Shoot Growth Cessation Research Articles

Active participation of the root/shoot transition region treated with triiodobenzoic acid in basipetal transport of 14C-indole-3-acetic acid and ethylene evolution in the stem of apple seedlings

Treatment with triiodobenzoic acid (TIBA) in lanolin to the root collar of 1-year-old apple seedlings cultivar ‘Antonovka’ 6 days before 14C-indole-3-acetic acid ( 14C-1-IAA) application reduced by half the distance of 14C basipetal transport compared with that of the controls (treated with lanolin only). The longer the time interval between TIBA and 14C-1-IAA application the more restricted was auxin transport. The mid-stem application of TIBA did not limit basipetal transport of 14C which reached, similar to controls, the point of the TIBA treatment within 24 h. In a parallel experiment with leafy seedlings, a high rate of ethylene evolution was observed in the youngest parts of stems of plants in which TIBA had been applied to the root collar. The total amount of ethylene evolved from the uppermost part of the seedlings increased significantly within 7–14 days after TIBA application to the root collar. This phenomenon was accompanied by a significant decrease in dark leaf respiration. It is suggested that TIBA application to the root collar but not to the mid-stem, restricts auxin transport from the apex, and causes a partial auxin depletion leading to a temporary cessation of shoot growth that favours acceleration of generative processes.

The effect of photoperiod on flowering and TPS production in the warm tropics

Three similar field experiments with five cultivars were carried out to evaluate the effect of a 5-hour extension of the natural daylength and a 3-hour night break on flowering and TPS production in the warm tropics. Shoot length, number of inflorescence positions per plant and number of flowers per inflorescence varied considerably between the experiments. In each experiment, the supplementary photoperiods delayed cessation of shoot growth and thereby increased the orders of branching and the number of inflorescence positions per plant. The photoperiod treatments significantly increased the number of flowers at the last produced inflorescence positions, but not at other ones. Pollen production and quality, berry set, seed set and 100-seed weight were not affected by the photoperiod treatments. TPS production was characterized by variability in flowering and low and variable seed production per flower.

Effects of Shoot Mortality on the Early Development of Afzelia quanzensis Seedlings

1. This study investigated the occurrence of shoot mortality and its effects on the development of seedlings of the economically valuable timber tree Afzelia quanzensis under natural conditions in the absence of fire at Lusaka, Zambia. 2. Mean seed germination was 86 and 99% in the laboratory and field, respectively. Seedling emergence occurred 2-4 weeks after planting in the laboratory compared to 3-10 weeks in the field. 3. Seedling mortality during the first year was low (12%), but shoots of 60% of the surviving seedlings died back to ground level, apparently because of water stress. 4. Maximum leaf production was in the middle of the rainy season, but leaf production and shoot growth ceased before it ended. Root growth continued for 2-3 months after cessation of shoot growth. 5. Seedlings whose shoots died back during the first year had much lower shoot and root biomass and fewer leaves at the end of the second growing season than seedlings without shoot die-back.

Influence of dormancy induction treatments on western hemlock seedlings. I. Seedling development and stock quality assessment

Western hemlock (Tsugaheterophylla (Raf.) Sarg.) seedlings were grown in a greenhouse and subjected to four dormancy induction treatments (DIT) (i.e., long-day dry, long-day wet, short-day dry, and short-day wet) during midsummer. In the late summer and fall, seedling development was monitored and it was found that (1) short-day DIT caused a rapid cessation of shoot growth; (2) short-day DIT caused rapid fall development of needle primordia, while long-day DIT took until midwinter to produce the same number of needle primordia; and (3) short-day DIT seedlings had lower saturated and turgor loss point osmotic potentials and greater maximum modulus of elasticity in October than long-day DIT. Seedlings were tested with a comprehensive stock quality assessment procedure just before late winter field planting. These tests showed the following: (1) morphological parameters: short-day DIT reduced shoot to root ratios; (2) pressure–volume analysis: short-day wet seedlings had the lowest osmotic potentials at saturation and turgor loss point; (3) soluble sugar analysis: greater levels of total soluble sugars were found in non water stressed DIT compared with water stressed DIT seedlings; (4) seedling water movement: short-day DIT seedlings had the lowest resistance to water movement at low root temperature (5 °C); (5) low root temperature response: short-day compared with long-day DIT seedlings had greater photosynthesis and stomatal conductance at low root temperatures; (6) root growth capacity: seedlings from all DIT were capable of growing roots at optimum root temperature (22 °C), but short-day compared with long-day DIT had greater root growth at low root temperatures; (7) drought stress response: short-day wet seedlings had the highest photosynthesis and stomatal conductance levels as predawn shoot water potentials decreased; and (8) frost hardiness: short-day wet seedlings had the least needle damage when tested at temperatures of −15 and −18 °C.

Effect of Photoperiod and Shoot Decapitation on Flowering of Leucospermum `Red Sunset'

Incandescent light night break (NB) and day continuation (DC) prevented flower formation in Leucospermum R.Br. cv. Red Sunset. Natural short days (NSD) during winter were inductive for flowering of intact shoots until 28 Aug. (Southern Hemisphere), but only until 24 July for decapitated shoots. Vegetative axillary buds released from correlative inhibition by shoot decapitation were less responsive to inductive short days (SD) than distal axillary buds on intact shoots. At least 42 inductive SD cycles were required for normal flowering after cessation of shoot growth. The effective length of the NB depended on the length of the NSD of winter. A 2-hr NB prevented flowering in vegetative buds released from correlative inhibition by shoot decapitation on 3 Mar., but was inadequate for axillary buds on shoots decapitated on 1 May. When the NB was begun during winter and discontinued before natural day (ND) lengths became too long in spring, the flowering time was delayed.

Effects of photoperiod and moisture availability on shoot growth, seedling morphology, and cuticle and epicuticular wax features of container-grown western hemlock seedlings

The influence of short-day and long-day photoperiods, and moderate drought stress (−1.0 MPa), all applied for 4 weeks beginning in mid-July, 1986, was studied on greenhouse-grown western hemlock (Tsugaheterophylla (Raf.) Sarg.) seedlings cultured in two Styroblock container cavity sizes. Shoot growth, morphology, and cuticle and epicuticular wax features were investigated. Weekly measurements of shoot growth were made from early June until growth cessation in October. Root collar diameter, shoot length, numbers of branches and needles, and needle lengths were recorded after shoot growth cessation in another subsample of trees. Shoot growth rapidly ceased under short days, whereas free growth continued under long days. Moisture stress had no effect on shoot growth phenology but significantly reduced final values for all morphological variables. The trends were similar in seedlings from both container sizes, but values were greater in those from the larger containers. Long days increased the total number of leaves and branches, especially under no moisture stress conditions. Under long days, stem unit and needle lengths were increased in the proximal portion of the shoot, whereas moisture stress alone reduced these values in the distal section of the shoot. Dormancy induction treatments had little effect on needle cuticle and epicuticular wax features, although fusion of wax rodlets in the stomata was less common under moisture stress conditions.

EFFECT OF CUTTING POSITION ON ROOTING, AXILLARY BUD BREAK AND SHOOT GROWTH IN STEPHANOTIS FLORIBUNDA

Shoot growth of rooted cuttings of Stephanotis floribunda is often delayed for a shorter or longer period. In some plants shoot abscission can occur. This invistigation shows that cuttings from the upper part of the stock plant produce less roots and have a higher percentage of axillary bud break than cuttings from the more basal part of the vine. Shoot growth cessation and shoot abscission occur more frequently in cuttings from the uppermost positions. With increasing distance from the shoot tip the frequencies of shoot growth cessation and shoot abscission are lowered.

Bud dormancy and vegetative growth in Salix polaris as affected by temperature and photoperiod

Vegetative growth of two ecotypes (lat. 78° 15′N and 69°37′N) of Salix polaris L. was studied in phytotron experiments. Dormancy of the winter buds was broken by chilling at 0.5°C for 14 to 42 days. Chilling requirement increased with decreasing growth temperature. The optimum temperature for bud break and shoot growth was about 15°C for both ecotypes. Cessation of apical shoot growth and abscission of shoot tip was not prevented by long photoperiods. However, at high temperature, 15°C or more, and in 18 to 24 h photoperiod, two or three growth flushes occurred frequently in both ecotypes. Leaf abscission in the arctic ecotype from lat. 78°N was not affected by photoperiod when grown at 6°C, but was stimulated by short photoperiod when grown at 15°C. In the ecotype from lat. 69°N leaf abscission was enhanced by short photoperiod even at 6°C.

Effect of Night Interruption on Cold Acclimation of Potted ‘Concord’ Grapevines

Abstract Two photoperiod regimes, natural daylength (ND) and night interruption (NI) of ND with a white light source, were used to test the importance of photoperiod on growth parameters, cold acclimation, and root conductance of potted ‘Concord’ grapevines (Vitis labruscana Bailey). By 3 Sept., NI-treated plants had a greater percentage of shoots with actively growing apices and a greater number of nodes per shoot than those untreated. No differences were seen in effect of light treatment on the extent of shoot maturation, as evidenced by shoot color change from green to brown. No consistent differences in hardiness of primary buds or canes of the first 12 nodes could be attributed to light regime. Apical tissues were less hardy than basal tissues for all regimes early in the acclimation period (10 Sept.). Root conductance, measured as suction-induced water flow, decreased throughout the acclimation period but did not differ between light treatments. Results are discussed in light of current hypotheses and of evidence of interrelationships among photoperiod, shoot growth cessation, shoot maturation, and cold acclimation.

Phenology and Control of Flowering in Tropical Trees

Descriptions of structure and flowering phenology of the tropical tree species Cedrela mexicana, Cordia glabra, Erythrina poeppigiana. Tabebuia rosea, and Tabebuia ochrea ssp. neochrysantha are used to analyze and illustrate the complex relations between structure, vegetative development, and flowering in tropical trees. Because of the strong positional differentiation within tree crowns and the repetition of vegetative and reproductive growth cycles in trees, flower development and its control are more complex than in herbaceous plants. Formation of terminal inflorescences, as found in Cedrela, Cordia, and Tabebuja, regularly occurs at the end of a flush of determinate shoot growth; flower initation, like shoot growth cessation, is therefore controlled by internal, correlative factors rather than by environmental changes. Initiation of lateral inflorescences is usually preceded by growth cessation in the indeterminate, vegetative shoot, but the timing and control of flower induction in lateral buds are unknown. For many tropical trees, particularly those growing in seasonal climates, flower development is discontinuous, i.e., flower initiation and anthesis are separated by a prolonged rest period and must be controlled separately. Delayed anthesis is usually triggered by rehydration of previously water-stressed trees resulting from leaf shedding or, in dry habitats, by rainfall. Because of different degrees of seasonal water stress, leaf fall and subsequent anthesis in several species extend over three to four months. The observed periodicity of anthesis in tropical trees is thus largely determined by seasonal changes in tree water status and is unlikely to be the result of selection for optimum tree-pollinator interaction. IN MOST TROPICAL TREES, flowering, like vegetative growth is episodic, and seasonal peaks of flowering have been recorded for many tropical forests (e.g., Fournier and Salas 1966, Janzen 1967). During recent years, tropical ecologists have considered the temporal pattern of flowering the result of coevolution of trees with pollinators and seed predators. It has been argued that peaks of flowering occur during periods of high pollinator activity, and that overlapping, but different, flowering periods in related species reduce competition for pollinators and assure a continuous source of nectar to pollinators (Janzen 1967, Gentry 1976, Stiles 1978). If the temporal pattern of flowering is adaptive, then mechanisms for the specific timing of flowering must have evolved in tropical trees. The timing of flowering in tropical trees usually has been ascribed to environmental control mechanisms analogous to those that have evolved in temperate plants to adapt vegetative and reproductive development to a growing season of limited duration (Larcher 1980). Relations between tree architecture, vegetative growth and flowering of tropical trees have been rarely considered. In this paper, I shall use descriptions of the flowering behavior of five tropical tree species as a basis for discussing the relations between tree architecture, vegetative development, and flowering, as well as our scant knowledge of their internal and environmental controls. I will show that evolution of the temporal pattern of flowering in tropical trees cannot be adequately explained as resulting from biotic interactions alone, but must be seen in the context of overall tree development as determined by a given set of climatic, edaphic, and biotic factors. STUDY SITES AND METHODS Most of the phenological observations on flowering of tropical trees discussed in this paper were made on the Pacific slope of Costa Rica, Central America, along an altitudinal gradient extending from the deciduous lowland forest of Guanacaste Province (Janzen 1967, Daubenmire 1972, Frankie et al. 1974, Opler et al. 1976, Reich and Borchert 1982, 1984) through the lower montane forest at Villa Col6n (800 m altitude) and Santa Ana (900 m; Fournier and Salas 1966, Fournier 1969) to the Central Valley of Costa Rica (La Sabana, 1100 m; San Pedro Montes de Oca, 1200 m; Granadilla, 1350 m) (Fournier 1969, Borchert 1980). The climate in the entire area is characterized by a dry season lasting from late November to April/May and a wet season providing adequate rainfall (approx. 2000 mm) for the remainder of the year. With increasing altitude, the severity of the dry season diminishes and some species change from a deciduous to an evergreen habit (e.g., Erythrina poeppigiana, Tabebuia rosea; Fournier 1969, Borchert 1980). The discussion of tree morphology is based on the analysis of tropical tree architecture by Hall6 et al. 1978, where definitions of all morphological terms can be found. MORPHOLOGY AND PHENOLOGY OF FLOWERING IN FIVE TROPICAL TREE SPECIES TABEBUIA ROSEA (BERTOL.) DC, BIGNONIACEAE.-The shoot system of T. rosea is composed of many orthotropic, symBIOTROPICA 15(2): 81-89 1983 81 This content downloaded from 157.55.39.17 on Fri, 02 Sep 2016 06:06:02 UTC All use subject to http://about.jstor.org/terms

Soil temperature and flooding effects on two species of citrus

Rough lemon (Citrus jambhiri Lush.) and sour orange (C. aurantium L.) seedlings were grown at constant soil temperatures of 16, 24, and 33 C for 3 months. Shoot and root growth of rough lemon was greatest at 33 C while growth of sour orange was greatest at 24 C. There were no significant effects of soil temperature on shoot: root ratio, leaf water potential or stomatal conductance. The hydraulic conductivity of intact root systems of both species was highest when seedlings were grown at 16 C. Thus, acclimation through greater root conductivity at low soil temperature may have compensated for decreased root growth at 16 C and negated effects of soil temperature on plant water relations. Half the plants growing at each soil temperature were subsequently flooded. Within 1 week, the soil redox potential (Eh) dropped below zero mV, reaching a minimum Eh of −250mV after 3 weeks of flooded conditions. Flooded plants exhibited lower root conductivity, a cessation of shoot growth, lower leaf water potentials, lower stomatal conductances, and visual sloughing of fibrous roots. Decreases in root conductivity in response to flooding were large enough to account for the observed decreases in stomatal conductance.

NATURALLY OCCURRING AUXINS AND INHIBITORS AND THEIR ROLE IN FRUIT GROWTH OF AONLA (EMBLICA OFFICINALIS GAERTN.)

Three acidic (a1, a2 and a3) and two non‐acidic (a4 and a5) auxins were detected in the immature fruit of aonla (Emblica officinalis Gaertn.). Chromatographic studies coupled with bioassays led to the tentative identification of a2, a4 and a5 as IAA, IAAld and IAN, respectively. Two growth inhibitors (R1 and R2) were also detected in the fruit. These behaved like naringenin and abscisic acid, respectively, in paper and thin‐layer chromatography.The inhibitors R1 and R2 were present in low concentrations in dormant fruits and did not appear to be the cause of dormancy. The factor playing a major role in the dormancy mechanism of the fruit appears to be auxin. Concentration of auxin increased in the fruit with the onset of dormancy and decreased to a low level prior to dormancy break. Shoots grew while fruits were dormant and dormancy break in fruits occurred after cessation of shoot growth. Since rise and fall in the rate of shoot growth corresponded with the period of rise and fall in the auxin content of dormant fruits and since shoot‐tips and dormant fruits contained identical auxins, it is proposed that the auxins translocated from the shoot‐tip to the fruit cause dormancy of fruits by a mechanism similar to that operative in apical dominance.

Role of Root Temperature on Shoot Growth of Two Kentucky Bluegrass Cultivars1

AbstractShoot growth inhibition and changes in carbohydrate levels occur in cool‐season grasses under midsummer conditions. Cultural practices, such at thatch removal or topdressing, could alter high temperature extremes of the crown and root. Thus, the objective of this study was to determine the role of root temperature on shoot growth rate and water soluble carbohydrate (WSC) levels in plant parts of ‘Merion’ and ‘Nugget’ Kentucky bluegrass (Poa pratensis L.).The turfgrasses were established from seed on coarse sand in the greenhouse. After 12 weeks the pots were transferred to an environmental growth chamber where air temperatures were increased from 22 to 38 C in 4 C increments every 2 weeks. The effects of root zone temperatures controlled at 22 C (CRT) were compared to noncontrolled temperatures (NRT) in which the root zone was allowed to equilibrate with the air temperature. Shoot growth above 4.0 cm. was clipped at the end of each temperature increment from 22 to 34 C. After the 38 C exposure plants were separated into verdure (live leaf tissue), “thatch” (dead leaf tissue), crowns, and roots.Shoot growth of Merion Kentucky bluegrass grown at NRT, was greatest at 26 C and was significantly reduced at 30 and again at 34 C. Shoot carbohydrate levels were lowest at 26 and 30 and highest at 34 C. At 38 C, verdure and crown carbohydrate levels were significantly higher than those of the roots.The growth rate of Nugget (NRT) at 26 C was not as rapid as for Merion. Shoot WSC levels were high at 26, 30, and 34 C compared to Merion Kentucky bluegrass. At 38 C, root WSC levels were significantly higher in roots than verdure or crown. The greater high temperature tolerance of Nugget was documented through a higher verdure‐thatch ratio.Survival of both cultivars was enhanced by controlling the root temperature at 22 C (CRT). Shoot WSC levels at all temperatures were significantly lower at CRT compared to NRT in Nugget. This was true in Merion only at 34 C. Root WSC levels in Merion at CRT were at the high level found for Nugget at both NRT and CRT. Shoot growth cessation at supraoptimal temperatures may result from a high temperature‐labile process in the root. Loss of root carbohydrates appears to increase the temperature lability of the process.

Endogenous Shoot Growth Rhythms and Indeterminate Shoot Growth in Oak

AbstractWide variations of shoot growth patterns in saplings of pin oak (Quercus palustris Muenchh.) have been observed as a consequence of varying environmental conditions, experimental manipulations, and vigor of trees. Shoot growth patterns range from a series of recurrent, determinate flushes, constituting a genuine endogenous rhythm, to continuous, indeterminate growth. Observed growth patterns agree well with those predicted by a model of rhythmic growth which assumes the dependence of shoot growth on the functional equilibrium between shoot and root system. Indirect evidence suggests that cessation of shoot growth under favorable environmental conditions might be a consequence of internal water deficits. Observed differences in shoot growth patterns between young and mature trees are discussed as logical consequences of the model.

RELATION OF SEXUPARA PRODUCTION IN THE WOOLLY PEAR APHID, ERIOSOMA PYRICOLA (HOMOPTERA: PEMPHIGIDAE), TO TREE GROWTH IN THE FIELD

AbstractSexupara production in the pear root aphid, Eriosoma pyricola Baker & Davidson, was closely associated with the cessation of shoot growth of its host in the field in irrigated and non-irrigated plots in two successive, but phenologically different years. Neither the environment nor the host plant were unfavorable at the time the sexuparae were formed, indicating that the aphid uses the host plant as a source of seasonal information.The nature of synchronization between active development of univoltine insects and trees is discussed. It is concluded that the initiation of dormancy in trees and diapause in insects is not likely to be synchronized by a common set of environmental factors. Either regulation of insect diapause by host trees is more common than is currently recognized, or environmental and age differences in tree growth have favored selection for obligate diapause.