Temperature winter hardening

Raffinose occurs only at low concentrations in the leaves of plants, but accumulates in the storage organs during the process of development. It has been generally observed that the level of raffinose increases as the tissue loses water this 108-1i3,u6-m js a characteristic feature of maturation of seeds and the hardening process of winter-hardy plants. The hardiness of several plants towards desiccation and elevated temperature may be compared to the property of frost resistance.125-134 When the heat resistance reaches a maximum in the summer, the frost resistance is at its minimum. 

Furthermore, leaves of winter rye have to develop at low temperatures in order to acquire increased resistance to photoinhibition. However, spinach, which has a very much bwer frost tolerance than winter rye, is reported to acquire increased resistance to photoinhibition during cold acclimation (4). Whether the different results obtained with winter rye and spinach, with respect of cold hardening induced resistance to photoinhibition, depend on different developmental strategies of the two species can not be said at present. In Chlamydomonas reinhardtii(5), however, an increased resistance to photoinhibition upon cold acclimation occurred in a culture of dividing and growing cells, which is a similar developmental strategy as that of winter rye. 

The crowns and leaves of the less winter hardy cultivars can tolerate -12 to -15 ° C for 1 to 2 hours after a period of 6 to 8 weeks of hardening. The crowns of very hardy winter wheats, e.g. Norstar can tolerate temperatures as low as -29°C for 1... 

The influence of freezing water in capillary pores is a very complex phenomenon and various processes accompany simple hydraulic pressure of ice on hardened cement paste, but the model proposed by Powers was universally accepted as explaining the destructive influence on concrete elements with acceptable agreement with experimental results. That model is considered as a basis for standardized requirements for the design of structures. Furthermore, there is strong experimental evidence that the distribution of the voids is a key factor governing the frost resistance of concrete. This statement is supported by experience and investigations in several countries where the temperature in winter falls below zero. An example of such... 

It has been reported that growth at low, cold-hardening temperature resulted in a specific 67% (thylakoids) to 74% (whole leaves) decrease in the 16 l(3t) acid level associated with winter rye PG [8]. However, our results show that in squash cotyledons, lowering the growth temperature induced an increase in 16 l(3t), mainly in PG 18 3/16 l(3t) molecular species (Fig. 2). 

In our recent studies we reported that growth of winter-hardy Puma rye at cold-hardening temperatures resulted in various structural alterations in the thylakoid membranes. Specifically, we observed changes in the size distribution of freeze fracture particles on the EF fracture face (Huner et al, 1983) and changes also in the stability of the pigment-protein complexes associated with PSII (Elfman et al,... 

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