Cessation Of Shoot Elongation Research Articles

Epigenetic memory effects in Norway spruce: are they present after the age of two years?

ABSTRACT Short-term trials on cultivated soil were planted with families of Norway spruce that had shown epigenetic memory effects in early tests up to age two years. Measurements and assessments were made of phenology traits, tree heights and stem defects until age 16 years in these trials. The memory effects of the temperature conditions during embryo development and seed maturation were confirmed for the timing of bud flush and for start and cessation of shoot elongation at age six years. The mean differences in timing of these events caused by temperature treatments were on average less than two days. They were considerably larger for families with strong effects on terminal bud set at the end of the first growing season. The memory effects did not result in a prolonged shoot growth period, nor did they affect height growth. Interaction effects expressed in adaptive traits between factorial treatments of temperature and daylength during seed production were large in the short-term trial and were still present at age nine years. The results presented demonstrate that strong memory effects observed in early tests may also be expressed in phenology traits for at least the next five growing seasons.

Genetic control of intra-annual height growth in 6-year-old Norway spruce progenies in Latvia

Coupling growth with periods of favourable weather conditions minimizes risks of frost damage and maximizes annual height increment. The phenology of the formation of height increment is therefore a trait related to the adaptability of trees to annual weather fluctuations. Strong genetic control of the timing of the onset and cessation of shoot elongation has been reported for Norway spruce, but little is known about its fluctuations that occur during the growth period. The strength of the genetic control of the height growth rate was assessed for young (6 years old) Norway spruce progenies originating from six open-pollinated stands from two local provenance regions. In 2010, the length of the growing period for the studied trees was ca. 60 days. Trees from the more continental provenance region, which had later onset and cessation of height growth (by ca. 2.5 days), exhibited slightly lower increments (by ca. 1%). Accordingly, the provenance region had a significant effect on height growth at the beginning and end of the growing period. Nevertheless, considerable genetic control of the growth rate was found throughout the entire growing period (particularly at the beginning and cessation, ha2 ≥ 0.20), except for a week-long interval around mid-summer (ha2 = 0.07). Similarly, the coefficient of additive genetic variation suggested that breeding could be applied for the improvement of height growth intensity throughout the season. The phenotypic correlations between weekly growth rates and tree height (before growth) were mostly non-significant, suggesting varying mechanisms of control, hence possibility for simultaneous improvement of the traits by breeding.

Genetic variation in phenology and growth among and within Norway spruce populations from two altitudinal transects in Mid-Norway

Progenies from open pollinated cones collected in natural populations of Norway spruce ( (L. Karst.)) distributed along two altitudinal transects in Mid-Norway were tested in the nursery, in short term tests and in long-term field trials. The populations showed clinal variation related to the mean annual temperatures of the populations, with the earliest bud flush and cessation of shoot elongation and lowest height at age nine years for the high altitude populations. Within population variation was considerable as the narrow sense heritability for these traits was 0.67, 0.31 and 0.09 in one transect and 0.55, 0.18 and 0.14 in the other transect, respectively. Lammas shoots occurred in the short term trials with large variation in frequency between years. There was significant family variation for this trait, but also interactions between populations and year. The variance within populations was considerably larger in the populations from low altitude compared to the high-altitude populations. Significant genetic correlations between height and phenology traits and damage scores indicate that families flushing early and ceasing growth late were taller. Taller families also had higher frequencies of damages. Selection of the top 20% families for height growth in short term tests at age nine years gave a simulated gain of 11% increased height growth at age 18 years in long term trials at altitudes similar to those of origin of the populations. The gain was negative when high altitude populations were selected based on testing in the lowland.Picea abies

Plant morphological characteristics for year-round production and its fruit quality in response to different light wavelengths in blueberry

In Japan, regular blueberry harvest season is very limited, from June to September. Due to the increased demand of Japanese customers, year-round production of blueberry fruit has become important to compensate the amount of import of fresh and frozen blueberry. Therefore, in Tokyo University of Agriculture and Technology (TUAT), we established a plant factory controlled environment with four seasons to develop new cultivation methods for year-round production by accelerating plant's life cycle. In this study, we investigated morphological characters of blueberry plants for year-round production and its fruit quality in response to different light wavelengths using light-emitting diodes (LEDs) in the plant factory. Three-year-old 'Sharpblue' plants were irradiated with 100% blue (B) (459 nm), 100% red (R) (631 nm), 1:1 = red:blue (R and B), respectively. Fluorescent light (F) was used as control. Other environmental factors were set the same for all treatments and control. At 165 days after treatment, (R and B) treated plants and control ones showed satisfying vegetative growth with flowers and high potential for continuous flowering, while plants under (B) were retarded in growth with cessation of shoot elongation, showing low potential for continuous flowering although many flowers were observed during the study. However, the strongest plant vigor with bigger leaves but few flowers were found in plants treated with (R). In terms of fruit quality, higher Brix% and less acidity were found in fruits under (R and B) and (B) than in those of the other plants applied with (R) and (F). Bigger fruit size and heavier fruit weights were found in plants under (R and B). Thus, these results suggest that light quality has a strong influence on continuous flowering for year-round and high-quality fruit production in blueberry.

Fertilization regime interacts with fall temperature in the nursery to determine the frost and drought tolerance of the Mediterranean oak Quercus ilex subsp. ballota

Nitrogen fertilization in the nursery usually improves the transplanting performance of Mediterranean oaks. However, high N fertilization can reduce seedling stress tolerance, probably depending on the environmental conditions under which plants grow. We hypothesize that high N fertilization under mild fall conditions reduces cold and drought acclimation. To assess this hypothesis, we studied if fall temperature differences among cultivation locations influence the effect of N fertilization regime on cold and drought tolerance, N status and growth in the evergreen Mediterranean oak Quercus ilex subsp. ballota (Desf.) Samp. Plants were cultivated in two nurseries of distinct fall temperature conditions (mild and cold fall nurseries) under four fertilization regimes: Low and high N at constant rate (total N, 33 and 175mgseedling−1), high N at exponential rate (175mgNseedling−1) and fall N loading (89mgNseedling−1). Seedling water relations, survival to a −12°C frost and leaf soluble carbohydrates concentration were assessed three times in the fall, and shoot elongation was measured weekly through the fall. Moreover, seedling mass and N concentration were measured at the end of the fall. Fall loaded seedlings had the highest tissue N concentration, while seedling mass was highest in the high N constant and exponential fertilization regimes. Seedlings at the cold fall nursery concentrated more N but were smaller than seedlings at the mild fall nursery. Cessation of shoot elongation in the mild fall nursery occurred 1month later than in the cold location and high N exponentially-fertilized plants ceased shoot elongation later than the rest of fertilization treatments. Seedlings at the mild fall location had lower drought and cold tolerance than plants at the cold fall site. At mid fall, exponential fertilization at the mild nursery reduced seedling frost and drought tolerance, but treatment differences vanished at the end of the fall. In contrast, fertilization regime did not affect either cold or drought tolerance of seedlings at the cold fall nursery. Across dates and nurseries, frost survival was positively related to leaf soluble carbohydrates concentration and dry weight fraction. Beside, degree of cold acclimation decreased with shoot elongation cessation date and increased with leaf soluble carbohydrates concentration, suggesting a link between shoot growth activity, soluble carbohydrates, and frost tolerance. We conclude that Q. ilex subsp. ballota hardening is reduced by high N exponential fertilization mainly under mild fall conditions, while fall loading and constant low N fertilization did not affect hardening.

PHENOLOGY OF AND HEAT UNIT REQUIREMENTS FOR GROWTH IN PROTEA 'CARNIVAL' INDUCED BY BENZYLADENINE-CONTAINING GROWTH REGULATORS

Benzyladenine (BA) application to induce budbreak and inflorescence initation in mature shoots in late summer to autumn has been studied as a tool for manipulation of flowering time in Protea. Dormant terminal buds on three-flush shoots of eight-year-old Protea 'Carnival' plants were treated with a single application of 500 mg·L -1 benzyladenine (BA), prepared by diluting either ABG-3062 (2% active ingredient w / w ) or Accel ® (1.8% active ingredient w / w ). Treatment dates were spaced two weeks apart starting from 14 March until 22 May 2003. Three phenological stages and the days required to complete each stage was recorded for all treatments. Monitored stages included: date of ABG-3062 or Accel ® application to green point; green point to cessation of induced shoot elongation and from the latter until anthesis. Base temperatures of 9, 6 and 1°C were determined for the respective stages. Between 17-57 days were required from date of ABG-3062 application to green point. No significant difference was obtained for means of Accel and ABG-3062 treatments. The number of days required from cytokinin application to green point was negatively correlated with the mean temperature that prevailed for that period. Shoots required approximately 5400 growing degree hours (GDH) to complete this phenological phase. The relationship between temperature and the number of days required to complete the phase 'green point to cessation of shoot elongation' was not clear. The phenological phase of 'cessation of shoot elongation to inflorescence anthesis' needed between 121-177 days to completion and the duration was negatively correlated with the prevailing temperatures. Inflorescences on three-flush shoots required between 53300 and 54400 GDH to anthesis.

Variation in shoot elongation patterns in Pinus contorta and Pinus sylvestris in north-west Russia

A phenological study of six lodgepole pine populations from Swedish seed orchards and one local Scots pine population was performed in a field trial located in Komi Republic (northern Russia) (61°40′ N, 51°03′ E, 132 m a.s.l.) at the age of 5 years. The species differences in annual shoot elongation, growth onset and cessation were significant (p<0.05). The annual growth of undamaged leader shoots varied considerably among the populations and the mean shoot length was 315 mm (range 291–333 mm) for lodgepole pine and 215 mm for Scots pine seedlings. The growth rate was also higher for lodgepole pine but this difference was not statistically significant. Lodgepole pine generally had earlier onset and later cessation of shoot elongation than Scots pine. The northern lodgepole pine populations tended to initiate and cease growth earlier than southern ones but these differences were insignificant.

Seasonal Ultrastructural Changes in Xylem Parenchyma Cells of Apple Twigs in Relation to Cold Hardiness

Ultrastructural changes in xylem parenchyma cells of apple twigs were studied in relation to seasonal fluctuation in cold hardiness. During active growth from mid-June to mid-July, the most striking changes were cell wall thickening and the formation of pits. In the cytoplasm, the appearance of rough endoplasmic reticulum (ER), polysomes, dictyosomes, and vesicles indicate that these organelles participate in cell wall thickening and the formation of pits. In early August immediately after cessation of shoot elongation, starch granules in the plastids began to increase in size and number; protein-lipid bodies appeared. During cold acclimation from late September to mid-October, the vacuoles shrank in size, and the cell became full of plastids containing large starch granules. In early November, unidentified organelles that were similar in size to plastoglobuli appeared near the thylakoid membranes in plastids. In mid-January when cold hardiness reached a maximal level, small vacuoles were dispersed throughout the cytoplasm. In late February, the formation of plastid initials occurred, while plasmodesmata formed in the pits. During deacclimation from late March to mid-April, the vacuoles enlarged, starch granules in the plastids decreased in size, and unidentified organelles reappeared in the plastids. At the onset of flowering in mid-May, starch granules in the plastids increased in size again. Moreover, during a one-year cycle, the rough ER was prominent along the cell wall, while mitochondria appeared to be adjacent or attached to the surface of the plastids. Based on these results, the relationship between ultrastructures in xylem parenchyma cells of the apple twigs and cold hardiness, especially the deep supercooling characteristic is discussed.

Seasonal Changes in Phenological Traits and Cold Hardiness of F1-populations from Plus-trees of Pinus sylvestris and Pinus contorta of Various Geographical Origins

A 3 yr phenological study of six F1-populations from plus-trees of Scots pine (Pinus sylvestris L.) from 61 to 68° N and five F1-populations from plus-trees of lodgepole pine (Pinus contorta var. latifolia Engelm.) from 55 to 63° N was performed in a Swedish field trial at latitude 64°15' N. Lodgepole pine generally dehardened slightly earlier in spring, and had earlier onset and later cessation of shoot elongation than Scots pine. Early onset and early cessation of shoot elongation were more closely related to a northern latitude of origin in Scots pine than in lodgepole pine. Frost hardiness, needle dry matter proportion, and needle attachment to current year shoots in late summer and autumn were positively related to the latitude of origin in both species. Freeze tests showed that the cold acclimation rhythm of lodgepole pine in the autumn was comparable to that of Scots pine of 5-9° of latitude more northern origin. With respect to timing of dehardening in spring, shoot elongation rhythm (excluding growth cessation), cold acclimation (cold tolerance) in the autumn and winter cold hardiness, lodgepole pine from above 60° N appears phenologically as adapted to the climate of the test site on latitude 64° N as the recommended Scots pine from latitude 66° N. However, later growth cessation, lower dry matter content and needle attachment in the autumn, and possibly a greater tendency to deharden occasionally in late winter indicated poorer adaptation of these northern lodgepole pine populations.

The relation between growth cessation and frost hardening in Scots pines of different origins

The cessation of shoot elongation, diameter growth and needle elongation were compared with the initiation of frost hardening of the stems and needles in an 8-year-old provenance trial of Scots pine (Pinus sylvestris L.) established in central Finland. The saplings were of six different origins ranging from Estonia to northern Finland, forming a latitudinal gradient of ca. 10°N. The frost hardiness of the stems of current-year shoots was assessed by electrical impedance analysis and that of current-year needles by electrolyte leakage and visual scoring of damage. Artificial freezing tests were used in the assessments. The pattern of growth cessation (shoot and needle elongation, diameter growth) tended to follow the latitude of origin, i.e. growth ceased in the northernmost provenance first and in the southernmost one last. Both stems and needles of the northern provenances hardened earlier than the southern ones, but the differences in hardiness disappeared as hardening progressed. Growth cessation and initial hardening to –15°C were clearly correlated at the provenance level, indicating that growth must cease prior to hardening, and that earlier cessation of growth predicts earlier frost hardening of stems and needles. No differences in frost hardiness of stems were found at the provenance level at the end of the growing period in August. At that time, the frost hardiness of needles of the northernmost provenance was higher than that of other origins. Within the provenance, the stems were less hardy than the needles.

「イチョウイモ」の花穂と新芋の発育に及ぼす日長と種芋重の組み合わせ処理の影響

'イチョウイモ'の主枝, 花穂, ムカゴおよび新芋の発育に及ぼす日長と種芋重の組み合わせ処理の影響について調べた.その結果, 主枝の発育は24時間日長と大きな種芋の組み合わせによって促進され, 8時間日長と小さな種芋の組み合わせによって遅延された.主枝の伸長停止時期は8時間日長と小さい種芋との組み合わせで早まった.花穂の発育は, 8時間日長でも24時間日長でも, 25g以上の種芋から育てられた個体で認められ, その割合は種芋重の重いほど高くなった.第1花穂着生節位は8時間日長の方が24時間日長よりも低く, 出蕾日も早かった.花穂数は24時間日長の方が8時間日長よりも多く, 種芋重の重くなるほど多かった.ムカゴと新芋の初期の発育は8時間日長の種芋重10&acd;50g区で旺盛で, 8時間日長の種芋重100gと24時間日長の種芋重5&acd;100gで遅れた.ムカゴと新芋の最終発育量は主枝の発育の優れた24時間日長区で大きく, 種芋の重いほど重くなった.しかし, 葉重に対するムカゴと新芋の合計重比は, 8時間日長でも24時間日長でも, 小さい種芋区ほど高かったので, 種芋の小さいほどムカゴと新芋の初期の発育は促進されたとみられた.

Gibberellins and Subapical Cell Divisions in Relation to Bud Set and Bud Break in Salix pentandra.

In young plants of Salix pentandra, a temperate zone deciduous woody species, elongation growth ceases and a terminal bud is formed at day lengths shorter than a critical length. This is the first step in dormancy development, making survival under harsh winter conditions possible. Early studies strongly indicate that gibberellin is involved in the photoperiodic control of bud set and bud break. GA(1) action was studied by application under short days to plants where cessation of shoot elongation had occurred, followed by subsequent anatomic investigations of shoot tips. Under short days the frequency of cell division decreased rapidly along with the earlier observed decrease in GA(1) levels. Application of GA(1) to short-day-induced terminal buds rapidly stimulated cell division in apices several days before visible shoot elongation in response to this treatment was observed. One day after GA(1) application a fourfold increase in cell division frequency in apices was observed, increasing to a maximum of sevenfold 2 days after application. Long-day treatment leading to induction of bud break after about 4-6 days was followed by slowly increasing frequency of cell divisions. In earlier studies of this species, short days and gibberellins had no effect on cell elongation. These data show that increased GA(1) content, by application or long-day treatment, results in increased frequency of mitosis. This strongly indicates that GA(1) affects stem elongation in connection with bud set and bud break primarily by affecting cell divisions in subapical tissues.

A localised decrease of GA1 in shoot tips of Salix pentandra seedlings precedes cessation of shoot elongation under short photoperiod

A localised decrease of GA1 in shoot tips of Salix pentandra seedlings precedes cessation of shoot elongation under short photoperiod

Stimulation of shoot elongation in Salix pentandra by gibberellin A9; activity appears to be dependent upon hydroxylation to GAl via GA20

Cessation of shoot elongation in seedlings of Salix pentandra L. is induced by short photoperiod. Gibbereliin A9 (GA9) applied either to the apical bud or injected into a mature leaf, induced shoot elongation under a short photoperiod of 12 h, and GA9 could completely substitute for a transfer to a long photoperiod. When [3H]GA9 or [2H2]GA9 was injected into a leaf, no [3H]GA9 was detected in the elongating apex and only traces of [3H]GA9 were found in the shoot above the treated leaf. By the use of gas chromatography‐mass spectrometry (GC‐MS), [2H2]GA20 was identified as the main metabolite of [2H2]GA9 in both the shoot and the treated leaf. In addition, [2H2]GA1 and [2H2]GA29 were also identified as metabolites of [2H2]GA9. These results are consistent with the hypothesis that exogenous GA, promotes shoot elongation in Salix through its metabolism to GA20 and GA,.

Adaptations of shoot growth and leaf production of laboratory-grown cuttings of Triplochiton scleroxylon K. Schum in response to changes of irradiance

Potted, rooted cuttings of Triplochiton scleroxylon were subjected to 92.2 W m −2 (high; H) and 61.2 W m −2 (medium; M) levels of artificial irradiance for 20 weeks. After the first 10 weeks, some of these plants were transferred to a light level of 34.6 W m −2 (low; L). Comparison of changes in morphological characters as a result of these treatments suggested that continuous exposure to high and medium levels of irradiance can result in cessation of shoot elongation in high irradiance but continuous shoot growth in medium irradiance. It was possible, however, that in plants in the H regime may have become pot bound and therefore nutrient limited. However, when H and M plants were transfered to the low-irradiance regime, they grew taller and produced proader new leaves, and a higher number of them, than was possible in H and M, although those transferred from H had higher shoot growth than those transferred from M. Production of new leaves and shading of old leaves was least in plants in medium irradiance. Consequently, these plants bore the greatest total leaf number at the end of the experiment. Specific leaf area increased with the degree of shading. Sprouting abilities of cut shoots were better at medium than at low irradiance levels. Although leaves are amphistomatous, stomata on the adaxial surfaces are confined to the immediate portion of the blade next to the midrib and main veins. The results suggest that under artificial lighting, high irradiance may not necessarily be the best light level for growth and leaf production of T. scleroxylon.

Quantitation of Gibberellins A1, A3, A4, A9 and a Putative A9-Conjugate in Grafts of Sitka Spruce (Picea sitchensis) during the Period of Shoot Elongation

The levels of endogenous gibberellin A(1) (GA(1)), GA(3), GA(4), GA(9), and a cellulase hydrolyzable GA(9) conjugate in needles and shoot stems of mature grafts of Sitka spruce (Picea sitchensis [Bong.] Carr.) grown under environmental conditions that were either inductive, hot, and dry, or noninductive, cool, and wet, for flowering, were estimated by combined gas chromatography-mass spectrometry selected ion monitoring using deuterated [(2)H(2)]GA(1), GA(3), GA(4), and GA(9) as internal standards. The samples were taken when the shoots had elongated about 30, 70, and 95% of the final shoot length and 17 days after elongation had terminated. The concentration of putative GA(9)-conjugate, estimated by GCSIM of GA(9) after cellulase hydrolysis of the highly water soluble fraction, was 33 nanograms per gram fresh weight in the needles of both heat and drought- and cool and wet-treated plants sampled just after bud burst. The concentration gradually decreased to a final value of 13 nanograms per gram fresh weight in the heat and drought-treated grafts and 6 nanograms per gram fresh weight in the cool and wet-treated grafts. The stems contained no detectable putative GA(9) conjugate. Free GA(9) was highest in heat and drought-treated material. For plants subjected to this treatment, GA(9) increased from 22 to 32 nanograms per gram fresh weight in needles and from 1 to 22 nanograms per gram fresh weight in stems during the rapid stem elongation phase. By day 17, after cessation of shoot elongation, GA(9) had decreased to 12 nanograms per gram fresh weight in needles and 9 nanograms per gram fresh weight in the shoot stems. The cool and wet-treated material also showed an increase in GA(9) concentration during shoot elongation. However, the concentration was not as high and was also delayed compared with heat and drought-treated material. By day 17, after cessation of shoot elongation, GA(9) concentration was 9 nanograms per gram fresh weight in needles and 5 nanograms per gram fresh weight in stems for cool and wet treatment plants. The concentration of GA(4) was very low in tissue from both treatments. Fluctuation in concentration of the more polar gibberellins, GA(1) and GA(3), showed the same pattern as fluctuations in the content of GA(9). However, the heat and drought-treated material had lower amounts of GA(1) and GA(3) during the later phases of shoot elongation, than the cool and wet-treated material. These results imply differential metabolism between clones treated with conditions inductive and noninductive for flowering. Higher concentrations of putative GA(9) conjugate and free GA(9) in the hot and dry treatment indicate a higher capacity of synthesizing, for flowering, the physiologically important GA(4) in the heat and drought-treated material. This synthesis does not, however, result in a buildup of the GA(4) pool, probably because of a high turnover rate of GA(4). The cool and wet-treated material had higher amounts of GA(1) and GA(3), indicating that the differentiation was preferentially directed toward vegetative growth.

Green Ash Establishment Following Transplant

Abstract Bare-root 1-year-old green ash (Fraxinus pennsylvanica Marsh.) seedlings were transplanted into root observation boxes under greenhouse conditions to study timing of budbreak, root regeneration, and subsequent shoot growth during establishment. Green ash seedlings began shoot growth before root growth. Seven to 20 days after transplant, intact second- and third-order lateral roots (referred to here after as intact roots) began to elongate, followed 10 to 19 days later by initiation of long roots from callus at pruned root surfaces. Plants with earlier budbreak were larger and regenerated more roots faster than plants that broke bud later. During establishment, there was a strong correlation between shoot and intact root elongation and a low correlation between shoot and long root elongation. Root pruning after establishment resulted in bud set and/or cessation of shoot elongation within 3 to 6 days in 1985 and within 20 to 28 days in 1986. The days to bud set and cessation of shoot elongation were positively correlated with increased numbers of regenerated roots from pruned surfaces (long roots). Only long root elongation was significantly correlated with shoot growth after root pruning. Root pruning also induced reductions (12 days) in net photosynthesis, transpiration, and stomatal conductance, and increased stomatal resistance to water loss; however, all recovered after root regeneration.

Effects of ABA application on cessation of shoot elongation in long-day grown Norway spruce seedlings.

Abscisic acid (ABA) was applied in lanolin to apical buds of Norway spruce (Picea abies (L.) Karst.) seedlings actively growing in a 24 h photoperiod. At a rate of 100 microg per plant, ABA suspended shoot elongation for about three weeks in the majority of plants but failed to induce normal winter buds. The role of ABA in the induction of dormancy is thus uncertain in conifers as well as in deciduous woody plants.

Effects of Three Nitrogen Levels on Tissue Nitrogen Fluctuation during a Flush of Growth on ‘Helleri’ Holly (Ilex crenata Thunb.)1

Abstract The effects of 3 nitrogen treatments on tissue N fluctuations of ‘Helleri’ holly. All N concentrations increased following the cessation of shoot elongation until a concentration of tissue N was reached where a new flush of growth began. Nitrogen concentrations at which new growth began were about the same for all N treatments. The time necessary to reach this concentration was dependent on the level of N added; 5 weeks for 300 ppm, 13 weeks for 150 ppm and 18 weeks for 50 ppm N. Once new growth began, tissue N concentrations began to decrease.

Effect of Photoperiod on Endogenous Abscisic Acid in Malus and Betula1

Abstract Seedlings of Malus hupehensis Rehd., M. domestica Borkh. cv. Northern Spy and Betula papyrifera Marsh were grown under short and long photoperiods, with other environmental conditions being similar. M. hupehensis seedlings stopped elongation under short days (SD) and continued growth under long days (LD). There was no significant difference in abscisic acid (ABA) content in shoot tips taken from seedlings under either photoperiod. ‘Northern Spy’ seedlings ceased growth under SD, but neither did they grow vigorously under LD. Shoot tips of these seedlings were not significantly higher in ABA content when grown under SD. Betula seedlings discontinued elongation under short photoperiods, while LD promoted growth. Betula shoot tips from LD seedlings had more ABA than from seedlings grown under SD. These data do not support the hypothesis that SD causes cessation of shoot elongation by inducing a build up of ABA.