Articles
INTERACTION BETWEEN DEVELOPMENT OF FROST RESISTANCE AND DORMANCY IN PLANTS
The frost resistant perennials using mechanism of rest can start preparation for winter, long before cold.
The onset of rest is not metabolism inhibition, but switching over to its pathways.
Turning off the high energy requirement forms of growth it let loose a lot of processes connected with the preparation of plants for winter.
Maximum hardening ability is developed to the end of rest.
Proper hardening is the temperature-reversible process, connected with alteration of substances and structures, which had been formed in the rest period.
The temperature lowering results in two processes: the rise of frost tolerance and the break of rest.
But hardening ability is preserved after rest and quiescence and lost with growth resumption and utilization of previously formed substances.
Frost resistance is minimal in the state of growth and the same time the period of vegetation prepares the tree for dormancy and hardiness.
Connection between hardiness and the onset of rest was observed by gardeners for a long time /Chandler 1954/. Dormancy and frost resistance until recently have been considered almost synonymous, but now some authors are disposed to deny any causal relation between them /Pieniazek 1974/. What are the reasons for it ? In woody species, such as apple tree cultivars, rest is terminated in December or January, while the maximum of frost resistance occurs in January-February.
The most resistant forms from Sibiria have the shortest rest period.
Not all species, entering into rest are capable to harden.
On the other hand, the species, lacking rest mechanism, can not increase resistance higher, than up to -20, -30°C. But among the plants, entering into rest, there are species surviving at -60°C and lower.
We attempt to discuss the literature data and results of our research, which as we hope will help us to understand better the role of rest in frost resistance.
In summer, growing shoots are damaged at temperature slightly lower than freezing point not only due to absence of conditions for hardening in nature at this time, but as well as of their incapacity to harden /Tumanov, Krasavtsev, 1959, Weiser 1970, Tyurina, Egurazdova 1974/. First of all