Yellow-Stripe Phenotype in Maize. I. Effects of ys1Locus on Uptake and Utilization of Iron

The yellow-stripe maize mutant (ys1) resembles maize plants grown on iron-deficient or low-iron media. Homozygous recessive ys1/ys1 plants have been shown to respond to various iron sources differently than do plants carrying at least one dominant allele at this locus. Normally green homozygous dominant (+/+) and heterozygous (+/ys1) plants are visually indistinguishable and appear to be members of a single population distinct from ys1/ys1. This investigation was planned to delimit the site of the lesion and to characterize processes associated with this locus. 2. Foliar tissues of plants of genotypes +/+, +/ys1, or ys1/ys1 metabolize either Fe++ or Fe+++ iron. 3. Plants with the ys1/ys1 genotype are visually indistinguishable from +/+ plants when grown in nutrient solutions containing 2 p.p.m. FeSO4 or Fe-HEDTA (iron chelate of trisodium N-hydroxy-ethylethylenediaminetriacetic acid) but display the yellow-stripe phenotype when supplied with iron as Fe-EDTA (ferric chelate of ethylenediaminetetraacetic acid) or certain other iron chelates. 4. Derooted ys1/ys1 plants utilize Fe-EDTA efficiently in complete nutrient solution, whereas intact ys1/ys1 plants remain yellow-striped. Thus it appears that the lesion for iron uptake is localized in the root tips of these plants. 5. Plants of genotypes ys1/ys1 and +/+ respond to iron supplied by the split root-system technique in the same manner as when nutrients are combined in a single solution. 6. Yeast extract enhanced greening of new leaves of ys1/ys1 plants grown in sterile culture with Fe-EDTA in a complete nutrient agar medium; casein hydrolysate, corn steep water, and partitions of the yeast extract were ineffective. Yeast extract did not affect utilization of Fe2O3. 7. Plants of genotype ys1/ys1 greened effectively on a phosphorus-deficient (-P) solution on all forms of soluble iron tested; Fe2O3 when supplied without phosphorus was utilized in sand cultures. 8. Low levels of organic or inorganic phosphate allowed iron utilization by intact plants; increased levels of phosphate affected ys1/ys1 plants more than those of the +/+ genotype. 9. Plants of the ys1/ys1 genotype interplanted in vessels of nutrient solution with +/+ maize, Lycopersicon, or Xanthium greened completely; plants in control vessels containing only the ys1/ys1 genotype remained yellow-striped. Furthermore, plants of the ys1/ys1 phenotype were able to take up iron, supplied as Fe-EDTA, from nutrient solutions in which +/+ plants had grown. This response was observed regardless of whether the nutrient solutions were supplemented with additional phosphate or not. Various of these data suggest that a natural iron chelator may be formed by +/+ maize and other species of plants but not by ys1/ys1 plants grown at levels of phosphorus normal for +/+ maize.