Cellular changes associated with rest and quiescence in winter-dormant vascular cambium of Pinus contorta

Abstract

In winter, dormant cambial cells contain many small vacuoles interspersed throughout the cytoplasm. This differs dramatically from actively growing cambial cells whose structure is dominated by large central vacuoles. Structure reported in studies using conventional chemical fixation and transmission electron microscopy (TEM) conflicts with that described earlier for live cambial cells using light microscopy. In this study, cryofixation (high-pressure freezing/freeze substitution) was used to preserve dormant Pinus contorta fusiform cambial cells, revealing structure more consistent with that in early micrographs of live cambial cells. At the ultrastructural level, the plasmalemma was consistently smooth and tightly associated with the cell wall, contrary to the highly in-folded plasmalemma seen in chemically fixed cambial cells. In addition, both TEM and live-cell confocal microscopy demonstrated that, in some places, dormant cells were partitioned into more numerous, smaller vacuoles than were observed after chemical fixation. Populations of different vacuoles were apparent based on size, shape and membrane staining. Larger vacuoles had prominent tonoplasts and were often present as axially elongated, interconnecting networks with associated microfilament bundles. Endoplasmic reticulum fragmented during rest into numerous vesicular structures similar to small vacuoles, then with the transition to quiescence reformed into the smooth cisternal form.

Cambial sensitivity to rising temperatures by natural condition and artificial heating from late winter to early spring in the evergreen conifer Cryptomeria japonica

“…We observed previously that, in deciduous diffuseporous hardwood hybrid poplar, longer heating was needed when we started heating stems in December (Begum et al 2007). Several studies have shown that cambial cells at the resting stage of dormancy are unable to divide, even when exposed to favorable conditions (Little and Bonga 1974;Little 1984, 1986;Sundberg et al 1987), while cambium in the quiescent stage has the potential to generate new cells (Barnett and Miller 1994;Begum et al 2007;Oribe and Kubo 1997;Oribe et al 2001Oribe et al , 2003Rensing and Samuels 2004;Savidge and Wareing 1981). The inability of cambial cells to produce new cells during the resting stage of dormancy has been attributed to a variety of causes, such as impaired basipetal transport of IAA, a lack of responsiveness to IAA, and a deficiency in levels of cytoplasmic RNA (Lachaud 1989;Lachaud et al 1999;Little and Bonga 1974;Little and Wareing 1981;Little 1984, 1986;Schrader et al 2003).…”

“…Winter cambial dormancy in trees consists of two stages, namely, the resting and the quiescent stages (Little and Bonga 1974;Mellerowicz et al 1992;Rensing and Samuels 2004;Little 1984, 1986;Sundberg et al 1987Sundberg et al , 2000. During the first 2-4 weeks of dormancy, the cambium is unable to produce new cells even when the plant hormone indole-3-acetic acid (IAA) is supplied under favorable environmental conditions (Little and Bonga 1974;Mellerowicz et al 1989Mellerowicz et al , 1992Little 1984, 1986;Sundberg et al 1987).…”

activité cambiale et la xylogenèse des tiges et des racines d'Abies balsamea (L.) MILL. et de Picea mariana (MILL.) B.S.P. /

“…Chez les espèces de la zone climatique tempérée, il est possible de retrouver une périodicité distincte dans la formation des cernes de croissance (Bannan 1955;Larson 1994;Vaganov et al 2006), c'est-à-dire une alternance entre une phase active (période de croissance) et une phase inactive (période de dormance hivernale) du cambium vasculaire (Mahmood 1971;Vysotskaya et Vaganov 1989;Sundberg et al 1987;Fahn et Werker 1990;Iqbal 1994;Rossi et al 2006a). Ce phénomène a pour conséquence la formation de cernes annuels distinguâmes les uns des autres (Bannan 1955;Antonova et Stasova 1997;Rensing et Samuels 2004). En effet, on observe une différence dans le diamètre radial des trachéides produites par le cambium vasculaire au début et à la fin de la saison de croissance (Wodzicki 1971;Vysotskaya et Vaganov 1989), ce qui engendre une transition graduelle entre le bois initial, qui sert principalement au transport de la sève brute et le bois final, qui sert surtout à stabiliser la plante (Whitmore et Zahner 1966;Schweingruber 1996).…”

“…Avec ce critère, les cellules dans la zone cambiale peuvent être difficiles à différencier de celles en élargissement radial, et inclurent les cellules initiales fusiformes indifférenciées du xylème qui entreront éventuellement en différenciation (Barman 1955;Kitin et al 1999;Savidge 2000;Deslauriers et al 2003;Rossi et al 2006a). Tout comme l'ont mentionné Rossi et al (2006a (Farrar et Evert 1997;Rensing et Samuels 2004;Frankenstein et al 2005). Toutefois, la méthodologie utilisée dans cette étude ne permet pas de quantifier de telles observations, et c'est pour cette raison que l'apparition de trachéides en élargissement radial constitue le critère principal pour déterminer le début de la croissance du xylème et la formation du cerne.…”

Modification of cambial cell wall architecture during cambium periodicity in Populus tomentosa Carr.

“…Our knowledge of the metabolism of cambial cells has expanded in the last two decades, especially in terms of phytohormone regulation (Little and Savidge 1987;Mellerowicz et al 2001;Aloni 2004;Mwange et al 2005) and gene expression analyses (Schrader et al 2004;Espinosa-Ruiz et al 2004;Li et al 2009). Many reports dealt with the cellular changes associated with cambium periodicity, especially changes in the cytoplasm (Larson 1994;Iqbal 1995;Farrar and Evert 1997;Rensing and Samuels 2004), but few paid attention to the cell wall (Catesson 1994;Chaffey et al 1998). The seasonal cycle of cambial activity and dormancy is correlated with changes in the cell wall (Catesson 1994;Mellerowicz et al 2001).…”