However, little progress has been made in understanding the mechanism of the reproductive systems in gymnosperms, especially in species able to express a bisexual condition. Understanding similarities of sexual expression between angiosperms and gymnosperms has been considered key to reconstruct the sexual state of the ancestral angiosperm (30). For example, the anther is bisporangiate in Cassytha and some genera (e.g. We made three slides per individual. Unlimited Access, Unlimited Time, on Unlimited Devices! Polyspory is occurrence of more than four spores in a tetrad. Number: It has small, vertically oriented leaf bases arranged in a tight spiral arising from a stigmarian rhizomorph; branch scars are of the Ulodendron type. Nectar, which accumulates at the base of the floral tube , is the apparent reward in all cases. It has two layers, outer exine and inner intine. A layer of callose develops around the generative cell which separates the cell from the pollen grain wall. Tapetum has a number of functions: (i) Nourishment of the developing microspore mother cells and pollen grains, (ii) It produces lipid rich Ubisch granules containing sporopol- lenin for exine formation, pollenkitt (oily, sticky covering of lipids and carotenoids) in case of entomophilous pollen grains, special proteins for the pollen grains to recognise compatibility and hormone IAA. Thus our investigation of P. Johannis suggests that these hypotheses are not mutually exclusive and that the origin of bisexual flowers could be due to the regulation (both up and down) of B‐class genes. Ovules on bisporangiate structures of Ephedra, Gnetum, and Welwitschia are reported to be sterile or abortive (54; 29; 45; 41). Some individuals develop allergy to them, producing respiratory disorders like rhinitis, asthma and bronchitis— bronchial allergy. Sections were stained with safranin‐green and toluidine blue. The material fixed in paraformaldehyde was rinsed with PBS 1×, dehydrated as described above, embedded in LR White Resin (medium grade; Electron Microscopy Sciences, Fort Washington, Pennsylvania, USA), and then sectioned at 0.80–1.5 µm with an ultramicrotome. The primary gynoecium primordium is differentiated into an ovary wall surrounding a central ovule (purple arrow). It has a large nucleus which is surrounded by a thin sheath of cytoplasm. Another common lycopsid believed to be a progenitor of, or have affinities with, the lepidodendrids is Sublepido-dendron songziense from the Upper Devonian of China (Q. Wang et al., 2002, 2003b). Therefore, it is likely that the genetic principles of sex determination of reproductive structures in gymnosperms—as well as its regulatory mechanisms—were present in the common ancestor of gymnosperms and angiosperms and are still conserved today. Pollen viability is little in flowers which are pollinated in bud condition. Therefore, homology between bisporiangiate cones and bisexual perfect flowers would be supported under the pseudoanthial scenario, where flowers are hypothesized to originate through a condensation of a multiaxial structure (5). 2D). In addition, pollen viability of P. johannis is high compared with other reports in pines (e.g., pollen viability of P. banksiana range from 54 to 98%; 13). Answer: (c) letrasporangiate. Seed, pollen, and bisporangiate cones were visually distinguished. Most flowers are bisporangiate. 3B, 3F). This test is Rated positive by 87% students preparing for Class 12.This MCQ test is related to Class 12 syllabus, prepared by Class 12 teachers. (i) (ii) (a) Four Two (b) Two One (c) Two Two (d) Four One . In Pinus, bisporangiate cones can form in natural conditions (31; 73; 105; 24; 59) or can be stimulated by exogenous hormonal application (38; 98, 99). blade -- Any broad and flattened region of a plant or alga, which allows for increased photosynthetic surface area. As a result the endothecium shortens and ruptures the anther lobe wall in the region of stomium. The pollen tube is covered over by in-tine. At this time, ovules develop in the ovulate cones (Fig. The phenomenon is called micro-sporogenesis. Then in 2009, they produced purely monosporangiate structures again. 3B). At this stage, empty pollen grains are observed in the micropyl and near the nucellus. Sections 10 µm thick were cut on a rotary microtome and mounted on slides. Thus the 6.3% success rate in crosses, using bisporangiate cones with more ovuliferous scales than microsporophylls, suggests that male and female functions are not altered in bisporangiate structures. Homologous genes that regulate sex expression in angiosperms have been observed in gymnosperms; such evidence supports a common ancestral mechanism for producing bisexual structures in seed plants. TOS 7. They are called germ pores (if rounded) or germinal furrows (if elongated). NCERT DC Pandey Sunil Batra HC Verma Pradeep Errorless. bract -- Any reduced leaf-like structure associated with a cone or flower. The tapetal cells were larger than the wall layer cells and had a single nucleus each. Although, from a paleobotanical perspective, there is more recent interest in such terata in all seed plants for the insights they might give to the evolution of flowers and for understanding potential neoGoldschmidtian or saltational evolutionary events in plants (see 4; 92). Flower evolution: The origin and subsequent diversification of the angiosperm flower, Conifer reproductive development involves B‐type MADS‐box genes with distinct and different activities in male organ primordia, Recurrent appearance of bisporangiate strobili with proliferation on Picea abies, The proper place of hopeful monsters in evolutionary biology, Gymnosperm orthologues of class B floral homeotic genes and their impact on understanding flower origin, Molecular mechanisms underlying origin and diversification of the angiosperm flower, Proliferated, bisporangiate, and other atypical cones occurring on young, plantation‐grown, Characterization of the expression patterns of, Lateral female strobili production in a Japanese red pine (, Promotion of lateral female strobili production in, The occurrence of bisporangiate strobili in subalpine black spruce, A new interpretation of microsporangiate cones in Cephalotaxaceae and Taxaceae, Overdominant lethals as part of the conifer embryo lethal system, Case history of an excellent, white spruce cone and seed crop in interior Alaska: Cone and seed production, germination, and seedling survival, Pine flowering and seed ripening in Texas. (E) Unitegmic and crassinucellated ovule and megaspore mother cell (arrow). Fertilization occurs 1 month later. The latter divides into one antheridial initial and the second prothallial cell (Fig. A dithecous anther consists of (i) microsporangia, (ii) in each lobe. Question 53. Before publishing your articles on this site, please read the following pages: 1. A typical anther is (a) Bisporangiate (b) Tetrasporangiate (c) Unisporangiate (d) Multisporangiate Answer: (b) Tetrasporangiate. Microsporangial wall has four types of layers epidermis (common anther covering), endothecium, 1-3 middle layers and tapetum. Middle Jurassic evidence for the origin of Cupressaceae: A paleobotanical context for the roles of regulatory genetics and development in the evolution of conifer seed cones. Defining the limits of flowers: The challenge of distinguishing between the evolutionary products of simple versus compound strobili. (D) Generative cell in the nucellus before spermatic cell formation. is bisporangiate, incumbent and with a five layered wall comprising an epidermis, an endothecium, two middle layers and a glandular tapetum of uninucleate cells. For most Pinaceae genera, there are reports of individuals that carry bisporangiate cones. For example, some individuals were predominantly male monoecious in 2006, but in 2007 and 2008, they had 15–50 bisporangiate structures. Stamen is the male reproductive organ or microsporophyll of a flower. Bisporangiate cones have features of ovulate cones toward the apex and of pollen cones toward the base, only until the release of pollen. Microsporophylls develop at the bottom of the cone, and ovuliferous scales (each one associated with a bract) are developed at the top (Fig. Start studying Organismic Bio Exam 2. It is … The anther wall consists of four wall layers where (a) tapetum lies just inner to endothecium (b) middle layers lie between endothecium and tapetum (c) endothecium lies inner to middle layers Ovulate cone development in P. johannis has a 16‐month cycle in the population studied. Prohibited Content 3. The dithecous anther consists of two sacs and is tetralocular or tetrasporangiate in as Datura. It has (i) Growth zone at tip (cap block) with dense active cytoplasm rich in vesicles, (ii) Nuclear zone containing tube nucleus and male gametes, (iii) Vacuolization zone rich in vacuolated cytoplasm between active and inactive cytoplasm with a series of callose plugs to separate older inactive cytoplasm. Tetrads of haploid microspores or pollen sac is a highly resistant wall on the stigma the compatible pollen through. Batra HC Verma Pradeep Errorless likely reflects that they are the closest extant relatives of the androecial... 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