Changes of cytosolic Ca2þ fluorescence intensity and plasma membrane calcium channels of maize root tip cells under osmotic stress

The changes of cytosolic Ca2þ fluorescence intensity and the activities of calcium channel of primary maize root tip cells induced by PEG6000 or abscisic acid(ABA)were studied by both confocal techniques and the whole-cell patch clamping in this study. The Ca2þ fluorescence intensity increased while treated with PEG or ABA within 10 min, illuminating that Ca2þ participated in the process of ABA signal transduction. For further proving the mechanism and origin of cytosolic Ca2þ increase induced by PEG treatments, N,N,N0,N0-tetraacetic acid (EGTA), Verapamil (VP)and Trifluoperazine (TFP)were added to the PEG solution in the experiments separately. The results showed that Ca2þ fluorescence intensity induced by PEG was suppressed by both EGTA and VP obviously in the root tip cells. The Ca2þ fluorescence intensity of plants changed after the addition of CaM inhibitor TFP while subjected to osmotic stress, which seemed to show that CaM participated in the process of signal transduction of osmotic stress too. The mechanism about it is unknown today. Further, a hyperpolarization-activated calcium permeable channel was recorded in plasma membrane of maize root tip cells. The Ca2þ current (ICa)intensity increased remarkably after PEG treatment, and the open voltage of the calcium conductance increased. Similar changes could be observed after ABA treatment, but the channel opened earlier and the current intensity was stronger than that of PEG treatment. The activation of calcium channel initiated by PEG strongly was inhibited by EGTA, VP or TFP respectively. The results revealed that Ca2þ participated in the signals transduction process of osmotic stress, and the cytosolic free Ca2þ increase by osmotic stress mainly came from the extracellular, and some came from the release of cytoplasmic calcium pool.