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Osmotic factors affecting sucrose storage and mobilisation in storage roots of Beta vulgaris LPerry, C. A. January 1986 (has links)
No description available.
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Expression analysis of genes involved in sucrose transport and metabolism during grain development in wheatSakthivel, Geethalakshmi 16 January 2012 (has links)
To gain an understanding of the transcriptional regulation of sucrose transport and metabolism in wheat and to examine their relationships with dry matter accumulation in seeds, this study has characterized the expression patterns of two sucrose transporters (TaSUT1 and TaSUT2) and two sucrose synthase (TaSuSy1 and TaSuSy2) genes in five spring wheat cultivars at different seed developmental stages. Cultivar ‘AC Andrew’ with higher TaSUT1 and TaSuSy2 transcript abundance particularly during the early grain filling stage, exhibited higher dry grain weight than other cultivars. The result, overall, suggests the significance of coordinated expression between TaSUT1 and TaSuSy2 for grain growth. This study also demonstrated the seed specificity of high molecular weight glutenin promoter subunit Dy10, which can be used as an important tool to drive the expression of any sucrose and starch related genes specifically in wheat grains to further our understanding of carbon partitioning and/or increase wheat starch yield.
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Expression analysis of genes involved in sucrose transport and metabolism during grain development in wheatSakthivel, Geethalakshmi 16 January 2012 (has links)
To gain an understanding of the transcriptional regulation of sucrose transport and metabolism in wheat and to examine their relationships with dry matter accumulation in seeds, this study has characterized the expression patterns of two sucrose transporters (TaSUT1 and TaSUT2) and two sucrose synthase (TaSuSy1 and TaSuSy2) genes in five spring wheat cultivars at different seed developmental stages. Cultivar ‘AC Andrew’ with higher TaSUT1 and TaSuSy2 transcript abundance particularly during the early grain filling stage, exhibited higher dry grain weight than other cultivars. The result, overall, suggests the significance of coordinated expression between TaSUT1 and TaSuSy2 for grain growth. This study also demonstrated the seed specificity of high molecular weight glutenin promoter subunit Dy10, which can be used as an important tool to drive the expression of any sucrose and starch related genes specifically in wheat grains to further our understanding of carbon partitioning and/or increase wheat starch yield.
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Remobilization of sucrose from the culm during germination of sugarcane settsBoussiengui-Boussiengui, Gino 12 1900 (has links)
Thesis (MSc (Botany and Zoology))--University of Stellenbosch, 2005. / The main substrate use during shoot establishment from the lateral bud of sugarcane setts
and enzymes involved in sucrose metabolism were investigated in the shoots and the
internodes acting as source of carbohydrates. Radiolabelling studies were conducted to
investigate the metabolism of sucrose and glucose during shoot establishment. The
internode’s total dry mass over the 21-day of shoot establishment period was reduced by
25% and 30% in plants incubated in dark/light and total darkness, respectively.
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Purification and characterisation of a SNF1-related protein kinase from developing endosperm of barley (Hordeum vulgare L.)Barker, Jacqueline H. A. January 1996 (has links)
No description available.
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Structural and kinetic analysis of carbon fixation and sucrose metabolism in sugarcaneMeyer, Kristy 03 1900 (has links)
Thesis (MSc (Biochemistry))--Stellenbosch University, 2008. / The aim of this study is the theoretical investigation of carbon fixation in sugarcane
leaves. Sugarcane has a well known reputation for accumulating sucrose in
the stalk to levels as high as 650 mM, almost a fifth of the plant’s fresh weight.
Although this is an efficient accumulating mechanism, there is an even more
efficient ‘carbon pump’ found in C4 plants. This is a well documented carbon
concentrating mechanism and one of the first to be studied. However scientists
are still trying to understand the carboxylating mechanism and the regulation
thereof. It has been speculated that this mechanism is at its saturation level and
elevating carbon dioxide will have little or no effect on further carbon fixation.
Futher, studies suggest that the sucrose accumulating sink is able to regulate photosynthesis.
Therefore a regulatory mechanism should exist from the sink to carbon
fixation in order for such regulation to occur. Thework in this thesis therefore
lays the foundation for investigating regulation of photosynthesis.
The field of systems biology is the study of cellular networks by assemblingmodels.
Pathways are considered as systems and notmerely collections of single components.
This allows the interaction of pathway metabolites and the regulation
that they have on one another to be studied. The questions asked pertaining to a
pathway, will determine the types of model analysis. Structural analysis is useful
for studying stoichiometric models, determining characteristics like energy
consumption, futile cycles and valid pathways through a system at steady-state.
Kinetic analysis on the other hand, gives insight into system dynamics and the
control exerted by the system components, predicting time-course and steady
states.
In this thesis we begin to investigate photosynthesis in sugarcane leaves and
the role it has in accumulating sucrose in the plant. Firstly, a structural model
was developed incorporating carbon fixation, sucrose production in the leaf and subsequent transport of sucrose to the storage parenchyma and accumulation.
The model was analysed using elementary mode analysis, showing that there are
twelve routes for producing sucrose with no pathway beingmore energy efficient
than any other. Further, it highlighted a futile cycle transporting triose phosphates
and phosphoglycerate between the two photosynthetic compartments in
the leaf. In the storage parenchyma, manymore futile cycleswere revealed,many
of them energetically wasteful. Three other sets of elementary modes describe
sucrose’s destination in either the vacuole or use in glycolysis or fibre formation,
each with a different amount of required energy equivalents. The fourth set describes
how sucrose cannot be converted to fibre precursors without also being
used for glycolyis building blocks.
Secondly, a kinetic model of carbon fixation in the leaf was assembled with the
primary goal of characterising thismoiety-conserved cycle. This included the collation
of kinetic data, incorporating volumes of the compartments and the areas
of the location of the transporters into the model. This model was then analysed
using metabolic control analysis. The model was able to predict metabolite concentration
in the pathway at steady-state which were compared to those found
experimentally. However, modifications need to be made to the model before
further analysis is done so that the model predicted values match the experimental
values more accurately. Time course analysis and response coefficients were
also calculated for the carbon fixation cycle.
Thework in this thesis therefore paves the way for understanding photosynthesis
and its regulation in sugarcane leaves. Such work has the potential to pinpoint
genetic engineering target points, allowing for better hybrid selection and propagation.
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Aspects of sucrose metabolism in transgenic tobaccoChampanis, Reinette 12 1900 (has links)
Dissertation (PhD) -- University of Stellenbosch, 2004. / ENGLISH ABSTRACT: In most plants the efficiency of sucrose production and the systemic distribution
thereof are the major determinants of growth, development and yield. The factors
governing sugar partitioning co-ordinate its distribution in response to intrinsic and
environmental signals. These factors include sugar transporters and invertases as
well as metabolites, including sucrose and glucose, which function as signalling
molecules to modulate gene expression.
The genetic transformation of plants and the subsequent development of
transgenic lines with disturbed sugar metabolism have made an unprecedented
impact on the study of sugar translocation and -partitioning. For instance, the
transformation of plants with a yeast-derived invertase targeted to different
subcellular compartments has led to the elucidation of several key aspects of sugar
metabolism, including phloem loading mechanisms, the regulation of photosynthesis
by sugars, the importance of sugar-metabolism compartmentation with regards to
sucrose biosynthesis, storage and distribution, as well as the role of cell-wall
invertase in phloem unloading and sink strength.
In this study, a similar strategy of transgenic plant analysis was employed to
expand our insight into the regulation of sugar partitioning. The yeast-invertase Suc2
gene, from Saccharomyces cere visiae , was overexpressed in either the cytosol,
vacuole or apoplast of transgenic tobacco plants. These transgenic lines displayed
varying increases in invertase activity, altered sugar levels and consequently
disturbed sink-source interactions and sugar partitioning. Transgenic lines
overproducing the yeast-derived invertase in either the vacuole (Vac-Inv) or apoplast
(Apo-Inv) were utilised to analyse the effect of the altered sugar levels in sink and
source organs on the expression of sugar transporters, as well as the endogenous
cell wall invertase and inhibitors in these plants.
Transcript levels of the sucrose transporter NtSUT1 and hexose transporter
NtMST1 encoding genes increased significantly in the source leaves and roots of
Vac-Inv lines, whereas increased NtMst1 transcript levels were also detected in the
roots of Apo-Inv lines. The increased mRNA levels could be correlated to the altered
invertase activities and sugar levels in these tissues. It is concluded that NtSUT1 and
NtMST1 are differentially regulated by sucrose and/or hexose content on a
transcriptional level. Furthermore, the regulatory effect of the altered sugar levels on
transporter expression depended on the subcellular compartment in which the yeast
invertase was expressed. It would seem that the subcellular compartmentation of
sugar metabolism is also fundamental to the regulation of sugar partitioning.
The transcription levels of the endogenous cell wall invertase (CWt) and cell
wall invertase inhibitor (Cwi-Inh) genes were examined in the various tissues of
Apo-Inv and Vac-Inv lines at both the vegetative and flowering growth stages. In
comparison with the control lines, the various tissues of the Apo-Inv and Vac-Inv lines displayed altered Cwi and Cwi-Inh expression levels, depending on the sink-source
status and growth stage. However, no obvious correlation between the Cwi and
Cwi-Inh expression levels and soluble sugar content of these tissues was found. It is
suggested that the post-transcriptional and post-translation control of these proteins
by sugars might play an important role in their regulation. Analysis of the Cwi:Cwi-lnh
mRNA ratio and growth observations of the various tissues of control as well as
Apo-Inv and Vac-Inv lines indicated that this transcription ratio could be an accurate
indicator of the sink strength of sink organs.
In addition, the influence of sink-source interactions on sugar partitioning was
investigated. Reciprocal grafting between Apo-Inv and control lines resulted in scions
with an altered sucrose metabolism in either the sink or source organs. These scions
were subjected to biomass distribution, soluble sugar quantification and C4C]-
radiolabelling experiments. The latter revealed an unaltered state of sugar
partitioning from the above-ground tissues of the Apo/GUS scions and a significant
shift in sugar partitioning towards the roots of the GUS/Apo scions in comparison to
the control GUS/GUS scions. Phenotypic changes, opposite to those observed in
Apo-Inv lines expressing the heterologous invertase in both sink and source organs,
could initially be observed in the GUS/Apo and Apo/GUS scions. However, no
significant differences in phenotype or biomass distribution could be observed
between the mature GUS/Apo, Apo/GUS and GUS/GUS scions seven weeks postgrafting.
This inconsistency between phenotype and sugar partitioning might be
explained by an increase in the respiration rate of the tissues as supported by the
soluble sugar content. These results highlight the complexity and adaptability of
sucrose metabolism and sugar partitioning. In addition, it confirms that sugar
partitioning can be modulated by sink-source interactions and emphasise the
importance of invertases in the regulation of sugar partitioning through its ability to
alter sink strength.
This study forms part of the rapidly expanding initiative to unravel the control
mechanisms of sugar partitioning. The results obtained in this study confirmed again
that the introduction and expression of a single heterologous gene in transgenic
plants could provide significant insight into the regulation of this process. It was
shown here that the expression of sugar transporters is closely regulated by sugar
levels and therefore fulfils a vital function in sugar sensing and consequently the
regulation of sugar partitioning. The data presented in this study also demonstrated
the intricate and flexible nature of the relationship that exists between sugar
metabolism, partitioning and growth phenomena. / AFRIKAANSE OPSOMMING: Die doeltreffendheid van sukroseproduksie, tesame met die sistemiese verspreiding
daarvan, is die vernaamste faktore wat die groei, ontwikkeling en opbrengsvermoë
van die meeste plante bepaal. Die faktore wat suikerverdeling beheer, funksioneer
om suikerverspreiding te koordineer in reaksie op beide inherente- en
omgewingsseine. Hierdie faktore sluit suikertransporters en invertases in, asook
metaboliete soos sukrose en glukose wat funksioneer as seinmolekule in die
modulering van geenuitdrukking.
Die genetiese transformasie van plante en die gevolglike daarstelling van
transgeniese lyne met veranderde suikermetabolismes het 'n beduidende inwerking
op die bestudering van suikervervoer en -verdeling gehad. Byvoorbeeld, die
transformasie van plante met 'n gis-invertase geteiken na verskillende sub-sellulêre
kompartemente, het tot die toeligting van verskeie aspekte van suikermetabolisme
gelei, insluitende dié van floëemladingsmeganismes, die regulering van fotosintese
deur suikers, die belang van kompartementalisering ten opsigte van
sukrosebiosintese, -opberging en -verspreiding, en die rol van selwand-invertases in
floëemontlaaiing en swelgpuntkrag.
In hierdie studie is van soortgelyke transgeniese plantontledings gebruik gemaak
om 'n dieper insig tot die regulering van suikerverdeling te verkry. Die gis-invertase
Suc2 geen, afkomstig van Saccharomyces cerevisiae, is ooruitgedruk in óf die
sitosol, vakuool óf apoplastiese ruimte van transgeniese tabakplante. Hierdie
transgeniese lyne het wisselende toenames in invertase-aktiwiteite en veranderde
suikervlakke getoon, asook gevolglike versteurde bron-swelgpunt interaksies en
suikerverdeling. Transgeniese lyne met ooruitdrukking van die gis-invertase in óf die
vakuool (Vac-Inv) óf die apoplast (Apo-Inv) is gebruik om die gevolg van die
veranderde suikervlakke in bron- en swelgpuntorgane op die uitdrukking van
suikertransporters, asook die endogene selwand-invertase en invertase-inhibitor in
hierdie plante te bepaal.
Transkripsievlakke van die sukrosetransporter NtSut1 en die heksosetransporter,
NtMst1, het beduidend toegeneem in die bron-blare en wortels van die
Vac-Inv lyne; 'n toename in NtMst1 transkripsievlakke is ook in die wortels van
Apo-Inv lyne bevestig. Die toenames in boodskapper RNA kon gekorreleer word met
die veranderde invertase-aktiwiteite en suikervlakke in hierdie weefsels. Die
gevolgtrekking word gemaak dat NtSUT1 en NtMST1 differensieël gereguleer word
op transkripsionele vlak deur die sukrose en/of heksose inhoud van weefsels. Meer
nog, die regulerende effek van die veranderde suikervlakke op transporteruitdrukking
het afgehang van die subsellulêre kompartement waarin die gis-invertase
uitgedruk is. Dit wil dus voorkom dat die subsellulêre kompartementalisering van
suikermetabolisme fundamenteel tot die deurgee en waarneming van suikerseine is,
met In gevolglike eweneens belangrike rol in die regulering van suikerverdeling. Die transkripsievlakke van beide die endogene selwand-invertase (CWI) en
die selwand-invertase-inhibitor (CWI-Inh) enkoderende gene is in verskeie weefsels
van die Apo-Inv en Vac-Inv lyne, tydens beide die vegetatiewe- en blomstadia,
bestudeer. Die onderskeie weefsels van die Apo-Inv en Vac-Inv lyne het, in
vergelyking met die kontrole lyne, veranderde Cwi en Cwi-inh transkripsievlakke
getoon wat bepaal is deur bron-swelgpunt status en groeistadium. Geen duidelike
korrelasie kon tussen beide Cwi en Cwi-inh uitdrukkingsvlakke en oplosbare suiker
inhoud gevind word nie. Daar word voorgestel dat post-transkripsionele en posttranslasionele
beheer deur suikers 'n belangrike rol in die regulering van hierdie
proteïne speel. Bestudering van die Cwi:Cwi-lnh mRNA verhouding, asook groei
verskynsels van die onderskeie weefsels van kontrole en Apo-Inv en Vac-Inv lyne,
dui daarop dat hierdie transkripsievlak-verhouding moontlik 'n akkurate aanwyser van
die swelgpuntkrag van 'n swelgpuntorgaan kan wees.
Voorts is die invloed van bron-swelgpuntorgaan interaksies op suikerverdeling
ondersoek. Omgekeerde enting tussen Apo-Inv en kontrole lyne het entlote met
gemodifiseerde suikermetabolisme in óf hul bron- óf hul swelgpuntorgane tot gevolg
gehad. Hierdie entlote is aan biomassaverspreidings-, oplosbare suiker kwantifisering
en C4C]-radiomerking eksperimente onderwerp. Hierdie resultate het gewys dat, in
vergelyking met die kontrole (GUS/GUS) ente, daar geen verandering in die status
van suikerverdeling vanaf die bogrondse plantdele in die Apo/GUS ente is nie, maar
wel 'n beduidende verskuiwing in suikerverdeling na die wortels van die GUS/Apo
ente. Fenotipiese veranderinge, wat teenoorgesteld van dié teenwoordig in die Apo-
Inv lyne waar die heteroloë invertase in beide bron en swelgpuntorgane uitgedruk
word, is aanvanklik in die GUS/Apo en Apo/GUS ente waargeneem. Geen verskille in
fenotipe of biomassa-verspreiding kon egter sewe weke na die entings prosedures
tussen die GUS/Apo, Apo/GUS and GUS/GUS ente gevind word nie. Dit mag
verduidelik word deur 'n moontlike toename in respirasietempo in die betrokke
weefsels; die oplosbare suikervlakke wat in die verskillende ente aangeteken is
ondersteun dié moontlikheid. Hierdie resultate as geheelonderstreep die
kompleksiteit en aanpasbaarheid van suikermetabolisme en -verdeling. Verder
bevestig dit dat suikerverdeling beïnvloed kan word deur bron-swelgpunt interaksies,
asook die belang van invertases in die regulering van suikerverdeling gegewe die
vermoë om swelgpuntkrag te verander.
Hierdie studie vorm deel van 'n vinnig groeiende inisiatief om die beheermeganismes
van suikerverdeling te ontrafel. Die resultate verkry in hierdie studie
bekragtig die belang van rekombinante DNA tegnologie in die bestudering van
fundamentele plantprosesse. Die invoeging en uitdrukking van 'n geteikende gisinvertase
in transgeniese plante het gelei tot veranderde suikervlakke en bronswelgpunt
interaksies in hierdie lyne met die gevolglike ontginning van waardevolle
inligting ten opsigte van die regulering van suikerverdeling in reaksie tot interne
seine. Daar is aangetoon dat suikertransporters onlosmaakbaar gekoppel is aan die
deurgee en waarneming van suikerseine, spesifiek op die vlak van transkripsionele regulering, en dus ook die regulering van suikerverdeling. Voorts wys die resultate op
die komplekse en aanpasbare aard van die verhouding wat bestaan tussen
suikermetabolisme, -verdeling en groeiverskynsels.
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Trehalose and carbon partitioning in sugarcaneBosch, Susan 12 1900 (has links)
Thesis (PhD (Genetics. Plant Biotechnology))--University of Stellenbosch, 2005. / The current understanding of the regulation of sucrose accumulation is still incomplete even
though many scientists have investigated this subject. Components of trehalose metabolism have
been implicated in the regulation of carbon flux in bacteria, yeast and more recently in plants. With
a view to placing trehalose metabolism in the context of cytosolic sugarcane sucrose metabolism
and carbon partitioning we have investigated the metabolites, transcripts and enzymes involved in
this branch of carbohydrate metabolism in sugarcane internodal tissues.
Sugarcane internodal trehalose levels varied between 0.31 ± 0.09 and 3.91 ± 0.99 nmol.g-1 fresh
weight (FW). From statistical analysis of the metabolite profile it would appear that trehalose does
not directly affect sucrose accumulation, although this does not preclude involvement of trehalose-
6-phosphate in the regulation of carbon partitioning. The metabolite data generated in this study
demanded further investigation into the enzymes (and their transcripts) responsible for trehalose
metabolism.
Trehalose is synthesised in a two step process by the enzymes trehalose-6-phosphate synthase
(EC 2.4.1.15, TPS) and trehalose-6-phosphate phosphatase (EC 3.1.3.12, TPP), and degraded
by trehalase (EC 3.2.1.28). Two novel sugarcane partial cDNAs that coded for trehalase (tre) and
actin (required for normalisation in profiling experiments) were isolated and used along with partial
transcripts for TPS and TPP to determine transcript levels in different tissue- and genotypes. A
putative full-length SugTPS cDNA was isolated and characterised. Enzyme activities for TPS, TPP
and trehalase were measured at levels of 2.7 nmol.min-1.mg-1protein, 8.5 nmol.min-1.mg-1protein
and 6.2 nmol.min-1.mg-1protein respectively, from young internodal protein extracts of sugarcane,
variety N19. TPP enzyme activity and transcript levels were higher in S. spontaneum than
Saccharum interspecific hybrids.
Kinetic analysis of TPP and trehalase activities were performed with the purpose of providing
parameters for an in silico kinetic model of trehalose and sucrose metabolism. Three isoforms of
TPP were identified and desingated TPPAI, TPPAII and TPPB. Both TPPA isoforms had pH
optima of 6.0, and TPPB of pH 6.5. Apparent Km values were determined as 0.447 ± 0.007 mM for
TPPAI, 13.82 ± 1.98 mM for TPPAII and 1.387 ± 0.18 mM for TPPB. Partial purification and
characterisation of trehalase demonstrated dual pH optima of 3.5 and 6.0, with Km values between
0.345 and 0.375 mM. These data were used as the basis for a kinetic model of trehalose
metabolism.
A previously described kinetic model of cytosolic sucrose metabolism has been expanded to
include the trehalose pathway (TPS, TPP and trehalase). The aim was to supplement the
available information on cytosolic metabolism in sugarcane storage parenchyma, identify points of
control between sucrose and trehalose metabolism, and provide a platform from which further
experimental and in silico modelling can be launched. The model predicted trehalose in the same
order of magnitude as those determined in the metabolite profiling experiments. The majority of
control of flux over the trehalose pathway resided in the TPS step, with flux control coefficients >
70% of the total pathway. Incorporation of the trehalose branch into the original sucrose model
showed that reactions from the original model significantly affected the steady-state attributes of
the trehalose pathway.
Due to the relatively low flux through the trehalose branch of the expanded model, complete
recycling of trehalose, and the lack of allosteric regulation by trehalose-6-phosphate or trehalose
on any of the reactions from the original sucrose model, incorporation of the trehalose branch had
no significant effect on either steady-state cytosolic sucrose concentration or flux of sucrose into
the vacuole. The expanded model affords a basis from which to further investigate trehalose
metabolism in the context of plant sucrose accumulation.
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Coupling kinetic models and advection-diffusion equations to model vascular transport in plants, applied to sucrose accumulation in sugarcaneUys, Lafras 12 1900 (has links)
Thesis (PhD (Biochemistry))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The sugarcane stalk, besides being the main structural component of the plant, is also the major
storage organ for carbohydrates. Sucrose forms the bulk of stored carbohydrates. Previous
studies have modelled the sucrose accumulation pathway in the internodal storage parenchyma
of sugarcane using kinetic models cast as systems of ordinary differential equations. Typically,
results were analysed with methods such as metabolic control analysis. The present study extends
those original models within an advection-diffusion-reaction framework, requiring the use
of partial differential equations to model sucrose metabolism coupled to phloem translocation.
Let N be a stoichiometric matrix, v a vector of reaction rates, s a vector of species concentrations
and r the gradient operator. Consider a coupled network of chemical reactions where
the species may be advected with velocities, U, or diffuse with coefficients, D, or both. We
propose the use of the dynamic system, s + r (Us) + r (Drs) = Nv;
for a kinetic model where species can exist in different compartments and can be transported
over long distances in a fluid medium, or involved in chemical reactions, or both. Darcy’s
law is used to model fluid flow and allows a simplified, phenomenological approach to be
applied to translocation in the phloem. Similarly, generic reversible Hill equations are used to
model biochemical reaction rates. These are also phenomenological equations, where all the
parameters have operationally defined interpretations.
Numerical solutions to this formulation are demonstrated with time-courses of two toy
models. The first model uses a simple “linear” pathway definition to study the impact of
the system geometry on the solutions. Although this is an elementary model, it is able to
demonstrate the up-regulation of photosynthesis in response to a change in sink demand. The
second model elaborates on the reaction pathway while keeping the same geometry definition as
the first. This pathway is designed to be an abstracted model of sucrose metabolism. Finally,
a realistic model of sucrose translocation, metabolism and accumulation is presented, spanning
eight internodes and four compartments. Most of the parameters and species concentrations
used as initial values were obtained from experimental measurements.
To analyse the models, a method of sensitivity analysis called the Fourier Amplitude Sensitivity
Test (FAST) is employed. FAST calculates the contribution of the possible variation in
a parameter to the total variation in the output from the model, i.e. the species concentrations
and reaction rates.
The model predicted that the most important factors affecting sucrose accumulation are the
synthesis and breakdown of sucrose in futile cycles and the rate of cross-membrane transport
of sucrose. The models also showed that sucrose moves down a concentration gradient from
the leaves to the symplast, where it is transported against a concentration gradient into the
vacuole. There was a net gain in carbohydrate accumulation in the realistic model, despite an
increase in futile cycling with internode maturity.
The model presented provides a very comprehensive description of sucrose accumulation
and is a rigorous, quantitative framework for future modelling and experimental design. / AFRIKAANSE OPSOMMING: Benewens sy strukturele belang, is die suikerrietstingel ook die primêre bergingsorgaan vir koolhidrate.
Die oorgrote meerderheid van hierdie koolhidrate word as sukrose opgeberg. Studies
tot dusver het die metabolisme rondom sukroseberging in die parenchiem van die onderskeie
stingellitte as stelsels gewone differensiaalvergelykings gemodelleer. Die resultate is ondermeer
met metaboliese kontrole-analise geanaliseer. Hierdie studie brei uit op die oorspronklike
modelle, deur gebruik te maak van ’n stromings-diffusie-reaksie-raamwerk. Parsiële differensiaalvergelykings
is geformuleer om die metabolisme van sukrose te koppel aan die vloei in die
floëem.
Gestel N is ’n stoichiometriese matriks, v ’n vektor van reaksiesnelhede, s ’n vektor van
spesie-konsentrasies en r die differensiaalvektoroperator. Beskou ’n netwerk van gekoppelde
reaksies waar die onderskeie spesies stroom met snelhede U, of diffundeer met koëffisiënte D,
of onderhewig is aan beide prosesse. Dit word voorgestel dat die dinamiese stelsel,
_s + r (Us) + r (Drs) = Nv;
gebruik kan word vir ’n kinetiese model waar spesies in verskeie kompartemente kan voorkom
en vervoer kan word oor lang afstande saam met ’n vloeier, of kan deelneem aan chemiese
reaksies, of albei. Darcy se wet word gebruik om die vloeier te modeller en maak dit moontlik
om ’n eenvoudige, fenomenologiese benadering toe te pas op floëem-vervoer. Eweneens word
generiese, omkeerbare Hill-vergelykings gebruik om biochemiese reaksiesnelhede te modelleer.
Hierdie vergelykings is ook fenomenologies van aard en beskik oor parameters met ’n duidelike
fisiese betekenis.
Hierdie omvattende raamwerk is ondermeer gedemonstreer met behulp van numeriese oplossings
van twee vereenvoudigde modelle as voorbeelde. Die eerste model het bestaan uit ’n
lineêre reaksienetwerk en is gebruik om die geometrie van die stelsel te bestudeer. Alhoewel
hierdie ’n eenvoudige model is, kon dit die toename in fotosintese as gevolg van ’n verandering
in metaboliese aanvraag verklaar. Die tweede model het uitgebrei op die reaksieskema
van die eerste, terwyl dieselfde stelselgeometrie behou is. Hierdie skema is ontwerp as ’n abstrakte
weergawe van sukrosemetabolisme. Ten slotte is ’n realistiese model van sukrosevervoer, metabolisme en berging ontwikkel wat agt stingellitte en vier kompartemente omvat. Die meeste
parameters en konsentrasies van biochemiese spesies wat as aanvanklike waardes in die model
gebruik is, is direk vanaf eksperimentele metings verkry.
Die Fourier Amplitude Sensitiwiteits-Toets (FAST) is gebruik om die modelle te analiseer.
FAST maak dit moontlik om die bydrae van parameters tot variasie in modeluitsette soos
reaksiesnelhede en die konsentrasies van chemiese spesies te bepaal.
Die model het voorspel dat sintese en afbraak van sukrose in ’n futiele siklus, asook transmembraan
sukrosevervoer, die belangrikste faktore is wat sukrose-berging beïnvloed. Die model
het ook getoon dat sukrose saam met ’n konsentrasiegradiënt beweeg vanaf die blare tot by
die stingelparenchiem-sitoplasma, van waar dit teen ’n konsentrasiegradiënt na die vogselholte
(vakuool) vervoer word. Volgens die realistiese model was daar ’n netto toename in die totale
hoeveelheid koolhidrate, ten spyte van ’n toename in die futile siklus van sukrose in die ouer
stingellitte.
Die model wat in hierdie proefskrif voorgestel word verskaf ’n uitgebreide, omvattende
beskrywing van sukroseberging. Voorts stel dit ’n rigiede kwantitatiewe raamwerk daar vir
toekomstige modellering en eksperimentele ontwerp.
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The metabolic fate of sucrose in intact sugarcane internodal tissue.McDonald, Zac. January 2000 (has links)
The study was aimed at determining the metabolic fate of sucrose in intact
sugarcane internodal tissue. Three aspects of the fate of sucrose in storage
tissue of whole plants formed the main focus of the work. These were the rate of
sucrose accumulation in the developing culm, the characterisation of partitioning
of carbon into different cellular organic fractions in the developing culm and the
occurrence of sucrose turnover in both immature and mature stem tissues.
Specific attention was paid to confirming the occurrence of sucrose turnover in
both immature and mature internodal tissue. This sucrose turnover has been
described previously in both tissue slices and cell suspension cultures. However,
certain results from previous work at the whole plant level have indicated that
sucrose turnover does not occur in mature internodal tissue.
Radiolabeled carbon dioxide (14CO2) was fed to leaf 6 of sugarcane culms of a
high sucrose storing variety (Saccharum spp. hybrid cv. Nco376). All plants were
of similar age (12 months) and were grown under similar conditions. The
movement and metabolic fate of radiolabeled sucrose was determined at four
time points, (6 hours, 24 hours, 7 days and 6 weeks) during a 6 week period.
The metabolic fate of sucrose was determined in internodes number 3, number 6
and number 9. Internode 3 was found to have a relatively high hexose sugar
content of 42 mg glc&fruc fw g-1 and a low sucrose content of 14 mg suc fw g-1.
In contrast the sucrose content of internode 9 was much higher at 157 mg suc fw
g-1 and the hexose sugar content much lower at 4.3 mg glc&fruc fw g-1. Based
on previous work, the sugar content of internode 3 and internode 9 are
characteristic of immature and mature tissues respectively. Internode 6 occupies
an intermediary position between internode 3 and 6 with its sucrose content
higher than its hexose sugar content, but with the hexose sugar content still
being notable at 15 mg glc&fruc fw g-1.
Although the metabolic fate of sucrose within sink tissue was the focal point of
the study, the experimental design also allowed for certain aspects of sucrose
production in the source to be investigated. The average photosynthetic rate for
leaf 6 in full sunlight was estimated at 48 mg CO2 dm-2 s -1. During
photosynthesis, only 30% of the fixed carbon was partitioned into the storage
carbohydrate pool while the remaining 70% was partitioned into sucrose for
immediate export from the leaf. This high rate of carbon fixation combined with a
high rate of carbon export is characteristic of C4 plants such as sugarcane.
On entering the culm, translocation of radiolabeled sucrose was predominantly
basipetal with relatively little acropetal translocation. The majority of the
radiolabeled carbon was found to be stored in mature internodes. No significant
loss of radiolabeled carbon was observed in mature and elongating internodes
over the study period. A 22% loss of total radiolabeled carbon was observed in
immature internodes over the same period. This can probably be attributed to
the higher rates of cellular respiration known to occur in immature tissues.
There appear to be three phases of sucrose accumulation in the developing
culm. Initially, the accumulation rate in rapidly growing tissue, as internode 3
develops into internode 6, is relatively low. This is followed by a rapid increase in
the rate of sucrose accumulation during internode elongation, as internode 6
becomes internode 9. Finally, a decrease in the rate of sucrose accumulation is
observed during late maturation, as internode 9 becomes internode 12.
Determination of the sucrose content in internodes 3, 6 and 9 revealed that there
is a notable increase in sucrose content during internode maturation. It is
proposed that the higher sucrose content of mature tissue is not merely a
consequence of the longer growth period of mature tissue, but is due to the
increased rate of sucrose accumulation observed during internode elongation.
Short-term (24 hours) analysis of carbon partitioning revealed that intemodal
maturation was associated with a redirection of carbon from non-sucrose cellulal
organic fractions to sucrose storage. In immature internodes only 20% of the
total radiolabeled carbon was present in the sucrose pool 24 hours after feeding.
In elongating internodes the figure increased to 54% while in mature internodes
as much as 77% of the total radiolabeled carbon was retained in the sucrose
pool. Concomitant with the increased carbon partitioning into stored sucrose
down the developing culm is a decrease in carbon partitioning into the hexose
sugar pool. In immature tissue, 42 % of the total radiolabel is present in the
hexose sugar pool, while in mature tissue the percentage drops to 11%. This
decrease is probably indicative of decreased levels of carbon cycling between
the sucrose and hexose sugar pool as a result of internode maturation.
Internode maturation was also found to be associated with a decrease in the
amount of carbon in the water insoluble matter pool and the amino acid/ organic
acid/ sugar phosphate pool. Thus, internode maturation is associated with a
redirection of carbon from total respiration to sucrose storage. Long-term (6
weeks) analysis of carbon partitioning confirmed that sucrose storage in mature
tissue is greater than that in immature tissue. From the 6 hour time point to the 6
week time point, an 87% reduction in the stored radiolabeled sucrose content
was observed in immature internodes. During the same period only a 25%
reduction in the stored radiolabeled sucrose was observed in mature internodes.
Radiolabel loss from the radiolabeled sucrose pool in both mature and immature
internodes was accounted for by relative radiolabel gains in other cellular organic
fractions.
At all time points during the study, and in all three tissues studied, radiolabel was
found in the sucrose pool, the hexose sugars pool, the ionic pool and the water
insoluble matter pool. The occurrence of radiolabel in the non-sucrose tissue
constituents suggests that sucrose turnover is occurring in both immature, and
mature internodal tissue. / Thesis (M.Sc.)-University of Natal, Durban, 2000.
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