Germination and storage reserve mobilization are regulated independently in Arabidopsis.
The phytohormone abscisic acid (ABA) inhibits the germination of many seeds, including Arabidopsis, but the mechanism for this is not known. In cereals, ABA inhibits the expression of genes involved in storage reserve mobilization. We have found that in Arabidopsis ABA decreases transcription from the promoters of marker genes for beta-oxidation and the glyoxylate cycle, essential pathways for the conversion of storage lipid (triacylglycerol) into sucrose. Thirty per cent of stored lipid is broken down over 6 days following imbibition of ABA-treated seed. Sucrose levels in ABA-treated seeds, rather than decreasing as under normal growth conditions, actually double during the 3 days following imbibition. This sucrose is derived from triacylglycerol as demonstrated by two mutants disrupted in the conversion of triacylglycerol into sucrose, kat2 and icl1, which do not accumulate sucrose in the presence of ABA. We conclude that the ABA block on germination is not a consequence of inhibition of storage lipid mobilization. Two independent programmes appear to operate, one that is blocked by ABA, governing developmental growth resulting in germination; and a second that governs storage lipid mobilization which is largely ABA-independent.
Centre for Novel Agricultural Products, Department of Biology, University of York, Heslington, York YO10 5YW, UK.
Sarah L
SL
Pritchard
Wayne L
WL
Charlton
Alison
A
Baker
Ian A
IA
Graham
D000040:Abscisic Acid / Q000494:pharmacology; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018525:Germination / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D006038:Glyoxylates / Q000037:antagonists & inhibitors / Q000378:metabolism; D050356:Lipid Metabolism; D009154:Mutation; D012639:Seeds / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism
D006038:Glyoxylates; D014280:Triglycerides; D013395:Sucrose; D000040:Abscisic Acid; C031150:glyoxylic acid