1 research outputs found
Temperature acclimation of root respiration in Douglas-fir and western red cedar seedlings
This study examined the ability of seedlings of coastal and interior
provenances of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and
western red cedar (Thuja plicata Donn) to acclimate root respiration rates to
growth temperature. A second objective was to determine whether acclimation
involved an increase in activity and/or capacity of the alternative path of electron
transport, a phenomenon observed in many crop species. Since western red
cedar has less genetic variation than Douglas-fir, one might expect better
acclimation in cedar.
Seedlings were grown hydroponically in computer-controlled mist boxes
placed inside an environmental chamber (18/6 hr photoperiod, day/night). This
allowed for precise manipulation of root temperature (11, 18, 25°C), while shoot
temperature was unchanged between treatments (25/18°C, day/night).
Respiration of excised root segments was measured with an oxygen electrode.
Potassium cyanide and salicylhydroxamic acid were used to estimate the
activity and capacity of the alternative path. Oxygen response curves were
constructed, seedling water potentials were determined and shoot samples
were analyzed for carbon isotope discrimination. Total plant weight, root to
shoot biomass and root density were also measured.
The results showed that both the coastal and interior provenances of
western red cedar and the coastal provenance of Douglas-fir were able to
acclimate, while interior Douglas-fir was not. Acclimation did not seem to
involve an increase in electron partitioning through the alternative path. It was
suggested that the increase in alternative path respiration that is often seen at
low temperatures is independent of compensatory respiration and sometimes
occurs coincidentally with it to reduce the damage caused by active oxygen species, which can be a problem at those temperatures. There is evidence that
the cold-grown roots were able to increase the supply of Oâ‚‚ to the mitochondria,
thus compensating for the increased Oâ‚‚ demand that occurs upon acclimation,
although the manner in which they did this remains unclear. Seedlings
appeared to be able to adjust stomatal conductance in order to avoid
experiencing water stress. The optimal root growth temperature was between
18 and 25°C for both species. It seems that root signalling could be involved in
rhodoxanthin accumulation in cedar shoots.Forestry, Faculty ofGraduat