Shoot Growth Initiation Research Articles

The effect of gamma radiation on seed germination and seedling growth of Lathyrus chrysanthus Boiss. under in vitro conditions

The effects of radiation at different doses (0, 50, 100, 150, 200 and 250 Gy) of radioactive cobalt (60Co) γ rays on seed germination and seedling growth of Lathyrus chrysanthus were investigated under in vitro conditions. The results showed that irradiated seeds had increased seed germination percentage, seedling and root lengths, seedling fresh weight, seedling dry matter content and total chlorophyll content in the leaves of seedlings. However, at higher doses stress was evident and significant decreases in all parameters were observed. The highest seed germination percentage was recorded as 62.4%, 7 days after study initiation when seeds were irradiated with 150 Gy gamma dose, while 100 Gy gamma dose was ranked in second order. Fourteen days after culture initiation, the best shoot growth initiation was again obtained from 150 Gy gamma dose as 75.7% and this was followed by 100 Gy gamma radiation as 74.6%. Gamma doses over 150 Gy resulted in sharp decreases in all parameters examined. On the 14th day, the highest shoot and root lengths were recorded from 150 Gy gamma dose as 1.2 and 2.9 cm, respectively. Twenty eight days after study initiation, the highest values of seedling and root lengths, seedling fresh weight, seedling dry matter content and total chlorophyll content were noted from 50 Gy gamma radiation as 9.7 and 6.3 cm, 0.39, 0.09 g (23.08%) and 471.6 μg/g fresh tissue, respectively. This study is important from the aspect of showing that stimulatory effect of low gamma doses for germination and seedling growth may not be the same.

Phytohormone balance and stress-related cellular responses are involved in the transition from bud to shoot growth in leafy spurge

BackgroundLeafy spurge (Euphorbia esula L.) is an herbaceous weed that maintains a perennial growth pattern through seasonal production of abundant underground adventitious buds (UABs) on the crown and lateral roots. During the normal growing season, differentiation of bud to shoot growth is inhibited by physiological factors external to the affected structure; a phenomenon referred to as paradormancy. Initiation of shoot growth from paradormant UABs can be accomplished through removal of the aerial shoots (hereafter referred to as paradormancy release).ResultsIn this study, phytohormone abundance and the transcriptomes of paradormant UABs vs. shoot-induced growth at 6, 24, and 72 h after paradormancy release were compared based on hormone profiling and RNA-seq analyses. Results indicated that auxin, abscisic acid (ABA), and flavonoid signaling were involved in maintaining paradormancy in UABs of leafy spurge. However, auxin, ABA, and flavonoid levels/signals decreased by 6 h after paradormancy release, in conjunction with increase in gibberellic acid (GA), cytokinin, jasmonic acid (JA), ethylene, and brassinosteroid (BR) levels/signals. Twenty four h after paradormancy release, auxin and ABA levels/signals increased, in conjunction with increase in GA levels/signals. Major cellular changes were also identified in UABs at 24 h, since both principal component and Venn diagram analysis of transcriptomes clearly set the 24 h shoot-induced growth apart from other time groups. In addition, increase in auxin and ABA levels/signals and the down-regulation of 40 over-represented AraCyc pathways indicated that stress-derived cellular responses may be involved in the activation of stress-induced re-orientation required for initiation of shoot growth. Seventy two h after paradormancy release, auxin, cytokinin, and GA levels/signals were increased, whereas ABA, JA, and ethylene levels/signals were decreased.ConclusionCombined results were consistent with different phytohormone signals acting in concert to direct cellular changes involved in bud differentiation and shoot growth. In addition, shifts in balance of these phytohormones at different time points and stress-related cellular responses after paradormancy release appear to be critical factors driving transition of bud to shoot growth.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0735-2) contains supplementary material, which is available to authorized users.

Whole-plant allocation to storage and defense in juveniles of related evergreen and deciduous shrub species.

In evergreen plants, old leaves may contribute photosynthate to initiation of shoot growth in the spring. They might also function as storage sites for carbohydrates and nitrogen (N). We hence hypothesized that whole-plant allocation of carbohydrates and N to storage in stems and roots may be lower in evergreen than in deciduous species. We selected three species pairs consisting of an evergreen and a related deciduous species: Mahonia aquifolium (Pursh) Nutt. and Berberis vulgaris L. (Berberidaceae), Prunus laurocerasus L. and Prunus serotina Ehrh. (Rosaceae), and Viburnum rhytidophyllum Hemsl. and Viburnum lantana L. (Adoxaceae). Seedlings were grown outdoors in pots and harvested on two dates during the growing season for the determination of biomass, carbohydrate and N allocation ratios. Plant size-adjusted pools of nonstructural carbohydrates in stems and roots were lower in the evergreen species of Berberidaceae and Adoxaceae, and the slope of the carbohydrate pool vs plant biomass relationship was lower in the evergreen species of Rosaceae compared with the respective deciduous species, consistent with the leading hypothesis. Pools of N in stems and roots, however, did not vary with leaf habit. In all species, foliage contained more than half of the plant's nonstructural carbohydrate pool and, in late summer, also more than half of the plant's N pool, suggesting that in juvenile individuals of evergreen species, leaves may be a major storage site. Additionally, we hypothesized that concentration of defensive phenolic compounds in leaves should be higher in evergreen than in deciduous species, because the lower carbohydrate pool in stems and roots of the former restricts their capacity for regrowth following herbivory and also because of the need to protect their longer-living foliage. Our results did not support this hypothesis, suggesting that evergreen plants may rely predominantly on structural defenses. In summary, our study indicates that leaf habit has consequences for storage economics at the whole-plant level, with evergreen shrub species storing less carbohydrates (but not N) per unit plant biomass than deciduous species.

Delayed harvest of reed canary grass translocates more nutrients in rhizomes

Two field experiments, one in large plots and the other in small framed plots, were conducted in Umeå, northern Sweden. The objectives were (1) to examine the seasonal patterns of rhizome growth and nutrient dynamics of the energy crop reed canary grass (Phalaris arundinacea L.) in ley I and II, and (2) to evaluate the roles of soil type (mineral vs. organic), fertilisation level (0, 50, and 100 kg N ha−1s), and season/harvest time (Oct-96, May-97, and Aug-97) on the rhizome growth and nutrient dynamics by means of a factorially designed experiment. The general pattern of rhizome growth was that biomass was low in June during initiation of shoot growth, but increased steadily during the growing season, reached a peak in late autumn, and remained high until next spring. The N and P accumulation in rhizomes followed a similar pattern. During ley years I and II, reed canary grass rhizome growth was less dependent on soil type, and more dependent on fertilisation and season, with fertilisation being the most important predictor of growth. The season/harvest time, followed by soil type, was the most important factor for both concentrations and therefore total uptake of N, P, and K in rhizomes. Soil type affected N content in rhizomes significantly, and also interacted with season and enhanced the effect on N, P, and K content in rhizomes. The seasonal dynamics of the nutrient content in rhizomes indicate a remobilisation of the nutrients from rhizomes to the regrowth of shoots and roots in spring and relocation/storage from aboveground shoots to rhizomes during late summer and autumn. The results of this study suggest that delaying the harvest to later than October would result in considerably more energy and nutrient resources being translocated from aboveground shoots to rhizomes for growth in the next season.

Subtractive cDNA Libraries Identify Differentially Expressed Genes in Dormant and Growing Buds of Leafy Spurge (Euphorbia esula)

Two subtractive cDNA libraries were developed to study genes associated with bud dormancy (reverse library) and initiation of shoot growth (forward library) in leafy spurge. To identify unique sequences represented in each library, 15744 clones were screened to reduce the level of redundancy within both libraries. A total of 516 unique sequences were obtained from 2304 minimally redundant clones. Radioactive probes developed from RNAs extracted from crown buds of either intact (para-dormant control) or a series of growth-induced (2 h, 2, and 4 d after decapitation) plants were used to identify differentially expressed genes by macroarray analysis. Semi-quantitative RT-PCR was used to confirm results obtained by macroarray analysis and to determine the expression profiles for other transcripts identified within the subtractive libraries. Selected clones were also used to examine gene expression in crown buds after growth induction and/or during normal seasonal growth. In this study, four distinct patterns of gene expression were observed during the transition from para-dormancy to growth-induction. Many of the differentially regulated genes identified have unknown or hypothetical functions while others are known to play important roles in molecular functions. Gene ontology analysis identified a greater proportion of genes involved with catalytic activity in the forward library while the reverse library had a greater proportion of genes involved in DNA/RNA binding.

Translocation of the Mango Florigenic Promoter

Floral induction of mango is determined by interaction of a short-lived, florigenic promoter that is up-regulated in leaves during exposure to cool temperatures and an age-dependent vegetative promoter at the time that initiation of shoot growth occurs. Research conducted during the past flowering season demonstrated that 1/4 of a leaf per stem was sufficient to stimulate flowering in 100% of the tested stems. Three or more leaves on a donor stem of an isolated branch also bearing five defoliated stems induced flowering on all six stems. One leaf on the donor stem was sufficient to induce flowering in all of the donor stems and most of the five defoliated stems, and 1/2 leaf on the donor stem stimulated flowering in that stem and in less than 1/2 of the defoliated stems. Stems that did not flower initiated vegetative shoots instead. Flowering occurred on those stems that were inserted into main branches in the same phylotaxic position as the leaf. Evidence suggests that leaves are capable of producing far greater amounts of florigenic promoter during floral inductive conditions than needed for induction of buds and that the promoter can move great distances in phloem aligned in the same phylotaxic position as the source leaf.

Correlation of Endogenous Gibberellic Acid with Initiation of Mango Shoot Growth

Stems of mango (Mangifera indica L.) rest in a non-growing, dormant state for much of the year. Ephemeral flushes of vegetative or reproductive shoot growth are periodically evoked in apical or lateral buds of these resting stems. The initiation of shoot growth is postulated to be primarily regulated by a critical ratio of root-produced cytokinins, which accumulate in buds and by leaf-produced auxin, which decreases in synthesis and transport over time. Exogenously applied gibberellic acid (GA 3 ) delays initiation of bud break but does not determine whether the resulting flush of growth is vegetative or reproductive. We tested the hypothesis that endogenous GA 3 , which influences release of these resting buds, may decrease in stem tips or leaves with increasing age of mango stems. GA 3 and several other GAs in stem tip buds and leaves were identified and quantified in stems of different ages. The major endogenous GAs found in apical buds and leaves of vegetative mango stems were early 13-hydroxylation pathway gibberellins: GA 1 , epi-GA 1 , GA 3 , GA 19 , GA 20 , and GA 29 , as identified by gas chromatography-mass spectrometry (GC-MS). A novel but unidentified GA-like compound was also present. The most abundant GAs in apical stem buds were GA 3 and GA 19 . Contrary to the hypothesis, the concentration of GA 3 increased within buds with increasing age of the stems. The concentrations of other GAs in buds were variable. The concentration of GA 3 did not change significantly with age in leaves, whereas that of most of the other GAs declined. GA 1 levels were greatest in leaves of elongating shoots. These results are consistent with the concept that rapid shoot growth is associated with synthesis of GAs leading to GA 1 . The role of GA 3 in delaying bud break in mango is not known, but it is proposed that it may enhance or maintain the synthesis or activity of endogenous auxin. It, thereby, maintains a high auxin/cytokinin ratio similar to responses to GA 3 that maintain apical dominance in other plant species.

Alterations in growth of tissue‐cultured tansy (Tanacetum vulgare L.) treated with antibiotics

Summary.Effects of three antibiotics (cefotaxime, rifampicin and gentamicin) were tested on in vitro shoots cultures of tansy (Tanacetum vulgare L.)‐ These antibiotics were selected because endophytic bacteria isolated from the in vitro shoot cultures of tansy showed that all bacteria were Gram‐negative and their growth was reduced by these three antibiotics. Five isolates were Enterobacteriaceae, three were fluorescent Pseudomonas, and two were aerobic bacteria. Increased concentrations of antibiotics caused usually linear or quadratic changes on the initiation of shoot growth, shoot number, growth rate, and shoot height. These changes and changes in pH of the culture media were tansy genotype‐dependent following treatments with gentamicin. Also, the treatment with rifampicin or cefotaxime showed a genotype‐dependent effect, because they resulted in significantly higher percentage of rooted plants in one of the three tansy genotypes tested. The growth rate and length of shoots were reduced in the media containing both gentamicin and rifampicin, but less so than in media containing both gentamicin and cefotaxime.

First-year growth of planted Douglas-fir and white fir seedling under different shelterwood regimes in California

A 17-ha area in the central California Sierra was harvested in 1979 to provide three shelterwoods with residual basal areas of 10, 15 and 20 m 2/ha. An adjacent uncut stand of 75 m 2/ha was used as a control. During the summer of 1980, seedling performance was assessed along with five microenvironmental characteristics. Maximum air temperature was similar among shelterwoods; minimum air temperature varied by about 3°C. Daily potential evaporation in all shelterwoods was similar and doubledfrom June to July and remained constant through September. Evaporation in the control was half of the shelterwoods. Subsurface soil temperature reached a maximum in August of 24°C in the least-dense shelterwood and 16°C in the control. Subsurface soil moisture was 35% for all treatments in May, but in September was 18% in the least-dense shelterwood and 12% in the control. Daily incident light in June ranged from 76% to 54% of maximum in the least-dense and most-dense shelterwood respectively, and 12% of maximum in the control. Survival of Douglas-fir was greater than 93% in all treatments. However, survival of white fir ranged from 63% to 85% as the overstory density increased; these differences were not significant. The period of rapid white fir mortality occurred later in the summer with increasing canopy cover. Height growth of both species was about 2.3 cm in the control to 3.1 cm under the least-dense shelterwood; however, treatment differences were significant only for white fir, Stem diameter growth of about 1.3 mm in treatments 10 and 15 was significantly greater than the growth of 0.3 mm in treatments 20 and the control. In Douglas-fir shoot: root ratios and biomass tended to increase with decreasing shelterwood. In white fir, the reverse trend was observed for shoot:root ratio but biomass production was similar in each shelterwood. Seedling sshowed the least overall growth in the uncut stand where plant moisture stress reached -19 bar (-1.9 MPa) in Douglas-fir and -22 bar (-2.2 MPa) in white fir. Results indicate that a 10 m 2/ha shelterwood provides conditions for successful 1st-year survival and growth of container-grown Douglas-fir, but a 15 m 2/ha density is preferable for bare-root white fir. Shoot growth initiation does not seem to be delayed under shelterwoods of up to 20 m 2/ha.

Seasonal woody plant shoot growth in Burkea afrieana — Ochna pulchra savanna

Seasonal changes in dry mass of shoots and their leaf and twig Components are described for Ochna pulchra and Burkea africana in a northern Transvaal savanna. Initiation of Shoot growth was found to correspond with a higher rate of temperature increase while time of leaf drop appeared to be affected by the rainfall of the current growth season. Later flushes of growth within a given season were relatively uncommon and where they did occur, they were of the order of half the magnitude of the first flush. Shoot growth per Ochna pulchra plant was found to relate to the previous season's rainfall and not to that of the current season of growth. In Burkea africana, a Similar relation was found, but only for rainfall toward the end of the previous season. From this and other evidence, it appears that shoot growth in these species depends more on carbohydrate reserves than on current photosynthate. The role of pleonanthic and hapaxanthic shoots in affecting relative growth of vegetative shoots per plant between seasons is discussed. Degree of syllepsis in Ochna pulchra affects aspects of canopy structure and the interseasonal changes in shoot growth. Plant size was found to relate inversely to individual shoot mass in Burkea africana and to relate directly to time of leaf fall in Ochna Pulchra. Shoot mortality between growth seasons was lower in Burkea africana than Ochna pulchra and was, in both species, greatest following a season of drought.

Seasonal root growth in the arctic tussock tundra.

The quantity of growing root tips per unit of soil volume was analyzed in a central Alaskan tussock tundra site. By June 10, the aboveground fraction of the vegetation had initiated the flush of spring growth and flowering while less than 5 active root tips cm-3 were found. By June 25 this value had increased to 30 root tips cm-3. Similar values in July were followed by a complete cessation of root growth after the first week of August. By then, leaf senescence had also become visible. In the spring, low root temperatures were responsible for the time lag between shoot growth initiation and the beginning of root growth. In early August, root growth stopped in spite of adequate soil temperatures and accumulated carbohydrate for root growth. It is proposed that use of reserve carbohydrate for root growth in August would compromise the flush of spring growth in the following year.

Freezing injury and shoot elongation in balsam fir

Three-year-old seedlings of balsam fir (Abiesbalsamea (L.) Mill.) representing provenances with different rates of shoot growth initiation were exposed to four temperatures between −3.3 and −8.5 °C at two different times during shoot elongation. Exposure at −3.3 °C resulted in no bud, shoot, or leaf injury. Exposure at −8.5 °C resulted in injury to 53% of 2000 buds and shoots tested. Differences in provenance and in timing of exposure were significant at lower temperatures. Freezing injury was largely a function of the developmental stage of buds and shoots at each temperature of −4.5 °C or lower. One-year-old leaves were severely damaged at lower temperatures and effects of provenance and timing of exposure were present.

Variation in balsam fir provenances planted in New England

After 3 years in the field, survival, date of shoot growth initiation, and total height of 15 provenances planted at three locations indicate moderate to large provenances effects. Relative provenance performance varied among locations for survival and total height but not for flushing date. Regression and correlation analyses indicated that both the temperature and moisture regimes at seed origin have acted as selective forces on the native population. Time of shoot growth initiation has been mainly influenced by the temperature regime, while total height was generally related to the moisture regime. Survival was not associated with any of the climatic variables used in the study.

Variation in seedling development of balsam fir associated with seed origin

Measurements of total height and frequency of frost damage on 5-year-old trees demonstrated moderate to large variation associated with seed origin. Total height was measured at three nurseries in Wisconsin and Minnesota. Frost damage was measured at one nursery in central Wisconsin. The tallest seedlings were from eastern provenances. The seedlings least damaged by spring frost were from Wisconsin and Michigan provenances. Periodic measurements of shoot elongation indicated that variation in rate of elongation was the chief determinant of variation in total shoot elongation. Variation in time of shoot growth initiation was one cause of observed variation in frequency of frost damage. Variation among maternal progenies from six populations in Wisconsin and Michigan was similar to variation among range-wide provenances.