In order to investigate the relationship between calcium signaling and negative phototropism of rice roots, different concentration of calcium signaling reagent such as CaCl2, organic calcium channel blocker(verapamil), inorganic calcium channel blocker(LaCl3), calcineurin inhibitor chloropromaize（CPZ), auxin polar transport inhibitor(NPA) were used to treat rice seminal roots which were unilaterally illuminated at an intensity of 100-200 μmol/(m2·s) for 24 h. Results showed that negative phototropism curvature and growth rate of rice roots were enhanced by a proper dose of CaCl2. Further experiments testified that it is because more IAA was transported from irradiated side to shaded side by exogenous Ca2+ that negative phototropism curvature was enhanced rather than increased growth rate. Simultaneously, negative phototropism curvature and growth rate of rice roots were inhibited by inhibitors above, and the inhibiting effects were enhanced as the rising concentration of inhibitors. Roots would stop growing and negative phototropism characteristic would disappear when the concentration reached a certain degree, such as 100 μmol/L verapamil, 12.5 μmol/L LaCl3, 60 μmol/L CPZ and 6 μmol/L NPA. 100 μmol/L CaCl2 relieved the inhibition degree of LaCl3, verapamil and NPA. The results indicated that calcium ion plays an important role as a second messenger in the process of light signaling regulating rice roots growth and negative phototropism.
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