Microfluidic communications in characean internodes at neutral and alkaline external pH

Area of Science:

• Plant cell physiology
• Photosynthesis research
• Intracellular transport mechanisms

Background:

• Cytoplasmic streaming (cyclosis) facilitates intracellular communication in plant cells, overcoming diffusion limitations.
• Cyclosis smooths concentration gradients caused by light variations and external pH.
• In Chara cells, light-induced reducing equivalents are transported via streaming, affecting chlorophyll fluorescence (F').

Purpose of the Study:

• To investigate the impact of high external pH on metabolite transport and chlorophyll fluorescence in Chara cells.
• To understand how cyclosis-transported metabolites interact with chloroplasts under alkaline conditions.
• To elucidate the role of action potential generation on non-photochemical quenching (NPQ) under varying pH.

Main Methods:

• PAM microfluorometry was used to measure chlorophyll fluorescence (F' and F'm).
• Chara internodal cells were exposed to a high pH solution (9.5) to mimic natural alkaline zones.
• Measurements were taken under simulated light conditions and during action potential generation.

Main Results:

• Chloroplasts in alkaline conditions responded to cyclosis-transported reducing equivalents and a novel metabolite that quenched fluorescence.
• The combined effects of different metabolites appeared to suppress microfluidic interactions.
• Action potential generation induced strong non-photochemical quenching (NPQ) at high pH, unlike at neutral pH.

Conclusions:

• High external pH alters intracellular metabolite transport and chloroplast responses.
• Restricted CO2 at high pH may induce electron transport rearrangements, increasing background NPQ.
• Chloroplasts become more sensitive to hydrogen peroxide (H2O2) delivered via cytoplasmic streaming under high pH and light stress.