Year: 2009
Type: dissertation
Abstract: Phosphate is an essential nutrient. In most soils it is limiting, which has resulted\nin that phosphate is supplied as fertilizer to increase crop yield. Through\nevolution, plants have adapted several mechanisms to increase phosphate\nuptake from the soil and to household with acquired phosphate. A recent\ndiscovered house-holding mechanism is that plants utilize the phosphate bound\nin the headgroups of phospholipids: under phosphate-limiting conditions,\nphospholipids can be replaced by the non-phosphate containing lipid\ndigalactosyldiacylglycerol (DGDG), previously assumed to reside in plastid\nmembranes. The extra-plastidial phospholipid-to-DGDG replacement occurs in\nplasma membrane, tonoplast and mitochondria and has led to discoveries of\nnew enzymes and metabolic pathways in plants.\nThis thesis reports that phosphate limitation-induced biochemical and lipid\ncompositional changes in oat root plasma membranes occur prior to any\nmorphological changes in the oat. The phospholipase kinetics suggests that the\nplasma membrane is continuously supplied with phospholipids and that the\nproducts of plasma membrane lipase activities, phosphatidic acid and\ndiacylglycerol, both are removed from the membrane. Furthermore, the\nphospholipid-to-DGDG replacement is reversible and when phosphate is\nresupplied the proportion of phospholipids increases and DGDG decreases in the\noat root plasma membrane.\nMembrane lipids are more than a two dimensional liquid where membrane\nproteins reside. The specific lipid composition and distribution enables the\nmembrane to function as a barrier to solutes and the interactions between lipids\nand proteins are important for the correct function. The lateral and transversal\nlipid distribution in oat root plasma membranes shows that DGDG does not\nreplace phospholipids molecule for molecule; whereas phospholipids occur in\nboth leaflets of the plasma membrane, DGDG is almost exclusively localized in\nthe cytosolic leaflet. Model membrane studies suggests that one of the reasons\nthat DGDG is absent in the apoplastic leaflet is its incompatibility to properly\ninteract with the high sterol content of this leaflet.\nThe oat seed contains enough phosphate to complete an entire generation\nwithout any exogenously supplied phosphate. The overall seed yield is much\nlower in phosphate-limited oat compared to fully fertilized oat, but the seed\nquality (starch, [beta]-glucan, lipid, soluble protein) is very similar, including that the\nphospholipids-to-DGDG replacement is absent from the mature oat seeds, here\nmembrane lipid composition is conserved. Oat thus produce a few seeds of\nacceptable quality rather than more seeds of poor quality.
Author: Henrik Tjellström
Language: English
Subfield: Biochemistry
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2138184927