MESURE DE L’ENDURCISSEMENT AU FROID ET DE LA VIABILITE DES PLANTES EXPOSEES AU GEL PAR LE DOSAGE DES PHOSPHATASES ACIDES LIBRES

Abstract

Cellular freezing induces leaking of non-specific acid phosphatase enzymes (EC. 3.1.3.2) from the cell walls of wheat crowns into the liquid medium surrounding the plant tissues. Those free enzymes leak both in the disorganized cytoplasm and in the external medium surrounding the tissues. The phosphastase activity index, measured in the external medium of the frozen plants as compared with the one of the non-frozen plants, decreases proportionally with the temperature of the freezing test until a minimum plateau is reached corresponding to the killing temperature of the plants. The determination of this phosphatase activity index can be used therefore as a quantitative method for the estimation of the viability of plants exposed to freezing. The initial drop of the phosphatase activity index precedes the viability loss as measured with the regrowth tests. The solubilization of those acid phosphatases previously bonded to the cell walls is one cause of the plant death rather than its consequence. The differentiating degrees of cold hardiness can be calculated from the changes in the phosphatase activity during a programmed freezing test among cultivars or species, immediately after running the test. Kharkov (Triticum aestivum L.) sampled in the fall shows + 13 °C differential of cold hardiness as compared with the one sampled in summer while Champlein (Triticum aestivum L.) has developed + 5 °C differential of cold hardiness. In the same conditions, another species (Medicago sativa L. cv. Saranac) shows − 9 °C differential of cold hardiness as compared with Kharkov. Temperatures near the freezing point stabilize instantly the attachment of enzymes to cell walls. This molecular rearrangement, at the enzymatic level, is related to the initial metabolism of cold hardening.