Gravity induces asymmetric Ca2+ 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 Ca²⁺ participated in plant gravity response. However, present information on the functions of Ca²⁺ in plant gravitropism was obtained mainly on coleoptiles, hypocotyls, and petioles, little is known about the dynamic changes of Ca²⁺ during root gravitropism. In the present study, the transgenic Arabidopsis thaliana 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 Ca²⁺ concentration, but also an accelerated occurrence of Ca²⁺ sparks in the root cap, especially in the lower side of the lateral root cap, indicating a strong tie between Ca²⁺ dynamics and gravistimulation during the early stage of root gravity response.