PETIT1, A CONDITIONAL GROWTH MUTANT OF ARABIDOPSIS DEFECTIVE IN SUCROSE-DEPENDENT ELONGATION GROWTH

The hypocotyl of Arabidopsis is well suited for the analysis of cell e longation because it elongates without cell division. We have isolated a new class of recessive mutants, petit1 (pet1), which are defective in aspects of hypocotyl elongation. The short-hypocotyl phenotype of p et1 is caused by shortened cells. The cells of the elongation zone of the hypocotyl are often deformed. pet1 also shows defects in elongatio n of the roots, flower stalk, leaves, petals, pedicels, and siliques, and these defects cannot be repaired by the application of auxin, gibb erellin, brassinolide, or an inhibitor of ethylene biosynthesis. The s hort-hypocotyl phenotype of pet1 is pronounced only in growth medium s upplemented with sucrose, which has promotive effects on hypocotyl elo ngation. In pet1 this effect is much reduced, causing the sucrose-depe ndent short-hypocotyl phenotype of pet1. pet1 accumulates more soluble sugars than the wild type and also shows more intensive iodo-starch s taining in the cotyledon and hypocotyl. These results indicate that PE TIT1 is involved in a sugar-dependent elongation process that may incl ude correct assembly of expanding cell wall architecture.