Some spices are seeds, including nutmeg, mustard, and fenugreek. What about grains, such as rice, corn, and cereal grains? Technically, grains are seeds that are fused to the ovary wall, so they are fruits, even though most of what we eat and nearly all of the nutritional value is the seed.
Do not despair: many common seeds of commerce are, in fact, seeds, including poppy, flax, and pumpkin seeds. The seed of Virola , a relative of nutmeg, is covered by a red fleshy layer. Photo by Lawrence Kelly. Examples of plants that lack seeds are ferns and mosses. Seed plants appear in the fossil record around million years ago, and they are now the most abundant and diverse plant group on earth, with nearly , species. Seeds come in a great variety of shapes and sizes, and a lot of the variation relates to dispersal mechanisms.
One of the largest seeds, that of the coco de mer , is approximately a foot long and weighs up to 40 pounds. This seed floats, allowing it to disperse between islands in the Seychelles archipelago in the Indian Ocean. These seeds are dispersed in the air like minute dust particles. They lack endosperm and have tiny, underdeveloped embryos. Some seeds have fleshy appendages that entice animal dispersers to eat them; some have hooks, barbs, or sticky hairs that attach to fur or feathers; and some have wings for wind dispersal.
Brazil nut fruit with seeds. Courtesy of Creative Commons. Seeds form from a fertilized ovule after pollination. Despite the importance of seeds in the life cycle of plants—not to mention as food for humans and other animals—we know relatively little about the genetic control of the growth and development of seeds.
Studies of Arabidopsis have helped to identify the genes that are involved in the development of its ovule and seed, but the lack of broad studies across a diversity of plant groups makes it impossible to understand how plants have come to have such a wild array of seed types.
Roots grow down to anchor the plant in the ground. Roots also take up water and nutrients and store food. A shoot grows skywards and develops into a stem that carries water and nutrients from the roots to the rest of the plant. The stem also supports leaves so they can collect sunlight. Leaves capture sunlight to make energy for the plant through the process of photosynthesis. When the seedling matures into an adult plant and is ready to reproduce, it develops flowers.
Flowers are special structures involved in sexual reproduction, which involves both pollination and fertilisation,. Pollination is the process by which pollen is carried by wind or animals such as insects or birds from the male part of a flower the anther to the female part the stigma of another or the same flower.
The pollen then moves from the stigma to the female ovules. Pollen has male gametes containing half the normal chromosomes for that plant. After pollination, these gametes move to the ovule, where they combine with female gametes, which also contain half the quota of chromosomes. This process is called fertilisation. After fertilisation, the combined cell grows into an embryo inside a seed.
The embryo is a tiny plant that has root, stem and leaf parts ready to grow into a new plant when conditions are right. Flowering plants all go through the same stages of a life cycle, but the length of time they take varies widely between species.
Some plants go though their complete cycle in a few weeks — others take many years. Annuals are plants that grow from a seed. The position in the inflorescence can affect seed development rate. For example, distal seeds in a wheat spike have slower growth rates and shorter seed filling periods than proximal seeds. Corn seeds at the tip of the ear are smaller than those at the base which has been attributed to inadequate photosynthetic supply. Soybean pods located in lower plant branches are produced before those located in the upper nodes and are affected by different environmental conditions during development and this causes differences in seed performance.
Smaller seeds are also produced from smaller fruits or those that mature later in the growing season or are exposed to unfavorable environmental conditions. The usual consequence is decreased seed germination and vigor. Sexual propagation involves the union of pollen from a male flower part with the egg of a female ovary to produce a seed.
Seed can be recalcitrant, inter mediator orthodox seed. The longevity of orthodox seeds is increased over a wide range of environmental conditions by decreasing storage temperature and seed water content without causing significant damage to seed metabolism. Orthodox seeds are, therefore, considered desiccation tolerant. Recalcitrant seeds, however, decrease in viability when their water content is reduced below a relatively high value. They are, therefore, considered desiccation intolerant.
The seed is made up of three parts: the outer seed coat, which protects the seed; the endosperm , which is a food reserve; and the embryo, which is the young plant itself. Figure 4 Seed germination is a critically important juncture in the plant life cycle and the decision made by an imbibing seed to initiate germination can be considered to be a critical regulatory step in plant development. Following initial water uptake, this phase of development is characterized by relatively little change in seed water content until it is terminated by the initiation of embryo growth.
After the seeds have germinated, they require favorable environment for their establishment. All these factors become available if the seeds have chance to germinate in their original ecology or if the original ecology is not seriously disturbed. Germination potential of seeds of many plants can be influenced by various environmental and the seed internal factors. Without understanding of such factors and appropriate knowledge of plant propagation techniques and their seed biology of indigenous trees, production of seedlings from seeds would be difficult.
One of the major strategies in seed physiology is: some seeds of indigenous tree species undergo the period of dormancy to pass unfavorable environmental or internal situations. The germination of seeds in a particular situation and season is determined by the interaction between the dormancy releasing factors, which influence on the termination of dormancy or initiation of germination and seedling growth in many plant species like Phyto-hormones, light, temperature, water, nutrients, moisture or mechanical cues.
Propagations of many indigenous tree species from seeds had been difficult due to lack of precise knowledge on their seed biology and germination physiology. So they must simultaneously sense a number of environmental conditions and fix time of seed maturation and germination and seedling emergence to particular periods of the year according to their habitat locations for successful establishment and survival.
Seed set and releases of seeds into the soil occur at the pick of the dry season and emergence of seedlings under this condition could jeopardize survival. Hence a structural or physiological adaptive mechanism called dormancy prevents seed germination. Seed dormancy is defined as the state in which otherwise mature and viable seeds will not germinate even when exposed to favorable growth conditions. Seeds will only germinate when the conditions are suitable.
Some causes of seed dormancy are:. For example, Acacia seeds dormancy removed by scarifying seed coat, Podocarpus falcatus dormancy removed by cracking away the latter using a piece of clean basalt rock ca The ability of seeds to germinate readily when conditions are suitable for successful growth and the ability to avoid germination at inappropriate times, through the maintenance of dormancy, can also be controlled by endogenous chemicals. For example, in tomato and strawberry. In some species, such as Pinus and Rananculus , the fruits are shed before the embryo fully matures.
Such physiologically immature seeds must undergo certain enzymatic and biochemical changes to attain maturity. Immature embryos cannot germinate. But such seeds can be matured artificially by storing fruits or cones for a certain period of time to allow embryos to mature completely and to germinate. Seed germination studies of Bixaorellana by Hill et al. For a given species, it is often the case that either the presence of an impermeable, leathery or hard seed coat or chemical inhibitors within the embryo or within the stored food of the seed or the embryo immaturity prevent seed germination.
However, it can sometimes happen that all the three factors can combine and prevent seed germination. Storage time and temperature: Seed germination can be determined by many factors including seed storage time and temperature. Legesse Negash indicated that germination of P. Temperature is the most important environmental factor that regulates the aging of seeds, partly due to the increased deterioration following long-term storage under high temperature or under poor storage conditions Legesse Negash, Storage time and temperature affects both germination percentage and rate of germination.
For example, Legesse Negash has indicated that germination rate of P. Germination percentage, unlike germination rate, may remain relatively constant, at least over the middle part of the temperature range if sufficient time is allowed for germination to occur. However, the processing, the rate of physiological change, storage and germination conditions for many indigenous tree seeds are poorly understood and hence they may look healthy but fail to germinate when planted due to seed short viability conditions as well as lack of the knowledge of their reproductive biology.
Viability is a measure of the propagation of seeds in a lot that are capable of germinating while longevity is a measure of how long seeds remain viable. Harrington ; cited in Hartmann et al.
Seeds of many fire-adapted plants are very difficult to germinate, and some species have been impossible to propagate by seeds. Smoke has been used to break dormancy and improve germination of seeds of common vegetables without obvious need of fire for their germination such as lettuce 39 and celery. Gibberellins are a group of plant growth regulators which play an important role in the regulation of seed germination and breaking dormancy.
Seed germination can be stimulated by applying artificially produced Phyto-hormones or by natural means. In a natural means of breaking dormancy, the gibberellins synthesizing mechanism is activated and the actual synthesis of gibberellins takes place when the seeds are transferred to a suitably higher temperature. Gibberellins promote growth by increasing plasticity of the cell wall followed by the hydrolysis of starch to sugar which reduces the potential in the cell, resulting in the entry of water into the cell causing elongation, hence, causing germination of seeds.
Releasing from dormancy can be affected by a variety of environmental and chemical stimuli. It is mediated through a common signal transduction chain that coordinates diverse cellular responses but that may differ between the seeds of different species and dormancy types. Gibberellic acid is known to break dormancy of several types of plant seeds: these are. Nitrogenous compounds, especially nitrates promote the seed germination of a wide range of plant species.
The effect of such a nitrate compounds on promotion of seed germination is best realized in combination with other factors such as temperature manipulations or light.
However, potassium nitrate KNO3 was most widely used chemical for promoting germination and for breaking seed dormancy. For this purpose solutions of 0. In conclusion seeds of different plants need different pretreatment to get vigor seedling and even for production. I would like to acknowledge all the previous investigators who produced valuable research articles and availed for this review paper. This is an open access article distributed under the terms of the, which permits unrestricted use, distribution, and build upon your work non-commercially.
Withdrawal Guidlines. Publication Ethics. Withdrawal Policies Publication Ethics. Advances in. Review Article Volume 8 Issue 4. Keywords: ovule, seed, dormancy, physiology, germination. Adaptive mechanism of plants on land The major challenge for early plants first migrating onto land was the lack of water. Each megaspore develops into a female gametophyte that bears only archegonia; a microspore develops into a male gametophyte, bearing only antheridia.
Although Heterospory was prerequisite to seed evolution, there are fossil plants that were heterosporous but had not evolved seeds, among these being species of Archeopteris.
Note that heterospory has evolved independently in other, non-seed plants, e. Endospory: Endospory is the complete development of the female gametophyte within the original spore wall.
The ancestral condition, in which the spore germinates and grows as an external gametophyte, is called exospory. Reduction of megaspore number to one: Reduction of megaspore number occurred in two ways. First, there evolved a reduction in the number of cells within the mega sporangium that undergo meiosis each termed a megasporocyteor megaspore mother cell was reduced to one.
After meiosis, the single diploid megasporocyte gives rise to four haploid megaspores. Second, of the four haploid megaspores produced by meiosis, three consistently abort, leaving only one functional megaspore.
This single megaspore also undergoes a great increase in size, correlated with the increased availability of space and resources in the mega sporangium. Retention of the megaspore: This was accompanied by a reduction in thickness of the megaspore wall. Evolution of the integument: Most likely, the final event in seed evolution was the envelopment of the mega sporangium by tissue, called the The integument grows from the base of the mega sporangium which is often called a nucellus when surrounded by an integument and surrounds it, except at the distal end.
Angiosperm Double fertilization, Flower, fruit, ovule and vessels 1. They are the main feature distinguishing the "hardwood" of angiosperms from the "softwood" of conifers Table 1 Four major groups of plant with their own key biological events or new biological structure summarized from Willis and McElwain, Figure 1 Seed Germinated structures for monocot and dicot plants.
Pollination and fertilization P ollination is the transfer of pollen from the anther to the stigma after it germinates. Ovule development The next step after fertilization is the development of the ovule containing the zygote and the 3n central cell into a seed.
General parameters to characterize seed maturation During the s and s, there was a significant effort by seed technologists to clarify the maturation process and to define the primary changes occurring during seed development. Among the differing physiological maturity concepts, three are dominant: 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 Physiological maturity occurs when seeds reach maximum dry weight, germination and vigor According to the prevailing concept, seed development ceases when physiological maturity is achieved, but this idea remains controversial because this expression is frequently used with different meanings.
Seed physiological maturity and harvest time Physiological maturity identifies the moment seeds possess or are close to their maximum physiological potential. Environmental factors affecting seed development Components of the environment factors that influence seed performance include soil fertility, water, temperature, light, and seed position on the plant.
Figure 3 Embryo development and double fertilization. Plant propagation is the sexual and asexual multiplication of plants, and has three aspects; Knowledge on the chemical, physical, and environmental manipulations, as well as command of the needed technical skills. Fundamentals of plant biology and physiology. Expertise on specific plant species. Figure 5 After the seeds have germinated, they require favorable environment for their establishment.
Some causes of seed dormancy are: Hard seed coat Embryo dormancy Immature embryo- the embryo is not fully developed when the seed is dispersed Chemical inhibitor Types of dormancy Quiescent seed dormancy -even a non-dormant or quiescent seed has a unique ability to revert to a dormant state under stressful conditions. Similarly seeds of Prunus africana were found to germinate by seed coat scarification. For example, exposure of lettuce seeds to red light about nm induces germination, but far red light nm inhibits it.
This makes the seed coat thinner so water can enter more easily. This method is best for smaller seeds that are hard to cut for example kaka beak. To do this easily you can shake the seeds forcefully in a container lined with sandpaper Chipping seeds: Chipping is cutting a small piece out of seed coat with a sharp knife.
Water can then enter the test a through the cut. This is useful on large seeds for example, sweet pea Soaking seeds: Soaking seeds in water overnight will soften the test a. This can be useful for seeds such as wattle, sweet pea and kowhai. Commercial growers use diluted acids on some seeds Immature embryo: the embryo is not fully developed when the seed is dispersed. Therefore, Store seeds before planting. Waiting for a period of time will allow the embryo to mature Chemical inhibitors : Some seeds contain chemicals that prevent germination.
This is common in fleshy fruit but it depends on the seed type as to what will get rid of the inhibitor The ability of seeds to germinate readily when conditions are suitable for successful growth and the ability to avoid germination at inappropriate times, through the maintenance of dormancy, can also be controlled by endogenous chemicals. Basic features of storage that increases the viability of seeds 26 include Protection from water, Avoidance of mixture with other seed, Protection from rodents, insects, fungi, and others.
Retention of viability also varies with the climatic factors of the area in which storage occurs. Gibberellic acid is known to break dormancy of several types of plant seeds: these are Light promoted seeds, such as grand rapids lettuce seed Lactuca sativa L.
Figure 5 Seed germination process with stages of development. Bhattacharya D, Medlin L. Algal Phylogeny and the Origin of Land Plants. Plant Physiol. The Evolution of Plants. Chicago: Oxford University Press; p. Towards a phylogenetic nomenclature of Tracheophyta.
The evolution of seeds.
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