Sugars affect a broad variety of processes,from growth and development to gene expression.Although it has already been shown that sugars act assignaling molecules, little is known about the mechanismsby which plants respond to them. Muchprogress has been made on understanding sugarsensing and signaling thanks to the analysis ofmutants with abnormal sugar response. Some of thegenetic strategies applied are based on the inhibitoryeffect of sugar on post-germinative development ofArabidopsis thaliana. High concentrations of exogenoussugars delay germination and arrest earlygrowth, preventing seedlings from expanding cotyledonsand developing true leaves and an extensive rootsystem. The characterization of several Arabidopsismutants identified for their altered sugar sensitivityhas disclosed a network in which sugars and planthormones cooperate to control seedling development.Remarkably, many mutations turned out to be novelalleles of hormone-related genes, mainly ABA andethylene.