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What do seeds store?
Carbohydrates STORED RESERVES Proteins Lipids IN SEED Other protective or metabolically important compounds Phytate or phytic acid Tannins Cork, mucilage, alkaloids Hormones, vitamins
Environmental effects
Soil fertility – seed size and weight.
Water availability –during flowering and seed fill decrease seed size. Early plant development - seed number
Maternal growth environment and seed reserves
http://financialpress.com/2012/08/05/congre ss-leaves-farmers-ranchers-high-and-dry/
Phases of Seed Development and Maturation Environmental effects
Seed depends on plant + environment Temperature – high temperatures during seed fill tend to reduce seed size and seed germination (Gibson and Mullen, 1996; Egli et al., 2005).
Light – in general, reduced light results in smaller Seed moisture & quality depends on seeds environment Position in the plant – related to sink- source effect and competition for limiting photosynthesis
Pollination & fertilization
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Substrates needed by the seed
A source of carbon for metabolic energy and synthesis of sugars and starch
A source of nitrogen for synthesis of amino acids
Other elements (potassium, calcium, phosphorus, etc.)
CARBOHYDRATES
• Cereal grain: only 15 – 20 % from carbohydrates stored in vegetative parts of the plant (pre-anthesis)
Where does the required C • 85 to 90% of C originates in current for seed filling comes from? photosynthesis
Mobilization of stored carbohydrates in the plant Carbohydrates
• Seed major sink for photosynthesis products • Starch is the main polysaccharide in during grain development the plants • Longevity of vegetative and reproductive • Starch granules consist primarily of biomass are critical amylose (~30%), amylopectin (~70%), and in some cases phytoglycogen
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Floury endosperm in sorghum at physiological maturity Floury endosperm in sorghum after defoliation showing starch granules and proteins
Goggi et al., 1993 Goggi et al., 1993
Carbohydrates - Storage polysaccharides Fig. 2.Ruthenium red staining of wild-type and mutant seeds. A, Wild-type seed placed other than starch directly into stain without agitation. Two layers of mucilage are present, an outer, cloudy layer, and an inner, intensely staining layer. B, Wild- • Hemicellulose (major carbohydrate in non- type seed first shaken in water, then stained; the outer layer of mucilage is not stained. Note endospermic seeds) are deposited in the cell sharp outline to the columellae. C, mum2-1 seed stained after shaking in water. No capsule of walls mucilage is apparent and the columellae are • Mucilage – usually a seed dispersal less defined than in B. D, mum5-1 seed stained after shaking in water. Columellae are sharply mechanism recovers seed coat in buckhorn outlined and a thin layer of palely staining mucilage is apparent directly around the seed. plantain and flax, also in endosperm of E, mum5-1 seed placed directly in stain without shaking. Both inner and outer layers of mucilage legumes are present, as in A. F, Wild-type seed stained after first shaking in presence of EDTA. Only a • Pectic compounds cell wall thin layer of palely staining mucilage is visible, as in D. Scale bars = 200 μm.
Western et al., 2001
Other carbohydrates stored in seeds
• 5 to 15 % of the dry matter in pea and bean seed are stored oligosaccharides of the raffinose family • Free sugars (rarely) – sugar maple up to 11% of dry wt. of mature seed PROTEINS
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The biological role of storage . 70 % of human demand proteins is to provide carbon, for protein is met by direct nitrogen and sulphur for seedling or indirect (animal) growth consumption of seed
• Cereals: 10 – 15% of DW • Legumes: up to 40 – 50% of DW
T.B. Osborne (1924) Classification of proteins according to solubility
• Albumins, soluble in H2O
• Globulins, soluble in diluted salt solutions
• Glutelins, soluble in diluted alkali and acids solutions
• Prolamins, soluble in aqueous ethanol Figure 2.20. (A,B) Changes in the endosperm protein fractions during kernel development of normal Bomi barley (A) and the high-Iysine barley mutant Risø 1508 (B). , Albumins (plus free amino acids); *, globulins; , hordeins (prolamins); , glutelins. (C) The accumulation of vicilin (), legumin (), and albumins () in developing cotyledons of broad bean (Vicia faba). (D) Accumulation of , ', and subunits of the 7 S storage protein -conglycinin in developing soybean seeds. A and B, after Brandt (1976); C, after Manteuffel et al. (1976); and D, after Gayler and Sykes (1981).
Storage Proteins
• Usually have no enzymatic activities • Hygroscopic nature aggregate into small particles • Deposited in the cell within protein bodies surrounded by a single membrane
LIPIDS Transmission electron micrographs of protein bodies from (A) normal sorghum. Henley et al., 2010. In: Advances in Food and Nutrition Research, Volume 60 (Chapter 2).
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Lipids . 20 % of human caloric uptake in industrialized countries Contained primarily in seed (fruits like olives and avocados) comes from plant fats
Source of C during seed germination . 10% of world production is used for industrial purposes
• Higher content of unsaturated fatty acids than animal fats
Lipids Lipids
For our purpose two kinds of lipids For our purpose two kinds of lipids Storage lipids – deposited in lipid bodies – Membranes – polar with a hydrophilic and Gycerol + fatty acid an hydrophobic end
. Table 1.4. The major fatty acid composition of commercial MEMBRANE STRUCTURE- oils of various plant sources [after Weber (1980) and Miller PHOSPHOLIPID BILAYER (1931)]. Palmitic Stearic Oleic Linoleic Linolenic Species (16:0) (18:0) (18:1) (18:2) (18:3) Sunflower 6 4 26 64 0 Maize 12 2 24 61 1 Soybeans 11 3 22 54 8 Canola 5 2 55 25 12 Cotton 27 3 17 52 0 Peanut 12 2 50 31 0 Oil Palm 49 4 36 10 0 Flax - - - 77 17 Animal fat 29 13 43 10 0.5
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Phytin: source of phosphate and mineral ions • 50 – 80 % of all P in the seed is in the form of phytate • Associated with protein bodies of the aleurone layer in cereals
Phytin
http://www.biologie.uni-hamburg.de/b- online/library/webb/BOT410/Angiosperm/ Seeds/Seed-6Cereal.htm
Physiological roles of phytin
Reserve compound for inositol, phosphate, and K, Mg, Ca, Fe, Mn
Control of physiological balance of P in developing seeds and seedlings
Important for plant adaptation to the surrounding environment Tannins
Tannin Other storage materials
Deposited in the cell wall of the seed coat • Cork cell walls with suberine between the (e.g. cocoa and beans) epidermis and other tissues of the seed • Alkaloids – morphine (poppy), strychnine (nux Defends the seed from attacks by vomica), caffeine (coffee, cocoa, tea), nicotine predator by making them less digestible (tabacco) Also protects the seed against light and delays seed decomposition in the soil
Restrict germination by limiting gas flow
Poppy seed Cork Oak seed
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Hormones in the Possible role of seed hormones developing seed Seed growth and development
Accumulation of storage reserves
• ABA Storage for later use during germination • Auxin Tissues close to the developing fruit • Gibberellins • Cytokinins
Vitamins Location of reserves
Storage Chemical Common name • All vitamins and precursors are synthesized in organ plants, although the role of many is unknown Cotyledon Proteins & Pea, broad bean, dwarf Carbs bean “ Lipids & Cucumber, squash, Prot. lettuce, soybean, cabbages Endosperm Prot. & Cereals and grasses Carbs
Stylized diagram of a seed cell to Location of reserves (2) show the major components. CW: cell wall; ER: endoplasmic reticulum and associated ribosomes of rough Storage Chemical Common name ER; G: Golgi apparatus; L: lipid organ bodies; M; mitochondrion; MB: microbodies or glyoxysomes; ML: middle lamella; N: nucleus Perispem mannans coffee containing dense nucleoliand disperse DNA chromatin ( c ); P: plastid; PD: plasmodesmata; R: Endosperm “ Fenugreek, caraway ribosomes; V: Vacuole (some store proteins, phytin, organic acids, phenolics, sugars, amino acids and hormones). From: Black, M., J.D. “ Lipids & Yucca Bewley and P. Halmer. Ed. 2006. Prot. The encyclopedia of seeds. CABI, Cambridge, MA.
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Figure 2,27, The synthesis of storage proteins and their sequestering within the vacuole/protein body, as occurs typically in the storage parenchyma cells of the cotyledons of legume seeds. ER, endoplasmic reticulum; G, Golgi apparatus; Gv, Golgi- derived vesicle; M, mitochondrion; N, nucleus; Nu, nucleolus; PI, plastid; V, vacuole. After Bewley and Greenwood (1990). From: Bewley, J.D. and M. Black. 1994. Seeds: physiology of development and germination, 2nd ed. pp. 79. Plenum Press, NY.
References
•Bewley, J.D. and M. Black. 1994. Seeds: physiology of development and germination, 2nd ed. Plenum Press, NY. •Egli, D.B., D. M. TeKrony, J. J. Heitholt, and J. Rupe.2005. Air temperature during seed filling and soybean seed germination and vigor. Crop Sci. 45:1329–1335. •Heldt, Hans W. 1997. Plant biochemistry & molecular biology. Oxford University Press. •Gibson, L. R. and R. E. Mullen. 1996. Soybean seed quality reductions by high day and night temperature. Crop Sci. 36:1615-1619. •Goggi, A.S., J.C. Delouche, and L.M. Gourley. 1993. Sorghum [Sorghum bicolor (L.) Moench] seed inernal morphology related to seed specific gravity, weathering, and immaturity. J. of Seed Techn. 17: 1-11. •Seed development and germination. 1995. Edited by J. Kiegel & G. Galili. Marcel Dekker, Inc. • Western, T. L., J. Burn, W. L. Tan, D. J. Skinner, L. Martin-McCaffrey, B.A. Moffatt, and G.W. Haughn. 2001. Isolation and Characterization of Mutants Defective in Seed Coat Mucilage Secretory Cell Development in Arabidopsis. Plant Phys.127:998–1011.
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