Abstract
BackgroundEuropean Flint maize inbred lines are used as a source of adaptation to cold in most breeding programs in Northern Europe. A deep understanding of their adaptation strategy could thus provide valuable clues for further improvement, which is required in the current context of climate change. We therefore compared six inbreds and two derived Flint x Dent hybrids for their response to one-week at low temperature (10 °C day/7 or 4 °C night) during steady-state vegetative growth.ResultsLeaf growth was arrested during chilling treatment but recovered fast upon return to warm temperature, so that no negative effect on shoot biomass was measured. Gene expression analyses of the emerging leaf in the hybrids suggest that plants maintained a ‘ready-to-grow’ state during chilling since cell cycle genes were not differentially expressed in the division zone and genes coding for expansins were on the opposite up-regulated in the elongation zone. In photosynthetic tissues, a strong reduction in PSII efficiency was measured. Chilling repressed chlorophyll biosynthesis; we detected accumulation of the precursor geranylgeranyl chlorophyll a and down-regulation of GERANYLGERANYL REDUCTASE (GGR) in mature leaf tissues. Excess light energy was mostly dissipated through fluorescence and constitutive thermal dissipation processes, rather than by light-regulated thermal dissipation. Consistently, only weak clues of xanthophyll cycle activation were found. CO2 assimilation was reduced by chilling, as well as the expression levels of genes encoding phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPDK), and the small subunit of Rubisco. Accumulation of sugars was correlated with a strong decrease of the specific leaf area (SLA).ConclusionsAltogether, our study reveals good tolerance of the photosynthetic machinery of Northern European maize to chilling and suggests that growth arrest might be their strategy for fast recovery after a mild stress.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0909-y) contains supplementary material, which is available to authorized users.
Highlights
European Flint maize inbred lines are used as a source of adaptation to cold in most breeding programs in Northern Europe
Leaf growth is suspended in cold The growth of 6 inbreds cultivated in phytotronic cabinets at 24 °C day/18 °C night was recorded by regular measurement of the decimal visible leaf (VL) stage (Fig. 1)
After return to warm conditions, growth recovered in all genotypes up to control rate level (Table 1), so that the impact of the treatment appeared as a short delay in visible leaf stage (VL)
Summary
Prominent in maize history is the early flowering Northern Flint race that adapted to cold temperate regions of Northeastern America and was introduced in Northern Europe probably at the beginning of the 16th century [1] In both American and European continents, Northern races were hybridized with late materials to produce new types adapted to mid-latitude climates, such as Corn Belt Dent in America resulting from the intercrossing between Northern Flint and Southern Dent races [2]. European Flint inbred lines provided valuable traits for regions with cool and wet spring conditions: cold tolerance, early vigor and short growing cycles [4]. Thanks to their good heterotic pattern with American Dent material, they have been widely used in Northern Europe for hybrid production [5]
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