3.5 â Activity of phenylalanine ammonia-lyase (PAL)
In each of the six cucumber genotypes, the PAL activities of the control
plants indicated no significant changes from day 7 to day 21 (Table 6).
In the resistant and moderately resistant genotypes, PAL activities
showing significant difference from the control at time point after
inoculation. After inoculation, PAL activity in the resistant genotype
Soheil increased, reaching its first peak on day 7 then, it decreased on
day 14 and increased to 1.86 U mgâ1 on day 21 after
inoculation (Fig 5. A). The CAT activity in resistant Ramezz increased
sharply to 2.17 U mgâ1 at 7 DAI and then decreased at
14 and 21 DAI (Table 6). The moderately resistant genotype, Baby, showed
behavior similar to that of the Soheil, but it increased sharply and
reached its maximum on day 21(5.20 U mgâ1). The two highly susceptible
genotypes Extrem and Mini 6-23 showed completely different patterns of
PAL activity, that in the both genotypes increased on day 7 and 14 and
then decreased on day 21 (Fig 5.D and E). Whereas on the other genotype
Yalda increased on day 7 and then decreased on day 14 and 21 (Fig 5.F).
Therefore, changes in PAL activity showed differences among different
genotypes and it was significantly higher in inoculated plants of both
moderately resistant and resistant genotypes, as compared to susceptible
genotypes. The significant negative correlations between activity of PAL
and damping-off susceptibility were only observed at 7 and 14 DAI
(Supplemental Table 1, r= -0.94 and r= -0.82, respectively), in the
highly susceptible genotypes, the increase of PAL activity was lower
than in the resistant genotypes.