INFLUENCE DE LA PHOTOPÉRIODE ET DE LA TEMPÉRATURE SUR L’ÉVOLUTION DE LA TOLÉRANCE AU GEL, DE LA CROISSANCE ET DE LA TENEUR EN EAU, SUCRES, AMIDON ET PROLINE DES RAMEAUX ET DES RACINES DE GENÉVRIER (Juniperus chinensis L. ’Pfitzerana’)

Abstract

Rooted cuttings of Juniperus chinensis L. ’Pfitzerana’ were exposed to a combination of three temperatures (1, 8 and 15 °C) and two photoperiods (8 and 16 h) for 42 d in growth chambers in order to study the influence of these factors on the evolution of growth and on changes in water, sugar, starch and proline contents of stems and roots during the cold-hardening process. The acclimation process for stems is different from that of roots. At 15 and 8 °C, under a short photoperiod, stems harden, even though growth continues: water, sugars and starch levels remain constant. Therefore, the complete cessation of growth is not necessary to initiate stem hardening. At 1 °C, stem hardening is no longer influenced by photoperiod; growth is negligible, and while water content is stable sugars are accumulated. Root hardening however, is only affected by temperature. At 15 °C, we did not observe any hardening; water, sugars and starch levels remained constant while growth continued. At 8 °C the beginning of hardening was noted, water content decreased, growth slowed and, despite some fluctuations, sugar and starch did not increase. At 1 °C, growth stopped, sugars and starch were accumulated and hardening reached its maximum. Proline levels increased in stems and roots under all treatments except for stems exposed to 15 °C and a 16-h photoperiod.Key words: Juniper, frost tolerance, photoperiod, sugar, starch, proline