N form-dependent growth retardation of Arabidopsis thaliana seedlings as revealed from physiological and microarray studies

: Hoffmann A, Milde S, Desel C, Humpel A, Kaiser H, Hammes E, Piippo M, Soitamo A, Aro EM, Gerendas J, Sattelmacher B, Hansen UP

Publisher: WILEY-V C H VERLAG GMBH

: 2007

Journal of Plant Nutrition and Soil Science

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE-ZEITSCHRIFT FUR PFLANZENERNAHRUNG UND BODENKUNDE

: J PLANT NUTR SOIL SC

: 170

: 1

: 87

: 97

: 11

: 1436-8730

DOI: https://doi.org/10.1002/jpln.200625032

Ammonium (NH4+) nutrition causes retardation of growth in many plant species. In Arabidopsis grown with NH4+ as the sole N source, growth retardation occurs already at early stages before photosynthesis has come to its full power. In order to describe the peculiarities of these retarded plants, they were compared with nitrate (NO3-)-grown plants of the same age of 15 d. Photosynthetic activity as measured by CO2 uptake per unit chlorophyll is half as high in NH4+-grown seedlings as in NO3--grown ones. This finding is confirmed by the analysis of chlorophyll fluorescence. Chloroplasts of NO-grown, but not of NH4+-grown, seedlings show starch deposits after 5 h of illumination with 40 mu mol m(-2) s(-1). Gene-expression analysis based on cDNA microarray and on Northern blots provide a clue about the biochemical background. After the first 2 weeks of growth, it seems that NO3--grown seedlings subsist mainly on normal photosynthesis, whereas NH4+-grown seedlings still use lipids from the seeds stored in oleosomes. Corresponding to this observation, the mRNAs for enzymes of beta-oxidation are more strongly expressed in NH4+-grown seedlings. Different carbohydrate sources for sucrose synthesis are indicated by different gene expression. Higher gene expression of fructose bisphosphate aldolase (cytosolic isoform) in NO3--grown seedlings indicates the dependence on photosynthesis, whereas a higher gene expression of PEP carboxykinase in NH4+-grown seedlings points to a prominent role of beta-oxidation of storage lipids still present.