Agriculture Reference
In-Depth Information
a
Comparison of transcript changes during nutrient starvations
> 2-fold
< 0.5-fold
S deficiency
1602 genes
N deficiency
3084 genes
S deficiency
874 genes
N deficiency
1816 genes
942
511
2037
748
98
1085
106
430
24
43
4
609
P deficiency
1240 genes
P deficiency
814 genes
661
177
b
Senescence associated genes (SAGs)
> 2-fold
SAGs (
827
genes)
100
80
60
40
20
0
S deficiency
53 genes
N deficiency
376 genes
< 0.5
13
9
188
25
154
0.5-2
6
> 2
P deficiency
271 genes
86
SNP
Fig. 8.5 Transcriptomic responses to sulfate, nitrate and phosphate (S, N and P) deficiencies. (a)
Transcriptome data of
Arabidopsis
seedlings exposed to nitrate, phosphate and sulfate starvation
were compared. The Venn diagrams show the overlap respectively, the specificity between the
data sets in terms of genes induced or reduced by a factor of 2, respectively. The data sets were
obtained from the following publications: S, low-sulfate for 7 days + sulfate-0 mM for 2 days
(Bielecka, unpublished data); N, full nutrient for 7 days + nitrate-0 mM for 2 days (Scheible
et al.
2004
); P, low-phosphate for 7 days + phosphate-0 mM for 1 day (Morcuende et al.
2007
). (b)
Nutrient starvation induces senescence related responses (NuDIS) and the changes of the
subfraction of senescence-associated genes (SAGs) are displayed. The percentage of SAGs
(total 827 genes) with
0.5-fold changes is calculated (Buchanan-Wollaston
et al.
2003
). The Venn diagram shows the overlap in SAGs between data sets, sulfate, nitrate
and phosphate deficiencies at a threshold of
2-fold and
>
<
2-fold. This depicts partial communalities between
the responses recruiting shared response mechanisms
>
consequences of the observed responses to nutrient deficiency are far from under-
stood. Under all three nutrient starvation conditions genes involved in the light
reactions, the Calvin-Benson cycle and photorespiration are downregulated. This
provides molecular support of previous findings on the effect of nutrient starvation
on photosynthesis. Nutrients are direct constituents of the photosynthetic apparatus,
such as N and S in protein and N and Mg in chlorophyll, which result in the fact that
24 % of leaf total N is located in the thylakoid membranes (Terashima and Evans
1988
). Fe and S are part of the iron-sulfur clusters of the photosynthetic machinery.
P is obviously an essential part of photosynthetic reactions due to the centrality of
energy-rich, phosphate-containing organic compounds (ATP, sugar phosphates). In
addition to direct involvement in photosynthesis and carbohydrate synthesis, nutri-
ent depletion usually results in retarded growth because carbohydrate backbones
cannot be utilised for the biosynthesis of amino acids and proteins, vitamins and
cofactors or energy-rich compounds containing P such as ATP (Hawkesford
2000
,
