Frost hardiness in spruce picea abies 1. control of frost hardiness carbohydrate metabolism and protein metabolism by photoperiod and temperature
Kandler, O.; Dover, C.; Ziegler, P.
Berichte der Deutschen Botanischen Gesellschaft 92(1): 225-242
Potted 4-6 yr old spruce trees (P. abies) were maintained under conditions of natural day length or short or long days either in the open air, in a greenhouse (temperature always at least 12.degree. C) or at a constant temperature of 20.degree. C in growth chambers. Trees from the open air conditions were artificially hardened with night temperatures of 0.degree. C or dehardened at 20.degree. C in growth chambers. The kinetics of hardening and dehardening and the accompanying changes in the amounts of sucrose, raffinose and borate-soluble protein in the needles were determined. The rate of protein synthesis during hardening was followed via the incorporation of 14C-leucine into borate-soluble protein. Changes in carbohydrate metabolism were strictly correlated with hardening and dehardening, even under artificial combinations of photoperiod and temperature. Short days were much more effective in inducing frost resistance than in stimulating raffinose synthesis and accumulation; low temperatures induced high levels of raffinose but only limited cold resistance under long day conditions. The enhancement of raffinose synthesis and the decrease in starch content were induced by the same factors as is cold resistance and appear to be causally related to hardiness. Raffinose accumulation is not the only or even the most basic factor in cold resistance, as shown by the lack of a close quantitative correlation between the 2 phenomena. The raffinose concentration under short day conditions at a constant temperature of 20.degree. C resulting in a pronounced cold resistance of -30.degree. C was 5-10 times lower than that associated with a comparable degree of hardiness under natural conditions. The degradation of raffinose during dehardening was virtually complete at a stage at which the degree of cold resistance was still -15.degree. to -20.degree. C. Changes in the content of borate-soluble protein of needles stored at -20.degree. C prior to analysis were qualitatively and quantitatively more closely correlated with cold hardiness than those of raffinose. All conditions inducing hardiness resulted in a concommitant, up to 2-fold, increase in borate-soluble protein nitrogen, which, especially in the case of short day adaptation, preceeded the hardiness increase somewhat. Dehardening was always closely paralleled by a decrease in borate-soluble protein content. This indicates that the soluble protein changes are indeed causally related to cold resistance. Such changes were not observed with freshly harvested needles, the soluble protein content of which remained at the level of the maximum values obtained for frost hardy needles after storage at -20.degree. C. Apparently the solubility, not the total amount of leaf protein, is correlated with cold hardiness. The higher rate of protein synthesis in summer than in winter and a reduction of this rate during hardening point to a modification of already existing protein rather than to a de novo synthesis of better soluble protein in this regard. The implications of the observed metabolic changes with respect to the problem of cold hardiness are discussed.