Transport and metabolism of 8(14C)t-Zeatin.
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Date
1982
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Abstract
A review of the literature established that there were
areas of cytokinin transport which needed further investigation,
in order to determine the function and/or
mode of action of cytokinins during certain stages of
plant development. Radioactive zeatin was applied to
plant systems suitable for determining more about specific
problems of cytokinin transport. The metabolism of the
radioactive zeatin was monitored in relation to transport.
The metabolism in, and possible export of, radioactive
zeatin out of immature, mature and senescing Ginkgo biloba
leaves was monitored using explants. The results showed
that approximately the same percentage radioactivity was
exported from the leaves at all three stages of their development.
This indicates that these deciduous leaves
could potentially export cytokinins, but the results were
not regarded as being significant. Cytokinins would not
have been expected to be transported out of expanding
leaves, which rapidly utilize cytokinins, and in comparison
greater cytokinin export would have been expected to occur
from senescing leaves, but this did not occur. The resuIts
could indicate that cytokinin glucosides in deciduous
leaves are primarily inactivation products rather than
storage compounds.
The metabolism and transport of radioactive zeatin, applied
to the leaves of Citrus sinesis trees, was monitored during the flush of new growth following a dormant period.
Some of the radioactive zeatin applied to these leaves
appeared to be utilized in the new shoot growth. This
could imply that accumulated cytokinin glucosides in these
evergreen leaves are exported out of the leaves and reutilized,
and thus fulfil a storage function; although
the extent to which export occurred as opposed to interconversion
and/or catabolic metabolism in the leaves could
not be determined.
The distribution of radioactive zeatin applied to the
xylem and phloem of Phaseolus vulgaris plants at three
stages of development was also monitored. There appeared
to be preferential transport of cytokinins in the transpiration
stream, that is, applied to the xylem. The
vegetative apices, buds and flowers appeared to be the
major sinks for radioactive compounds in the vegetative
and flowering plants, and the leaves were the most important
sink in the fruiting plants. Radioactive zeatin
in the phloem appeared to move passively with the assimilate
stream. The transport of radioactive zeatin applied to
the primary leaves appeared to confirm that cytokinins in
the phloem were transported along with the assimilate
stream. The results also indicated that the accumulated
cytokinin glucosides in these annual leaves were primarily
inactivation products, involved in regulating leaf
metabolism, although some re-utilization of these cytokinins
could potentially take place. could have reflected normal cytokinin transport occurring
in the tissues. The main metabolic pathway, oxidation,
did not, however, appear to be the main metabolic pathway
in the plant tissues and may have been the result of the
exogenous application of zeatin. The fact that metabolism
did not appear to be the normal metabolism of the
tissues, could potentially have affected transport.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1982.
Keywords
Phloem., Xylem., Plant translocation., Biology--Experiments., Cytokinins., Theses--Botany.