Plant Bible

                                                            EMBRYOGENY BY DICOTYLEDON   Based on the plane of division of the apical cell in the 2-celled proembryo, and the contribution of the basal cell ( cb ) and the apical cell ( ca ) in the formation of embryo proper, five chief types of embryogeny have been recognized by Maheshwari (1950) A. The apical cell of the 2-celled proembryo divides longitudinally (1) The basal cell plays only a minor role or none in the subsequent development of the embryo proper Crucifer Type or Onagrad Type (eg., Annonaceae, Brassicaceae, Onagraceae, Pedaliaceae, Ranunculaceae. Scrophulariaceae) (2) The basal cell and apical cell both contribute to the development of embryo - Asterad Type (eg. Asteraceae, Balsaminaceae. Violaceae, Vitaceae) B. The apical cell of the 2-celled proembryo divides transversely i- The basal cell plays only a minor role or none in the subsequent development of the embryo proper (3) The basal cell usually fo

                                                                 Embryogeny in Monocotyledons   The main difference between the mature embryos of monocotyledon and dicotyledon is in the number of cotyledons. The single cotyledon in monocotyledons has been regarded by many authors as a terminal structure. Wardlaw (1955) remarked: “In the dicotyledonous embryo the plumule is typically distal and is situated symmetrically between two equivale cotyledons in the monocotyledonous embryo the shoot apex occupies a lateral position in the somewhat cylindrical embryo and cotyledon terminal”. However, extensive ontogenetic work on monocot Swamy and his co-workers is Lakshmanan, 1972) has established that the epicotyl in monocotyledonous embryos is truly a terminal structure both epicotyl and cotyledon are from one and the same terminal their. The apparent lateral position of the epicotyl is due to early growth of the cotyledon, the epicotyl, alter initiation, shows slow growth.  Development

                                                                                       APOMIXIS   The normal sexual cycle (amphimixis) involves two important processes (a) Meiosis, this transforms a diploid sporophytic cell (megaspore mother cell, MMC) into four haploid gametophytic cells, and (b) Fertilization, In which two haploid gametes of opposite sex fuse re-establishing the diploid sporophytic generation. Thus, in a sexual cycle a diploid generation (sporophytic) alternates with a haploid generation (gametophytic) In angiosperms the gametophytic generations are very short and are represented by embryo sac on the female side and microspores or pollen grains on the male side. In some plants meiosis and syngamy are interrupted and still a viable embryo is formed within the confines of the seed-coat. Such asexual seeds, which produce progeny identical to the female parent, are called apomictic seeds, and the phenomenon is known as apomixis (Apo = away from + mixis = act of mixin

  EMBRYO The fertilized egg is called zygote Following a predetermined mode f development (embryogeny) it gives rise to an embryo, which has the potentiality form a complete plant. A typical dicotyledonous embryo seen in median longitudinal section. It comprises an embryonal axis with two cotyledons attached to laterally. The portion of embryonal axis above the level of cotyledons is called epicotyl, and the portion below the level of cotyledons is known as hypocotyl. The epicotyl terminates into plumule (embryonic shoot), and the hypocotyl at its lower end bears radicle (embryonic root). The embryo of a monocotyledon differs from that of a dicotyledon mainly in having only one cotyledon. The embryos of grasses show a highly specialized structure. In this chapter the chief structural changes associated with principal types of embryogeny in angiosperms are described. At the end some aspects of the physiology, genetics and nutrition of embryo are discussed. ZYGOTE: From the time of

                                                                                     Heterosis Discovery: Heterosis (hetero- different; sis - condition) G.H. Shull was the first scientist to use the term heterosis in 1912.  Definition: The superiority of the F1 hybrid in performance over its parents is called heterosis or hybrid vigour. Vigour refers to increase in growth, yield, greater adaptability of resistance to diseases, pest and drought. Vegetative propagation is the best suited measure for maintaining hybrid vigour, since the desired characters are not lost and can persist over a period of time. Many breeders believe that the magnitude of heterosis is directly related to the degree of genetic diversity between the two parents. Depending on the nature, origin, adaptability and reproducing ability heterosis can be classified as: Euheterosis - This is the true heterosis which is inherited and is further classified as: a. Mutational Euheterosis –   Simplest type of euhetero

  TYPES OF EMBRYO SAC Monosporic Embryo Sac The embryo sac in which only one out of four megaspores is involved in the development of the embryo sac is called as Monosporic Embryo Sac. Since all the nuclei in such embryo sac are derived through mitoses of a single nucleus, hence all nuclei are genetically identical. On the basis of number of nuclei in the mature embryo sac, Maheshwari recognised two types - 8 - nucleate and 4- nucleate. 8- nucleate or Polygonum type: This type of embryo sac development was first discovered in Polygonum divaricatum for the first time by Strasburger, hence it is called as polygonum type. Since, this is common in Angiosperms(81%), it is called as normal type. Of the four megaspores formed from the megaspore mother cell, only one megaspore situated towards chalazal end remains functional and the remaining three situated towards micropylar end degenerate. The functional megaspore divides and gives rise to 2 nuclei, one of which moves to the microp

                                                                       FERTILIZATION   POLLEN TUBE GROWTH: The microspore is the first cell of the male gametophyte and is haploid. The development of male gametophyte takes place while they are still in the microsporangium. The nucleus of the microspore divides mitotically to form a vegetative and a generative nucleus. A wall is laid around the generative nucleus resulting in the formation of two unequal cells, a large irregular nucleus bearing with abundant food reserve called vegetative cell and a small generative cell. Generally at this 2 celled stage, the pollens are liberated from the anther. In some plants the generative cell again undergoes a division to form two male gametes. The pollen is liberated at this 3 celled stage. In 60% of the angiosperms pollen is liberated in 2 celled stage. Further, the growth of the male gametophyte occurs only if the pollen reaches the right stigma. The pollen on reaching the stigma absorbs m

                                                                           ENDOSPERM Definition: Endosperm is unique among the plant tissues with regard to its origin and development. Endosperm is the most common nutritive tissue for the developing embryo in angiosperms. Endosperm is the product of fertilization and is triploid. After double fertilization the egg is called zygote, and the fusion product of polars and the second ale gamete is termed as the primary endosperm nucleus. The former develops into an originated embryo whereas the latter gives to an almost formless tissue, the endosperm. Types of Endosperms: Nuclear endosperm Cellular endosperm Helobial endosperm Cereal endosperm Ruminate endosperm Nuclear endosperm:                 In this type of endosperm the division of the primary endosperm nucleus and few subsequent nuclear divisions are not accompanied by wall formation. This results in a condition where the central cell of the embryo sac has form

                                                                       PARTHENOCARPY   Definition: According to Noll (1902), who introduced the term, parthenocarpy means the development of fruits without pollination or any other stimulus. Since then the definition of parthenocarpy has undergone slight modification and, according to the present concept, it refers to “the formation of fruits without fertilization” (Nitsch, 1965). The parthenocarpic development of fruit may require the pollination stimulus (stimulative parthenocarpy) or it may occur in unpollinated flowers (vegetative parthenocarpy) “seedless fruits” should not be considered synonymous to “parthenocarpic fruits” because in a seedless fruits the ovules may have been fertilized and later aborted, as in some strains of vitis vinfera var. concor (Nitsch et al., 1960) . also, there may be parthenocarpic fruits in citrus sp., grapes, watermelon and pineapples. The seeds in such fruits are really pseudo-seeds, lacking se