Abstract
It is well established that both salt and reactive oxygen species (ROS) stresses are able to increase the concentration of cytosolic free Ca(2+) ([Ca(2+)]i), which is caused by the flux of calcium (Ca(2+)). However, the differences between these two processes are largely unknown. Here, we introduced recombinant aequorin into rice (Oryza sativa) and examined the change in [Ca(2+)]i in response to salt and ROS stresses. The transgenic rice harbouring aequorin showed strong luminescence in roots when treated with exogenous Ca(2+). Considering the histological differences in roots between rice and Arabidopsis, we reappraised the discharging solution, and suggested that the percentage of ethanol should be 25%. Different concentrations of NaCl induced immediate [Ca(2+)]i spikes with the same durations and phases. In contrast, H₂O₂ induced delayed [Ca(2+)]i spikes with different peaks according to the concentrations of H₂O₂. According to the Ca(2+) inhibitor research, we also showed that the sources of Ca(2+) induced by NaCl and H₂O₂ are different. Furthermore, we evaluated the contribution of [Ca(2+)]i responses in the NaCl- and H₂O₂-induced gene expressions respectively, and present a Ca(2+)- and H₂O₂-mediated molecular signalling model for the initial response to NaCl in rice.
Highlights
Rice (Oryza sativa L.) is the staple food for more than half of the world’s population
The aequorin-based luminescence signal was only observed in roots and we failed to detect any signal in shoots when treated with Ca2+ (Fig. 1D compared to bright-field et al, 2009), we re-examined the percentage of ethanol in the discharging solution for the rice experiment
GAL4 transactivation of aequorin in enhancer trap lines enabled the testing of the stimulus- and cell-specific [Ca2+]i signalling in specific tissues of Arabidopsis (Kiegle et al, 2000; Martí et al, 2013)
Summary
Rice (Oryza sativa L.) is the staple food for more than half of the world’s population. To improve the rice yield under saline conditions, it is important to understand the molecular mechanisms involved in how rice responds to salt stress (Kumar et al, 2013). A well-defined pathway is the Salt Overly Sensitive (SOS) signalling pathway, which comprises SOS3, SOS2 and SOS1 (Zhu, 2000), and is required to mediate the highly complex regulatory networks involved in plant response to salinity (Ji et al, 2013). The SOS signal transduction cascade is activated by a calcium (Ca2+) spike, which is caused by the flux of Ca2+ This salt stress triggered increase of cytosolic free Ca2+ ([Ca2+]i) is considered to be the first recorded response to salt stress (Knight et al, 1997; Tracy et al, 2008). Ca2+ is an essential second messenger in the sophisticated network of plant signalling pathways responding to a large array of external stimuli, including salt stress
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