Vergara - 1976 - Physiological and morphological adaptability of ri

STERILE-TYPE COOL twunr IN PADDY RICE PLANTS 293
tive to coolness. Even if the inhibition 0f transport of nutrients is the cause of
sterility, this may result chiefly from the refusal of microspores to receive the
nutrients.
Mechanism of tapetal hypertrophy
Nishiyama (l970b, 1970c) made electron microscopical observations and showed
that the hill type of tapetal hypertrophy in the cross sections resulted from the
fusion of several tapetal cells due to breakage of the intertapetal walls. In the
fused cells just after the breakage of walls, almost all cell organelles were still
nonnal. In enlarged and dilated tapetal cells, the nuclei were deformed, endoplasmic
rcticula were swollen, and the broken cell walls (and cell membranes)
remained as traces. Mitochondria, protoplastids, and other cell components
seemed to be morphologically normal. but they proliferated greatly.
When the abnormal accumulation of reducing substances (presumably reducing
sugars) in the tapetal cells of damaged anthers (Murakami el al, 1958) is
considered With the electron microscopical trbservations on breakage of intertapetal
walls, it may be said that the fusion of tapetal cells may have commenced
due to the abnormal accumulation of sugars, leading to the breakage of intertapetal
walls. This is only an interesting txtorking hypothesis. In the anthers
cooled at the early microspore stage, Ito (unpublished. Fig. 5) observed that the
cooled anthers had a higher sucrose content than control anthers during cooling
treatment. He did not detect any other differences in the composition until
4-5 days after cooling treatment. Therefore, the change in sucrose is the first to
be recognized during cooling treatment. Since this result is based on the whole
anthers. the distribution of sucrose in the anther tissues remains unknown. It
is assumed that the abnormal acetimulation of sucrose in the tapetal cells raises
Sacrose Lug lonther l
S. Effect of cooling treatment on sucrose of anthers
(Ito_ impiibltshed).
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