Abstract
Aims To investigate the changes in physiological
parameters in leaves of field-grown rice genotypes
differing in their salt tolerance.
Methods Thirty rice cultivars classified as tolerant
(T; 11), moderately tolerant (MT; 5), moderately sensitive
(MS; 7) and sensitive (S; 7) based on the previous
screening at the seedling stage were established in a
greenhouse. Thirty-day-old seedlings were then transplanted
to a rice field, situated in a moderately saline
area in northeastern Thailand, where EC slowly increased
from 2.03 to 6.46 dS m−1 from the transplanting
date to harvest. Leaf samples (the third leaves from the
top or the flag leaves during the vegetative or the reproductive
phase, respectively) were collected, at 1 month
intervals, when the plants were 60-, 90-, 120- and 150-
day-old corresponding to active tillering, early reproductive,
late reproductive and harvest stage, respectively.
Leaf samples were analyzed for changes in proline,
chlorophyll and malondialdehyde (MDA). The harvested
panicles were evaluated for the percentage of
filled grain weight and the concentration of Na+ and
K+ in the top internode.
Results The patterns of change and the mean concentrations
of most physiological parameters in rice
leaves during the course of development were strikingly
similar for the four classes of salt tolerance.
Proline concentration remained relatively constant
throughout the development and finally showed a
dramatic increase in the flag leaves at harvest. MDA
concentration tended to increase with age reaching the
maximum in the flag leaves at harvest. The chlorophyll
concentration was higher during the vegetative
stage than the reproductive stages. At harvest
corresponding to the time of maximum salinity, the T
group tended to contain higher proline and stayed
green longer than the other groups. Moreover, the T
group showed higher percentage filled grain weight
which was associated with lower Na+/K+ ratio in the
top internode. The percentage filled grain weight was
negatively correlated with Na+ concentration and
Na+/K+ ratio in the top internode and proline concentration
in flag leaves, but did not correlate with chlorophyll
and MDA in flag leaves