Expressions of Three Members of ACS Gene Family Induced by Ethephon Relationship of Ethylene Production and Sugar Accumulation in Sugarcane Stems Cleavage of the Carboxyl-Terminus of LEACS2, a Tomato 1-Aminocycl-opropane-1-Carboxylic Acid Synthase Isomer, by a 64-kDa Tomato Metalloprotease Produces a Truncated but Active Enzyme