No chitinase activity. Essential for normal plant growth and development. Regulates cell expansion extent and differentiation at least in roots and hypocotyls. Prevents lignin accumulation in the pith. May modulate ethylene-mediated regulation during development. Probably required to establish thermotolerance acclimation. Plays a role for controlled anisotropic cell expansion in the regulation of waving during root gravitropism and thigmotropism. Involved in the root system architecture adaptation to multiple environmental conditions such as nitrate. Contributes to salt tolerance and possibly to drought by preventing the overaccumulation of sodium ions. Mostly expressed in seedlings shoots and roots, stems, and flowers, and, to a lower extent, in flowers, mature leaves and roots. Repressed after wounding or treatment with ethylene. Abnormal root expansion with ectopic root-hairs, reduced growth, excess lateral stems and smaller leaves. Loss of regulation of the extent of root epidermal and cortex cell expansion. Ectopic deposition of lignin and aberrant shapes of cells with incomplete cell walls in the pith of inflorescence stems. Exaggerated hook curvature, reduced length and increased diameter of hypocotyls in dark-grown seedlings, and reduced root length and increased number of root hairs in light-grown seedlings. Increased ethylene production. Exhibit also thermotolerance defect. Lacks the lefthanded root epidermal cell file rotation (CFR) and enhanced root skewing in response to low doses of propyzamide. Aberrant reduced tolerance to salt and drought stresses, with accumulated of sodium ions. Belongs to the glycosyl hydrolase 19 family.