Novel Salicyl Glycoconjugates as Elicitors against Plant Diseases
Finally, the hydrazides 5a–d were reacted with aldehyde 6 by
condensation to form the glycosyl hydrazones 7a–g.
by jasmonic acid. In each defense pathway, there are specific
marker genes which expression could be influenced by corre-
sponding signaling molecules. In order to unveil the mode of
action of our designed compounds, RT-PCR was performed to
check the expression patterns of pathogenesis-related genes (PR1a,
PR8, LOX1, Cs-AOS2) (Figure 6). Among them, PR1a and PR8
were the specific marker genes mediated by salicylic acid, whereas
LOX1 and Cs-AOS2 were the specific marker genes mediated by
jasmonic acid. Our results showed that expressions of the LOX1
and Cs-AOS2 genes were significantly induced by hydrazide 5d,
and the expression level was comparable with that mediated by
BTH (S-methyl benzo [1,2,3]thiadiazole-7-carbothioate). Howev-
er, hydrazide 5d had no obvious effect on the expressions of PR1a
and PR8.
Fungicidal activity
The in vitro fungicidal results were shown in Table 1. The
hydrazides 2a and 2b showed excellent activity against the tested
fungi (Figures 2 and 3). For example, the inhibitory rates of the
hydrazides 2a and 2b against C. orbiculare were 97.3% and
95.4%, which were better than thiophanate-methyl (91.0%). After
modification of sugars, the in vitro activity of all the derivatives
was decreased and they exhibited poor inhibitory rates. Although
the in vitro activity of these glycosides was not encouraging, the
in vivo tests gave promising results (Table 2), with all the
carbohydrate derivatives showing considerable activity, especially
against F. oxysporum (Table 2), C. orbiculare (Figure 4), and S.
fuliginea (Figure 5). Among them, hydrazide 5d and hydrazone
7f had activity of 71.0% and 74.9% on F. oxysporum, respectively,
which is similar to the control benomyl (74.5%) against the same
pathogen. 5d also showed good activity of 68.6% and 73.9%
against C. orbiculare and S. fuliginea, respectively. Some
hydrazones 7 exhibited promising activity against P. capsici. For
examples, 7c showed an inhibitory rate of 83.5%, and the
inhibitory rates of 7a, 7d and 7e were more than 75%.
The bioassay results showed that the tested compounds had
in vivo antifungal activity against pathogenic fungi of Ascomycota
(C. orbiculare, F. oxysporum and S. fuliginea), Basidiomycota
(R. solanii), and Oomycete (P. capsici). The observed in vivo
antifungal activity also had some association with the issue of
pathogen biology. The tested compounds exhibited activity not
only against the obligatory parasite pathogen (S. fuliginea), but
also against the facultative parasite pathogens (C. orbiculare,
F. oxysporum, R. solanii and P. capsici). The tested compounds
also showed good activity against the soil-borne fungal disease
(F. oxysporum, R. solanii and P. capsici). Also, we confirmed that
all of these test compounds were safe for the host plants.
Conclusions
A new series of glycosyl hydrazines and hydrozone derivatives
were designed and synthesized. Their antifungal tests indicated
that most of the salicylic glycoconjugates had no in vitro fungicidal
activity but showed considerable in vivo antifungal activity. The
plant defense activity showed that expressions of the LOX1 and
Cs-AOS2 genes were significantly induced by hydrazide 5d, but
the compound had no effect on the expressions of PR1a and PR8.
Intriguingly, although the designed compounds were the deriva-
tives of salicylic acid, they did not mimic the mode of action of
salicylic acid, but seem to follow the jasmonic acid mediated
pathway to induce the plant defense resistance.
Supporting Information
Table S1 Primers Used in This Study.
(DOC)
Author Contributions
Conceived and designed the experiments: ZC YA YN. Performed the
experiments: ZC JI HD. Analyzed the data: ZC HD YN. Contributed to
the writing of the manuscript: ZC YN.
Defense activity of designed compound in plant
There are two important defense signaling pathways in plant
system. One is mediated by salicylic acid and the other is mediated
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September 2014 | Volume 9 | Issue 9 | e108338