The effect of temperatures on cold acclimation and deacclimation in foliage tissues was studied in Solan commersonii (Oka 4583), a tuberbearing potato. The threshold temperature for cold acclimation was about 12 C. In a temperature range of 2 to 12 C, the increase in hardiness was dependent on the acclimating temperature; the lower the acclimating temperature, the more hardiness achieved. A day/night temperature of 2 C, regardless of photoperiod, appeared to the optimum acclimating temperature for the SoIuuam species studied. A subfreezing temperature hardened plants less effectively. The maximum level of hardiness could be reached after 15 days of cold acclimation. However, it took only I day to deacclimate the hardened plants to a preacclimation level when plants were subjected to a warm regime from cold. The degree of deacclimation was dependent on the temperature of the warm regime.Based on cold tolerance and the capacity to acclimate to cold, tuberbearing Solawun species could be grouped into five categories. Chilling injury was also observed in some of the tuber-bearing Solanum species.

The induction of stem frost hardiness by low temperature, water stress, short days, and their combinations in 2-and 4-month-old growing dogwoods ( Cornus stolonifera) were investigated. When plants were subjected to more than one factor, the increased hardiness was the sum of the effects of the individual factors involved. No interactions among these factors on hardiness were observed during a 3-week treatment. Results indicate that low temperature, water stress, and short days initially trigger independent frost-hardening mechanisms. Plant ages significantly influenced the change in low temperature-induced frost hardiness, but not the water stress or short day-induced frost hardiness.Frost hardiness in woody perennials can be induced by either low temperature (5-7), water stress (15), short days (4, 7), or their combinations (4, 6, 7). In red osier dogwoods: (a) short days alone induced frost hardiness to some extent (10, 13); (b) water stress also increased frost hardiness under either long day or short day regimes (2, 3); and (c) low temperature alone did not induce hardiness very effectively in long day regimes but was effective after growth cessation in short days (9, 13). There has been relatively little study on interactions of low temperature and water stress, or of low temperature, water stress, and short days in the induction of stem frost hardiness in red osier dogwoods. Therefore, a study was carried out and results are reported here. MATERIALS AND METHODSPlant Culture. Red osier dogwood plants, Cornus stolonifera Michx., were propagated by tip cuttings from the same genetic clones. Plants were then transplanted in 15-cm pots with a 3:2:2 mixture of soil, sand, and peat. Plants were maintained in a greenhouse under an approximately 16-hr-long day and 20/15 C day/night temperatures. Three weeks after transplanting, plants were trimmed to two leaders/pot to provide uniform experimental materials. After 2 months of growth, half of the plants were transferred to controlled environment chambers for treatments (trial I). The other half remained in the greenhouse for an additional 2 months of growth and were then transferred to growth chambers for treatments (trial II randomized design. This included (a) two photoperiods-16-hr LD2 and 8-hr SD; (b) two controlled water supplies-plants were watered once daily either to the point of saturation or with 30 ml of water/pot (WS); and (c) two temperatures-20/15 C day/night warm temperature and 5/5 C day/night LT. Each pot constituted an experimental unit and each treatment was replicated three times. Through the combining of LT, WS, and SD, eight treatments including a control were imposed. Prior to treatments, all plants were watered to field capacity and each pot was wrapped with a plastic bag to eliminate evaporation during the experiment (3). Hardiness determinations were carried out after 0, 7, 14, and 21 days of treatment. The status of soil moisture content and stem water potential under 30 ml/pot day WS was reported elsewhere (2).Evaluation of Frost...

Biochemical changes in potato leaves during cold acclimation have been examined and compared between a frost-tolerant S. acauk and a frostsusceptible S. tuberosum species. Changes were also examined in S. tuberosum, S. acauk, and S. commersonii species when they were hardened at different temperatures to varying hardiness levels.During three weeks of stepwise cold accfimation, S. acauk increased frost hardiness from -6.0 C (killing temperature) to -9.0 C, whereas frost hardiness of S. tuberosum remained unchanged at -3.0 C. Decreases in DNA content on a dry weight basis in both species suggest that matured leaf cells accumulated more dry matter during acclimation. The advantage of using DNA as a reference for comparing metabolite changes during cold acclimation is discussed.Under the stepwise acclimating conditions, both species showed the same trends for increasing total sugar and starch with an insignificant decrease in leaf water content. High levels of total RNA, rRNA, and total and soluble protein were observed in treated S. acauke plants as compared with controls, but not in S. taberoswn. Levels of total lipid and phospholipid also were high in treated S. acauk plants as compared with controls but decreased in S. tuberosum during acclmation.When S. tuberosum, S. acaukl, and S. commersonii potatoes were coldtreated at constant day/night temperatures of 10, 5, and 2 C with 14-hour daylength, each species responds differently in terms of frost hardiness increase upon subjecting plants to a low temperature. For instance, after 20 days at 2 C, a net frost hardiness of 3 and 7 C was observed in S. acaude and S. coumersonii, respectively, whereas the frost hardiness in S. tuberoswn remained unchanged. Also, various levels of frost hardiness can be achieved in a species by subjecting plants to different low temperature treatments. Under a warm regime of 20/15 C day/night temperatures (14-hour light), both S. acauk and S. conunersonii can survive at -4.5 C or colder, whereas S. tuberosum can survive only at -2.5 C.Biochemical changes in the leaf tissue of these species were investigated at 5-day intervals during low temperature treatments. Increases in total sugar and starch were found in all three species during hardening, although S. tuberosum failed to harden. Soluble protein contents were increased in both S. acead and S. commersonii but decreased in S. tuberosunL RNA contents change in a pattern similar to the soluble protein. Net increases of the soluble proteins were positively and significantly correlated with net

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Several tuber-bearing Solanum species with different levels of frost hardiness and different capacities for cold acclimation were studied for the interrelationship of freezing and heat tolerance after cold and heat acclimation. Cold acclimation could increase the frost hardiness in some species as previously reported, but except for S. commersonii it did not change the heat hardiness in species studied. Heat acclimation, on the other hand, could increase the heat hardiness in all tested species without affecting their frost hardiness. There is no systematic relationship between freezing and heat tolerance and no correlation in heat hardiness between the controls and the heat acclimated plants. The results indicate that the mechanisms of cold and heat acclimation in the potato appear to be independent of each other.