Body-inclusive large-eddy simulations of disk wakes are performed for a homogeneous fluid and for different levels of stratification. The Reynolds number is 5 × 10
4
and the Froude number (
$Fr$
) ...takes the values of
$\infty$
, 50, 10 and 2. In the axisymmetric wake of a disk with diameter
$L_{b}$
in a homogeneous fluid, it is found that the mean streamwise velocity deficit (
$U_{0}$
) decays in two stages:
$U_{0}\propto x^{-0.9}$
during
$10<x/L_{b}<65$
and, subsequently,
$U_{0}\propto x^{-2/3}$
. Consequently, none of the simulated stratified wakes is able to exhibit the classical 2/3 decay exponent of
$U_{0}$
in the interval before buoyancy effects set in. Stratification affects the wake within approximately one buoyancy time scale, after which, we find three regimes: weakly stratified turbulence (WST), intermediately stratified turbulence (IST) and strongly stratified turbulence (SST). WST begins when the turbulent Froude number (
$Fr_{h}$
) decreases to
$O(1)$
, spans
$1\lesssim Nt_{b}\lesssim 5$
and, while the mean flow is strongly affected by buoyancy in WST, turbulence is not. During IST, which commences at
$Nt_{b}\approx 5$
when
$Fr_{h}=O(0.1)$
, the mean flow has arrived into the non-equilibrium (NEQ) regime with
$U_{0}\propto x^{-0.18}$
, but the turbulence state is still in transition, as indicated by progressively increasing turbulence anisotropy. When
$Fr_{h}\sim O(0.01)$
at
$Nt_{b}\approx 20$
, the wake transitions into SST, where the turbulent vertical Froude number (
$Fr_{v}$
) asymptotes to a
$O(1)$
constant. There is strong anisotropy (
$u_{z}^{\prime }\ll u_{h}^{\prime }$
), and both
$u_{h}^{\prime }$
and
$U_{0}$
satisfy
$x^{-0.18}$
decay, signifying the arrival of the NEQ regime for both turbulence and mean flow. Turbulence is patchy and temporal spectra are broadband in the SST wake. The wake height decreases as
$L_{V}\sim O(U_{0}/N)$
in IST/SST. Energy budgets reveal that stratification prolongs wake life during WST/early-IST by both an energy transfer from mean potential energy to mean kinetic energy and reduction of turbulent production. In the late-IST/early-SST stages, production is enhanced and, additionally, there is injection from turbulent potential energy slowing down turbulent kinetic energy (TKE) decay. Only in the SST stage, when NEQ is realized for both the mean and turbulence, does the turbulent buoyancy flux become negative again, acting as a sink of TKE.
Catharanthus roseus
(L.) G. Don, also known as Madagascar periwinkle or Sadabahar, is a herbaceous plant belonging to the family
Apocynaceae
. Being a reservoir for more than 200 alkaloids, it ...reserves a place for itself in the list of important medicinal plants. Secondary metabolites are present in its leaves (e.g., vindoline, vinblastine, catharanthine, and vincristine) as well as basal stem and roots (e.g., ajmalicine, reserpine, serpentine, horhammericine, tabersonine, leurosine, catharanthine, lochnerine, and vindoline). Two of its alkaloids, vincristine and vinblastine (possessing anticancerous properties), are being used copiously in pharmaceutical industries. Till date, arrays of reports are available on in vitro biotechnological improvements of
C. roseus
. The present review article concentrates chiefly on various biotechnological advancements based on plant tissue culture techniques of the last three decades, for instance, regeneration via direct and indirect organogenesis, somatic embryogenesis, secondary metabolite production, synthetic seed production, clonal fidelity assessment, polyploidization, genetic transformation, and nanotechnology. It also portrays the importance of various factors influencing the success of in vitro biotechnological interventions in
Catharanthus
and further addresses several shortcomings that can be further explored to create a platform for upcoming innovative approaches.
Key Points
• C. roseus yields anticancerous vincristine and vinblastine used in pharma industry.
•
In vitro biotechnological interventions prompted major genetic advancements.
• This review provides an insight on
in vitro
-based research achievements till date.
• Key bottlenecks and prospective research methodologies have been identified herein.
Direct numerical simulations are performed to investigate a stratified shear layer at high Reynolds number ($Re$) in a study where the Richardson number ($Ri$) is varied among cases. Unlike previous ...work on a two-layer configuration in which the shear layer resides between two layers with constant density, an unbounded fluid with uniform stratification is considered here. The evolution of the shear layer includes a primary Kelvin–Helmholtz shear instability followed by a wide range of secondary shear and convective instabilities, similar to the two-layer configuration. During transition to turbulence, the shear layers at low $Ri$ exhibit a period of thickness contraction (not observed at lower $Re$) when the momentum and buoyancy fluxes are counter-gradient. The behaviour in the turbulent regime is significantly different from the case with a two-layer density profile. The transition layers, which are zones with elevated shear and stratification that form at the shear-layer edges, are stronger and also able to support a significant internal wave flux. After the shear layer becomes turbulent, mixing in the transition layers is shown to be more efficient than that which develops in the centre of the shear layer. Overall, the cumulative mixing efficiency ($E^C$) is larger than the often assumed value of 1/6. Also, $E^C$ is found to be smaller than that in the two-layer configuration at moderate Ri. It is relatively less sensitive to background stratification, exhibiting little variation for $0.08 \leqslant Ri \leqslant 0.2$. The dependence of mixing efficiency on buoyancy Reynolds number during the turbulence phase is qualitatively similar to homogeneous sheared turbulence.
The present study reports enhanced in vitro mass propagation, synthetic seed production and its regeneration, acclimatization, and genetic fidelity assessment of in vitro regenerants of
Bacopa ...monnieri
(L.) Pennell; a medicinal plant renowned for its memory-enhancing property. For the first time,
meta
-Topolin (
m
T) as well as N
6
-benzyladenine (BA) and kinetin at their variable concentrations (0.5, 1. 1.5, 2 and 2.5 mg/l) were supplemented individually in Murashige and Skoog (Physiol Plant 15:473–497, 1962) (MS) basal medium to induce multiple shoots from shoot tip explants, initially collected from two-month-old vegetatively propagated plants. The best result in terms of multiplication (~ 7 shoots/explant) and biomass accumulation (~ 451.3 mg fresh weight, ~ 104.3 mg dry weight) was obtained in MS medium supplemented with 1 mg/l
m
T. For rooting of in vitro shoots, supplementation of 1.5 mg/l IAA and 0.5 mg/l IBA in MS media resulted in induction of the maximum number (~ 20) and highest length (~ 5.5 cm) of roots, respectively. Most efficient indirect regeneration and biomass production from green and hard basal calli (induced spontaneously in BA-supplemented media) was recorded in a simple MS medium. Synthetic seeds were produced from in vitro shoot tips using 2.5% sodium alginate and 75 mM calcium chloride solutions and were successfully regenerated in half-strength MS medium. Six-week-old in vitro regenerants were transferred to different substrates for acclimatization, among which cocopeat was found to be the best exhibiting the highest survival and growth in external conditions. Finally, molecular marker-(ISSR) and phenology-based genetic fidelity assessment of the in vitro regenerants exhibited that the in vitro regenerants were true-to-type in nature within themselves as well as with the mother plant.
Direct numerical simulations are performed to study the evolution of a towed stratified wake subject to external turbulence in the background. A field of isotropic turbulence is combined with an ...initial turbulent wake field and the combined wake is simulated in a temporally evolving framework similar to that of Rind & Castro (J. Fluid Mech., vol. 710, 2012a, p. 482). Simulations are performed for external turbulence whose initial level varies between zero and a moderate intensity of up to 7 % relative to the free stream and whose initial integral length scale is of the same order as that of the wake turbulence. A series of simulations are carried out at a Reynolds number of 10 000 and Froude number of 3. Background turbulence, especially at a level of 3 % or above, is found to have substantial quantitative effects in the stratified simulations. Turbulence inside the wake increases due to the entrainment of external turbulence, and the energy transfer through turbulent production from mean to fluctuating velocity also increases, leading to reduced mean velocity. The profiles of normalized mean and turbulence quantities in the stratified wake exhibit little change in the vertical direction but the horizontal spread increases in comparison to the case with undisturbed background. The spatial organization of the internal wave field is disrupted even at the 1 % level of external turbulence. However, key characteristics of stratified wakes such as the formation of coherent pancake vortices and the long lifetime of the mean wake are robust to the presence of fluctuations in the background. A corresponding series of simulations for the unstratified situation is carried out at the same Reynolds number of 10 000 and with similar levels of external turbulence. The change of mean and turbulence statistics is found to be weaker in the unstratified cases compared with the corresponding stratified cases and also weaker relative to that found by Rind & Castro (J. Fluid Mech., vol. 710, 2012a, p. 482) at a similar level of external turbulence relative to the free stream and similar integral length scale. Theoretical arguments and additional simulations are provided to show that the level of external turbulence relative to wake turbulence (dissimilar between the present investigation and Rind & Castro (J. Fluid Mech., vol. 710, 2012a, p. 482)) is a key governing parameter in both stratified and unstratified backgrounds.
Direct numerical simulations (DNS) of axisymmetric wakes with canonical towed and self-propelled velocity profiles are performed at Re = 50 000 on a grid with approximately 2 billion grid points. The ...present study focuses on a comparison between towed and self-propelled wakes and on the elucidation of buoyancy effects. The development of the wake is characterized by the evolution of maxima, area integrals and spatial distributions of mean and turbulence statistics. Transport equations for mean and turbulent energies are utilized to help understand the observations. The mean velocity in the self-propelled wake decays more rapidly than the towed case due to higher shear and consequently a faster rate of energy transfer to turbulence. Buoyancy allows a wake to survive longer in a stratified fluid by reducing the 〈u1′u3′〉 correlation responsible for the mean-to-turbulence energy transfer in the vertical direction. This buoyancy effect is especially important in the self-propelled case because it allows regions of positive and negative momentum to become decoupled in the vertical direction and decay with different rates. The vertical wake thickness is found to be larger in self-propelled wakes. The role of internal waves in the energetics is determined and it is found that, later in the evolution, they can become a dominant term in the balance of turbulent kinetic energy. The non-equilibrium stage, known to exist for towed wakes, is also shown to exist for self-propelled wakes. Both the towed and self-propelled wakes, at Re = 50000, are found to exhibit a time span when, although the turbulence is strongly stratified as indicated by small Froude number, the turbulent dissipation rate decays according to inertial scaling.
Two-dimensional numerical simulations are performed to examine internal wave reflection at a sloping boundary. Owing to reflection, the reflected wave amplitude and wavenumber increase. At low values ...of the incoming wave amplitude, the reflected wave beam is linear and its properties agree well with linear inviscid theory. Linear theory overestimates the reflected wave Froude number,
$Fr_{r}$
, for higher values of incoming wave amplitude. Nonlinearity sets in with increasing value of incoming wave Froude number,
$Fr_{i}$
, leading to parametric subharmonic instability (PSI) of the reflected wave beam: two subharmonics emerge from the reflection region with frequencies
$0.33{\it\Omega}$
and
$0.67{\it\Omega}$
and wavenumbers that add up to those of the reflected wave. The amplification of Froude number due to reflection must be sufficiently large for PSI to occur implying that the off-criticality in wave angle cannot be too large. The simulations also show that, all other parameters being fixed, a threshold in beam amplitude is required for the onset of PSI in the reflected beam, consistent with results from a previous weakly-nonlinear asymptotic theory for a freely propagating finite-width beam. Growth rates of subharmonic modes at moderate reflected wave amplitude are in reasonable agreement with that theory. However, for
$Fr_{r}>0.5$
, small scale fluctuations becomes prominent and the subharmonic energy growth rates saturate in the simulations in contrast to the theoretical prediction. Increasing the incoming beam thickness (number of carrier wavelengths) increases the strength of PSI. Keeping the incoming Froude number constant and increasing the incoming Reynolds number by a factor of 50 does not have an effect on the unequal division of frequencies among the subharmonic modes that is found in the simulations.
Rauvolfia serpentina
(L.) Benth. ex Kurz., popularly known as Indian Snakeroot plant, belonging to Apocynaceae family, holds immense medicinal importance, owing to its rich source of multiple ...secondary metabolites such as ajmaline, ajmalicine, reserpine, and serpentine. To meet the constant demands for the key secondary metabolite (reserpine) by majority of the pharmaceutical industries, the present study assessed the effects of direct and indirect regeneration system on amelioration of reserpine accumulation in shoots of
R. serpentina
. In vitro multiple shoot cultures were established using shoot tip explants. Best results for shoot initiation, multiplication, and biomass production were obtained in case of Murashige and Skoog medium, supplemented with 1 mg/l
N
6
-benzyladenine. The multiple shoots were then sub-cultured on cytokinin–auxin combination media for further proliferation. Highest shoot and leaf multiplication rates and the most enhanced biomass were obtained in case of 1–1.5 mg/l Kinetin + 0.2 mg/l α-naphthalene acetic acid (NAA). Callus induction and its subsequent proliferation was obtained using 1.5 mg/l 2,4-dichlorophenoxyacetic acid. The best indirect shoot regeneration with highest shoot and leaf proliferation from calli was observed in case of 1 mg/l thidiazuron + 0.2 mg/l NAA. Reserpine content estimation via HPTLC from in vitro shoots (direct regeneration) and calli (indirect regeneration) were recorded to undergo an almost three-fold and two-fold increment (respectively) in comparison to that of the mother plant. Thus, in vitro direct regeneration system proved to be more effective and efficient in ameliorating the reserpine content.
An efficient in vitro protocol for high-frequency polyploidization for the first time in gerbera hybrid (BGC-2019-01) was developed in the present study. Two-week-old in vitro-developed shoots (tips) ...were treated individually with 0.1%, 0.25% and 0.5% (
w
/
v
) colchicine solutions for 4, 6, 8, and 12 h. The colchicine-treated shoot tips were then inoculated on Murashige and Skoog (MS) medium fortified with 1.5 mg/l
meta
-Topolin for multiple shoot proliferation and later transferred into 1.5 mg/l indole-3-acetic acid-fortified MS medium for rooting of shoots. The ploidy levels of the colchicine-treated and regenerated plantlets along with the non-treated ones were confirmed via flow cytometry analysis and metaphasic chromosome count. The highest frequency of tetraploid plantlets (50%) were obtained when shoot tips were treated with 0.1% colchicine for 4 h. Morphological observations revealed that induced tetraploid plantlets exhibited delayed fresh shoot initiation, fewer but longer shoots, as well as fewer but broader leaves. Likewise, the study of stomata revealed that in comparison to their diploid counterparts, the tetraploid plantlets exhibited less frequent yet significantly larger stomata, and higher number of chloroplasts. The tetraploids were recorded with significantly higher chlorophyll, carotenoid, and anthocyanin content during the photosynthetic pigment analyses. During ex vitro acclimatization and field growth, the tetraploid plants exhibited delayed proliferation but with higher vigor and thickened broad leaves. The genetic uniformity among the diploid and the tetraploid plants was confirmed using conserved DNA-derived polymorphism (CDDP), directed amplification of minisatellite-region DNA (DAMD), inter simple sequence repeats (ISSR), and start codon targeted (SCoT) polymorphism marker systems. The tetraploids developed in the present study would be of immense importance for the genetic improvement of gerbera as far as its ornamental values are concerned.
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