Metabolism and composition of barley aleurone phosphatidic acid in response to hormonal treatment

VILLASUSO AL; DI PALMA MA; AVELDAÑO M; PASQUARE SJ; RACAGNI GE; GIUSTO NM; MACHADO EE

Mendoza

Congreso; XLVII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2012

Phosphatidic acid (PA) is a lipid signalling and intermediary in abscisic acid (ABA) signalling. ABA plays an important role in seed germination by inhibiting GA response in aleurone. By using aleurone 32P-Glycerophospholipids (GPL) as substrates, an active phospholipase D (PLD) was present. This PLD produced 32P-PA rapidly (min) in the presence of ABA, and transiently, indicating rapid PA removal after generation. The PA removal by phosphatase 1 and 2 isoforms was verified in aleurone membranes, the former but not the latter being specifically responsive to GA/ABA. In contrast to PA kinase, which down-regulates PA levels by GA/ABA-dependent phosphorylation to DGPP, DGPP phosphatase was unmodified. A high long-term 32P PA/PC labeling ratio after long-term (hs) incubations of aleurone layers in the absence of GA or ABA suggested that PLD targeted part of the synthesized 32P-PC. The lipid and fatty acid composition of unlabeled aleurone confirmed this. A marked accumulation of PA, highly enriched in 18:2n-6, concurred with a relatively low amount of GPL, especially low amounts of 18:2n-6-rich species of PC. The PC/PA ratio was maintained high after incubations in the presence of GA/ABA. Somewhat less GPL including 18:2-PC were formed with ABA than with GA because with ABA but not with GA part of the 18:2-PA was converted to 18:2-DGPP by ABA-responsive PA kinase.