Introducing sucrose phosphorylase activity into plants by transformation with a gene for the enzyme increases the rate of sucrose hydrolysis, leading to increased starch, oil, and/protein levels. Sucrose phosphorylase genes from Streptococcus mutans and Leuconostoc mesenteroides have been found particularly advantageous for use in the present invention. Surprisingly, in potatoes transformed to express these genes in tubers, reduced bruise discoloration susceptibility and increased uniformity of starch deposition throughout the tuber are achieved.