ABA plays important roles in many cellular processes
and environmental stress responses of plants and high ABA
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In our study, a higher level of ABA was observed in cucumber
leaves when challenged with salt vs. the non-salt groups,
and the application of T. asperellum Q1 to salinized cucum-
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in cucumber seedlings (Fig. 5). This might be due to high
production of ABA by T. asperellum Q1 to ameliorate adverse
effects of salinity. While T. asperellum Q1 did not induce
high ABA accumulation in cucumber leaves under non-salt
conditions, which is in accordance with the results of T. harzianum
strain T22 (Sofo et al. 2011). This may be explained
by the statement that exogenous ABA accumulation can be
regulated negatively by activating its catabolic enzymes,
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Krochko 1999; Xiong and Zhu 2003). ABA overproduction
correlated with the over accumulation of the catabolite supports
the notion that ABA might restrict its own accumulation
by activating its degradation, at least under non-stressful
conditions (Qin and Zeevaart 2002; Xiong and Zhu 2003).
However, the degradation of ABA appears to be suppressed
by salt stress; therefore T. asperellum Q1 induced a higher
level of ABA in cucumber leaves under salt conditions