Subcellular Localization of Dhurrin β-Glucosidase and Hydroxynitrile Lyase in the Mesophyll Cells of Sorghum Leaf Blades

Abstract

At root temperature below 14 C the absorption of ¹⁵N from NH₄⁺ greatly exceeded that from NO₂⁻ by tillers of Lolium multiflorum and Lolium perenne under conditions where pH, external concentration, plant N status, and pretreatment temperature were varied. There was a marked increase in the temperature sensitivity of NO₃⁻ transport below 14 C, irrespective of the temperature at which plants were grown previously. A marked increase in the temperature sensitivity was also seen for NH₄⁺ transport, but this occurred at the lower temperature of 10 C. Pretreatment of roots at 8 C lowered this still further to 5 C. Above and below these transition temperatures the Q₁₀ values for NO₃⁻ and NH₄⁺ transport were similar. Thus, the increased absorption of NH₄⁺ relative to NO₃⁻ at low temperatures seems to be related primarily to the difference in transition temperatures.