widely variable and depends upon nuclear background. The expression of iojap in homozygous plants can include white, white striping, pale green "grainy", patterned rather than clonal expression of color, arrested leaf growth, and arrested embryos. These expressions are influenced by the nuclear background and by growth rate, and appear to involve non-clonal processes. Maternally transmitted effects of iojap include pure white seedlings, clonally sectored plants, arrested embryos, and arrested (and white) seedlings. Sorting out of mixed organelles in maternal sectorial plants is very rapid, and a small number of genetically effective units is indicated. For maize, while maternal transmission of plastids is the rule, occasional paternal transmission has been considered but not rigorously tested. Study of the interplay of nucleus and plastid genomes is by no means simple, and promises to reveal interesting complexity.