Vergara - 1976 - Physiological and morphological adaptability of ri

224 CLIh-IATE AND RICE
capacity adapted to such climate. Most species of Gramineae of tropical origin.
such as maize. sugar cane. sorghum. and barnyard grass. assimilate C0; through
the C, dicarboxylic acid pathway (C, species), and do not show photorespiration.
Under high light intensity’ and high temperature. the photorsynthetic rate
of rice is usually lower than that of C4 species.
The culture of rice has been developed under different climatic conditions,
ranging from the tropics to temperate regions and from rainy seasons to dry
seasons. Man has devoted considerable effort to select varieties which adapted
well to the given environment. as well as to improve cultural techniques.
In this reviewz attention will be focused on the complex interrelationships
betyveen climatic factors, photosynthesis. photorespiration. and dark respiration,
as well as on the difference in climatic response of photosynthesis according to
varieties and cultural management. The discussion opens with a brief review on
the chill injury’ to photosynthesis ofriee.
TEIVIPERATIJRE RESPONSES OF
PHOTOSYNTHESIS AND RESPIRATION
Chill injury‘ to photosynthesis ofthc rice plant
The photosymthesis of rice is seriously; damaged by exposure to low temperature.
even above the freezing point. Suspension of photosynthesis in chilled leaves
and its recovery is one of the most important problems in rice culture in temperate
regions and mountainous areas of the tropics.
Low temperature may inhibit the photosynthetic rate through the inactivation
of enzymes in chloroplasts as well as by stomatal closure caused by reduced
water uptake. The photosynthesis and transpiration of the rice plant. as shown in
Table 1. were considerably reduced by chilling at 5°C for l9 hours, although no
signs of chill injury’ such as discoloration and xviltiny’ were observed. Rectweqt of
photosynthesis in chilled leaves significantly varied according to rice varieties.
The photosynthesis after chilling was markedly higher in Nankal 43 of japonica
rice than in 1R8 of indica rice. while there was no great difference in transpiration
rate between the two varieties. The varietal difference in photosynthesis by
chilling may be attributed to enzyme inactivation by the denaturation of protein
in chloroplasts rather than to the decrease in carbon dioxide diffusion through
stomata.
The photosynthetic rate of rice plants increaser with diminishing oxygen
concentration in air, because of depressed photorespiration. Table l shows that
chilling brings about an important change in the photosynthetic response to
oxjyigen. Before chilling. the photosynthetic rate in 3% tixygen was significantly
higher than that in 2] % oxygen, whilejtist after chilling the former was a little
lower than the latter. However, when the photosynthetic capacity somewhat
rectwered. the positive effect of low oxygen reappeared. Jolliffe and Tregunna
(1968) reported that at low temperature below lO°—l3°C. the photosynthesis of
wheat in 3 % oxygen was as much as or lower than that in 21 % oxygen. A similar