seed development stages

Seed development and maturation

Sunil Kumar

Published on Sep 19, 2014

Seed development, seed maturation, endosperm development,

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  1. 1. Embryo and Endosperm development BY MEDIDA SUNIL KUMAR PH. D FIRST YEAR DEPT. OF AGORONOMY LEC: 3
  2. 2. Female gametophyte development
  3. 3. Male gametophyte development
  4. 4. Angiosperm Double Fertilization
  5. 5. Overview of plant embryogenesis Abbreviations: T, Terminal cell; B, Basal cell; EP, Embryo Proper; S, Suspensor; Bc, Suspensor Basal Cell; Pd, Protoderm; u, Upper Tier; I, Lower Tier; Hs, Hypophysis; Pc, Procambium; Gm, Ground Meristem; C, Cotyledon; A, Axis; MPE, Micropylar end; CE, Chalazal End; SC, Seed Coat; En, Endosperm; SM, Shoot Meristem; & RM, Root Meristem.
  6. 6. Types of embryogeny Based on the type of divisions pro-embryos are classified as • Crucifer • Asterad • Solanad • Caryophyllad • Chenopodiad • Piperad
  7. 7. Polyembryony Polyembryony is the phenomenon of two or more embryos developing from a single fertilized egg Types of Polyembryony: 1. Simple Polyembryony: More than one egg cells get fertilized. Eg: Brassica 2. Mixed Polyembryony: When more than one pollen tube enters into an embryo sac and extra-male gametes fuse with synnergids or antipodal cells. Eg: Allium 3. Adventives Polyembryony: Sometimes, the diploid nucellar or integumentary cells may develop additional embryos. Eg: Citrus 4. Cleavage Polyembryony: Occurs due to cleavage of the embryos as in the case of the Orchids
  8. 8. Endosperm development • Endosperm is the nutritive tissue formed as a result of triple fusion in the angiosperms. • Endosperm formation starts prior to embryo formation. • Reaches its maximum morphological development at physiological maturity Based on the mode of development of endosperms:  Nuclear  Cellular  Helobial
  9. 9. Nuclear endosperm Primary endosperm nucleus divides repeatedly to form a large number of free nuclei. No cell plate formation takes place at this stage and a central vacuole appears later.  It is followed by cell plate formation which is centripetal.  It is the most common type of endosperm e.g., Cotton, Maize, Capsella, Coconut (milk), wheat, etc .
  10. 10. Cellular endosperm  Cell wall formation occurs immediately after division  Subsequent divisions also accompanied by cell plate formation.  As a result, the endosperm becomes cellular from the beginning.  Eg: – Balsam, Petunia, barley, grasses, Petunia, Utricularia, Coconut (copra).
  11. 11. Helobial endosperm Intermediate above two type e.g., members of order helobiales (Monocot) First division is cellular (i.e., wall formation follows the first division) However, inside each of these newly formed cells, free nuclear divisions occur. But finally, the endosperm becomes cellular following the pattern of development of nuclear endosperms.
  12. 12. Perisperm • The nucellus is the central portion of the ovule inside the integuments. • After fertilization, the nucellus may develop into the perisperm that feeds the embryo. • An integument is a protective cell layer surrounding the ovule. • Gymnosperms typically have one integument (unitegmic) while angiosperms typically have two (bitegmic). • The inner integument has been proposed to have formed from sterile branches surrounding a terminal mega sporangium. • The integuments develop into the seed coat when the ovule matures after fertilization.
  13. 13. Seed coat • Primine Testa (external) • Secundine Tegma (inner) Functions of seed coat: • Protection against action of biotic and abiotic factors • Regulation of water and gaseous exchange • Regulation of germination and dormancy mechanisms • Control of seed dispersion: wings, hairs, mucilages, etc • The integuments do not enclose the nucellus completely but leave an opening at its apex referred to as the micropyle. • The micropyle opening allows pollen to enter the ovule for fertilization. • Located opposite from the micropyle is the Chalaza where the nucellus is joined to the integuments. • Nutrients from the plant travel through the phloem of the vascular system to the funiculus and outer integument and from there apoplastically and symplatically through the chalaza to the nucellus inside the ovule. • In chalazogamous plants, the pollen tubes enter the ovule through the chalaza instead of the micropyle opening.
  14. 14. Stages of seed development • Histo differentiation: – Cell division • Seed expansion (maturation): – Genes for synthesis of reserves are expressed, deposition of reserves. • Maturation (drying) / desiccation: – Water loss, embryo becomes quiescent state (metabolically inactive).
  15. 15. Key Processes During Seed Maturation  Accumulation of food reserves  Hardening of seed coat & accumulation of antimicrobial compounds  Mechanisms of seed dispersal – flyers  Synthesis of protective compounds that allow the seed to withstand some degree of water loss and adverse environmental conditions. Eg. antioxidants, antimicrobial, resistance to pathogens.  Dormancy: – can happen for many years, needs signals or conditions to break the dormancy (eg. conifers at moist and low temperatures) or smoke
  16. 16. Longitudinal sections through ripe seeds
  17. 17. Phases in Seed Development • Phase I – Cell Division • Phase II – Expansion of the cell • Phase III – Accumulation of Dry mass • Phase IV – Seed Moisture loss
  19. 19. Environmental factors effecting Seed Development Decline in seed number  Seed weight  Physiological potentiality Degree of damage depends on  Stage of stress occurrence  Type of stress  Intensity of stress  Duration of stress
  20. 20. Components of Environment  Soil Fertility  Water  Temperature  Light  Seed position on the plant
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Seed development, seed maturation, endosperm development,

Seed development stages

Biology of a process

The majority of higher plants derive energy for growth and development solely from photosynthesis (autotrophic nutrition). However, each plant undergoes in its ontogenesis a short but important stage of heterotrophic nutrition. The germinating embryo prior appearance of the first photosynthetic structures is fed exclusively by storages accumulated during the seed formation (i.e., proteins, fats, and carbohydrates) [West M.A.L. and Harada J.J. 1993, Shewry P.R., 1995]. As is well known, the main function of a plant seed is to provide a viable offspring. The storage substances play a key role, by providing nutrition of a seedling during the heterotrophic stages of its development. Seed formation passes several overlapping but rather independent stages. Before the beginning of flowering, an embryonic structures are formed out of apical meristem. The switch from the vegetative stage of development to the reproductive one is regulated by different mechanisms. Among these mechanisms are inner biological clock, hormonal background, and environmental conditions such as a day length, temperature fluctuations, humidity, etc.

1. At the first stage, a pollination followed by fertilization occur.
2. The second stage is characterized by establishment of a general composition of the future plant. Embryonic tissues (protoderm, procambium, ground meristem) are being differentiated. The axis of development of an embryo is being formed, with apical meristem of a root from one side and apical meristem of a stem – from the other.
3. At the following stage, storage substances are being intensively worked out, these substances will be necessary at subsequent stages, during seed germination.
4. Seed development is finished by preparation of a seed to the dormancy stage and final maturation at the dormancy stage.
5. Dormancy stage.

Seed development stages Biology of a process The majority of higher plants derive energy for growth and development solely from photosynthesis (autotrophic nutrition). However, each plant