Author:
Grantz David A.,Farrar John F.
Abstract
This paper originates from a presentation at the International Conference on Assimilate Transport and Partitioning, Newcastle, NSW, August 1999
The rate of export of recent photoassimilate from source leaves of Pima cotton
(Gossypium barbadense L.) is inhibited by ozone
(O3). To characterize these effects on export, source
leaves of Pima cotton were exposed to pulses (0.75 h) of
O3 (0.0, 0.2, 0.5 and 0.8 L
L–1) followed by pulses of
14CO2. Leaves were monitored by
gas exchange and with a Geiger–Muller tube, for a sufficient period to
characterize carbon assimilation (A) and a rapid and a
slower phase of export. Double exponential decay functions (two-compartment
model) were fitted and a compartmental analysis conducted.
O3 reduced by half the fast rate constant describing
export from a transport pool, without affecting the rate constants for
transport from or to a storage compartment. Measured soluble sugar contents
increased slightly from control concentrations (1.2 g C
m–2) by about 5–10% at all
O3 concentrations. The calculated soluble sugar content
in the transport pool increased from about 200 to 300 mg C
m–2 with increasing exposure to
O3. The calculated storage pool did not respond to
O3 but exceeded measured contents. This discrepancy is
attributed to starch deposition and mobilization, which are not considered in
the two-compartment model, uncertainties in slower decay parameters, and
non-steady-state A induced by O3
exposure. Specific inhibition of rapid efflux suggests oxidant damage at the
plasmalemma or plasmodesmata of mesophyll or phloem companion cells, and
little effect on the tonoplast. A was affected less than
export. Future research should target oxidation of components involved in
phloem loading.
Subject
Plant Science,Agronomy and Crop Science
Cited by
41 articles.
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