Agriculture Reference
In-Depth Information
various metabolic processes e.g. the induction of a bypass pathway of glycolysis
and mitochondrial electron transport to replace ATP as an energy resource
(Theodorou and Plaxton
1993
; Duff et al.
1989
). All these metabolic changes
contribute to a better internal P utilisation when P
i
is limiting.
The genetic background for these responses and their potential as targets for crop
genetic improvement based on studies with model plants will be described below.
Efficient Phosphate Nutrition in Model Plants
Phosphate acquisition and use efficiency (PAE, PUE) represent capabilities to cope
with either P limiting conditions or growth maintenance under P deficiency stress,
utilising morphological, biochemical and molecular changes without sacrificing
yields (Chiou and Lin
2011
). The P
i
-starvation adaptation response (PSR)
consisting of the regulation or coordination of the P
i
-starvation inducible genes
(PSI) in order to maintain P homeostasis has been investigated predominantly in the
model plant
Arabidopsis thaliana
, in white lupine, in rice and in maize using
forward (mutants) and reverse genetic approaches (Alexova and Millar
2013
;
Calder´n-V´zquez et al.
2008
; Li et al.
2010
; Nilsson et al.
2007
,
2010
; Bustos
et al.
2010
; Oono et al.
2011
; Uhde-Stone et al.
2003
; Rubio et al.
2001
; Aung
et al.
2006
;S
´
nchez-Calder
´
n et al.
2006
; Franco-Zorrilla et al.
2007
; Miura
et al.
2011
; Shin et al.
2006
; Duan et al.
2008
).
PSI genes and enzymes, which are induced or suppressed at the molecular level,
and commonly used as markers for monitoring PSR, are described below. Bio-
chemical and morphological changes have been elucidated to a much larger extent,
whereas information on phosphate sensing and signal transmission is more limited
(Chiou and Lin
2011
). Nonetheless, the lack of studies investigating genotypic
variation in a broad spectrum of cultivars makes it difficult to draw conclusion for
enhancing PUE in crops (Alexova and Millar
2013
; Calder´n-V´zquez et al.
2011
;
Veneklaas et al.
2012
).
Root Morphology
Among common responses to P starvation are changes in root morphology such as
increasing root hair density, reduction of primary root growth and promoted lateral
root initiation, which are well described in
Arabidopsis
(Williamson et al.
2001
;
L´pez-Bucio et al. 2000; S´nchez-Calder´n et al.
2006
) and have been recently
studied in cereals (Hochholdinger and Zimmermann
2008
). For instance, a root-
hairless mutant of
Arabidopsis
(Bates and Lynch
2001
) and a barley root-hair-
deficient mutant (Gahoonia et al.
2001
) grew poorly under low P
i
. The root cap is
the site of sensing local P
i
concentrations initiating spatial changes, comprising
inhibition of cell division activity of primary meristematic cells and root cell
