Cellular Basis of Tissue Toughness in Carrot (Daucus carota L.) Storage Roots

Abstract

Carrots are brittle, tending to split and break on harvesting as a result of impacts. Since the phloem tissue of carrot storage roots is largely parenchymatous, there is little to resist the propagation of a fracture once initiated. In carrots, fracture toughness is inversely related to water potential, whereas tensile strength is virtually independent of water status. Fracture toughness tend to reflect changes in root water potential, but tensile strength increases on two separate occasions despite the fact that root and cell expansion is accompanied by a reduction in apoplast volume fraction. Possible mechanisms to account for carrot tissue toughening towards the end of crop growth are discussed.