Cold Hardening in ‘Redblush’ Grapefruit as Related to Sugars and Water Soluble Proteins1

Abstract

Abstract ‘Redblush’ grapefruit seedlings were exposed to hardening temperatures in the presence and absence of light. Both reducing and non-reducing sugars increased in leaves and wood of hardened plants and non-reducing sugars increased in roots of hardened plants. The primary sugars involved were glucose, fructose, and sucrose. Plants exposed to hardening temperatures in the dark did not harden, and water soluble proteins did not materially change in the leaves during hardening in the light. Lower temperatures were required to kill leaves without ice on the surface than with ice, and lower temperatures were required to kill hardened leaves. Hardened leaves developed a small capacity to recover from cell dehydration due to ice nucleation indicating changes in protoplasm stability and membranes during hardening