Greater antioxidant and respiratory metabolism in field‐grown soybean exposed to elevated O 3 under both ambient and elevated CO 2

• Published in: Plant, cell and environment Vol. 35; no. 1; pp. 169 - 184
• Main Authors: GILLESPIE, KELLY M., XU, FANGXIU, RICHTER, KATHERINE T., MCGRATH, JUSTIN M., MARKELZ, R. J. CODY, ORT, DONALD R., LEAKEY, ANDREW D. B., AINSWORTH, ELIZABETH A.
• Format: Journal Article
• Language: English
• Published: 01-01-2012
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/j.1365-3040.2011.02427.x

ABSTRACT
Antioxidant metabolism is responsive to environmental conditions, and is proposed to be a key component of ozone (O
3
) tolerance in plants. Tropospheric O
3
concentration ([O
3
]) has doubled since the Industrial Revolution and will increase further if precursor emissions rise as expected over this century. Additionally, atmospheric CO
2
concentration ([CO
2
]) is increasing at an unprecedented rate and will surpass 550 ppm by 2050. This study investigated the molecular, biochemical and physiological changes in soybean exposed to elevated [O
3
] in a background of ambient [CO
2
] and elevated [CO
2
] in the field. Previously, it has been difficult to demonstrate any link between antioxidant defences and O
3
stress under field conditions. However, this study used principle components analysis to separate variability in [O
3
] from variability in other environmental conditions (temperature, light and relative humidity). Subsequent analysis of covariance determined that soybean antioxidant metabolism increased with increasing [O
3
], in both ambient and elevated [CO
2
]. The transcriptional response was dampened at elevated [CO
2
], consistent with lower stomatal conductance and lower O
3
flux into leaves. Energetically expensive increases in antioxidant metabolism and tetrapyrrole synthesis at elevated [O
3
] were associated with greater transcript levels of enzymes involved in respiratory metabolism.
This study investigated the molecular, biochemical and physiological changes in soybean exposed to elevated [O
3
] in a background of ambient [CO
2
] and elevated [CO
2
] in the field. Principle components analysis was used to separate variability in [O
3
] from variability in other environmental conditions (temperature, light and relative humidity). The key results show that energetically expensive increases in antioxidant metabolism and tetrapyrrole synthesis at elevated [O
3
] were supported by greater respiratory metabolism.