Abstract
Auxin-induced elongation is thought to be caused by acid-growth and wall modifying proteins, particularly in Graminiae by an expression of endo-1,3:1,4-β-glucanase (EI). However, expression of EIwas detected only after 4-hr treatment with auxin. When the segments were treated with IAA in the presence or absence of 2% of sucrose, sucrose slightly enhanced IAA-induced elongation. Analysis of the level of glucose in hemicellulosic fraction of treated segments revealed that IAA alone reduced the glucose level, but sucrose suppressed this IAA effect, suggesting that exogenously supplied sucrose inhibited the degradation of 1,3:1,4-β-glucan in the cell walls. Next we examined the expression of EI gene by RT-PCR . IAA alone promoted the expression of EI, but this effect was cancelled by the presence of sucrose. These results indicated that the degradation of hemicellulosic 1,3:1,4-β-glucan in barley coleoptile cell walls was not a cause of IAA-induced elongation growth.
