Parent Shoot Research Articles

Spatiotemporal distribution of epicormic shoots and their architecture in branches of Fraxinuspennsylvanica

Epicormic shoots in the branch systems of Fraxinuspennsylvanica var. subintegerrima (Vahl) Fern, (green ash) were more common on lower order shoots and arose periodically over a number of years, resulting in a greater number in older crown regions. Nevertheless, considerable variation existed among trees, ranging from 3 to 34 epicormic shoots per branch sample. Epicormic shoots were generally located near the distal end of parent shoots, suggesting their origin from persistent buds in these regions. The mean divergence angle of epicormic shoots was almost 10° greater than that of nonepicormic shoots. Mean length did not differ between epicormic and nonepicormic shoots, but the length of daughter terminal shoots extending epicormic shoots was considerably less than the length of those extending nonepicormic shoots. The number of lateral shoots produced by the two shoot types did not differ. The significance of epicormic shoot production to crown development and maintenance is discussed.

Shoot-length frequencies in black birch (Betula lenta)

Lengths of all parent and current shoots were measured on three 8- to 10-year-old black birch (Betulalenta L.) trees with branches <8 years old. Older branches had more short shoots (<1 cm long) and shorter long shoots (>2 cm long) than younger branches. Parent long shoots produced three to nine basal short shoots. Observations on short-shoot production were consistent with the hypothesis that only buds with adequate nutrition formed long shoots. Three growth rules were developed for a model that simulated individual branch growth: (i) a regression predicting lateral shoot number from each parent shoot length; (ii) probabilities for the number of short shoots produced by a parent shoot based on the total number of current shoots produced per parent shoot; (iii) a regression predicting current shoot length from parent shoot length, current shoot position (longest to shortest), branch age, and main-axis elongation in the current and previous year. Simulations of 81 branches using these rules predicted shoot numbers and total shoot lengths close to those of the actual branches (R2 = 0.73–0.84).

Growth of dormant buds on severed rhizomes of Calamagrostis canadensis

The regeneration potential and dormancy of lateral buds on rhizome segments near the parent shoot base or the distal rhizome apex of Calamagrostis canadensis were assessed. Apical and basal segments of various length, with and without the parental shoot base or rhizome apex attached, were planted 1 cm deep in loam soil. When the apex or base was attached axillary buds on the rhizome usually remained dormant. When the parental shoot base was excised, the bud closest to the rhizome base was more likely to sprout than more distal buds. When the apex was excised from the apical segments, more axillary buds emerged but no priority of bud development arose. Buds near the apex position generally had a higher frequency of sprouting than buds adjacent to the parental base. Rhizome segments adjacent to the apex were heavier and had a higher nonstructural carbohydrate content than rhizome segments adjacent to the parental base. Key words: Calamagrostis canadensis, rhizome, dormancy, apical dominance, competition

Preformed and neoformed extension of shoots and sylleptic branching in relation to shoot length in Tsuga canadensis

Shoot systems developed over 3 successive years were investigated on 55 understorey Tsuga canadensis (L.) Carr. trees. Paired comparisons of preformed-leaf content of terminal buds and numbers of leaves produced on new shoots showed that neoformed leaves were produced in large numbers. Parent-shoot character was not useful in predicting numbers of preformed leaves, was better related to total leaves produced, but left the majority of the variation unexplained. This reflected the capacity of any terminal bud to produce a shoot with more or less neoformation, depending on conditions for growth. All shoots over 6 cm long produced sylleptic shoots that bore from two to many leaves and were arranged in a mesitonic pattern along the parent. Some of the longer sylleptic shoots produced lateral buds or second-order sylleptic shoots. Monopodial second-year extensions of sylleptic-shoot axes followed an acrotonic pattern, as did proleptic shoots from the few lateral buds borne on the parent shoots. Such lateral buds were more frequent on shorter parent shoots: they typically occurred near the proximal and distal ends. Duration of shoot extension was positively correlated with shoot length: terminal buds became evident as shoot extension neared cessation.

Apical dominance in Phaseolus vulgaris: effect of the nitrogen supply

Nitrogen is one of the most effective of the many factors that can influence the degree of apical dominance, but the mechanism involved has not been determined. In experiments with Phaseolus vulgaris, grown in sand culture under controlled conditions, increasing the nitrogen concentration in the nutrient solution from 52.5 to 315 mg/L released the bud at the primary leaf node from inhibition. Precise measurements (± 1 μm) with a strain gauge transducer showed that the bud growth response was initiated ca. 3 h after increasing the N supply. The increase in the total N content of the buds of the high-N plants was significantly correlated with their uptake of water. Increases in the amino-N content of the buds of the high-N plants over the first 24 h of the treatment period were correlated with significant increases in their total water potential and pressure potential, but their solute potential was unaffected. The absence of any reduction in their solute potential was attributed to the dilution effect of the increased uptake of water. These results are consistent with the hypothesis that N initiates the release of buds from apical dominance by an osmotic effect that increases their capacity to compete for water with the parent shoot. Key words: apical dominance, nitrogen, Phaseolus, water potential.

Influence of Male and Female Cones on Needle CO 2 Exchange Rates of Field-Grown Pinus contorta Doug. Trees

In autumn, needles on the parent shoot of branches of Pinus contorta Doug. bearing male cones had significantly higher photosynthetic rates compared to needles on vegetative shoots and those branches bearing female cones. There were no significant differences between the assimilation rates of needles on vegetative shoots and branches bearing female cones in any of the three sample periods (spring, summer or autumn). It was suggested that needles on branches bearing male cones had higher autumn assimilation rates because of: (1) reduced needle complement on the current year's growth and (2) presence of a developing male cone bud. Needles on branches bearing female cones had higher respiration rates than needles on vegetative branches, at all three sample times, and significantly higher respiration rates than needles on branches bearing male cones in the spring and summer sample periods. It is suggested that the higher dark respiration rates associated with branches bearing female cones were the result of the simultaneous growth and extension of both female cones and the current year's shoots. Key-words: Assimilation rates, female cones, male cones, Pinus contorta, respiration rates

An analysis of architectural parameters of male and female Fraxinus pennsylvanica in relation to crown shape and crown location

Architectural variables from male and female green ash (Fraxinus pennsylvanica var. subintergerrima (Vahl) Fern.) comprising three different crown-shape classes were analyzed at four different crown levels to determine which variables influenced crown shape. The narrow conical shape class had the largest mid shoot diameters and the smallest shoot tip abortion frequencies. The broad to round shape class had greater abortion frequency overall. In addition, there was less difference in shoot length between the top and bottom of the crown. The more oval shape class was intermediate for both shoot diameters and abortion frequency. Parent and daughter shoot lengths were longer, midshoot diameters larger, and elevation angles greater with increasing sampling height in the tree. Male trees had shorter shoot lengths and shorter and fewer daughter lateral shoots than female trees. Principal component analysis was used to identify shoot lengths, elevation angles, and abortion frequencies as potentially key variables in understanding crown shape in green ash. Interrelationships of many of the architectural variables suggest that a significant change in one may lead to changes in others, which ultimately would lead to changes in overall crown shape.

Growth of Current Shoot Populations on White Pine Branches: Test of a Model

WILSON, B. F. (Dept. Forestry and Wildlife Management, Univ. Massachusetts, Amherst, MA 01003). Growth of current shoot populations on White Pine branches: Test of a model. Bull. Torrey Bot. Club 117: 215-220. 1990.-Data from 49 8-year-old eastern white pine (Pinus strobus L.) branches were used to test a model which generates current shoot-length frequency distributions. The numbers and lengths of current shoots from parent shoots of all 1 cm length classes were determined. In the first simulation of each individual branch growth the annual elongation of the main axis for each year was specified for each branch; other population growth variables did not change from year to year. In simulated, compared to real, populations: total shoot numbers and lengths were similar (R2 of 0.60 and 0.66 respectively), but were overestimated in small branches and underestimated in large branches; shoot-length frequencies were similar except in the short length classes where the 1 and 2 cm classes were underestimated and the 3 cm class overestimated; and the number of long shoots was overestimated when annual elongation of the main axis decreased rapidly. A second simulation of each branch accounted for annual differences in terminal shoot elongation related to changes in elongation of the main axis. This simulation reduced, but did not eliminate, the systematic errors.

In vitro propagation of mulberry ( Morus alba L.) through nodal segments

Nodal explants of mulberry ( Morus alba L.), bearing an axillary bud, and obtained from in vitro raised seedlings were used to initiate shoot cultures. Murashige and Skoog medium supplemented with 3% sucrose and 2.5 μM N 6-benzyl adenine resulted in a maximum rate of shoot multiplication (up to 13-fold) as expressed in terms of the number of nodes (propagules) formed per shoot. Nodal segments from 3–4-year-old greenhouse-grown plants behaved similarly. Nodal explants from different seedlings exhibited highly significant differences in the rate of shoot multiplication. In addition, the position of the nodal segment on the parent shoot determined the rate of shoot multiplication, with a basipetally increasing gradient in the growth response of the segments being observed. The cultured nodal segments could be cold stored at 4°C for at least 6 months without any loss of multiplication rate on subsequent culture at 25°C. The in vitro formed shoots underwent spontaneous rooting, after being on shoot proliferation medium for more than 4 weeks. Addition of activated charcoal (0.05 or 0.1%) to the shoot proliferation medium speeded up the production of adventitious roots by at least 2 weeks and inhibited the formation of callus at the basal end of the shoots. The rooted shoots could be transplanted to sand-vermiculite (1:1) mixture in the greenhouse with 100% transplantation success.

The relationship between some morphological and chemical features of Sphagnum cuspidatum Ehrh. and physical characteristics of the environment

SummaryThe frequency (No. 1000 fascicles−1) of innovations (branches resembling the parent shoot) on plants of Sphagnum cuspidatum Ehrh. was determined at IX sites on or near the Silver Flowe National Nature Reserve on six occasions. The capitula were analysed for nitrogen, phosphorus and potassium.When the sites were arranged in order of increasing mean innovation frequency it was found that the frequency at ombrotrophic sites was less than that at rheotropic sites. Interfascicle length was directly related to innovation frequency but no evidence of a relationship between either interfascicle length or innovation frequency and capitulum dry weight was found. During the course of each growing season the variances of the means of interfascicle length and capitulum dry weight declined.Multiple regression analysis indicated that the capitulum dry weight and interfascicle length were negatively and positively related respectively to the nitrogen content of the capitula. The regression of innovation frequency on N, P and K in the capitula was not significant (P > 0.05).Two experiments were undertaken in which shoots of Sphagnum cuspidatum were reciprocally transplanted between a rheotrophic and an ombrotrophic site. During the course of a single growing season the mean interfascicle length, the mean capitulum dry weight and the mean concentrations of N, P and K in the capitula became much more similar to those of the controls. At the beginning of each experiment all visible innovations were removed from the plants. At the end of the experiment in 1983 innovation frequencies on the transplants were intermediate between those on the ombrotrophic and rheotrophic controls. In 1984 innovation frequencies on both controls and transplants were relatively low and an attempt is made to explain this in terms of the climatic conditions of that year.

Shoot production in Douglas-fir branches

Of the 3981 shoots present in 1986 on 16 Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) branches, 6–12 years old, only 1933 produced new shoots in 1987, and of these only 311 produced more than one shoot. Length of new terminal shoots was determined primarily by the length of the parent shoot (R2 = 0.57). Shoots that did not elongate had blunt buds, < 1 mm long, with no leaf primordia; shoots that elongated had pointed buds, > 2 mm long, with many leaf primordia. Buds < 1 mm long survived up to 3 years without elongating; needles on these shoots survived an additional 2 years. Parent shoots longer than 13 cm all elongated. The percentage of parent shoots < 14 cm long that did not elongate, and would have subsequently died, increased with (i) decreasing parent shoot length; (ii) increasing whorl number along the main axis of the branch (toward the branch base); (iii) decreasing total elongation of all shoots on the branch, a measure of branch vigor.

An architectural analysis of Shepherdia canadensis and Shepherdia argentea: patterns of shoot development

In the context of an architectural analysis, the seasonal pattern of shoot development of Shepherdia canadensis and S. argentea (Elaeagnaceae) was examined. In both species floral bud burst was the first outward manifestation of seasonal activity. Vegetative shoots of S. canadensis expanded 3 – 5 pairs of preformed leaves during a period of 9 – 10 weeks. There was no pattern of internodal length that identified annual increments. In S. argentea, 6 – 18 pairs of leaves expanded during a period of 15 – 17 weeks, the variation being related to the extent of neoformation. There was a distinct pattern of internodal length, with a maximum in midseason, so that annual increments could be recognized subsequently. Lateral buds in S. canadensis expanded only proleptically as either short shoots or long shoots. Most had declining growth rates in the subsequent year and within 5 to 7 years had undergone abscission. In S. argentea. lateral buds expanded both sylleptically and proleptically as short shoots, long shoots, or thorns. The distribution pattern of these lateral types was related to the vigour of parent shoot growth. Some abscission of short shoots was noted. For each species a stochastic flow chart of shoot development was prepared and a computer program incorporating actual data was written that simulated shoot development for up to four generations of growth. Comparison of the two species indicates that S. argentea is more plastic in response to environmental conditions.

Continuous growth and clump maintenance of Potamogeton crispus L. in Narutoh River, Japan

To account for the continuous growth and clump maintenance of Potamogeton crispus L. in a lotic habitat, phenological and quantitative observations were made in a small river in Japan from April 1981 to August 1982. Favourable water temperatures (8.7–24.7°C) for shoot growth prevailed throughout the study period and, thus, the adventitiously rooting shoots grew successively from buried stems and rhizomes all the year round. Total stem length (including above- and underground stems) reached a maximum of 4690 m m −2 in April 1982. Flowering and turion formation occurred almost simultaneously from late May until late October when water temperatures were higher than 20°C and the photoperiod was longer than 12 h. Though the plant produced numerous turions (> 9600 turions m −2 year −1), they were small (5–15 mg dry wt. turion −1) and assumed to be less important than underground stems for clump maintenance; while the stems were firmly rooted in bottom sand and protected by sediment from being swept away, most of turions were washed downstream immediately after they detached from the parent shoots. Among the total number of turions collected, only 2.7% were those which remained and germinated in the clump. Distinctive features of this plant in lotic and lentic habitats are also presented.

GROWTH IN MEDEOLA VIRGINIANA CLONES I. FIELD OBSERVATIONS.

The pattern of clonal growth in Medeola virginiana was mapped over twelve square meters in a successional white pine forest of eastern Massachusetts. From these maps and an additional sample of excavated plants, the distances and angles of divergence of daughter ramets from the base of the parent shoot were measured for 213 plants. All clonal growth parameters were found to be highly variable in the ñeld, with coefficients of variation ranging from 17-92%. The rules describing the pattern of growth of daughter ramets were found to be considerably more complicated than previously reported (Bell, 1974). The mortality of tubers, the natural variation of parameters of growth, and the complex patterns of daughter production all call into question the ability of idealized, deterministic models of growth to predict the form of clones and the position of ramets in the field.

Regulation of glutathione S-transferases of Zea mays in plants and cell cultures

An antiserum to glutathione S-transferase (EC 2.5.1.18) from maize (Zea mays L.) responsible for herbicide detoxification has been raised in rabbit. The antiserum was specific to the Mr 26000 subunit of the enzyme from maize seedlings and suspension-cultured cells, and recognized the isoenzymes active toward both atrazine and metolachlor. When plants were treated for 24 h with the herbicide antidote N,N-diallyl-2-2-dich-loroacetamide (DDCA), enzyme activities toward metolachlor were doubled in the roots and this was associated with a 70% increase in immunodetectable protein. Translation of polysomal RNA in vitro showed that the increase in the transferase in root tissue was brought about by a ninefold increase in mRNA activity encoding the enzyme. Treatment of suspension-cultured cells with cinnamic acid, metolachlor and DDCA raised enzyme activities but did not increase synthesis of glutathione S-transferase. In cultured maize cells, enzyme synthesis was maximal in mid-logarithmic phase, coinciding with the highest levels of enzyme activity. When callus cultures were established from the shoots of a maize line known to conjugate chloro-s-triazines, enzyme activity towards atrazine was lost during primary dedifferentiation. However, levels of total immunodetectable enzyme and activity toward metolachlor were increased in cultured cells compared with the parent shoot tissue.

Crown architecture of Larix laricina saplings: an analysis of higher order branching

Quantitative analysis and simulation modelling of Larix laricina (Du Roi) K. Koch branches revealed a complex system of architectural patterns and correlations. Numbers of lateral buds and long shoots were positively correlated with parent-shoot length, but the relationships varied among shoot orders and for sylleptic shoots. For order 2 and sylleptic shoots, numbers of lateral long shoots were also correlated with associated terminal-shoot lengths. Sylleptic shoots produced more lateral long shoots than equivalent proleptic shoots. Lateral long-shoot lengths decreased basipetally and were correlated with terminal-shoot lengths. Lengths of order 2 lateral long shoots also varied independently with crown position. Generally, the degree of apical control decreased and the proportion of short shoots increased with positions of less vigour in the crown. Terminal long-shoot lengths varied with parent-shoot length, location, and to some extent parent-axis leader length. Terminal short-shoot production was associated with shorter parent shoots. Shorter order 2 shoots (<60 mm) and most order 3 shoots produced no lateral long shoots. The net result was that branch structural development ceased in less vigorous crown positions. The spatial disposition of shoots, as defined by elevation and divergence angles, varied with position of origin around and along parent shoots. Although variable, elevation angles decreased and divergence angles increased basipetally.

Crown architecture of Larix laricina saplings: sylleptic branching on the main stem

Sylleptic branching occurred on the current (1983) height-growth increment in 44% of Larix laricina (Du Roi) K. Koch (tamarack) saplings sampled from a natural population near Fredericton, N.B. Although variable, the occurrence and amount of syllepsis tended to increase with parental shoot length. Sylleptic shoots were generally located on the proximal halves of parental shoots. In most cases, the proximally and distally situated sylleptic shoots were somewhat shorter than those in between. The lengths of terminal shoots arising from sylleptic shoots were significantly correlated with parental shoot length, current tree leader length, and location of the branch on its parental shoot. The lengths and elevation angles of terminal extensions from sylleptic shoots tended to be greater than those from nonsylleptic (proleptic) lateral long shoots borne in the same region of the height-growth increment. Architectural characteristics of the extensions resembled those of the more distal proleptic shoots, which develop into major branches. Thus, an additional complement of major lateral branches appeared to be developing where syllepsis occurred. Quantitative relationships depicting sylleptic branching patterns were incorporated into a previous architectural model and simulations of crown architecture which included syllepsis were obtained.

Evidence of competition for water as a factor in the mechanism of root-bud inhibition in milkweed (Asclepias syriaca)

In experiments with seedlings of milkweed, Asclepias syriaca L., grown in sand culture under controlled conditions, growth of the root buds was significantly increased within 24 h of the excision of the parent shoot. However, only a few of the measured buds continued to grow, the growth of most of the remianing buds being arrested within 48 h of their release from inhibition. At low humidity (approx. 30–50% relative humidity (RH)), the decapitated disbudded stem, bearing only a single pair of leaves, promoted the early growth of the root buds but strongly inhibited their subsequent elongation and emergence as shoots. The mature stem itself, when completely defoliated, also exerted a significant degree of inhibition of root-shoot production. At high humidity (93–100% RH), which reduced transpiration by approximately 50%, this inhibiting effect of mature shoot tissue was either eliminated or greatly reduced, while the rate of emergence and subsequent growth of shoots produced from the root buds following the complete removal of the parent shoot were also significantly increased. The results suggest, as a working hypothesis, that transpiration-induced reduction in water potential (ψ) plays a major role in the mechanism of root-bud inhibition.

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.

The morphology and growth of Arctostaphylos uva-ursi (bearberry): an architectural model simulating colonizing growth

Plan view simulations of the growth and spread of the prostrate shrub, Arctostaphylos uva-ursi (L.) Spreng. (bearberry) are presented using quantitative data from the colonizing zone in open sand-dune sites. The model was based on statistical analyses of the lengths of dominant horizontal shoots, the frequency and location of daughter shoots on parental shoots, and the divergence angles between daughter and parental shoots. A sequence of 10 rules was devised which described the structural relationship between parent and daughter shoots. To accommodate observed variability in architectural parameters, several stochastic elements were incorporated into the model. Consequently, there was virtually no possibility of two simulations being identical. The simulations showed growth patterns similar to colonizing complexes observed in nature. The advantages and limitations of the model are discussed.