The Effects of Dwarfing Genes Rht1 and Rht2 on Cellular Dimensions and Rate of Leaf Elongation in Wheat*

The gibberellin insensitivity genes, Rht1 and Rht2, reduced epidermal cell lengths in leaves of isogenic lines of field- and laboratory-grown wheat (Triticum aestivum L.). Rht dosages of zero (wild type), two (semi-dwarf) and four alleles (double dwarf) had a linear negative effect on cell length in flag leaves of field-grown plants, and in the sheaths and blades of leaf number 1 in laboratory grown plants. Decrease in cell length, rather than reduced cell number, accounted for most to all of the reduction in blade and sheath length. In sheaths, cell width increased with Rht dosage, but not sufficiently to compensate for decreased length in determining average projected surface area. Rates of extension of leaf number 1 in laboratory-grown plants were negatively and linearly correlated with Rht dosage. Maximal growth rate was maintained longer in wild type than in double dwarf, but the total duration of measurable extension in leaf number 1 was not affected by Rht dosage.