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Plant and Cell Physiology, 1982, Vol. 23, No. 7 1219-1227
© 1982

Article

Freezing Tolerance of Shoot and Flower Primordia of Coniferous Buds by Extraorgan Freezing1

Akira Sakai

The Institute of Law Temperature Science, Hokkaido University Sapporo 060, Japan

Shoot and flower primordia of vegetative and flower buds of extremely or very hardy conifers belonging to the subfamily Abietoideae of the Pinaceae, survived between –40 and –70°C by extraorgan freezing, which differed greatly depending upon species. The water in these organs gradually froze out with decreasing temperatures when cooled very slowly, which enabled these organs to survive %40°C or below. The same ice segregation in shoot and flower primordia by extraorgan freezing was observed in most of the temperate conifers belonging to Taxaceae, Cephalotaxaceae, Taxodiaceae and Cuppressaceae, making them resistant to temperatures between –15 and –25°C. In these conifers, scales acted as an ice sink, unlike the conifers of Abietoideae. The rates of cooling and exosmosis of water in the shoot or flower primordia, their size, and their ability to tolerate freeze-dehydration or its related stress play an important role in determining whether death is caused by freeze-dehydration or intraorgan freezing.

Even in very hardy conifers, low temperature exotherms from freezing within the shoot primordia appeared between –30 and –35°C on the DTA profiles when cooled continuously under laboratory conditions from 5°C to –50°C at 2 to 5°C/h. Appearance of low temperature exotherms always resulted in death. However, in the coldest area of Hokkaido, where the air temperature cools down to –40°C or below nearly every year, such an intraorgan freezing seems seldom to occur, especially in natural stands. On the other hand, low temperatures below –25°C seldom occur in warm-temperate climates. Thus, it may be considered that in both boreal and temperate conifers their shoot and flower primordia seem to tolerate freeze dehydration by extraorgan freezing under natural conditions.

1 Contribution No. 2431 from the rnstitute of Low Temperature Science.

(Received March 27, 1982; Accepted August 12, 1982)
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