DORMANCY AND LIKE-DORMANCY IN ASH-TREES DEPRIVED OF SEASONAL-VARIATIONS

Ash-seedlings were cultivated for 7 years, in a phytotron room under c ontrolled conditions, with no seasonal variation. In the terminal bud, the sequence of rest and of growth activity was characterized as a fu nction of time. The G0-1 blockage of the nuclei in rest was recognizab le by 3 markers, the distribution of nuclear DNA content, the water co ntent and the presence of intravacuolar polyphenolic compounds in the shoot-apex of the ash-bud. The terminal buds deprived of seasonal vari ations, alternated between rest and active growth. The ability to foll ow the seasonal cycle was shown during the first years. This was progr essively lost and after 5 years after germination, all the terminal bu ds were asynchronous. However, the ability to seasonal dormancy was im mediately expressed when these young plants were replanted outdoor, ju st before the summer solstice, and submitted to the natural conditions : the synchronism of bud-opening was restored and the survival rate wa s 85% after 3 years. Thus, the bud-dormancy, i.e. the seasonal period of rest, is based on the connection of 2 components: one, the alternat ion of G0-1 blockage and active growth, which is the expression of a c ycling growth from rest to rest, endogeneous, permanent and transmitte d from generation to generation; second, the regulation to maintain th e synchronisation between this permanent programming and the seasonal cycle. When the germination timed the growth recovery after the G0-1 b lockage, the asynchronism between the different buds was not manifest immediately but progressive, year after year: it resulted in a ''like- dormancy''.