Gravity Induces Asymmetric Ca Spikes in the Root Cap in the Early Stage of Gravitropism

Gravitropism is an important strategy for the adaptation of plants to the changing environment. Previous reports indicated that Ca participated in plant gravity response. However, present information on the functions of Ca in plant gravitropism was obtained mainly on coleoptiles, hypocotyls, and petioles, little is known about the dynamic changes of Ca during root gravitropism. In the present study, the transgenic R-GECO1 was placed horizontally and subsequently vertically on a refitted Leica SP8 laser scanning confocal microscopy with a vertical stage. Real-time observations indicated that gravistimulation induced not only an increase in the Ca concentration, but also an accelerated occurrence of Ca sparks in the root cap, especially in the lower side of the lateral root cap, indicating a strong tie between Ca dynamics and gravistimulation during the early stage of root gravity response.