Vergara - 1976 - Physiological and morphological adaptability of ri

176 rim-tam AND RICE
60°—62°C. A large number of thermal anomalies have been observed at or near
these temperatures in divergent physical properties of water in the ydcinities of
interfaces.
Physiological propeflies must be influenced by these thermal anomalies for
water, because biological systems contain water in abundance. Furthermore.
water in biological syistems is largely interfacial with biological polymers. that is,
proteins. lipids. polysaccharides. or nucleic acids. Surveys and experiments
showed that a great number of thermal anomalies in physiological properties
occur primarily in the vicinities of four specific temperatures which identically
coincide tvith those for interfacial tvater (Drost-Hansen. 1966, 1971; Nishiy-"ama.
1970a, 1970b, 1972). Thus. Drost-Hansen (1971) inferred that thermal anomalies
in biological systems are the manifestation of higher order phase transitions
in water structure in the vicinity‘ of interfaces. Some alternative hytptitheses
are tenable as to the cause of physiological thermal anomalies. for instance.
the lipid phase-change theory‘ and the metabolic unbalance theory‘.
However, neither of these theories is applicable to thennal anomalies for purified
enzymes tvhich have been reported by a number of researchers. Thus, the
water theory seems to be most vridely applicable to physiological thermal
anomalies. More precisely. refer to a review by Nishiyama (1975).
This theory by Drost-Hansen can be applied generally to various kinds of
physiological properties and also to divergent phydtigenetical groups including
animals. plants. and microorganisms (and, of course, rice plants).
Dispersion of the critical temperature
Figure 7 shows the effect of water temperature in deep irrigation at the meiotic
stage on the fertility of rice plants (Nishiyarna et a1. 1969). l-layayuki is one of
the most cool-tolerant varieties and Norin 20 is a rather weak one. The critical
temperature differs among different varieties and according to cultivation conditions.
from 10° to 20°C, or 15°C i 5°C.
The dispersion in the critical temperature for this sterile-type c001 weather
injury is rather wide. This is because the effect is remote from the cause. and the
causal relation is much more complex. The cause of this injury is low temperatures
at the meiotic stage (more precisely} the young microspore stage), and the
effect is unfertilization at anthesis. There are a number of developmental steps of
pollen and anthers between the cause and the effect: growth of microspores,
degradation of tapetal cells. pollen mitosis. growth of pollen, dehiscence of
anthers. shedding of pollen on stigmata. elongation of pollen tubes. and fertilization.
Tetrad and nascent microspores are the most sensitive to, and directly
affected by‘. cool temperatures (Nishiyama. 1970c). For the primary injuries at
these stages, the dispersion in the critical temperature is expected to be much
narrower. llowever. ‘various factors can affect the final effect, fertility, through
the steps after the occurrence of the primary injuries (Ito et al.. 1970). For instance,
the abilities of pollen maturation. anther dehiscence. and pollen tube
elongation differ among different varieties, or among plants which have been