Cytoplasmic pH dynamics in maize pulvinal cells induced by gravity vector changes

Area of Science:

• Plant Biology
• Plant Physiology
• Gravitropism

Background:

• Maize (Zea mays) stems perceive gravity via pulvinal tissue, leading to differential growth and upward bending.
• Amyloplast-rich bundle sheath cells are gravity perception sites, but early signaling remains unclear.
• Cytoplasmic pH (pH(c)) was previously identified as a gravitropic signaling mediator in Arabidopsis roots.

Purpose of the Study:

• To investigate the role of cytoplasmic pH (pH(c)) in early gravitropic signaling in maize stems.
• To determine if pH(c) changes are involved in gravity vector perception in maize pulvinal cells.

Main Methods:

• Confocal ratiometric imaging using a fluorescent pH indicator (carboxy seminaphtorhodafluor acetoxymethyl ester acetate).
• Measurement of pH(c) in maize pulvinal cells (bundle sheath and parenchyma) during gravistimulation.
• Assessment of cell responses to external stimuli like propionic acid, auxin, and pH changes.

Main Results:

• Gravity-induced pH(c) changes were observed exclusively in bundle sheath cells, not parenchyma cells.
• Gravistimulation caused cytoplasmic acidification at cell sides and alkalinization at the base, correlating with amyloplast sedimentation.
• Parenchyma cells and isolated bundle sheath cells showed no gravity-induced pH(c) changes but responded to external stimuli.

Conclusions:

• Cytoplasmic pH (pH(c)) plays a significant role in the early signaling pathways of maize stem gravitropism.
• Differential pH(c) changes within bundle sheath cells are crucial for gravity perception and signal transduction in maize stems.