Agriculture Reference
In-Depth Information
reflects both plant age and adaptation to environment (
e.g.
light intensity, photo-
period, temperature and nutrient availability). The approach based on natural
variation aims to use naturally occurring differences to improve our knowledge
about complex physiological responses of plants to their environment, including
nutrition efficiency.
Plant morphology and physiology are complex quantitative traits, implying that
they are genetically controlled but also influenced by the environment. The mea-
surements of such traits show differences of averages between genotypes as well as
variations due to chance and technical inaccuracies. Therefore, the investigation of
such complex traits needs statistical tools for taking into account fluctuations due to
chance in order to correctly understand the genetics behind them.
Investigation of natural variation is of interest from two general points of view.
First, analysing this variation makes it possible to identify the function of individual
genes. Despite the fact that mutant approaches have been very powerful for
functional analysis, the small number of genetic backgrounds analysed limits the
definition of gene functions using these procedures. Ultimately, the sort of mutant
phenotypes that can be identified depends on the wild type genotype (Koornneef
et al.
2004
). There are specific alleles in nature that would not be easily recognised
in mutant screens because they require very specific amino acid changes and
therefore appear at an extremely low frequency (El-Din El-Assal et al.
2001
).
Second, analysis of natural variation has an increasing interest from an ecological
and evolutionary perspective since diversity of physiologies and evolved responses
in nature result from millions of generations of evolution (Ungerer et al.
2008
).
While much has been learned from bringing organisms into the laboratory to study
elements of their biology in isolation, ignoring the ecological context in which these
elements arose and persist runs the risk of a suboptimal understanding of particular
biological responses and processes. Thus, the patterns of phenotypic and molecular
variation observed are analysed to elucidate the mechanisms generating and
maintaining this variation, and to identify which allelic variants are adaptive
under specific environmental conditions.
Several recent papers demonstrated that natural variation exists for the different
steps of plant nutrition: nutrient uptake and roots to shoot translocation, their
assimilation in leaves, as well as their recycling and remobilisation for seed filling.
The uptake efficiency is dependent on the root system architecture (Dunbabin
et al.
2004
), and specific software have been developed for analysis (Armengaud
et al.
2009
; Ristova et al.
2013
; Galkovskyi et al.
2012
). It has long been known that
root architecture and plasticity reveal a response of plants to scarce nutrients, and
natural variation exists for these traits in different species, related to potassium
(Kellermeier et al.
2013
; Jia et al.
2008
), nitrogen (De Pessemier et al.
2013
), and
phosphorus availability (Wang et al.
2010
). Natural variation for NUpE has been
shown directly by measuring a specific mineral content in different genotypes, as
Burns et al. demonstrated for nitrate in different varieties of lettuce. Otherwise, a
complementary approach aimed at studying the activity of enzymes involved in
mineral assimilation in roots can be used. For example, Blair et al. (
2010
) identified
important differences between varieties of beans for their ability to reduce iron
