Journal
JOURNAL OF PLANT PHYSIOLOGY
Volume 163, Issue 10, Pages 1061-1070Publisher
ELSEVIER GMBH, URBAN & FISCHER VERLAG
DOI: 10.1016/j.jplph.2005.10.012
Keywords
asparagine synthetase; germination; natural senescence; nitrogen mobilization
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Sunflower (Helianthus annuus) contains three active asparagine synthetase (EC 6.3.5.4, AS) genes: HAS1, HAS1.1 and HAS2. Asparagine content and AS gene expression were determined during germination and leaf and cotyledon natural senescence to assess the rote of asparagine as well as the extent of participation of each AS gene in different nitrogen mobilizing processes. Asparagine accumulated in the dry seed and was the predominant amide throughout germination. During cotyledon senescence, the asparagine level was slightly higher than that of glutamine. The opposite was true for leaf senescence. According to transcript accumulation data, most of the asparagine newly synthesized for germination and cotyledon expansion was due to HAS2 activity, with little contribution of the other AS genes. However, all three genes work together to synthesize asparagine for leaf senescence. The absence of significant AS gene expression in cotyledon senescence differentiates leaf and cotyledon senescence, and suggests a cotyledon-specific regulation. (c) 2005 Elsevier GrnbH. All rights reserved.
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