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#plant membranes

2 public questions tagged with this topic.

Glycolipid and Phospholipid

Which lipid is absent in most prokaryotic and plant membranes?

Evolutionary lipidomics reveals sterol distribution discontinuous across domains life reflecting oxygen dependent biosynthesis pathway complexity. Eukaryotes animals synthesize cholesterol via HMGCoA reductase squalene monooxygenase epoxidase lanosterol fourteen demethylase CYP51 DHCR enzymes pathway requiring molecular oxygen maintaining thirty to forty percent plasma membrane buffering fluidity organizing rafts signaling. Fungi use ergosterol additional double bonds methyl group phytosterol plants stigmasterol sitosterol campesterol from cycloartenol SMT sterol methyltransferase modification. Most bacteria lack sterol biosynthetic enzymes squalene cyclization and sterol auxotrophy; membranes composed phosphatidylethanolamine phosphatidylglycerol cardiolipin hopanoids pentacyclic triterpenoids surrogate sterol function rigidify Methylococcus planctomycetes providing order stability. Mycoplasma pneumoniae lacking cell wall scavenges cholesterol host serum incorporating membrane requiring exogenous cholesterol growth. Sphingomyelin also predominantly animal glycosphingolipid rare prokaryotes. Therefore cholesterol truly absent most prokaryotic plant membranes explaining differential susceptibility cholesterol binding toxins perfringolysin O Streptolysin O polyenes amphotericin B selective antimicrobial strategies. Phylogeny underlies membrane evolution topics microbiology textbooks and cell biology comparisons across kingdoms for structure function diversity.

Ref: Nes WD, Chem Rev 2011, Sterol biosynthesis diversity bacterial absence cholesterol and hopanoids.

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Glycolipid and Phospholipid

Which sterol is abundant in plant membranes?

Plant membranes replace cholesterol phytosterols where stigmasterol and sitosterol are prominent structurally related functionally overlapping but distinct regulation. Both derive cycloartenol via CYP51 SMT1 SMT2 sterol methyltransferases, with sitosterol bearing twenty four alpha ethyl group dominating sixty percent free sterols stigmasterol bearing additional trans double bond C22 C23 introduced CYP710A comprising ten to thirty percent campesterol ten percent remainder. In most crops soybean Arabidopsis tomato sitosterol quantitative major but stigmasterol characteristic marker plasma membranes detergent resistant rafts showing inducible increase pathogen challenge avirulent bacteria senescence mediated PLD phospholipase D signaling and ROS tolerance membrane remodelling. Cholesterol minor less than five percent, ergosterol dominates fungi mycobacteria. Phytosterols regulate membrane order permeability ion channels H ATPase activity auxin transport PIN localization brassinosteroid precursor campesterol growth regulation. Ratio sitosterol stigmasterol modulates fluidity freezing tolerance via CBF pathway COR genes. Understanding phytosterol diversity illustrates evolutionary adaptation where cholesterol function fulfilled ethyl sterols explaining dietary plant sterol interference human cholesterol absorption via Niemann Pick C1 Like one transporter NPC1L1 competitor heart health and plant physiology cold adaptation topics in exams.

Ref: Schaller H., Plant Physiol 2003, Plant sterols stigmasterol sitosterol biosynthesis and membrane functions.

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