Differential sensitivity of oleosins to proteolysis during oil body mobilization in sunflower seedlings.
Until now, there has been no conclusive demonstration of any in vivo oleosin degradation at the early stages of oil body mobilization. The present work on sunflower (Helianthus annuus L.) has demonstrated limited oleosin degradation during seed germination. Seedling cotyledon homogenization in Tris-urea buffer, followed by SDS-PAGE, revealed three oleosins (16, 17.5 and 20 kDa). Incubation of oil bodies with total soluble protein from 4-day-old seedlings resulted in oleosin degradation. In vitro and in vivo degradation of the 17.5-kDa oleosin was faster than the other two, indicating its greater susceptibility to proteolysis. Oleosin degradation by the total soluble protein resulted in a transient 14.5-kDa polypeptide, followed by an 11-kDa protease-protected fragment, which appeared post-germinatively and accumulated corresponding to increased rate of lipid mobilization. A 65-kDa protease, active at pH 7.5-9.5, was zymographically detected in the total soluble protein. Its activity increased along with in vivo accumulation of the protease-protected fragment during seed germination and accompanying lipid mobilization. Protease-treated oil bodies were more susceptible to maize lipase action. Differential proteolytic sensitivity of different oleosins in the oil body membranes could be a determinant of oil body longevity during seed germination.
Sadeghipour
Hamid Reza
HR
Department of Botany, University of Delhi, Delhi 110007, India.
Bhatla
Satish Chander
SC
D003624:Darkness; D010450:Endopeptidases / Q000187:drug effects / Q000378:metabolism*; D018525:Germination; D006368:Helianthus / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008053:Lipid Mobilization / Q000502:physiology*; D008623:Mercaptoethanol / Q000494:pharmacology; D010938:Plant Oils / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D012639:Seeds / Q000254:growth & development; D014357:Trypsin / Q000378:metabolism
D010938:Plant Oils; D010940:Plant Proteins; C079350:oleosin, Helianthus annuus; D008623:Mercaptoethanol; D010450:Endopeptidases; D014357:Trypsin