Adult Growth Phase Research Articles

Divergent selection for timing of vegetative phase change

AbstractVegetative phase change is a key trait in plant development and marks the transition from juvenile to adult growth phases. In maize (Zea mays L.), juvenile plants and plants with a late phase change can be identified by the increased production of tillers, aerial roots, and distinctive epicuticular wax. Resistance to agronomically significant pathogens can also differ between juvenile and adult plants. Using last leaf with juvenile wax as the target of selection, the maize population Minnesota 11 underwent 16 cycles of divergent selection. The objectives of this research were to identify emergent trends for each trait and to determine the magnitude and direction of phenotypic changes over long‐term selection compared to the source population. Phenotypic data on plant architecture traits, ear traits, and common rust resistance were collected in 2020 and 2021 by concurrently growing plants from selection cycles representing both directions of selection. Last leaf with juvenile wax, the direct target of selection increased to leaf 17.8 in the late phase change population and decreased to leaf 5 in the early phase change population from leaf 9 in the source population. Late vegetative phase change was positively correlated with increased common rust infection and plant height, and negatively correlated with ear size traits. This study shows that the observed phenotypic changes follow patterns of genetic variation consistent with divergent selection, but with possible effects of inbreeding.

Microbiota of the rhizosphere zone of Calamagrostis epigeios from a coal mine waste dump

The microbiota plays an important role in the processes of plant overgrowth of coal mine waste dumps, enabling the transformation of numerous compounds into forms available to plants. The overgrowth of coal mine dumps is influenced by many factors. Pioneers are plant species that have a wide ecological and phytocenotic amplitude. Calamagrostis epigeios (L.) Roth. occupies a special place among them. The composition of the microbiota of the rhizosphere zone of C. epigeios was studied in relation to the age of the plants and the stage of the succession of the “Vizeyska” mine dump (Ukraine). It was established and confirmed as a result of two-factor variance analysis that the growth phase of C. epigeios and the stage of the succession of coal mine waste dumps have different effects on the number of microorganisms from the rhizosphere zone of plants. The number of pedotrophic microorganisms, microorganisms that metabolize nitrogen of organic compounds, cellulose-degrading microorganisms, and microscopic fungi depended more on the age of C. epigeios, and not on the stage of the succession of the studied area. The number of chemolithotrophic bacteria, particularly thiobacteria, decreased with the change of the growth phase of C. epigeios. The number of acidophobic thiobacteria depended more on the stage of succession, and the number of acidophilic thiobacteria depended more on the age of the C. epigeios. The number of microorganisms that metabolize nitrogen of organic compounds, oligonitrophilic microorganisms and microorganisms that metabolize nitrogen of inorganic compounds in the samples of tailings from the area with grasses and perennials and from the area with grasses, shrubs, and sun-loving trees was higher, compared to the number of these groups of microorganisms in the control and changed with the change in the growth phase of C. epigeios. The number of microorganisms that metabolize nitrogen of organic compounds, oligonitrophilic microrganisms and microorganisms that metabolize nitrogen of inorganic compounds was the highest in the samples from the area with grasses, shrubs, and sun-loving trees during the adult growth phase of C. epigeios. In the area where C. epigeios dominated within the vegetation, the highest number of microorganisms that metabolize nitrogen of organic compounds was also during the adult phase of C. epigeios, and the number of bacteria that assimilate mineral forms of nitrogen and oligonitrophilic microorganisms was the highest during the sub-adult stage. The index of pedotrophicity is higher in the samples taken in the area where C. epigeios prevails among other herbaceous plants, and where in the tree layer there are Betula pendula, Populus tremula with an admixture of Pinus sylvestris. Pedotrophicity indices which were calculated for these samples do not depend on the growth stage of C. epigeios and are higher than for the control area. Immobilization-mobilization of nitrogen indices in samples of tailings from the area with grasses and perennials and from the area with grasses, shrubs, and sun-loving trees ranged from 1.94 to 3.52 and were higher compared to the control site.

Ontogenetic Scaling of Skeletal Components in the Common Sea Urchin Lytechinus variegatus

Ontogenetic allometric analyses can provide novel insights into aspects of evolution, ecology, and conservation. The present study exploits a model sea urchin to evaluate the ontogenetic allometry of skeletal defense and feeding efficiency. Individuals of Lytechinus variegatus were sampled from St. Joseph Bay, FL, and a range of different-sized late juvenile to adult individuals were weighed, measured, and dissected into skeletal components. Skeletal defense was evaluated by examining whole-body wet mass versus primary spine density (number/cm2), length (mm), breakage strength (N), and magnesium calcite levels (%). Feeding efficiency was indirectly inferred from the relationship between whole-body wet mass versus whole lantern dry weight and magnesium calcite content. It was found that between the late juvenile to adult growth phase, L. variegatus displays nonlinear and isometric scaling between body size and various metrics of skeletal spine defense. Intriguingly, most metrics of spine defense against predators displayed a nonsignificant, body-size-independent relationship, indicating L. variegatus invests heavily in spine defenses at an early age. In contrast, hyperallometric scaling best described the relationship between body size and lantern size (feeding efficiency) reflecting the potential importance of elevating food intake with increasing age.

Changes in Haemolymph Biochemical values during different growth phases in African Giant Land Snail (Archachatina Marginata) Swainson

The impact of growth phases on the haemolympy biochemical value of African giant land snail Archachatina marginata was studied. The growth phases were: snailet, juvenile and Adult based on the number of whorls on the shell and weight of the snails. Highest concentration of glucose and lipids were recorded at the juvenile phase (40.20mg/dl), while least values for glucose (20.00mg/dl) and lipids (37.80mg/dl)were recorded during snailer and adult phases respectively. A progressive increase in the concentration of protein was observed as the snails moved from snailetphase to adult phase, hence snails in adult phase had highest concentration of protein in their haemolymph. Growth phases significantly (p<0.05) affected the haemolymph mineral composition of the snails, juvenile phase had the highest values in ca2+,PO4+ and Na+, while the adult phase recorded the least concentration in ca2+, Na amd cl-2. Juvenile growth phase of A. marginata thus has better haemolymph biochemical values than both snailet and adult growth phases.

Alpine Holocene tree-ring dataset: age-related trends in the stable isotopes of cellulose show species-specific patterns

Abstract. Stable isotopes in tree-ring cellulose are important tools for climatic reconstructions even though their interpretation could be challenging due to nonclimate signals, primarily those related to tree aging. Previous studies on the presence of tree-age-related trends during juvenile as well as adult growth phases in δD, δ18O, and δ13C time series yielded variable results that are not coherent among different plant species. We analyzed possible trends in the extracted cellulose of tree rings of 85 larch trees and 119 cembran pine trees, i.e., in samples of one deciduous and one evergreen conifer species collected at the tree line in the Alps, covering nearly the whole Holocene. The age trend analyses of all tree-ring variables were conducted on the basis of mean curves established by averaging the cambial-age-aligned tree series. For cambial ages over 100 years, our results prove the absence of any age-related effect in the δD, δ18O, and δ13C time series for both the evergreen and the deciduous conifer species, with the only exception being larch δD. However, for lower cambial ages, we found trends that differ for each isotope and species; i.e., mean δ13C values in larch do not vary with aging and can be used without detrending, whereas those in cembran pine show a juvenile effect, and the data should be detrended. Mean δ18O values present two distinct aging phases for both species, complicating detrending. Similarly, mean δD values in larch change in the first 50 years, whereas cembran pine changes between 50 and 100 years. Values for these two periods of cambial age for δD and δ18O should be used with caution for climatic reconstructions, ideally complemented by additional information regarding mechanisms for these trends.

A comparative analysis of leaf shape of wheat, barley and maize using an empirical shape model

The phenotypes of grasses show differences depending on growth conditions and ontogenetic stage. Understanding these responses and finding suitable mathematical formalizations are an essential part of the development of plant and crop models. Usually, a marked change in architecture between juvenile and adult plants is observed, where dimension and shape of leaves are likely to change. In this paper, the plasticity of leaf shape is analysed according to growth conditions and ontogeny. Leaf shape of Triticum aestivum, Hordeum vulgare and Zea mays cultivars grown under varying conditions was measured using digital image processing. An empirical leaf shape model was fitted to measured shape data of single leaves. Obtained values of model parameters were used to analyse the patterns in leaf shape. The model was able to delineate leaf shape of all studied species. The model error was small. Differences in leaf shape between juvenile and adult leaves in T. aestivum and H. vulgare were observed. Varying growth conditions impacted leaf dimensions but did not impact leaf shape of the respective species. Leaf shape of the studied T. aestivum and H. vulgare cultivars was remarkably stable for a comparable ontogenetic stage (leaf rank), but differed between stages. Along with other aspects of grass architecture, leaf shape changed during the transition from juvenile to adult growth phase. Model-based analysis of leaf shape is a method to investigate these differences. Presented results can be integrated into architectural models of plant development to delineate leaf shape for different species, cultivars and environmental conditions.

Polychlorinated biphenyl (PCB) load, lipid reserves and biotransformation activity in migrating Atlantic salmon from River Mörrum, Sweden

Atlantic salmon accumulate high levels of contaminants such as polychlorinated biphenyls (PCBs) in their lipids during the adult growth phase spent at sea. The lipids are later utilized during migration for swimming and biological adaptations. We hypothesize that migrating salmons' biotransformation processes are affected by the high levels of built-up PCBs compared to salmon that in a pre-migrational stage. For these analyses we sampled adult Atlantic salmon during migration in the Swedish River Mörrum and measured the 21 most common PCB congeners (∑PCB) and lipid levels in muscle tissue, aryl hydrocarbon receptor (AHR2) and cytochrome P4501A1 (CYP1A1) transcript levels as well as ethoxyresorufin-O-deethylase activity (EROD) in liver. We also determined which AHR2 genotypes the salmon carried. We show that EROD activity is correlated to CYP1A1 level but not to ∑PCB concentration. ∑PCB concentration does not predict levels of neither the AHR2 nor CYP1A1 genes. We find no associations between specific AHR2 transcription levels and AHR2 genotypes or a correlation between AHR2 and CYP1A1 transcription levels, which is in direct contrast to pre-migrational adult salmon from the Baltic Sea. When we compare River Mörrum to salmon we have previously sampled in the Baltic Sea we show that migrating salmon have significantly lower lipid levels in their muscles; higher muscle concentrations of ∑PCB on a lipid basis; and significantly lower CYP1A1 and EROD levels compared to salmon from the Baltic Sea. Also, transcript levels of three out of four AHR2 genes are significantly different. In conclusion, migrating Swedish Atlantic salmon carry higher concentrations of PCBs in their lipids compared to salmon in the Baltic Sea, but have lower activation of biotransformation genes and enzymes. Our results indicate that accumulated pollutants from the Baltic Sea are deactivated inside the migrating salmon's lipid tissues and increase in concentration when migration is initiated thereby limiting their impact on biotransformation processes.

Differential MMP‐2 and MMP‐9 Activity and Collagen Distribution in Skeletal Muscle from pacu(Piaractus mesopotamicus)During Juvenile and Adult Growth Phases

Here, we evaluated collagen distribution and matrix metalloproteinases (MMPs) MMP-2 and MMP-9 activities in skeletal muscle of pacu (Piaractus mesopotamicus) during juvenile and adult growth phases. Muscle samples from juvenile and adult fishes were processed by histochemistry for collagen system fibers and for gelatin-zymography for MMP-2 and MMP-9 activities analysis. Picrosirius staining revealed a myosept, endomysium, and perimysium-like structures in both growth phases and muscle types, with increased areas of collagen fibers in adults, mainly in red muscle. Reticulin staining showed that reticular fibers in the endomysium-like structure were thinner and discontinuous in the red muscle fibers. The zymography revealed clear bands of the pro- MMP-9, active- MMP-9, intermediate- MMP-2, and active- MMP-2 forms in red and white muscle in both growth phases. MMP-2 activity was more intense in juvenile than adult muscle fibers. Comparing the red and white muscle types, MMP-2 activity was significantly higher in red muscle in adult phase only. The activity of MMP-9 forms was similar in juvenile red and white muscles and in the adult red muscle, without any activity in adult white muscle. In conclusion, our results show that, in pacu, the higher activities of MMP-2 and -9 are associated with the rapid muscle growth in juvenile age and in adult fish, these activities are related with a different red and white muscle physiology. This study may contribute to the understanding muscle growth mechanisms and may also contribute to analyse red and the white muscle parameters of firmness and softness, respectively, of the commercial product.

Expression analysis and genetic mapping of three SEPALLATA-like genes from peach (Prunus persica (L.) Batsch)

SEPALLATA (SEP) MADS box genes play essential and diverse roles in reproductive organ development. To investigate the SEP gene function in peach we isolated three SEP-like genes, PrpMADS2, PrpMADS5, and PrpMADS7, which belong to distinct SEP gene clades. They appeared as single copy genes in the peach genome and were found to preferentially express in flowers and fruits. Arabidopsis transformants expressing 35S: PrpMADS2 were indistinguishable from wild-type plants. Overexpression of PrpMADS5 led to earlier flowering. Through chimeric repressor silencing technology, PrpMADS5 was found to function in floral organ development. Expression of PrpMADS7 in Arabidopsis caused a dramatic attenuation of both juvenile and adult growth phases and, in severely affected plants, it led to flower formation immediately after the embryonic phase. Two microsatellite markers were developed for PrpMADS2 and PrpMADS5 and assigned to the genetic linkage groups 5 and 1, respectively. PrpMADS7, previously identified as PrpAGL2, and PrpMADS5 were identified as potential loci to modify the flowering time and floral organs in Prunus species. Moreover, our results showed the diversification of SEP genes in peach.

The MADS‐box gene DAL1 is a potential mediator of the juvenile‐to‐adult transition in Norway spruce (Picea abies)

Progression through the plant life cycle involves change in many essential features, most notably in the capacity to reproduce. The transition from a juvenile vegetative and non-reproductive to an adult reproductive phase is gradual and can take many years; in the conifer Norway spruce, Picea abies, typically 20-25 years. We present a detailed analysis of the activities of three regulatory genes with potential roles in this transition in Norway spruce: DAL1, a MADS-box gene related to the AGL6 group of genes from angiosperms, and the two LEAFY-related genes PaLFY and PaNLY. DAL1 activity is initiated in the shoots of juvenile trees at an age of 3-5 years, and then increases with age, whereas both LFY genes are active throughout the juvenile phase. The activity of DAL1 further shows a spatial pattern along the stem of the tree that parallels a similar gradient in physiological and morphological features associated with maturation to the adult phase. Constitutive expression of DAL1 in transgenic Arabidopsis plants caused a dramatic attenuation of both juvenile and adult growth phases; flowers forming immediately after the embryonic phase of development in severely affected plants. Taken together, our results support the notion that DAL1 may have a regulatory role in the juvenile-to-adult transition in Norway spruce.

Fecundity and size at maturity of Palaemon longirostris (Decapoda, Palaemonidae) in the Mira River estuary (SW Portugal)

Summary The reproductive traits of female Palaemon longirostris were examined in this study. The mean fecundity was 957±282 SD. The mean egg volume increased 17% from the early to the late development stage. By using the allometric model, no simple volumetric relationship was found between brood size and carapace length at any egg stage. For both early and late egg stages, a negative allometric level was obtained. During embryogenesis, egg loss was estimated at 5%, with no apparent effect on female size. Size at maturity was studied using morphometric analyses, assuming that the attainment of sexual maturity involves morphological changes of the pleura in order to form a brood chamber. A Mature 1 analysis evidenced overlapping “growth-phase” lines, suggesting that adult females may moult to a resting condition after breeding. The obtained regression lines indicate the presence of different morphotypes, but do not correspond to young and adult prawns. To determine size at maturity, a Mature 2 analysis was run for the young-like morphotype in an attempt to locate an intersection point delimiting the young and the adult growth phases. The estimated size closely matched the size of the smallest ovigerous prawn.

Increased body weight in C57BL/6 female mice after exposure to ionizing radiation or 60Hz magnetic fields

Purpose: The purpose of this investigation was to determine whether early treatment with ionizing radiation and/or chronic magnetic field (MF) exposure affected body weight in female mice. Materials and methods: Weanling C57BL/6 female mice were irradiated with four equal weekly cobalt-60 exposures (total cumulative doses: 3.0, 4.0, 5.1Gy) and/or received chronic lifetime exposure to 1.4mT 60 Hz circularly polarized MF or ambient MF. The body weights of 2280 mice were recorded at 35 age intervals, and analysis of variance was used to compare the mean differences from baseline weights between treatment groups and sham-exposed controls. Results: A highly statistically significant effect of ionizing radiation on body weight was observed at 28 age intervals (p h 0.001), and for MF exposure at 10 age intervals (p h 0.001). During the young adult growth phase, mice exposed only to MF exhibited h 0.5g greater weight gain relative to sham-exposed controls (p = 0.0001). The effect of ionizing radiation alone was inversely related to dose, with the largest weight increases observed in all of the irradiated groups after 9-12 months (p = 0.0001). Conclusions: Treatment with split-dose ionizing radiation at an early age and chronic exposure to a residential power frequency MF were found to produce small but significant increases in body weight.

Micropropagation of gum karaya (Sterculia urens) by adventitious shoot formation and somatic embryogenesis.

Nodal explants from selected trees of gum karaya (Sterculia urens Roxb.) in the adult growth phase cultured on Murashige and Skoog (MS) medium supplemented with 6.62 μM N6-benzylaminopurine (BAP) produced an average of six adventitious shoots in 30 days. Shoots were rooted in vitro on 1/4-strength MS medium containing 9.82 μM indole-3-butyric acid. Nodulated callus was produced from hypocotyl explants cultured on MS medium supplemented with 4.52 μM 2,4-dichlorophenoxyacetic acid and 8.90 μM BAP. Somatic embryos developed when the nodulated callus was transferred to MS medium containing 0.45 μM thidiazuron (TDZ). TDZ treatment for 2 days gave the optimum response. Over 30% of the somatic embryos developed into plantlets when transferred to 1/4-strength MS basal medium without any growth regulators. Plantlets produced from adventitious shoots and somatic embryos were acclimatized to ex vitro conditions and established in the field.

Propagation of Quercus myrsinifolia and Quercus canbyi by Stem Cuttings

Abstract Stem cuttings of two clones (clone 1 and 2) of Quercus myrsinifolia Bl. (Chinese evergreen oak), and one clone of Quercus canbyi Trel. (Canby's oak), of seedling origin and in the adult growth phase, were taken on various dates representing specific growth stages. Cuttings of clone 1 of Q. myrsinifolia were collected at the semi-hardwood, hardwood, or softwood stages in addition to a transitional stage between softwood and semi-hardwood. For clone 2, stem cuttings were taken only at the softwood and transitional softwood/semi-hardwood stages. Cuttings of Q. canbyi were collected at the semi-hardwood, hardwood, or softwood stages. Cuttings of both species were treated with 0, 1500 (0.15%), 3000 (0.3%), 6000 (0.6%), or 9000 ppm (0.9%) indolebutyric acid (IBA) in 50% isopropanol. All cuttings were placed in a raised greenhouse bench and rooted under intermittent mist. Semi-hardwood or hardwood cuttings of Q. myrsinifolia or Q. canbyi did not root. Responses of stem cuttings of Q. myrsinifolia to IBA treatment varied by growth stage. For softwood cuttings response to IBA was quadratic with the greatest rooting noted for clones 1 (56%) and 2 (72%) when treated with 1500 and 3000 ppm IBA, respectively. Treatment with IBA had no effect on percent rooting of softwood/semi-hardwood cuttings of clone 1, with rooting ranging from 47% to 58%. However, a linear decrease in rooting in response to IBA was observed fordone 2 with the greatest rooting occurring for the nontreated cuttings (89%). Softwood cuttings of Q. canbyi responded quadratically to IBA treatment, with maximum rooting of 33% noted for cuttings treated with 1500 ppm IBA.

Propagation of Quercus phillyreoides by Stem Cuttings

Abstract Stem cuttings of two clones (clones 1 and 2) of seedling origin of Quercus phillyreoides A. Gray (ubame oak) in the adult growth phase were taken on four dates that represented four growth stages (semi-hardwood, hardwood, softwood, and transitional growth between softwood and semi-hardwood). All cuttings were treated with selected concentrations and formulations of indolebutyric acid (IBA) and placed under intermittent mist for rooting. Greatest rooting for both clones was achieved with softwood cuttings with 97% and 56% rooting for clones 1 and 2, respectively, treated with 8000 ppm (0.8%) IBA in talc. Six weeks later when cuttings were in a softwood/semi-hardwood condition, rooting of clone 1 was still comparable to softwood cuttings whereas clone 2 rooted poorly. For both clones, rooting of semi-hardwood cuttings was poor, which was the same for hardwood cuttings of clone 2. Moderate rooting of 58% was noted for nontreated hardwood cuttings of clone 1. Auxin treatments generally increased root number. As mean root number increased mean root length decreased. Greater overwinter survival was observed for rooted softwood cuttings, which produced a flush of new growth following rooting in comparison to softwood/semi-hardwood cuttings that did not flush following rooting.

Micropropagation of Pieris floribunda

Abstract Shoot tips excised from actively growing stock plants of Pieris floribunda (Pursh ex Sims) Benth. and Hook. (mountain andromeda) in the adult growth phase, were surface disinfested, the terminal portions removed (decapitated), and the shoots placed horizontally on agar-solidified Woody Plant Medium (WPM) supplemented with 8 ppm 6-(γ,γ-dimethylallylamino)-purine (2iP), 80 ppm adenine hemisulfate, and 200 ppm NaH2PO4. Within 1 month, multiple shoot formation began and axillary shoots were excised from the original explants. These shoots were decapitated and placed on WPM with the aforementioned supplements. After 3 subcultures and 3 transfers (6 months), eight-node axillary shoots were excised, decapitated, and cultured on agar-solidified WPM supplemented with 0, 0.5, 1, 2, 4, 8, or 16 ppm 2iP. The greatest number of microcuttings ≥ 20 mm (0.8 in) having low hyperhydricity and moderate dry weight was produced at 4 ppm 2iP. Attempts at ex vitro rooting were unsuccessful and rooting was accomplished in vitro. In vitro rooting of microcuttings was optimal (75% rooting) when placed in WPM containing 15 ppm of the potassium (K) salt of 1H-indole-3-butyric acid (K-IBA) for 10 days followed by transfer to WPM lacking K-IBA. Rooted microcuttings were placed in a plug tray containing a sterile medium of 1 peat: 1 vermiculite (v/v) and transferred to high humidity (> 80% RH) for acclimatization. After 2 weeks under high humidity, plantlets were transferred to a glasshouse resulting in 49% survival.

Differential Response of Luteinizing Hormone Receptor and Steroidogenic Enzyme Gene Expression to Human Chorionic Gonadotropin Stimulation in the Neonatal and Adult Rat Testis*

To study further the functional differences of the fetal-neonatal and adult growth phases of Leydig cells, neonatal (5-day-old) and adult (60-day-old) male rats were challenged with a 600 IU/kg injection of human CG (hCG). Certain Leydig cell responses were monitored 1, 2, and 3 days after the hCG injection. The down-regulation of LH receptors and blockage of the 17-hydroxylase/C17-20 lyase step in adult testis, and the absence of these responses in neonatal testis were confirmed. Novel data were obtained on concomitant responses of LH receptor and steroidogenic enzyme messenger RNAs (mRNAs). The LH receptor mRNA was increased 4-5-fold by 2 days after hCG injection in the neonatal testis (P less than 0.05), but in the adult was decreased during all 3 days by 50% (P less than 0.05). The mRNA level of the cytochrome P450 for cholesterol side chain cleavage responded similarly at both ages, with a 180-260% increase during 2 and 3 days (P less than 0.05-0.01). In contrast, the 17-hydroxylase/17,20-lyase cytochrome P450 mRNAs displayed opposite responses, increasing 4.5-fold in 2 days (P less than 0.01) in the neonates, but decreasing by 80% in 1 day in the adults (P less than 0.01). No response of the aromatase cytochrome P450 mRNA to hCG stimulation was found at either age studied. These results demonstrate that the functional differences of the neonatal and adult Leydig cells to high gonadotropic stimulation occur at the level of expression of specific genes, including those of the LH receptor and the 17-hydroxylase/17,20-lyase cytochrome P450. Although aromatization of testicular androgens has been suggested to mediate the blockade of the 17-hydroxylase/C17-20 lyase step in adult testes, altered steady state levels of aromatase mRNA are not involved in this response. LH receptor mRNA decreases in adult rat testis in response to treatment with high levels of hCG. Thus, this phenomenon of down-regulation of membrane receptors includes a decreased LH receptor mRNA as well as cellular internalization of the existing receptors.

In vitro rooting of the apple rootstock M 26 in adult and juvenile growth phases and acclimatization of the plantlets

In order to obtain optimum conditions for in vitro propagation of the apple rootstock M 26 (Malus pumila Mill.) in adult and juvenile growth phases, several rooting experiments were performed. Supraoptimal concentrations of indole‐3‐butyric acid (IBA) added to the rooting media resulted in profuse callus formation. Since extensive callus production is detrimental to the survival of the plantlets, modified culture conditions were established to reduce callus formation. A reduction of the time of exposure to IBA to 5 days and, thereafter, transfer to a hormone‐free medium did not eliminate callus production. Exposure to darkness during the root initiation phase increased rooting. When the rooting medium was based on the Lepoivre formula instead of the Murashige and Skoog formula, callus formation was reduced. Optimum conditions for rooting were obtained at much lower concentration than earlier reported, being 1.25 μM for the juvenile and 0.5 μM for the adult growth phase in the range of IBA concentrations tested. Anatomical studies revealed that root initials are formed after 5 days of IBA‐treatment. Therefore, we transferred shoots directly to non‐sterile conditions after the root‐inducing phase. This resulted in a 90% survival of the plantlets. Subculture on hormone‐free medium can thus be eliminated when the optimum auxin concentration is known.

The rooting ability of shoots raised ‘in vitro’ from the apple rootstock A2 in juvenile and in adult growth phase

The apple rootstock A2 can be readily propagated in vitro both in the juvenile and in the adult growth phase. Shoots were produced by meristem tip culture from the apple rootstock A2 in different growth phases. The influence of growth phases and different concentrations of PG and IBA was investigated as to rooting percentage, survival percentage, number of roots per rooted shoot, root length, shoot length and formation of callus. IBA at 15 μM without PG gave a significantly lower rooting percentage than 5 and 10 μM IBA. PG together with IBA stimulated rooting, the optimum concentrations of PG being, however, not the same for the different growth phases. For the adult growth phase, 10−4M PG promoted rooting, whereas 10−3M PG markedly inhibited rooting. In the juvenile growth phases, both 10−4 and 10−3M PG stimulated rooting. PG at 10−4M also increased the number of roots. The longest roots were obtained at 10−3M PG and 5 μM IBA. PG at 10−3M reduced callus formation at all IBA concentrations used. Neither shoot length nor root length influenced the survival percentage.

Effects of emersion and temperature upon growth of the tropical brown alga Padina japonica, using a tide-simulation apparatus

A simple tide-simulation apparatus was used to investigate the influence of emersion and temperature on the intertidal growth of Padina japonica Yamada in both the juvenile and adult growth phases. The upper zonation limits are not determined by the sensitivity of any particular growth phase, since all phases show the same emersion tolerance limits. The species grows best when continuously submerged, and growth rates decrease with increasing emersion up to a clear upper zonation boundary. High temperature reduces the emersion tolerance and is therefore an important factor in tropical intertidal zonation.