Thesis (MSc)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: The changes in carbon allocation to sucrose, hexoses, fibre, starch and respiration
were investigated in developing internodes of sugarcane. Radiolabelling studies were
conducted on internode 3, 6 and 9 tissue, representing three stages of increasing
maturity. It was apparent that a high rate of cycling between triose-phosphate and
hexose-phosphate occurred. A maximum of 50% of carbon entering triose-phosphates
was returned to hexose-phosphate in internode 3 tissue, and this flux decreased with
tissue maturity to 30%. Carbon partitioning into sucrose increased from 34% of total
14C uptake in internode 3, to 61% in internodes 6 and 9. In immature tissue, the
protein and fibre components were the dominant competing sinks with sucrose for
incoming carbon, to which 14 and 16% of carbon were allocated respectively.
Increased carbon allocation to sucrose with tissue maturity, coincided with a decrease
in partitioning to fibre. This indicated that previous studies had underestimated total
carbon allocation to respiration, since the protein component was not considered. In
contrast with earlier work, the respiratory pathway was the strongest competitor with
sucrose for incoming carbon, even in mature tissue. Between internodes 3 and 6,
carbon allocation to total respiration did not change significantly, but decreased 50%
in mature tissue. Starch was a weak competitor with sucrose, for incoming carbon, to
which a maximum of 2% of 14Cwas allocated in immature tissue. In cane harvested in
early spring, radiolabelled maltose was recovered in internode 3 tissue of ripening
cane, indicating that concomitant starch synthesis and degradation occurred. The.
redistribution of C-1 and C-6 in starch glucose was analysed following feeding of
tissue with [1_14C]_and [6_14C]_glucose. Randomization of label in starch indicated
that the pathway for carbon movement into sugarcane plastids for starch synthesis is
primarily through the triose-phosphate translocator. Finally, this study indicated that
radiolabelling of tissue discs is a suitable experimental system to determine carbon
flux in sugarcane. During the 3 h labelling period the rate of 14C02 release became
linear, indicating that the system approached isotopic steady state between the external
and internal glucose pool; and the respiratory processes involved in CO2 release. / AFRIKAANSE OPSOMMING: Die veranderinge in koolstoftoedeling na sukrose, heksoses, vesel, stysel en respirasie
is in ontwikkelende internodes van suikerriet ondersoek. Die koolhidraatmetabolisme
in internodes 3, 6 en 9, wat drie stadiums van toenemende rypheid verteenwoordig, is
met behulp van 14Cmerkingstudies ondersoek. Dit is duidelik dat daar 'n hoë mate van
koolstofsirkulering tussen die heksose- en triose-fosfaat poele voorkom. In internode 3
word tot 50% van die koolstofwat in triose-fosfate geïnkorporeer is, weer na heksosefosfaat
omgeskakel. Selfs in volwasse weefsel vind daar nog soveel as 30%
koolstofsirkukering plaas tussen die twee poele plaas. Koolstoftoedeling vanaf
glukose na sukrose het van 34% in internode 3, tot 61% in internodes 6 en 9
toegeneem. Proteïn en selwandkomponente was die belangrikste swelgpunte vir
koolstof in onvolwasse weefsel gewees. Namate die weefsel meer volwasse word,
word sukrose 'n belangriker swelgpunt. Die koolstoftoedeling aan sukrose is veral ten
koste van toedeling aan die selwandkomponente. Die bevinding dat die proteïenpoel 'n
sterk swelgpunt is dui aan dat vorige studies die belang van respiratoriese
koolstofvloei onderskat het. In teenstelling met vorige aansprake is dit duidelik dat
selfs in volwasse weefsel respirasie die grootste swelpunt vir die inkomende organiese
koolstof in die internode vorm. Koolstoftoedeling aan respirasie het nie
noemenswaardig tussen internodes 3 en 6 verskil nie, maar het met 50% in volwasse
weefsel afgeneem. Stysel is deurgaans 'n swak swelgpunt vir koolstof met die hoogste
toedeling aan die poel (2%) in die jong weefsel (internode 3) . Na toediening van [U-
14C]-glukose is radioaktief gemerkte maltose gevind in suikerriet wat vroeg in die
lente geoes is. Dit dui aan dat gelyktydige afbraak en sintese van stysel plaasgevind
het. Die herverdeling van C-l en C-6 in glukose afkomstig van stysel is na toediening
van [1_14C]_ en [6-14C]-glukose ontleed. Die ewekansige verspreiding van
radioaktiwiteit tussen koolstof 1 en 6 van die glukose in stysel dui aan dat dit
hoofsaaklik die triose-fosfaat translokeerder is wat in die plastied verantwoordelik is.
Hierdie studie het ook aangetoon dat radioaktiewe merking van weefselsnitte 'n
geskikte eksperimentele sisteem is om koolstoftoedeling in suikerriet te ondersoek.
Die patroon van 14C02 vrystelling dui daarop dat die weefsel na 'n 3 h
inkuberingsperiode isotopiese ewewig tussen die eksterne en interne glukose poele en
die respiratoriese prosesse begin bereik het.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51642 |
| Date | 12 1900 |
| Creators | Bindon, Keren (Keren Ann) |
| Contributors | Botha, F., Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 77 p. : ill. |
| Rights | Stellenbosch University |
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