Root Bud Growth Research Articles

Sugars, hormones, and environment affect the dormancy status in underground adventitious buds of leafy spurge (Euphorbia esula)

Signals from both leaves and apical or axillary meristems of leafy spurge are known to inhibit root bud growth. To test the hypothesis that carbohydrates and growth regulators affect root bud growth, decapitated leafy spurge plants were hydroponically treated with glucose, sucrose, gibberellic acid (GA), abscisic acid (ABA), 1-naphthaleneacetic acid (NAA), 6-benzylaminopurine (BA), and a GA biosynthesis inhibitor, paclobutrazol. Both glucose and sucrose caused suppression of root bud growth at concentrations of 30 mM. The inhibitory effect of sucrose was counteracted by GA at 15 μM. In contrast, BA, ABA, NAA, and paclobutrazol inhibited root bud growth at concentrations as low as 1, 2, 1, and 16 μM, respectively. Sugar and starch levels were also determined in root buds at various times after decapitation. Buds of intact plants contained the highest level of sucrose compared with buds harvested 1, 3, and 5 d after decapitation. To determine how seasonal changes affect root bud dormancy, growth from root buds of field-grown plants was monitored for several years. Root buds of field-grown leafy spurge had the highest level of innate dormancy from October to November, which persisted until a prolonged period of freezing occurred in November or early December. Our data support the hypothesis that carbohydrates may be involved in regulating dormancy status in root buds of leafy spurge.

Root formation, bud growth and survival of ornamental shrubs propagated by cuttings on different planting dates

SummarySemi-hardwood cuttings of Cornus alba ‘Sibirica’, Deutzia ‘Mont Rose’, Forsythia × intermedia ‘Lynwood’, Ligustrum vulgare ‘Liga’, Philadelphus × virginalis, Potentilla fruticosa ‘Goldfinger’, and Spiraea × vanhouttei were planted on seven dates from July to October in two years and at three locations to investigate the effect of planting date on root formation, axillary bud growth, and plant survival. Cuttings were planted directly in the field and covered with polyethylene. Generally, root formation, bud growth, and plant survival were similar both years and at the three locations. All species except Deutzia had relatively constant rooting percentages at planting dates until mid August. For all species rooting percentages declined from mid August to October. Except for Deutzia, plant survival the following spring was constant or decreasing with planting date. For all species except Potentilla axillary bud growth and survival of cuttings planted in late September or October tended to increase while rooting percentages continued to decrease. In all species there was a close relationship between axillary bud growth and survival. Results revealed that many roots per cutting accelerated axillary bud growth.

Role of mature leaves in inhibition of root bud growth inEuphorbia esulaL.

Earlier studies on the source of signals controlling correlative inhibition of root buds (underground adventitious buds located on the lateral roots) inEuphorbia esulaindicated that either growing meristems (apical or axillary buds) or fully expanded leaves could prevent root buds from breaking quiescence. An investigation of the production and transport requirements of the leaf-derived signal is described. As few as three leaves remaining on budless stems greatly reduced the growth of (but not the number of growing) root buds. Also, light and CO2fixation were necessary for the leaf effects on root bud growth, but not necessary for correlative inhibition imposed by growing axillary buds. Treatment of plants with Ametryn induced root bud growth on budless plants but not on plants with intact axillary buds. The polar auxin transport inhibitor N-1-naphthylphthalamic acid prevented transmission or the signal from growing axillary buds, but it had only a minor effect on the transmission of the leaf-derived signal. Treatment of plants with gibberellic acid (GA) induced growth of root buds under otherwise noninducing conditions to some extent in all plants. However, the greatest effects of GA were on plants with intact leaves (meristemless/budless and meristemless). GA had no significant effect on root bud quiescence under conditions that induced root bud growth.

The role of specific plant organs and polar auxin transport in correlative inhibition of leafy spurge (Euphorbia esula) root buds

Localization of the source of the signal(s) controlling correlative inhibition of leafy spurge root buds (underground adventitious shoot buds located on the lateral roots) was studied by sequential removal of various plant organs. It was determined that full correlative inhibition of root buds was lost only after excision of all aerial tissue from the plant, or after excision of all aerial tissue except the stem. If mature leaves or growing axillary buds (or both) were left intact, no growth of root buds was observed. The synthetic auxin, alpha-NAA, prevented release of apical dominance and subsequent outgrowth of stem and crown buds when applied to the cut end of the stem or crown. Exogenous application of NAA to either the stem or the crown had little effect on root bud growth. Application of the auxin transport inhibitor NPA around the base of the crown had no effect on root bud quiescence. These data are not consistent with the previous studies (Weed Sci. 35: 155-159 (1987)) that indicate a role for auxin in maintenance of correlative inhibition of root bud growth in leafy spurge. The results of auxin transport inhibitor studies presented here suggest that correlative inhibition of root bud growth does not rely on the classic polar auxin transport system.Nomenclature: leafy spurge, Euphorbia esula L. #3 EPHES; NAA, naphthalene acetic acid; NPA, N-1-naphthylphthalamic acid; TIBA, 2,3,5-triiodobenzoic acid.Key words: root buds, apical dominance, auxin, NPA.

Technique for evaluating the potential for growth of shoot and root buds of white clover (Trifolium repens)

SUMMARYAn assay was developed for assessing the potential for growth of shoot and root buds of white clover. This paper describes the technique and the experimental results on which it was based. The assay involved the incubation of nodes under standard conditions and the monitoring of bud activity at the nodes. Shoot buds were of primary interest but the assay was also used to investigate the activity of root primordia. Correlative influences were reduced by separating individual nodes and by removal of their subtending leaves and petioles. The optimal environmental conditions for incubation were: a constant temperature of 20 °C, a 24 h photoperiod of low irradiance (4 W/m2) and a high relative humidity (≥ 90%). The technique proved suitable for the monthly screening of 1000–2000 nodes sampled from field populations of white clover.

Modification of root bud growth in Canada thistle with selected plant growth regulators: effects on translocation of glyphosate

Root applications of 0.1 μM 6-benzyladenine (BA) and 10.0 μM indole-3-butyric acid (IBA) enhanced or inhibited, respectively, root bud growth in hydroponically grown Canada thistle [Cirsium arvense (L.) Scop.]. Translocation of14C-glyphosate [N-(phosphonomethyl)glycine] into roots was positively correlated with this growth. Foliar applications of ethephon or chlorfluorenol also enhanced root bud growth, but glyphosate translocation was only weakly correlated with such growth in soil-grown Canada thistle. At glyphosate rates above 0.56 kg/ha, root bud growth was not stimulated by plant growth regulators (PGRs) and basipetal translocation was not enhanced. Paradoxically, ethephon and chlorflurenol restrained root bud growth in the field since thistle control steadily improved during the 3 years following treatment.

Correlative Inhibition and Dormancy in Root Buds of Leafy Spurge (Euphorbia esula)

Root buds of leafy spurge (Euphorbia esulaL. # EPHES) were found to be quiescent during most of the growing season due to correlative inhibition rather than innate dormancy. Excised root buds taken from plants that were fully flowering showed reduced elongation, indicating a period of innate dormancy. This innate dormancy could be eliminated by chilling plants for 8 days at 4 C. Root buds from plants showing late summer regrowth were no longer innately dormant. IAA (indole-3-acetic acid) and NAA (1-napthaleneacetic acid) completely inhibited the growth of excised leafy spurge root buds at concentrations of 10−3and 10−5M, respectively. A significant increase in root bud elongation was produced by 1 mM TIBA (2,3,5-triiodobenzoic acid) applied to stem and root tissue. These data provide further evidence for the involvement of IAA in correlative control of root bud growth in leafy spurge.

Some Effects of Humidity on the Growth and Development of Cirsium arvense

Seedlings of Canada thistle Cirsium arvense (L.) Scop. were grown in sand culture under controlled conditions at low (30%-50%) and high (90%-100%) relative humidity (RH). High RH increased stem height by 50% and shoot and root dry weights by 50% and 80%, respectively, but had no significant effect on root bud growth. When the root buds were released from correlative inhibition by removal of the main shoot, increasing the RH from ca. 50% to 100% significantly increased their rate of emergence and resulted in a twofold increase in the length and dry weight of emergent shoots after 7 days of growth. At low RH, growth of the root buds was significantly inhibited not only by mature leaves but also by mature stem tissue. The root buds were released from the stem-induced inhibition by keeping the stem at a high RH. These results, and supporting evidence from previous investigations with other species, indicate that the correlative inhibition of root buds is caused primarily by competition for water between the r...

Seasonal Variations in Canada Thistle (Cirsium arvense) Root Bud Growth and Root Carbohydrate Reserves

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.

Chlorsulfuron Effects on Shoot Growth and Root Buds of Canada Thistle (Cirsium arvense)

The effect of 67 g ai/ha chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-amino] carbonyl] benzenesulfonamide} on Canada thistle [Cirsium arvense (L.) Scop. ♯ CIRAR] root bud growth was examined in a series of greenhouse trials in which potted plants were treated with foliar sprays. Injury to root buds was assayed by determining their ability to form secondary shoots. Added surfactant, 0.2% (v/v) oxysorbic [oxysorbic (20 POE) polyethylene sorbitan monooleate], did not enhance chlorsulfuron-induced inhibition of parent shoot growth, but it increased root bud injury from foliarly applied chlorsulfuron. Cuttings taken from controls formed more secondary shoots than did chlorsulfuron-treated plants 2 weeks following spraying. However, root fresh weight and final secondary shoot growth from cut roots were unchanged 3 weeks after chlorsulfuron treatment compared to the time of spraying. Foliar treatment or a combination of foliar and soil treatment inhibited root fresh weight accumulation and secondary shoot growth equally 1 month following treatment relative to harvest controls. Soil treatment alone did not reduce either root fresh weight gains or secondary shoot outgrowth from root buds. Foliar treatment of vegetative Canada thistle with chlorsulfuron inhibited subsequent secondary shoot outgrowth from root buds more than did treatment at flowering.

Effect of shoot decapitation on the translocation of 2,4-D in Cirsium arvense

When 14C-labelled 2,4-D [(2,4-dichlorophenoxy)acetic acid] was applied to the basal leaves of Canada thistle (Cirsium arvense L.), prior removal of approximately the upper two-thirds of the flowering shoot resulted in a 20 to 30% increase in total 14C exported from the treated leaves and a twofold to threefold increase in the amount in the roots. Removing only the apical region of the shoot had the opposite effect, markedly reducing 14C export from the treated leaves and translocation to the roots. Provision of a higher N level more than doubled 14C translocation from the treated leaves and caused a threefold increase in 14C content of the roots of undecapitated plants. The reduction in basipetal transport produced by apical decapitation was attributed to the inhibiting influence of subapical lateral shoots on basal branching and root bud growth. When apical decapitation was combined with removal of the axillary buds in the subapical region, basal branching and root bud growth were promoted and 14C translocation into the roots was significantly increased.

Some effects of the nitrogen supply on growth and development of Cirsium arvense

The influence of nitrogen nutrition on the growth and development of Canada thistle, Cirsium arvense (L.) Scop., was investigated by growing seedlings in sand culture under controlled conditions. A preliminary experiment showed that seedlings at the cotyledon stage were very susceptible to injury by high salt concentration; a 10 × dilution of Hoagland's solution was required for successful establishment. Nitrate-N at 210 ppm caused severe leaf necrosis and inhibition of shoot and root bud growth, but provision of ammonium-N eliminated these effects.When seedlings were supplied with NH4NO3 at levels that ranged from 5.25 to 420 ppm N, shoot dry weight and root bud growth increased up to 210 ppm but decreased at 420 ppm, probably as a result of ammonium toxicity. By clearing roots with lactic acid it was shown that while growth of the root buds increased with the N level, the number of buds initiated was significantly reduced. When plants were grown initially at a low N level, a subsequent increase in the N supply permitted the root buds to escape from inhibition and develop as leafy shoots. This response suggested that under the experimental conditions, bud inhibition was due to internal competition for a limiting N supply.

Developmental studies on Euphorbia esula. The influence of the nitrogen supply on the correlative inhibition of root bud activity

When seedlings of leafy spurge (Euphorbia esula L.) were grown at a low nitrogen level (10.5 ppm) the growth of the lateral buds on the shoot was completely arrested by apical dominance while the buds on the roots, although also inhibited, showed considerably greater activity. At a higher nitrogen level (210 ppm) apical dominance was markedly reduced but the resulting outgrowth of the lateral buds increased the inhibiting capacity of the shoot, limiting root bud response. When the main shoot was decapitated the degree to which root bud growth was suppressed by a given number of lateral shoots was inversely related to the nitrogen supply. Inhibition of the root buds by the lateral shoots could be significantly reduced by growing the plants initially at a low nitrogen level so that growth of the lateral buds was arrested. A subsequent increase in the nitrogen supply strongly promoted the growth of the roots buds, some of which were sufficiently released from inhibition to emerge as leafy shoots.