Low night temperature and inhibition of gibberellin biosynthesis override phytochrome action and induce bud set and cold acclimation, but not dormancy in PHYA overexpressors and wild‐type of hybrid aspen

Abstract

Juvenile trees of temperate and boreal regions cease growth and set buds in autumn in response to short daylengths (SD) detected by phytochrome. Growth cessation and bud set are prerequisites for the development of winter dormancy and full cold hardiness. In this study we show that the SD-requirement for bud set and cold hardening can be overcome in hybrid aspen ( Populus tremula L. ¥ ¥ ¥ ¥ tremuloides Michx.) by low night temperature and inhibition of gibberellin (GA) biosynthesis. Bud set and increased cold hardiness were observed under normally non-inductive long day-length (LD) in wild-type plants, when exposed to low night temperature and paclobutrazol. In addition, the effect of PHYA overexpression could be overcome in transgenic plants, producing bud set and cold acclimation by treatment with: SD, low night temperature and paclobutrazol. After cold acclimation, the degree of bud dormancy was lower for wild-type plants prior treated with LD and transgenic plants (overexpressing PHYA ), than SD-treated, wild-type plants. Thus, low night temperature in combination with reduced GA content induced bud set and promoted cold hardiness under normally noninductive photoperiods in hybrid aspen, but was unable to affect development of dormancy. This might suggest separate signalling pathways from phytochrome regulating the induction of cold/cold hardiness and bud dormancy in hybrid aspen or alternatively, there might be one pathway that fails to complete its action in the transgenic and paclobutrazol treated plants.

CENL1Expression in the Rib Meristem Affects Stem Elongation and the Transition to Dormancy inPopulus

“…In line 22 (hereafter called P35S:AsPHYA), this defect is specific to the photoperiodic pathway as their capacity to cease elongation growth under adverse conditions is not impaired. Cold stress or inhibition of gibberellin (GA) biosynthesis, for example, can arrest elongation growth of both the wild type and P35S:AsPHYA independent of photoperiod (Welling et al, 2002;Mølmann et al, 2005), while in P35S:AsPHYA, a combination of cold, SDs, and inhibition of GA biosynthesis were required to eventually obtain a bud-like structure (Mølmann et al, 2005). To establish the specific roles of the SAM and the RM/RZ in photoperiodic responses, we have dissected the quantitative and qualitative changes in growth and development of P35S:AsPHYA.…”

A Molecular Timetable for Apical Bud Formation and Dormancy Induction in Poplar

“…Moreover, the simultaneous activity of various closely intertwined cellular, physiological, and morphological processes confounds the dissection of the underlying developmental programs and their respective signals. Only in a few cases could processes be separated and assigned to the action of a particular signaling route (Welling et al, 2002;Mølmann et al, 2005).…”

Dormancy Behaviors and Underlying Regulatory Mechanisms: From Perspective of Pathways to Epigenetic Regulation

“…Detection of increased levels of DNA methylation in dormant chestnut buds further supports the role of DNA methylation in dormancy induction (Santamaria et al 2009). Cold temperatures might also regulate histone modification through the mode of action of ABA because coldinduced dormancy is concomitant with ABA increase and ABA alone acts as a sole dormancy inducer in many species (Hansen et al 1999;Arora et al 2003;Molmann et al 2005;. ABA has been shown to down-regulate Arabidopsis HISTONE DEACETYLASE 2C ( AtHD2C) (Sridha and Wu 2006), and up-regulate HIGH EXPRESSION OF OSMOTIC STRESS RESPONSIVE GENES 15 ( HOS15) that codes for a H4 deacetylase (Zhu et al 2007).…”

“…Earlier research on dormancy has implicated plant hormones, especially GA and abscisic acid (ABA), as key dormancy regulators that orchestrate cell growth and cell 4 Dormancy Behaviors and Underlying Regulatory Mechanisms division-related processes (Hansen et al 1999;Arora et al 2003;Molmann et al 2005;). In addition, water status of plant meristems is also critical for dormancy regulation.…”