Ecological Life Cycle of Seed Plants

Abstract The life cycle of eukaryotic, sexual species is divided into haploid and diploid phases. In multicellular animals and seed plants, the diploid phase is dominant, and the haploid phase is reduced to one, or a very few cells, which are dependent on the diploid form. In other eukaryotic species, however, the haploid phase may dominate or the phases may be equally developed. Even though an alternation between haploid and diploid forms is fundamental to sexual reproduction in eukaryotes, relatively little is known about the evolutionary forces that influence the dominance of haploidy or diploidy. An obvious genetic factor that might result in selection for a dominant diploid phase is heterozygote advantage, since only the diploid phase can be heterozygous. In this paper, I analyze a model designed to determine whether heterozygote advantage could lead to the evolution of a dominant diploid phase. The main result is that heterozygote advantage can lead to an increase in the dominance of the diploid phase, but only if the diploid phase is already sufficiently dominant. Because the diploid phase is unlikely to be increased in organisms that are primarily haploid, I conclude that heterozygote advantage is not a sufficient explanation of the dominance of the diploid phase in higher plants and animals.

Download Full-text

Sex and the Single Cryptogam

10.1093/oso/9780190490263.003.0017 ◽

2018 ◽

Author(s):

Lincoln Taiz ◽

Lee Taiz

Keyword(s):

Life Cycle ◽

Pollen Tube ◽

Female Parent ◽

Seed Plants ◽

Cell Theory ◽

Entire Life ◽

Entire Life Cycle ◽

Cell Divisions ◽

Material Substance ◽

Alternation Of Generations

As Chapter 17 makes clear, the asexualist/sexualists controversy continued even as Johann Hedwig and Karl von Nägel demonstrated the existence of sex in cryptogams by discovering the Alternation of Generations (1782, 1784), hybridizers A. F. Wiegman and Carl Friedrich von Gaertner recieved prestigious prizes for their work, and Giovanni Battista Amici and Adolphe-Theodore Brongniart discovered—and confirmed—the pollen tube. Unconvinced, Matthias Jacob Schleiden, co-founder of the cell theory, insisted that ferns grow asexually from spores, and that spores, not seeds, are the primary units of propagation in seed plants also. He argued (1853) that the entire life-cycle of seed plants is based on duplicative cell divisions that produce seeds entirely by vegetative processes. Following the Aristotelian doctrine that the female parent provides the material substance of the embryo, he concluded pollen must be a female structure that reproduces vegetatively—thus making the case for a unisexual, plants-as-female model.

Download Full-text

A meta-analysis of the effects of treatments used to break dormancy in seeds of the megagenus Astragalus (Fabaceae)

Seed Science Research ◽

10.1017/s0960258520000318 ◽

2020 ◽

Vol 30 (3) ◽

pp. 224-233

Author(s):

Elias Soltani ◽

Jerry M. Baskin ◽

Carol C. Baskin ◽

Fatemeh Benakashani

Keyword(s):

Life Cycle ◽

Sulphuric Acid ◽

Life Form ◽

Meta Analysis ◽

Seed Plants ◽

Physical Dormancy ◽

Edaphic Conditions ◽

Geographic Boundaries ◽

Physiological Dormancy ◽

Breaking Seed Dormancy

AbstractAstragalus is the largest genus of seed plants with 3000 or more species that occurs naturally on several continents. The genus has some use as a forage and medicine and in industry, and many of the species are rare endemics threatened with extinction. The seeds are reported to be dormant at maturity, and various treatments have been used in an attempt to germinate them. Our primary aim was to determine via a meta-analysis the most effective way(s) to break dormancy in seeds of this species-rich genus. Mechanical and chemical (conc. sulphuric acid) scarification were by far the best of 12 treatments for breaking seed dormancy of the 40 species included in our meta-analysis, whereas prechilling, gibberellin and smoke were ineffective. These results along with those of imbibition tests confirm that seeds of the examined Astragalus species have physical dormancy (PY). Further, PY in these 40 species and (its documented occurrence) in 118 species that could not be included in our meta-analysis transcends climatic and geographic boundaries, edaphic conditions, life cycle/life form types and infrageneric phylogeny. Thus, it seems likely that most species of Astragalus have PY. However, in addition to PY, physiological dormancy (PD), that is, combinational dormancy (PY + PD), has been reported in a few species of Astragalus. This study should be useful to both basic and applied scientists who want to germinate seeds of Astragalus.

Download Full-text

A Small Number of Gametophytes with Gametangia and Stunted Sporophytes of Antrophyum obovatum Baker (Pteridaceae): The Suppression of Functional Sporophyte Production by Prezygotic and Postzygotic Sterility

Plants ◽

10.3390/plants10010170 ◽

2021 ◽

Vol 10 (1) ◽

pp. 170

Author(s):

Sang Hee Park ◽

Jung Sung Kim ◽

Hyoung Tae Kim

Keyword(s):

Life Cycle ◽

Dna Barcoding ◽

Environmental Conditions ◽

Gene Sequence ◽

Jeju Island ◽

Seed Plants ◽

Rbcl Gene ◽

Microenvironmental Factors ◽

Sporophyte Production ◽

Dominant Phase

Ferns have conspicuous sporophytes as the dominant phase in their life cycle; however, the gametophytes are completely separated from the sporophytes and supply their own nutrition, unlike in bryophytes and seed plants. Among the gametophytes, some maintain their populations in the gametophyte phase without progressing to sporophyte production and are known as independent gametophytes. Independent gametophytes of Antrophyum obovatum Baker were recently reported in one population on Jeju Island, Korea. In the present study, we surveyed more places to find new independent gametophyte populations of A. obovatum using the rbcL gene sequence-based DNA barcoding technique. We identified two new sites inhabited by independent gametophytes. Archegonia and juvenile sporophytes were independently observed in each location under slightly different environmental conditions. Consequently, in the case of this species, functional sporophyte production is likely suppressed by prezygotic and postzygotic sterility, depending on microenvironmental factors.

Download Full-text

The relationships of vascular plants

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2000.0619 ◽

2000 ◽

Vol 355 (1398) ◽

pp. 847-855 ◽

Cited By ~ 42

Author(s):

P. Kenrick

Keyword(s):

Life Cycle ◽

Fossil Record ◽

Vascular Plants ◽

Vascular Plant ◽

Comparative Morphology ◽

Life Cycles ◽

Plant Evolution ◽

Seed Plants ◽

Geological Conditions ◽

Life Cycle Evolution

Recent phylogenetic research indicates that vascular plants evolved from bryophyte–like ancestors and that this involved extensive modifications to the life cycle. These conclusions are supported by a range of systematic data, including gene sequences, as well as evidence from comparative morphology and the fossil record. Within vascular plants, there is compelling evidence for two major clades, which have been termed lycophytes (clubmosses) and euphyllophytes (seed plants, ferns, horsetails). The implications of recent phylogenetic work are discussed with reference to life cycle evolution and the interpretation of stratigraphic inconsistencies in the early fossil record of land plants. Life cycles are shown to have passed through an isomorphic phase in the early stages of vascular plant evolution. Thus, the gametophyte generation of all living vascular plants is the product of massive morphological reduction. Phylogenetic research corroborates earlier suggestions of a major representational bias in the early fossil record. Megafossils document a sequence of appearance of groups that is at odds with that predicted by cladogram topology. It is argued here that the pattern of appearance and diversification of plant megafossils owes more to changing geological conditions than to rapid biological diversification.

Download Full-text

Ultrastructural analysis of “Sensory” surface nerve endings and “putative” neurotransmitter sites in Schistosoma mansoni Miracidia

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100156791 ◽

1989 ◽

Vol 47 ◽

pp. 962-963

Author(s):

Betty Ruth Jones ◽

Steve Chi-Tang Pan

Keyword(s):

Nervous System ◽

Life Cycle ◽

Schistosoma Mansoni ◽

Snail Host ◽

Complex Life Cycle ◽

Rational Approach ◽

Effective Control ◽

The Social ◽

Social And Economic Development ◽

Basic Biology

INTRODUCTION: Schistosomiasis has been described as “one of the most devastating diseases of mankind, second only to malaria in its deleterious effects on the social and economic development of populations in many warm areas of the world.” The disease is worldwide and is probably spreading faster and becoming more intense than the overall research efforts designed to provide the basis for countering it. Moreover, there are indications that the development of water resources and the demands for increasing cultivation and food in developing countries may prevent adequate control of the disease and thus the number of infections are increasing.Our knowledge of the basic biology of the parasites causing the disease is far from adequate. Such knowledge is essential if we are to develop a rational approach to the effective control of human schistosomiasis. The miracidium is the first infective stage in the complex life cycle of schistosomes. The future of the entire life cycle depends on the capacity and ability of this organism to locate and enter a suitable snail host for further development, Little is known about the nervous system of the miracidium of Schistosoma mansoni and of other trematodes. Studies indicate that miracidia contain a well developed and complex nervous system that may aid the larvae in locating and entering a susceptible snail host (Wilson, 1970; Brooker, 1972; Chernin, 1974; Pan, 1980; Mehlhorn, 1988; and Jones, 1987-1988).

Download Full-text

A freeze-fracture-etched study of the physarum polycephalum plasma membrane during early formation of the macroplasmodial stage

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100147570 ◽

1993 ◽

Vol 51 ◽

pp. 346-347

Author(s):

Randolph W. Taylor ◽

Henrie Treadwell

Keyword(s):

Plasma Membrane ◽

Life Cycle ◽

Growth Phase ◽

Filter Paper ◽

Physarum Polycephalum ◽

Freeze Fracture ◽

Petri Dish ◽

Wire Screen ◽

Wide Mouth ◽

Sterile Filter

The plasma membrane of the Slime Mold, Physarum polycephalum, process unique morphological distinctions at different stages of the life cycle. Investigations of the plasma membrane of P. polycephalum, particularly, the arrangements of the intramembranous particles has provided useful information concerning possible changes occurring in higher organisms. In this report Freeze-fracture-etched techniques were used to investigate 3 hours post-fusion of the macroplasmodia stage of the P. polycephalum plasma membrane.Microplasmodia of Physarum polycephalum (M3C), axenically maintained, were collected in mid-expotential growth phase by centrifugation. Aliquots of microplasmodia were spread in 3 cm circles with a wide mouth pipette onto sterile filter paper which was supported on a wire screen contained in a petri dish. The cells were starved for 2 hrs at 24°C. After starvation, the cells were feed semidefined medium supplemented with hemin and incubated at 24°C. Three hours after incubation, samples were collected randomly from the petri plates, placed in plancettes and frozen with a propane-nitrogen jet freezer.

Download Full-text