Stages of seed development
- 7. SEED DEVELOPMENT • The Integument of the ovule – seed coat • Nucellus – absorbed and absent • Endosperm Monocot : Max morphological development Dicot : Used up by the developing embryo.
- 8. EMBRYO DEVELOPMENT • The first few cell division from the zygote forms the Pro-embryo. Although the mature embryo of monocotyledons and dicotyledons appears considerably different, their pattern of embryogeny are similar.
- 9. • The Pro-embryo is divided into Suspensor and Embryo proper. • The suspensor forms into a chain of cells, pushing the embryo proper into the center of the ovule thus making it in contact with the available food supply
- 11. ENDOSPERM DEVELOPMENT • Endosperm formation starts prior to embryo formation. • Reaches its maximum morphological development at physiological maturity.
- 12. • There are 3 types of endosperm development (a) nuclear - where the endosperm nucleus undergoes several divisions prior to cell wall formation, e.g., wheat apple, squash. (b) cellular - in which there is no free nuclear phase
- 13. (c) helobial - where the free nuclear division is preceded, and is followed by cellularization as in some monocots
- 14. SEED GROWTH & MATURATION • The seed is said to have physiologically matured only when it attains maximum dry weight, germinability and vigour. • Normally the seed is harvested at field maturity, a stage when the moisture content is reduced to about 6-10 % in wheat.
- 15. PHYSIOLOGICAL CHANGES • Water uptake • Respiration • Mobilization of reserve materials BIOCHEMICAL CHANGES • Nucleic acids • Proteins • Carbohydrates • Inorganic nutrients
- 16. ENVIRONMENTAL FACTORS • SOIL FERTILITY • TEMPERATURE • WATER • LIGHT
- 17. MATURATION & DRYING • Physiological maturity is identified as maximum seed dry matter accumulation • Physiological maturity is reached when there is no further significant increase in seed dry weight
- 18. • The first concept of physiological maturity was proposed by Shaw and Loomis in 1950 as the stage in which the seed possesses maximum dry weight and yield. • Physiological maturity has also been termed “relative maturity” by Aldrich in 1943, morphological maturity” by Anderson in 1955 while others prefer to use terms such as “harvest maturity”& “agronomic maturity”
- 19. • Probably the most accurate method of determining physiological maturity is the measurement of 14C assimilate uptake by the developing seed. This was demonstrated by TeKrony et al. (1979) • Finally, the definition of physiological maturity based on seed maximum dry weight should be considered a reference point to characterize the end of seed development.