Vergara - 1976 - Physiological and morphological adaptability of ri

STERlLE-TYPE com. twitter IN morn’ arcs PLANTS 289
Injuries before anthesis
Recently. we made some physiological studies by newly developed microanalysis
methods (Nishiyiama. l97'0a'. Satake and Hayase, I970". Ito. unpublished).
Cooling treatment at the meiotic stage delayed the growth of palea in
length. but did not affect the final length. On the other hand. it shortened anther
length at heading by 10-20 percent. Furthermore. it decreased the dry weight per
anther and the content of protein, nitrogen. phosphate. and potassium. and
respiratory activity. Their decreased rate at heading coincided with the decrease of
fertility due to cooling treatment. These abnormalities could be detected 4-5
days after the cooling treatment. Before this time there were no significant differences
in these characters between cooled and healthy anthers. The plI value
and respiratory quotient in anthers were not changed by cooling treatment.
lt is well known that the proline fraction is the greatest of all amino acids
in normal anthers and that its content is remarkably decreased in genetic or
physiological sterile anthers (Fukasawa. I954; Khoo and Stinson, 1959; Ozaki
and Tai. I961 1 Hosokawa et al.. 1963'. Tupy. 1963; Fujishita, 1970). Ito(l972)
evaluated the change of amino acid content in rice anthers cooled at the meiotic
stage. In cooled rice anthers. almost all kinds ofamino acids decreased. Prolinc.
especially‘. comprising more than 40 percent of the total amino acids in normal
rice anthers. nras sharply decreased by the cooling treatment. On the contrary.
asparagine was increased. The difference between cooled and healthy anthers
became perceptible in the contents of proline and total amino acids 4 days after
the cooling treatment.
Time of appearance of injuries
These results support the conclusion that the main cause of sterility is pollen
immaturity’, and indicate that the delay in maturation has already commenced
at the microspore stage before pollen division. Even when rice plants were grown
under favorable growmg conditions after fairly strong cooling treatment at the
meiotic stage. considerable high sterility alvt-‘ayrs occurred. This indicates that
some decisive injuries might have occurred during cooling treatment. All of the
above-mentioned physiological abnormalities appeared 4-6 days after cooling
treatment. They were not the primary cause of cooling injury. but the results.
The time to investigate for phyrsiological injuries has been shifted from 4—6 days
after cooling treatment, to soon after and during the treatment.
PRECISE ESTIMATION OF THE STAGE SENSITIVE TO COOLNESS
Procedures for estimation
For more than 30 years since the experiment of Kakizaki and Kido (1938), it
has been believed that the stage most sensitive to sterile-type cool injury of rice
plants is the meiotic division stage of PMCs A series in our experiment using
uniform materials led us to doubt the correctness of their results and stimulated