Hemoglobin expression affects ethylene production in maize cell cultures.

Area of Science:

• Plant Physiology
• Biochemistry
• Molecular Biology

Background:

• Ethylene is a crucial plant hormone regulating various growth and stress responses.
• Class-1 hemoglobin (Hb) plays a role in oxygen sensing and nitric oxide (NO) metabolism in plants.
• The precise function of Hb in ethylene biosynthesis regulation remains unclear.

Purpose of the Study:

• To investigate the role of hypoxically inducible class-1 hemoglobin in regulating ethylene formation in maize (Zea mays L.) cell suspension cultures.
• To determine the impact of oxygen levels and nitric oxide (NO) on ethylene production in relation to Hb expression.
• To elucidate the molecular mechanisms underlying Hb-mediated ethylene regulation.

Main Methods:

• Utilized maize cell lines with either over-expressed (Hb+) or down-regulated (Hb-) class-1 hemoglobin.
• Measured ethylene production under varying oxygen concentrations and in the presence of a nitric oxide (NO) donor (sodium nitroprusside, SNP).
• Assessed 1-amino-cyclopropane-1-carboxylic acid (ACC) oxidase (ACO) mRNA levels and enzyme activity.

Main Results:

• Ethylene levels were 5-6.5 times higher in the Hb- line compared to the Hb+ line and 4-5 times higher than the wild type under all conditions.
• Low oxygen impaired ethylene formation in maize cell cultures.
• ACO activity was significantly enhanced in the Hb- line, increasing under hypoxia and upon NO treatment, while ACO mRNA levels remained constant.

Conclusions:

• Limiting class-1 hemoglobin synthesis enhances ethylene formation in maize suspension cells.
• The results suggest that class-1 hemoglobin modulates ethylene production, potentially through the regulation of nitric oxide (NO) levels.
• Class-1 hemoglobin's role in plant stress responses and hormone signaling is further elucidated.