01 Reproduction in Lower and Higher Plants - part 10 - Seed and Fruit Development

01 Reproduction in Lower and Higher Plants - part 10 - Seed and Fruit Development


Seed and Fruit Development : 
  • The goal of reproduction, in every living organisms including plants, is to create offsprings for the next generation. 
  • One of the ways that plants can produce offpsrings is by forming (making) seeds. 
  • The flowers must be pollinated in order to produce seeds and fruit. Seed development is initiated by fertilization. 
  • The integuments of the fertilized ovulepersist and get transformed into the seed coat of mature seed.
  • Seed sometimes consists of two distinct coverings, a typical outer seed coat, the testa and the inner thin, membranous tegmen. 
  • The nucellus in the ovule may persist in some genera like black pepper and beet as a thin, papery layer, the perisperm. 
  • In some seeds, the food reserves in the endosperm are partially used up in the development of an embryo. 
  • Obviously, in such seeds the endosperm remains conspicuous and fills a greater part of the seed. 
  • Thus, the resultant seed is endospermic or albuminous e.g. Castor, Coconut, Maize, etc. 
  • In other seeds, embryo absorbs food reserve from the endosperm completely during its developmental stages. 
  • Thus, endosperm disappears (disorganizes) in mature seeds. 
  • The resultant seed is non-endospermic or exalbuminous e.g.Pea, bean, etc. 
  • The cotyledons in some non-endospermic seeds act as a food storage and in others they are the first photosynthetic organs. 
  • Micropyle persists as a small pore in seed coat to allow the entry of water and oxygen during soaking. 
  • Fruit development is triggered by hormones produced by developing seeds. 
  • As mentioned earlier, after fertilization the zygote is formed and the ovary begins to differentiate into the fruit and ovary wall develops into pericarp. 
  • Pericarp is basically three layered which get differentiated in the fleshy fruit like mango, coconut, etc.
 Significance of seed and fruit formation : · 
  • Fruits provide nourishment to the developing seeds.
  • Fruits protect the seeds in immature condition. 
  • Seeds serve as important propagating organs (units) of plant. 
  • Seeds and fruits develop special devices for their dispersal and thus help in the distribution of the species
Dormancy  : 
  • It is a state of metabolic arrest that facillitates the survival of organisms during adverse environmental conditions. 
  • Structural or physiological adaptive mechanism for survival is called dormancy. 
  • Mature and viable seeds will not germinate even in the presence of favourable conditions and they are dispersed at different places during dormancy. 
  • Viable seeds germinate only after completion of dormancy period.
  • Some examples of oldest mature seeds that have grown into viable plants are as follows : 
  1. Lupinus arcticus - 10,000 years 
  2. Phoenix dactylifera - 2000 years 
  • Some seeds are short lived, e.g. Citrus. 
  • Some tiny seeds are easy for dispersal. e.g. Striga, Orchids, Orobancha.

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