Changes in the freezing tolerance of spinach (Spinacia oleracea L.) and komatsuna (Brassica campestris L.) from autumn to early spring in an unheated greenhouse
2002
Tamura, A. (Akita-ken. Agricultural Experiment Station (Japan))
The relationships between freezing tolerance of spinach (Spinacia oleracea L.) and komatsuna (Brassica campestris L.) plants and air temperature, water content, and sugar concentration were investigated in an unheated greenhouses from autumn to early spring in 1996 - 99. Freezing tolerance was expressed as the temperature at which 15% (T sub(EL15)) or 50% (T sub(EL15)) of electrolyte leakage from leaf blade tissues occurred. The T sub(EL15) and T sub(EL15) of spinach and komatsuna decreased gradually from October to January. In the coldest season, the T sub(EL15) and T sub(EL15) were decreased to -12 - -16degC and -13 - -18degC in spinach, and -12 - -14degC and -13 - -17degC in komatsuna, respectively. From mid-February, the T sub(EL15) and T sub(EL15) of spinach and komatsuna increased with a rise of air temperature. There was a high correlation between the freezing tolerance and the mean minimum air temperatures for 7 days before the measurement were made. The freezing tolerance of spinach and komatsuna increased only slightly when the mean minimum air temperature was between 8 and 2degC, but increased considerably when the temperature decreased below 2degC. The changes in the freezing tolerance of spinach and komatsuna also correlated with leaf water content. The freezing tolerance increased as the leaf sugar content increased from 10 to 20mg/g**-1 FW in spinach and from 10 to 35mg/g**-1 FW in komatsuna. Further increases in sugar content had no effect on freezing tolerance in both species.
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