tailieunhanh - Báo cáo khoa học: "Some aspects of phytohormonal participation in the control of cambial activity and xylogenesis in tree stems"

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài:"Some aspects of phytohormonal participation in the control of cambial activity and xylogenesis in tree stems. | 273s Ann. Sci. For. 1989 46 suppl. 273s-276s Forest Tree Physiology E. Dreyer et al. eds. Elsevier INRA Some aspects of phytohormonal participation in the control of cambial activity and xylogenesis in tree stems s. Lachaud Laboratoire de Biologie et de Physiologie Végétale UPA81 Station Biologique de Beau-Site 25 rue du Faubourg St-Cyprien 86000 Poitiers France Introduction Early investigations concerning the regulatory role of phytohormones in cambial activity were based on the assumption that a clear correlation exists between hormonal level and response. More recently precise measurements of endogenous hormone levels using rigorous techniques have often shown the importance of phytohor-monal intervention being challenged rather than elucidating how these substances might actually regulate cambial growth. This paper which summarizes a review in preparation refers to some recent findings and hypotheses about 3 important questions. How can auxin IAA regulate seasonal variations in cambial activity and xylogenesis During the period of cambial activity the intensity of cell production and some features of the resulting wood radial enlargement vessel development are often positively correlated with the auxin level in the cambial zone. Furthermore the early wood-latewood transition is associated in time in Abies basalmea with the largest decrease in the IAA level Sundberg et al. 1987 . However according to these authors the duration of the cambial activity period appears to be independent of auxin content and the regulation of this duration is still poorly understood. During the rest period the IAA level often remains relatively high in the cambial zone treatment with exogenous IAA cannot then induce the resumption of cambial activity. Thus the responsiveness of cam-bial cells to auxin varies with the season. Their ability to respond marking the end of cambial rest is recovered after exposure to chilling temperature Riding and Little 1984 . Does the seasonal variation

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