Figure 4.

Starch accumulates within visibly senescing regions of sbe2a leaves. A to D, Wild-type Sbe2a (A) and homozygous sbe2a mutant (C) leaves exhibiting visibly senescing regions (hatched boxes and arrowheads) were harvested at 8 am, decolorized in boiling ethanol, and stained with iodine to visualize increased starch levels (B and D). E, Starch was extracted and quantified from leaves similar to A. Because senescing regions contain less moisture than nonsenescing leaves, starch values were normalized to the dry weights of the samples. Green and senescing leaf samples from sbe2a plants had significantly higher starch contents as compared with the wild type (denoted by the asterisk; P < 0.001). Error bars represent se of six biological replicates.