Water Content during Abscisic Acid Induced Freezing Tolerance in Bromegrass Cells

Area of Science:

• Plant Physiology
• Biochemistry
• Cell Biology

Background:

• Cold acclimation is crucial for plant survival in freezing temperatures.
• Abscisic acid (ABA) is a key plant hormone involved in stress responses.
• Previous studies suggested reduced cell water content during cold hardening.

Purpose of the Study:

• To investigate the role of abscisic acid (ABA) in the cold hardening of bromegrass cells.
• To determine the changes in cell water content and dry weight during ABA-induced freezing tolerance.
• To re-evaluate the relationship between water content, dry matter, and freezing tolerance.

Main Methods:

• Bromegrass cells were cultured and treated with ABA (7.5 x 10(-5) M) or left untreated.
• Cells were subjected to cold acclimation at -28°C (LT50) or -5°C.
• Water content (percent H2O, g H2O/g DW, mg H2O/10^6 cells) and dry weight (mg DW/10^6 cells) were measured over 7 days.
• Osmotic potential was assessed to understand cellular changes.

Main Results:

• ABA treatment significantly reduced cell growth rate, primarily by decreasing cell number.
• ABA-treated cells showed decreased water content when expressed as % water or g H2O/g DW.
• Crucially, ABA-treated cells exhibited increased dry matter mass per cell (mg DW/10^6 cells).
• Cell water content per cell (mg H2O/10^6 cells) did not differ between treated and control cells.
• Osmotic potential changes were observed, but not linked to increased ion uptake.

Conclusions:

• ABA induces freezing tolerance in bromegrass cells without a net decrease in cellular water content.
• Increased dry matter accumulation per cell is a primary mechanism for ABA-mediated cold acclimation.
• The expression of cell water content relative to cell number provides a more accurate assessment during dry matter changes.