| Summary: | 碩士 === 國立中興大學 === 植物學系 === 83 === Rices (Oryza sativa L.) were grown in media supplemented
with 150mM NaCl using hydroponic culture system or with
256mM NaCl using tissue culture system. In both cases, the
plant growth were arrested, the fresh weight and dry weight
were decreased as well. Further analysis of photosynthesis
and dark respiration rate indicated that both processes were
inhibited by salt stress. A higher degree of inhibition by
salt were found in salt-sensitive varieties, including IR34
and TNG72. In all varieties, the decreased respiration rate
was due to decreased activity of cytochrome pathway, whereas
the activity of alternative pathway was increased. Total
soluble sugar and proline contents of rice leaves under salt
stress were increased. Both sugar and proline have been
shown to serve as compatible solutes which have been known
involved in the mechanism of salt-stress tolerance. Analysis
of constitutes of total soluble sugars with HPLC indicated
fructose, glucose, sucrose contents were increased under
salt stress. Among them, sucrose content was the highest.
Along with the increased sucrose content under salt stress,
the enzymes in the pathway for sucrose synthesis ,e.g. SPS
and SS activity were also increase. Acid invertase activity
was decreased under salt stress while the activity of
neutral invertase remained relatively unchanged. These
results indicated that both SPS and acid invertase are con-
tributed to the sucrose accumulation in response to salinity
in rice leaves. Photosynthesic rate of rice leaves under
salt stress were decreased and the ratios of sucrose to
starch were increased. The increased ratio of sucrose to
starch in salt-tolerance varieties were more significant,
such as IR44 and TNS19. These changes were in part due to
more in partitioning of photosynthates into sucrose synthesis
pathway. These results suggest a role of sucrose accumulation
in adaptation
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