Sucrose regulates elongation of carrot somatic embryo radicles as a signal molecule.
Elongation of carrot somatic embryo radicles was inhibited by sucrose at or above 5% (145 mM). This effect would not be released until the sucrose concentration was lowered again. Morphological and cytological studies as well as determination of ABA content and analysis of the expression mode of a Lea gene, all point to its similarity to natural dormancy and germination of seeds. Use of monosaccharides (glucose and fructose), other disaccharide (maltose), and isomolar concentration of osmotica (mannitol and sorbitol), did not show similar regulatory effect. It is thus clear that the regulatory effect is not a result of simple osmotic stress. Hexokinase inhibitors such as glucosamine and N -acetyl-glucosamine did not exert any influence on the regulation-deregulation effects of sucrose. Mannose, which inhibits germination of Arabidopsis seeds, did not prevent carrot somatic embryo radicles from elongating. It is thus inferred that this sucrose-signaling pathway may be independent of hexokinase. As a first step to understand the molecular mechanism of this process, a carrot sucrose transporter gene ( cSUT ) expressed in the embryos and roots specifically was isolated. Studies on transformed yeast mutant with cSUT cDNA identified its sucrose transport activity. Northern hybridization and gel retardation experiment revealed that there is a marked increase in expression of cSUT at the beginning of somatic embryo germination, and this is attributed to regulation on the level of transcription. This suggested the possibility that cSUT has an important role in this sucrose signal regulation system.
Yang
Zhipan
Z
Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100080, China.
Zhang
Lei
L
Diao
Fengqiu
F
Huang
Meijuan
M
Wu
Naihu
N
D000040:Abscisic Acid / Q000378:metabolism; D000595:Amino Acid Sequence; D001483:Base Sequence; D001692:Biological Transport / Q000187:drug effects; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D018552:Daucus carota / Q000187:drug effects* / Q000196:embryology / Q000235:genetics; D004187:Disaccharides / Q000494:pharmacology; D005632:Fructose / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology; D006593:Hexokinase / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D009005:Monosaccharides / Q000494:pharmacology; D009997:Osmotic Pressure; D010940:Plant Proteins / Q000235:genetics*; D018517:Plant Roots / Q000187:drug effects* / Q000254:growth & development; D011401:Promoter Regions, Genetic / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D017422:Sequence Analysis, DNA; D015398:Signal Transduction; D013213:Starch / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism / Q000494:pharmacology*; D013997:Time Factors
D018076:DNA, Complementary; D004187:Disaccharides; D026901:Membrane Transport Proteins; D009005:Monosaccharides; D010940:Plant Proteins; C066246:late embryogenesis abundant protein, plant; C078729:sucrose transport protein, plant; D005632:Fructose; D013395:Sucrose; D000040:Abscisic Acid; D013213:Starch; D006593:Hexokinase; D005947:Glucose