Involvement of nitrogen and cytokinins in photosynthetic acclimation to elevated CO2 of spring wheat

Abstract

Acclimation of photosynthetic capacity to elevated CO₂ involves a decrease of the leaf Rubisco content. In the present study, it was hypothesized that nitrogen uptake and partitioning within the leaf and among different aboveground organs affects the down-regulation of Rubisco. Given the interdependence of nitrogen and cytokinin signals at the whole plant level, it is also proposed that cytokinins affect the nitrogen economy of plants under elevated CO₂, and therefore the acclimatory responses. Spring wheat received varying levels of nitrogen and cytokinin in field chambers with ambient (370 μmol mol⁻¹) or elevated (700 μmol mol⁻¹) atmospheric CO₂. Gas exchange, Rubisco, soluble protein and nitrogen contents were determined in the top three leaves in the canopy, together with total nitrogen contents per shoot. Growth in elevated CO₂ induced decreases in photosynthetic capacity only when nitrogen supply was low. However, the leaf contents of Rubisco, soluble protein and total nitrogen on an area basis declined in elevated CO₂ regardless of nitrogen supply. Total nitrogen in the shoot was no lower in elevated than ambient CO₂, but the fraction of this nitrogen located in flag and penultimate leaves was lower in elevated CO₂. Decreased Rubisco: chlorophyll ratios accompanied losses of leaf Rubisco with CO₂ enrichment. Cytokinin applications increased nitrogen content in all leaves and nitrogen allocation to senescing leaves, but decreased Rubisco contents in flag leaves at anthesis and in all leaves 20 days later, together with the amount of Rubisco relative to soluble protein in all leaves at both growth stages. The results suggest that down regulation of Rubisco in leaves at elevated CO₂ is linked with decreased allocation of nitrogen to the younger leaves and that cytokinins cause a fractional decrease of Rubisco and therefore do not alleviate acclimation to elevated CO₂.

Influence of root-bed size on the response of tobacco to elevated CO2 as mediated by cytokinins

“…Under that condition, the observed C/N ratios are understandable by assuming carbon limitation of growth under ambient CO 2 and nitrogen limitation under enhanced CO 2 . Similar effects have been reported for a variety of other plant species (Yin 2002; for a review, see Taub and Wang 2008), and in more detail recently for wheat (Gutiérrez et al 2013; Wang et al 2013). Leaves of tobacco plants grown under high CO 2 were consistently bigger than corresponding leaves of plants growing at ambient CO 2 (Table 1), and if nutrient uptake by the roots does not match plant growth a reduced nutrient content must result.…”

Nitrate supply and plant development influence nitrogen uptake and allocation under elevated CO2 in durum wheat grown hydroponically

“…2). In contrast, CO 2 enrichment decreased N allocation to flag leaves of wheat crops in field chambers at anthesis (Del Pozo et al 2007;Aranjuelo et al 2011;Gutiérrez et al 2013), independently on whether total aboveground plant N decreased (Del Pozo et al 2007;Bloom et al 2010;Aranjuelo et al 2011) or remained unchanged (Gutiérrez et al 2013) with elevated CO 2 . The disparity of results may be due to the increase with CO 2 in dry matter production, and presumably enhanced N sink strength of fast growing plant parts such as the last stem internode or the ear in these earlier studies.…”

Effects of pre-industrial, current and future [CO2] in traditional and modern wheat genotypes

“…Rubisco accounts 552 for more than 50% of total soluble protein and over 25% of the 553 total nitrogen of leaves (Makino et al, 1984;Hawkesford and 554 Barraclough, 2011). Therefore, plants at future [CO 2 ] had less con-555 tent in terms of Rubisco and proteins, and for the same reason, 556 plants had less N content in leaves (Gutierrez et al, 2013). At pre-557 industrial [CO 2 ], plants were seen to have more N concentration 558 (40 and 50% for Blanqueta and Sula, respectively) and lower NUE 559 (Polley et al, 1995 ; Fig.…”