Abstract
Background and aims
Sulfate, the main source of sulfur in natural soil, is critical for plant growth and development, as well as plant responses to environmental stress, including drought. However, our understanding of the detailed mechanisms of sulfate-modulated drought tolerance in crop plants is far from complete. In the present study, by using foxtail millet (Setaria italica L.), an emerging model crop, we investigated the possible mechanisms involved in sulfate-induced crop tolerance to drought stress.
Methods
A combination of biochemical and molecular approaches, as well as stomatal apertures analyses were applied to determine the effect of sulfate application on sulfur assimilation, ABA biosynthesis, and stomatal movement.
Results
Upon drought exposure, sulfate (4 mM) pretreatment significantly alleviated the decrease in relative water content in foxtail millet leaves. Exogenous sulfate increased endogenous sulfate content and markedly enhanced the enzyme activity of sulfite reductase (SiR) and O-acetylserine(thiol)lyase (OASTL), as well as levels of their transcripts, leading to an increase in cysteine (Cys) production in drought-stressed leaves. Furthermore, in comparison with drought stress alone, sulfate application significantly upregulated the transcriptional expression of SiABA3 and SiAAO3, which contributed to the increased ABA levels in the leaves of drought-stressed foxtail millet seedlings. Moreover, the addition of sulfate decreased stomatal aperture, thus resulting in reduced leaf water loss in foxtail millet exposed to drought.
Conclusion
Our data suggest that sulfate application was able to promote drought tolerance of foxtail millet plants, at least partially by increasing ABA biosynthesis and triggering stomatal closure.