Vergara - 1976 - Physiological and morphological adaptability of ri

20 (JLlMA'l‘E AND tour;
Dcrkness lhr) before 50% rmhtlimtim
5O
20-
Nigrl tqwerulwtlTl
4. Effect of temperature on the time in darkness required
for 50% mobilization from the leafof "C-labelled
reserves from photosynthesis during the preceding day
(Lush and Evans, 1974).
t0 be particularly sensitive to cool temperatures, but some C, plants have
invaded temperate areas and display a limited adaptation to cool conditions.
For example, Kawanabe (1968) found high-altitude races of Chloris gqvanr:
from Kenya to be more tolerant of low temperatures than low-altitude races.
Similarly, Duncan and Hesketh (1968) showed that races of maize from high
altitudes were better adapted than low-altitude races to cool temperatures in
rates of photosynthesis and leaf growth.
There is considerable interest in attempts to extend the adaptive range ofC,
plants to cooler areas. one of the major objectives of the New Zcaland phytotron.
but the reasons for their poor growth at cool temperatures remain unclear
and in need of further analysis. To mention only one possibility‘, we found
mobilization of starch stored in the leaves of C, grasses by day to be greatly
delayed by cool night temperatures (Fig. 4). Cr grasses known to be better
adapted to temperate climates appeared to get around this problem by storing
less starch in their leaves during the day for export the following night (Lush
and Evans, 191M).
On the other side of the temperature optimum. greater tolerance to hot conditions
may come from hybridization programs. Langridge and (trifling (1959)
showed that a high proportion ofArabidops/s mutants sensitive to high temperatures
could have their growth at high temperatures restored by the applica-