Journal of Plant Physiology 169 (2012) 1392–1400 Contents lists available at SciVerse ScienceDirect Journal of Plant Physiology j ourna l ho mepage: www.elsevier.de/jplph Growth under elevated atmospheric CO 2 concentration accelerates leaf senescence in sunflower (Helianthus annuus L.) plants Lourdes de la Mata, Purificación Cabello, Purificación de la Haba, Eloísa Agüera ∗ Departamento de Botánica, Ecología y Fisiología Vegetal, Área de Fisiología Vegetal, Facultad de Ciencias, Universidad de Córdoba, Campus de Rabanales, Edificio Celestino Mutis (C4), 3 a planta, E-14071 Córdoba, Spain a r t i c l e i n f o Article history: Received 5 February 2012 Received in revised form 24 April 2012 Accepted 21 May 2012 Keywords: Elevated CO2 Hexoses Oxidative status Photosynthetic pigments Senescence Sunflower a b s t r a c t Some morphogenetic and metabolic processes were sensitive to a high atmospheric CO 2 concentration during sunflower primary leaf ontogeny. Young leaves of sunflower plants growing under elevated CO 2 concentration exhibited increased growth, as reflected by the high specific leaf mass referred to as dry weight in young leaves (16 days). The content of photosynthetic pigments decreased with leaf develop- ment, especially in plants grown under elevated CO 2 concentrations, suggesting that high CO 2 accelerates chlorophyll degradation, and also possibly leaf senescence. Elevated CO 2 concentration increased the oxidative stress in sunflower plants by increasing H 2 O 2 levels and decreasing activity of antioxidant enzymes such as catalase and ascorbate peroxidase. The loss of plant defenses probably increases the concentration of reactive oxygen species in the chloroplast, decreasing the photosynthetic pigment con- tent as a result. Elevated CO 2 concentration was found to boost photosynthetic CO 2 fixation, especially in young leaves. High CO 2 also increased the starch and soluble sugar contents (glucose and fructose) and the C/N ratio during sunflower primary leaf development. At the beginning of senescence, we observed a strong increase in the hexoses to sucrose ratio that was especially marked at high CO 2 concentration. These results indicate that elevated CO 2 concentration could promote leaf senescence in sunflower plants by affecting the soluble sugar levels, the C/N ratio and the oxidative status during leaf ontogeny. It is likely that systemic signals produced in plants grown with elevated CO 2 , lead to early senescence and a higher oxidation state of the cells of these plant leaves. © 2012 Elsevier GmbH. All rights reserved. Introduction Continuous emissions of CO 2 from the burning of fossil fuels are expected to raise global atmospheric CO 2 concentrations. Human activities not only affect CO 2 concentrations, but also alter the global nitrogen cycle by increasing the inputs of fixed forms of nitrogen, mainly through extensive use of chemical fertilizers. The Intergovernmental Panel on Climate Change (IPCC) has predicted that the CO 2 concentration may increase by 660–790 L L -1 from 2060 to 2090 (IPCC, 2007). This is expected to raise global temper- atures due to the CO 2 capacity to absorb infrared light (Schneider, 1989; Taylor and MacCracken, 1990). Therefore, continuous emis- sions of this gas at high levels are believed to cause climate change. One of the most obvious effects of climate change is its effect Abbreviations: APX, ascorbate peroxidase; DW, dry weight; ROS, reactive oxygen species; RuBP, ribulose-1,5-bisphosphate; rubisco, ribulose-1,5-bisphophate car- boxylase/oxygenase; SLM, specific leaf mass; XET, xyloglucan endotransglycosidase. ∗ Corresponding author. Tel.: +34 957218367; fax: +34 957211069. E-mail addresses: b42matsl@uco.es (L. de la Mata), bv1cahap@uco.es (P. Cabello), bv1hahep@uco.es (P. de la Haba), vg1agbue@uco.es (E. Agüera). on living beings, especially on plants, which have been found to exhibit alterations potentially affecting some steps of their growth cycle. Studies on various plant species have suggested that climate changes will affect the development, growth and productivity of plants through alterations in their biochemical, physiological and morphogenetic processes (Bazzaz and Fajer, 1992). Senescence is a stage of the plant growth cycle that involves strong metabolic and structural changes. Markers associated with leaf senescence in sunflower plants have shown that senescence initiates and progresses in primary leaves aged between 28 and 42 days (Cabello et al., 2006). Senescence typically involves ces- sation of photosynthesis and degeneration of cellular structures, with strong losses of chlorophyll (Ougham et al., 2008), carotenoids and proteins and a great increase of lipid peroxidation (Srivalli and Khanna-Chopra, 2004; Agüera et al., 2010). Senescence is not only a degenerative process, but also a recycling process by which nutrients are translocated from senescing cells to young leaves, developing seeds or storage tissues (Gan and Amasino, 1997). Leaf senescence is therefore an active, highly regulated and pro- grammed degeneration process, required for plant survival and controlled by multiple developmental and environmental signals (Lim et al., 2003). Senescence induction and development are both 0176-1617/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.jplph.2012.05.024