Drought- and low temperature-acclimation in carrot (Daucus carota L.) roots

The effects of mild drought and low temperature on water relations of carro t (Daucus carota L. var. Nanthya and Bolero, respectively) storage roots we re investigated to characterize their ability for osmotic and elastic adjus tment. The roots were either stored at 18 degreesC (RT) and 5 degreesC (LT) for 15 d (short-term experiment) or at LT for 120 d (long-term experiments ). Air humidity was always close to saturation. Root water potential was me asured with a pressure bomb. The pressure-volume technique was applied to e laborate saturation water content, relative water deficit, osmotic potentia l at water saturation and at wilting point, and the volumetric modulus of e lasticity. The compressive modulus of elasticity was determined from force- deformation measurements using a material-testing machine. Storing roots in nearly water vapour saturated air at RT exposed carrots to a moderate drou ght stress which led to a gradual decline in water content. Carrots showed a small osmotic adaptation response as indicated by the decrease in their o smotic potential at water saturation. However, this could only partially de lay the reduction of water potential, pressure potential and apparent modul us of elasticity. At IT osmotic adaptation was more pronounced. It was acco mpanied by elastic adjustment (i.e. increased maximum volumetric modulus of elasticity). The decline in maximum osmotic potential was only due to a ne t increase in osmotically active solutes because saturation water content d id not decrease during storage. The ability to adjust osmotically and elast ically increased with the age of the roots and with the progression of the season. All these reactions observed indicate the metabolic adaptation to l ow temperature, which may prepare winter dormancy. Both the increase in osm otic content and in the modulus of elasticity are mechanisms that increase drought and freezing tolerance.