Field research was conducted to characterize hemp dogbane crown root carbohydrates, to quantify crown root lipids, and to determine seasonal fluctuation of each. The effect of day length on the release of hemp dogbane crown bud dormancy was studied in growth chambers. Total nonstructural carbohydrate (TNC) levels fluctuated with seasonal lows occurring during bud to mid-flowering and seasonal highs in fall predormancy periods. Starch was the primary storage carbohydrate, comprising up to 39.6% of crown root dry weight at the highest seasonal level. Ethanol soluble reducing sugar levels were negatively correlated with seasonal starch levels, and appeared to be maltose and glucose accumulated before conversion to sucrose for translocation. Most lipids were in ethanol soluble fractions and were inversely correlated with seasonal TNC patterns. The maximum level of total lipids in crown roots was 6%. Lipids appeared to be by-products of metabolism in nonarticulated lacticifers and not a significant carbon energy source. An 18-h day length resulted in a 10-fold increase in intact, 2-yr-old crown root dormancy release compared with 10- or 14-h day lengths in growth chamber studies. Seasonal carbohydrate fluctuations in hemp dogbane suggest the most effective control with mowing or tillage would occur when applied at mid- to full flower before root carbohydrates begin to recover. The most effective translocation of phloem mobile herbicides to crown roots would occur after mid- to late flower through leaf senescence when carbohydrates are being stored in the roots.

Laboratory, greenhouse, and field experiments were conducted at the Lacombe Research Station to determine if CCC, ethephon, or CCC/ethephon had direct activity on quackgrass rhizome buds, and to determine if foliar applications of CCC/ethephon could predispose quackgrass to more effective control with sethoxydim. CCC, ethephon, and CCC/ethephon had growth regulating effects on the axillary buds and the apex of detached quackgrass rhizomes. CCC increased rhizome bud sprouting on rhizomes with the apex excised, but not on rhizomes with an intact apex. Ethephon or CCC/ethephon inhibited bud sprouting on rhizomes with an intact or excised apex. CCC/ethephon, but not CCC or ethephon alone, increased rhizome elongation on rhizomes with intact apices. In the greenhouse, pretreatments of CCC/ethephon increased sethoxydim activity on quackgrass rhizome buds and caused lower shoot emergence from one-bud rhizome segments. Results of field experiments were less consistent than those in the greenhouse. However, sometimes CCC or CCC/ethephon pretreatments resulted in increased quackgrass control in the field with sethoxydim.

We examined effects of supplementary nitrogen on young Canada thistle stands in Alberta, Canada. Urea applied at 70 or 100 kg N ha–1 increased shoot population densities, mostly through increased root growth in the top 20 cm of soil rather than through released root bud dormancy. Nitrogen fertilization, therefore, may increase the severity of a Canada thistle infestation. In 1-yr-old stands, the number of emerged and unemerged root buds/m of root was higher near the soil surface in fertilized plots than in unfertilized plots, and no underground shoots were detected at the time of sampling. In 2-yr-old stands, more unemerged root buds/m of root were found at depths below 20 cm in fertilized plots than in unfertilized plots, and twice as many underground shoots/m of root occurred between 20 and 40 cm in fertilized plots as in unfertilized plots. However, no effect of nitrogen on the number of emerged root buds was detected. Nitrogen treatment increased shoot production only for those replanted root fragments from deeper than 60 cm in 1-yr-old stands and deeper than 160 cm in 2-yr-old stands.

Distribution of 14C-glyphosate [N-(phosphonomethyl)glycine] in chemically treated and physically manipulated common milkweed [Asclepias syriaca (L.) ♯ ASCSY] was studied in greenhouse and growth chamber experiments. Pretreatment with glyphosate at 0.6 and 1.1 kg ae/ha 3 days prior to 14C-glyphosate application to leaves reduced the concentration of 14C recovered from shoots and leaves above the 14C-glyphosate-treated leaves but had no influence on the concentration of 14C in proximal root buds. Partial removal of the shoot and root prior to the application of 14C-glyphosate increased bud respiration and the concentration of 14C in the proximal root buds. Proximal root buds treated with 1 mM of 6-benzyl-aminopurine (BAP) for 6 days (3 days prior to application of 14C-glyphosate) contained seven times more 14C/mg than root buds of BAP-untreated plants, suggesting that dormant buds could be chemically stimulated to accumulate higher concentrations of glyphosate. BAP-treated buds were killed by foliar applications of glyphosate at 1.1 kg/ha, indicating that proximal root buds can be stimulated to acquire lethal concentrations of glyphosate.

Absorption and translocation of the growth regulator 14C-chlorflurenol (methyl-2-chloro-9-hydroxyfluorene-9-carboxylate) and of the herbicide 14C-dicamba (3,6-dichloro-o-anisic acid) were studied in Canada thistle [Cirsium arvense (L.) Scop.]. Also investigated was how foliar treatments with chlorflurenol affected leaf uptake and distribution of dicamba by Canada thistle. Plants were grown in aerated nutrient solution. 14C-chlorflurenol showed strong acropetal and weak basipetal movement. Thirty-two percent of the foliar applied 14C-dicamba was absorbed and most of the radioactivity tended to accumulate in the young growing leaves. Only 0.6% of the applied radioactivity moved to the roots. Leaf absorption and basipetal translocation of 14C-dicamba were increased two- and ten-fold, respectively, by the simultaneous addition of chlorflurenol at 0.6 kg/ha. Root bud activity was increased when 4-week-old Canada thistle plants were foliarly treated with chlorflurenol at 0.6 kg/ha. Field work demonstrated that Canada thistle control could be enhanced by chlorflurenol addition to dicamba.

Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] root samples were collected at monthly intervals over a 2-yr period from two locations to determine seasonal fluctuations in the presence and growth potential of root buds. Root bud growth was highest during late fall and winter months following death of the aerial shoots. Root fragments incubated at a constant 15 C for 2 weeks in continuous light consistently had more buds than nonincubated roots, which indicated active bud differentiation during the incubation period. Incubated roots produced 3 to 9 cm of new shoot length/cm root length. There were no obvious seasonal patterns in the presence of root buds or their ability to elongate at different times of the year. Carbohydrate reserves were stored preferentially in roots rather than in developing root buds or the bases of shoots. These reserves ranged from as low as 3% of root fresh weight during spring months to as high as 26% in late fall months, although the levels did not increase consistently during summer months over the locations and years of this study.

Microarray analysis was used to follow changes in gene expression coinciding with seasonal changes in the dormancy status of crown buds of field-grown leafy spurge. Known cold-regulated genes were induced, and numerous gibberellic acid–responsive genes were down-regulated during the transition from paradormancy to endodormancy. Genes involved in photomorphogenesis were induced during endodormancy. Also, ethylene signaling responses were observed during ecodormancy rather than endodormancy. These results provide additional insights into the signals regulating expression of several genes previously associated with transition from paradormancy to growth in root buds.

We have isolated both a genomic and near full length cDNA clone for a D-class cyclin gene from the perennial weed leafy spurge. Sequence analysis indicates that this gene has the highest similarity to CYCLIN D3-2 of Arabidopsis. This gene is preferentially expressed in growing shoot apices and is up-regulated in adventitious buds on resumption of growth following loss of correlative inhibition (apical dominance). CYCLIN D3-2 is also induced in nongrowing adventitious buds of plants treated with gibberellic acid or after removal of leaves—treatments known to up-regulate expression of G1 to S phase transition–specific genes such as HISTONE H3 in adventitious buds. CYCLIN D3-2 was not induced on removal of the apical and axillary buds. Expression of CYCLIN D3-2 is down-regulated in adventitious crown buds during initiation of ecodormancy in early winter. Sequence comparisons of CYCLIN D3-2 with its putative orthologue from Arabidopsis identified several conserved motifs in the promoter region and a conserved region capable of forming a stable hairpin loop in the 5′ untranslated region. Conservation of these noncoding sequences across species strongly suggests they have a regulatory function.

Bud dormancy is the primary mechanism by which the many perennial weeds escape herbicidal and mechanical control. We developed a 2,654-element Euphorbiaceae cDNA microarray using 1,886 sequenced cDNAs from the model perennial weed leafy spurge, 384 cDNAs from cassava, and 384 control genes from other plant, animal, and bacterial species. This array was used to follow changes in gene expression in root buds of leafy spurge following loss of paradormancy. The differential expression of several genes previously identified as being induced following loss of paradormancy was confirmed by microarray analysis. In addition, genes encoding an asparagine synthase, a phosphate-inducible protein, and a curculin-like (mannose-binding) lectin family protein were found to be rapidly up-regulated upon loss of paradormancy. Several genes involved in flavonoid biosynthesis were found to be rapidly down-regulated upon loss of paradormancy. The potential impact of flavonoid biosynthesis on auxin transport in response to bud growth is discussed.

Several physiological processes controlling tree phenology remain poorly understood and in particular bud dormancy. Many studies have emphasised the action of chilling temperatures in breaking dormancy. However, the effect of the preceding summer temperatures has rarely been investigated although there is some evidence that they may be involved in the settlement and intensity of dormancy as well as cold acclimation. In this paper, thermal time to budburst in relation to the duration of chilling outdoors, preceding summer temperatures and forcing temperatures was studied by outdoors experiments in seedlings of Platanus acerifolia, Vitis vinifera, Quercus pubescens and Castanea sativa. Results showed that temperatures of the preceding summer had no significant effect on the timing of budburst, P. acerifolia and Q. pubescens showed a very weak response to the duration of chilling, and the phenological characteristics of each species were found to be adapted to the climate conditions of its own geographical area. The phenological model used in this study explained 82–100% of the variance of the data without taking into account summer temperatures. Thus, although summer temperatures may be well involved in the intensity of dormancy and cold hardiness, they do not significantly affect budburst and therefore may not need to be considered in phenological models for predicting budburst.