The gravistimulation-induced very slow Ca2+ increase in Arabidopsis seedlings requires MCA1, a Ca2+-permeable mechanosensitive channel
Masataka Nakano, Takuya Furuichi, Masahiro Sokabe, Hidetoshi Iida, Hitoshi Tatsumi
Abstract
Abstract Gravity is a critical environmental factor affecting the morphology and function of plants on Earth. Gravistimulation triggered by changes in the gravity vector induces an increase in the cytoplasmic free calcium ion concentration ([Ca 2+ ] c ) as an early process of gravity sensing; however, its role and molecular mechanism are still unclear. When seedlings of Arabidopsis thaliana expressing apoaequorin were rotated from the upright position to the upside-down position, a biphasic [Ca 2+ ] c -increase composed of a fast-transient [Ca 2+ ] c -increase followed by a slow [Ca 2+ ] c -increase was observed. We find here a novel type [Ca 2+ ] c -increase, designated a very slow [Ca 2+ ] c -increase that is observed when the seedlings were rotated back to the upright position from the upside-down position. The very slow [Ca 2+ ] c -increase was strongly attenuated in knockout seedlings defective in MCA1, a mechanosensitive Ca 2+ -permeable channel (MSCC), and was partially restored in MCA1 -complemented seedlings. The mechanosensitive ion channel blocker, gadolinium, blocked the very slow [Ca 2+ ] c -increase. This is the first report suggesting the possible involvement of MCA1 in an early event related to gravity sensing in Arabidopsis seedlings.