There is considerable intra-and interspecific variation in boron (B) toxicity
tolerance in crop plants. In this study, we aimed to investigate the
mechanisms involved in tolerance to excess B in barley (Hordeum vulgare) in
the early stages of plant development. To do this, B-sensitive (B?lb?l-89)
and B-tolerant (Tarm-92) barley cultivars were grown hydroponically under
control and B stress conditions (10 mM H3BO3) for 4 or 7 days. The hydrogen
peroxide (H2O2), malondialdehyde (MDA), total phenolic, total flavonoid,
anthocyanin, proline, and total sugar contents, as well as DPPH radical
scavenging capacity, were then determined for both cultivars. Our results
showed that B treatment led to significant increases in the B concentration
of the barley cultivars for both exposure times. However, there were no
drastic differences in the B concentration of the roots and shoots between
the sensitive and tolerant cultivars. While the dry root weight of B?lb?l-89
was reduced after 7 days of B stress (p < 0.05), such a decrease was not
observed in Tarm-92. The H2O2, MDA, proline, total sugar, and anthocyanin
contents of both cultivars increased considerably in response to excess B
during at least one treatment period (p < 0.05). The H2O2 content of Tarm-92
under control and B stress conditions was significantly greater than that of
B?lb?l-89, but there was no difference in the MDA content and radical
scavenging capacity between the two cultivars. Finally, a 35% increase was
found in the total flavonoid content of the Tarm-92 seedlings exposed to B
stress for 4 days. In conclusion, the findings of this study suggest that
tolerance to B toxicity in barley seedlings may be related to their capacity
to tolerate higher levels of reactive oxygen species.
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