Agriculture Reference
In-Depth Information
systems in IR 50 were damaged severely by chilling, which led
to lower photosynthetic rate (Guo-Li and Zhen-fei 2005). Leaf
photosynthesis was reduced from 8.1 to 5.2 percent along with
each 1°C reduction of water temperature. Stomatal conductance
showed a similar response to photosynthesis and demonstrated
that the differences of reduction in stomatal conductance for
each degree centigrade or more was 2.6 and 3.7 percent.
However, the daily transpiration rate per plant was greater
in cold tolerant cultivars compared with sensitive ones (Dai et
al. 1993) due to wide stomatal opening.
Seminal rice (
Oryza sativa
L. CV. Taichung native 1) roots were
grown
in vitro
to investigate the relationships among polyamine
biosynthesis, root growth and chilling tolerance. At 25ºC, the
level of free putrescine, the activities of arginine decarboxylase
(ADC) and ornithine decarboxylase (OX) increased as growth
progressed. While the levels of free spermidine/spermine and
the activity of S-adensosylmethionine decarboxylase (SAMDC)
decreased. Exogenously applied putrescine, ranging from
0.01 to 1 mM, enhanced the elongation of roots grown at 25ºC
whereas application of spermidine or spermine inhibited root
elongation, O-Difl uoromethylarginine (DFMA) at 5 OM or
C-Difl uoromethyl ornithine (DFMO) at 10 OM inhibited the
increase in root length and the levels of free putrescine at 25ºC,
these effects were reversed by the addition of 1 mM putrescine.
Roots exposed to 5ºC ceased growth and lost their re growth
ability after 9 days of chilling. The level of free putrescine and
the activity of ADC in chilled roots increased before returning
to normal at day 3 and then decreased to a plateau after 9
days. The levels of free spermidine and spermine increased
after 9 days. When putrescine was applied at concentrations
greater than 0.1mM, the chilled roots partially recovered their
re-growth ability. Contrary to DFMO (10 OM) DFMA (5 OM)
inhibited both the chilling induced free putrescine. These
