Journal of Experimental Botany 61: 491-502 (2010)

Peroxidases identified in a subtractive cDNA library approach show tissue-specific transcript abundance and enzyme activity during seed germination of Lepidium sativum ^[W][OA]

Abstract
The micropylar endosperm is a major regulator of seed germination in endospermic species, to which the close Brassicaceae relatives Arabidopsis thaliana and Lepidium sativum (cress) belong. Cress seeds are about twenty times larger than the seeds of Arabidopsis. We used this advantage to construct a tissue-specific subtractive cDNA library of transcripts that are up-regulated late in the germination process specifically in the micropylar endosperm of cress seeds. The library showed that a number of transcripts known to be upregulated late during germination are upregulated in the micropylar endosperm cap. Detailed germination kinetics of SALKlines carrying insertions in genes present in our library showed that the identified transcripts indeed play roles during germination. Three peroxidases were present in the library. We identified these peroxidases as orthologues of Arabidopsis AtAPX01, AtPrx16 and AtPrxIIE. The corresponding SALKlines displayed significant germination phenotypes. We quantified their transcripts in specific cress seed tissues during germination in the presence and absence of ABA and found them to be regulated in a tissue-specific manner. Peroxidase activity and particul

arly its regulation by ABA also differed between radicles and micropylar endosperm caps. Possible implications of this tissue-specificity are discussed.

Key words: Arabidopsis thaliana, cress (Lepidium sativum), micropylar endosperm cap, peroxidases, seed germination, subtractive cDNA library

Financial support: Our work is funded by grants of the Deutsche Forschungsgemeinschaft (grant no. DFG LE720/6) to G.L.-M., which is gratefully acknowledged.