seed physiology - reserve synthesis and deposition

protein, carbohydrates, oil

endosperm and cotyledons store mostly carbs and proteins, oil found in canola, pine

sucrose transfers from parent to seed via phloem

--------- PROTEINS eg. legumes ------------
Classification of seed storage proteins
Protein Type Solubility Characterisitic
Albumins 2S Water or dilute buffers at neutral pH
Globulins 7S Vicilins Salt solutions
11S Legumins / Glycinin?
12s Glycinin
Prolamins Aqueous alcohols (70-90%)
Glutelins Dilute acid or alkaline solutions

5'upstream - promoters, transcription control, enhancers
5'utr - indicate translation, untranslated region
coding region - exon/intron
3'utr - poly-A tail, stability

storage protein in peas - **vicilin, convicilin, *legumin, albumin

legumins - hexamer, 40 and 20kda

analyzing expression
dna (genomic southern blot), mrna (northern blot), protein and protein post-processing (western blot)

synthesis and processing of soybean glycinin


1. transcription in nucleus
2. translation of mrna in cytosol (cytoplasm matrix)
3. synthesis in the ER (preprolegumin - has signal),
4. then signal is cleaved (prolegumin) forms disulfide bond to form trimer
5. transport from golgi to protein body (e.g. vacuole - needs vacuolar targeting signals) to become hexamer (holoprotein) to become legumin
6. proteolytic cleave of proteins happen in vacuoles

parenchyma cells of cotyledons gets packed with protein bodies/protein storage vacuoles (PSV) (needs vacuolar targeting signals) (in dicots - storage is in vacuoles, in cereals - storage in rough ER)

default pathway is secretion, unless there's a vacuolar targeting signal, then it goes to vacuoles

3 types of targeting signals: continuous at N or C termini, discontinous signal patches, non-specific aggregation

--------- OILS eg, canola ------------
TAG(triacylglycerols) comprise the storage lipids of seeds (eg. canola, castor bean) and are accumulated in the oil body interior

oil bodies - half-unit membrane (one layer) that buds off from ER membrane bilayer

roles of oleosin:
1. maintain integrity of oil bodies during seed dessication (drying)
2. docking site for lipases that breaks down TAGs

central domain is highly conserved and important for targeting the protein to oil body membrane


---------- STARCH eg. maize/corn ------------
3 major enzymes in starch synthesis
1. ADP glucose pyrophosphorylase (ADPGlcPPase) - forms ADP-glucose
2. Starch synthase (SS) - connects ADP-glucose to the long alpha-1,4-glucan primer
3. Starch branching E (SBE) - moves alpha-1,4-glucan to another one via alpha-1,6 linkage