Chlorophyll fluorescence monitoring of freezing point exotherms in leaves

Abstract

Following supercooling prompt chlorophyll fluorescence and delayed fluorescence from leaves undergo transients simultaneous with the freezing point exotherm. The degree of supercooling and, hence, the temperature at which the exotherm occurs is dependent upon the leaf water content. Winter wheat leaves ( Triticum aestivum L.) that had the lowest water content (hardened “Kharkov”) supercooled to a greater degree than those leaves with a higher water content (hardened “Rescue” and unhardened “Kharkov” or “Rescue”). Seeding the leaves with ice increased the temperature at which the exotherm occurred and decreased the difference between varities but not between hardened and unhardened material. Our results suggest that freeze-avoidance via supercooling may be one mechanism in winter wheat for withstanding subfreezing temperatures.