" The Big Picture!" by Mr C

Principles of life Plant summary

 

Evolution of Plants concept 21.1 Primary Endosymbiosis Produced the First Photosynthetic Eukaryotes

 

• Primary endosymbiosis gave rise to chloroplasts and the subsequent diversification of the Plantae. The descendants of the first photosynthetic eukaryote include glaucophytes, red algae, several groups of green algae, and land plants, all of which contain chlorophyll a. Review Figure 21.1
• Streptophytes include the land plants and two groups of green algae. Green plants, which include the streptophytes and the remaining green algae, are characterized by the presence of chlorophyll b (in addition to chlorophyll a). Review Figure 21.1
• Land plants, also known as embryophytes, arose from an aquatic green algal ancestor related to today’s charophytes. Land plants develop from embryos that are protected by parental tissue. Review Figure 21.1

concept 21.2 Key Adaptations Permitted Plants to Colonize Land

• The acquisition of a cuticle, stomata, gametangia, a protected embryo, protective pigments, thick spore walls with a protective polymer, and a mutualistic association with a fungus were all adaptations of land plants to terrestrial
• All land plant life cycles feature alternation of generations, in which a multicellular diploid sporophyte alternates with a multicellular haploid gametophyte. Review Figure 21.4
• The nonvascular land plants comprise the liverworts, hornworts, and mosses. These groups lack specialized vascular tissues for the conduction of water or nutrients through the plant body.
• The life cycles of nonvascular land plants depend on liquid water. The sporophyte is usually smaller than the gametophyte and depends on it for water and nutrition.
• In many land plants, spores form in structures called sporangia and gametes form in structures called gametangia. Female and male gametangia are, respectively, an archegonium and an antheridium. Review Figure 21.6

concept 21.3 Vascular Tissues Led to Rapid Diversification of Land Plants

• The vascular plants have a vascular system consisting of xylem and phloem that conducts water, minerals, and products of photosynthesis through the plant body. The vascular system includes cells called tracheids.
• The rhyniophytes, the earliest known vascular plants, are known to us only in fossil They lacked true roots and leaves but apparently possessed rhizomes and rhizoids.
• Among living vascular plant groups, the lycophytes (club mosses and relatives) have only small, simple leaflike structures (microphylls). True leaves (megaphylls) are found in monilophytes (which include horsetails and leptosporangiate ferns). The monilophytes and the seed plants are collectively called
• Roots may have evolved either from rhizomes or from stems. Microphylls probably evolved from sterile sporangia, and megaphylls may have resulted from the flattening and reduction of a portion of a stem system with overtopping growth. Review Figure 21.10
• The earliest-diverging groups of vascular plants are homosporous, but heterospory—the production of distinct megaspores and microspores—has evolved several times. Megaspores develop into female megagametophytes; microspores develop into male microgametophytes. Review Figure 21.11

concept 21.4 Seeds Protect Plant Embryos

• All seed plants are heterosporous, and their gametophytes are much smaller than (and dependent on) their sporophytes. Review Figure 21.12
• Seed plants do not require liquid water for fertilization. Pollen grains, the microgametophytes of seed plants, are carried to a megagametophyte by wind or by animals. Following pollination, a pollen tube emerges from the pollen grain and elongates to deliver gametes to the megagametophyte. Review Figure 21.14
• An ovule consists of the seed plant megagametophyte and the integument of sporophytic tissue that protects it. The ovule develops into a seed. Review Figure 21.14B
• Seeds are well protected, and they are often capable of long periods of dormancy, germinating when conditions are favorable.
• Fossils of woody seed ferns are the earliest evidence of seed The surviving groups of seed plants are the gymnosperms and angiosperms. Review Figure 21.1
• The gymnosperms produce ovules and seeds that are not protected by ovary or fruit tissues. The major gymnosperm groups are the cycads, ginkgos, gnetophytes, and Review Figure 21.15
• The megaspores of conifers are produced in woody cones called megastrobili; the microspores are produced in herbaceous cones called microstrobili. Pollen reaches the megagametophyte by way of the micropyle, an opening in the integument of the ovule. Review Figure 21.16 and Figure 21.17,

concept 21.5 Flowers and Fruits Increase the Reproductive Success of Angiosperms

• Flowers and fruits are unique to the angiosperms, distinguishing them from the gymnosperms.
• The xylem of angiosperms is more complex than that of the gymnosperms. It contains two specialized cell types: vessel elements, which function in water transport, and fibers, which play an important role in structural support
• The ovules and seeds of angiosperms are enclosed in and protected by carpels.
• The floral organs, from the base to the apex of the flower, are the sepals, petals, stamens, and pistil. Stamens bear microsporangia in anthers. The pistil (consisting of one or more carpels) includes an ovary containing ovules. The stigma is the receptive surface of the pistil. Review Figure 21.14B and WEB ACTIVITY 21.5
• The structure of flowers has evolved over time. A flower with both megasporangia and microsporangia is referred to as perfect; a flower with only one or the other is imperfect. Some plants with perfect flowers have adaptations to prevent self-fertilization. Review Figure 21.21 and Figure 21.22
• A monoecious species has megasporangiate and microsporangiate flowers on the same plant. A dioecious species is one in which megasporangiate and microsporangiate flowers occur on different plants.
• Flowers may be pollinated by wind or by animals. Many angiosperms have coevolved with their animal pollinators.
• Nearly all angiosperms exhibit double fertilization, resulting in the production of a diploid zygote and an endosperm (which is triploid in most species). Review Figure 21.25 and ANIMATED TUTORIAL 21.3
• The oldest evolutionary split among the angiosperms is between the clade represented by the single species in the genus Amborella and all the remaining flowering plants. Review Figure 21.26
• The most species-rich angiosperm clades are the monocots and the eudicots. The magnoliids are the sister group to the monocots and eudicots.

 

Concept 24.1 The Plant Body Is Organized and Constructed 24.1 in a Distinctive Way

 

• The vegetative organs of flowering plants are roots, which form a root system, and stems and leaves, which (together with flowers, which are sexual organs) form a shoot system. Review Figure 24.1
• Plant development is influenced by three unique properties of plants (compared to animals): apical meristems, the presence of cell walls, and the totipotency of most plant cells. Review Figure 24.2
• During embryogenesis, the apical-basal axis and the radial axis of the plant body are established, as are the shoot apical meristem and the root apical meristem. Review Figure 24.3 and Figure 24.4
• Three tissue systems, arranged concentrically, extend throughout the plant body: the dermal tissue system, ground tissue system, and vascular tissue system. Review Figure 24.5
• The vascular tissue system includes xylem, which conducts water and mineral ions absorbed by the roots to the shoot, and phloem, which conducts the products of photosynthesis through- out the plant body.

Concept 24.2 Meristems Build Roots, Stems, and Leaves

• Primary growth is characterized by the lengthening of roots and shoots and by the proliferation of new roots and shoots through branching. Some plants also experience secondary growth, by which they increase in thickness.
• Apical meristems generate primary growth, and lateral meristems generate secondary growth. Review Figure 24.6
• Apical meristems at the tips of shoots and roots give rise to three primary meristems (protoderm, ground meristem, and procambium), which in turn produce the three tissue systems of the plant body.
• The root apical meristem gives rise to the root cap and the three primary meristems. The cells in the root tip are arranged in three zones that grade into one another: the zone of cell division, zone of cell elongation, and zone of cell maturation. Review Figure 24.7
• The vascular tissue of roots is contained within the stele. It is arranged differently in eudicot and monocot roots. Review Figure 24.8 and WEB ACTIVITIES 24.1 and 24.2
• In stems, the vascular tissue is divided into vascular bundles, which containing both xylem and phloem. Review Figure 24.10 and WEB ACTIVITIES 24.3 and 24.4
• Eudicot leaves have two zones of photosynthetic mesophyll cells that are supplied by veins with water and minerals. Review Figure 24.12 and WEB ACTIVITY 24.5
• Two lateral meristems, the vascular cambium and cork cambium, are responsible for secondary growth. The vascular cambium produces secondary xylem (wood) and secondary phloem (inner bark). The cork cambium produces a protective tissue called cork. Review Figure 24.13 and Figure 24.14 and ANIMATED TUTORIAL 24.1

concept 24.3 Domestication Has Altered Plant Form

• Although the plant body plan is simple, it can be changed dramatically by minor genetic differences, as evidenced by the natural diversity of wild plants.
• Crop domestication involves artificial selection of certain desirable traits found in wild populations. As a result of artificial selection over many generations, the body forms of crop plants are very different from those of their wild relatives. Review Figure 24.15

 

Concept 24.1 The Plant Body Is Organized and Constructed 24.1 in a Distinctive Way

 

• The vegetative organs of flowering plants are roots, which form a root system, and stems and leaves, which (together with flowers, which are sexual organs) form a shoot system. Review Figure 24.1
• Plant development is influenced by three unique properties of plants (compared to animals): apical meristems, the presence of cell walls, and the totipotency of most plant cells. Review Figure 24.2
• During embryogenesis, the apical-basal axis and the radial axis of the plant body are established, as are the shoot apical meristem and the root apical meristem. Review Figure 24.3 and Figure 24.4
• Three tissue systems, arranged concentrically, extend throughout the plant body: the dermal tissue system, ground tissue system, and vascular tissue system. Review Figure 24.5
• The vascular tissue system includes xylem, which conducts water and mineral ions absorbed by the roots to the shoot, and phloem, which conducts the products of photosynthesis through- out the plant body.

Concept 24.2 Meristems Build Roots, Stems, and Leaves

• Primary growth is characterized by the lengthening of roots and shoots and by the proliferation of new roots and shoots through branching. Some plants also experience secondary growth, by which they increase in thickness.
• Apical meristems generate primary growth, and lateral meristems generate secondary growth. Review Figure 24.6
• Apical meristems at the tips of shoots and roots give rise to three primary meristems (protoderm, ground meristem, and procambium), which in turn produce the three tissue systems of the plant body.
• The root apical meristem gives rise to the root cap and the three primary meristems. The cells in the root tip are arranged in three zones that grade into one another: the zone of cell division, zone of cell elongation, and zone of cell maturation. Review Figure 24.7
• The vascular tissue of roots is contained within the stele. It is arranged differently in eudicot and monocot roots. Review Figure 24.8 and WEB ACTIVITIES 24.1 and 24.2
• In stems, the vascular tissue is divided into vascular bundles, which containing both xylem and phloem. Review Figure 24.10 and WEB ACTIVITIES 24.3 and 24.4
• Eudicot leaves have two zones of photosynthetic mesophyll cells that are supplied by veins with water and minerals. Review Figure 24.12 and WEB ACTIVITY 24.5
• Two lateral meristems, the vascular cambium and cork cambium, are responsible for secondary growth. The vascular cambium produces secondary xylem (wood) and secondary phloem (inner bark). The cork cambium produces a protective tissue called cork. Review Figure 24.13 and Figure 24.14 and ANIMATED TUTORIAL 24.1

concept 24.3 Domestication Has Altered Plant Form

• Although the plant body plan is simple, it can be changed dramatically by minor genetic differences, as evidenced by the natural diversity of wild plants.
• Crop domestication involves artificial selection of certain desirable traits found in wild populations. As a result of artificial selection over many generations, the body forms of crop plants are very different from those of their wild relatives. Review Figure 24.15

 

Concept 24.1 The Plant Body Is Organized and Constructed 24.1 in a Distinctive Way

 

• The vegetative organs of flowering plants are roots, which form a root system, and stems and leaves, which (together with flowers, which are sexual organs) form a shoot system. Review Figure 24.1
• Plant development is influenced by three unique properties of plants (compared to animals): apical meristems, the presence of cell walls, and the totipotency of most plant cells. Review Figure 24.2
• During embryogenesis, the apical-basal axis and the radial axis of the plant body are established, as are the shoot apical meristem and the root apical meristem. Review Figure 24.3 and Figure 24.4
• Three tissue systems, arranged concentrically, extend throughout the plant body: the dermal tissue system, ground tissue system, and vascular tissue system. Review Figure 24.5
• The vascular tissue system includes xylem, which conducts water and mineral ions absorbed by the roots to the shoot, and phloem, which conducts the products of photosynthesis through- out the plant body.

Concept 24.2 Meristems Build Roots, Stems, and Leaves

• Primary growth is characterized by the lengthening of roots and shoots and by the proliferation of new roots and shoots through branching. Some plants also experience secondary growth, by which they increase in thickness.
• Apical meristems generate primary growth, and lateral meristems generate secondary growth. Review Figure 24.6
• Apical meristems at the tips of shoots and roots give rise to three primary meristems (protoderm, ground meristem, and procambium), which in turn produce the three tissue systems of the plant body.
• The root apical meristem gives rise to the root cap and the three primary meristems. The cells in the root tip are arranged in three zones that grade into one another: the zone of cell division, zone of cell elongation, and zone of cell maturation. Review Figure 24.7
• The vascular tissue of roots is contained within the stele. It is arranged differently in eudicot and monocot roots. Review Figure 24.8 and WEB ACTIVITIES 24.1 and 24.2
• In stems, the vascular tissue is divided into vascular bundles, which containing both xylem and phloem. Review Figure 24.10 and WEB ACTIVITIES 24.3 and 24.4
• Eudicot leaves have two zones of photosynthetic mesophyll cells that are supplied by veins with water and minerals. Review Figure 24.12 and WEB ACTIVITY 24.5
• Two lateral meristems, the vascular cambium and cork cambium, are responsible for secondary growth. The vascular cambium produces secondary xylem (wood) and secondary phloem (inner bark). The cork cambium produces a protective tissue called cork. Review Figure 24.13 and Figure 24.14 and ANIMATED TUTORIAL 24.1

concept 24.3 Domestication Has Altered Plant Form

• Although the plant body plan is simple, it can be changed dramatically by minor genetic differences, as evidenced by the natural diversity of wild plants.
• Crop domestication involves artificial selection of certain desirable traits found in wild populations. As a result of artificial selection over many generations, the body forms of crop plants are very different from those of their wild relatives. Review Figure 24.15

 

Concept 25.1 Plants Acquire Mineral Nutrients from the Soil

 

• Plants are photosynthetic autotrophs that require water and certain mineral nutrients to survive. They obtain most of these mineral nutrients as ions from the soil solution.
• The essential elements for plants include six macronutrients and several micronutrients. Plants that lack a particular nutrient show characteristic deficiency symptoms. Review Figure 25.1 and ANIMATED TUTORIAL 25.1
• The essential elements were discovered by growing plants hydroponically in solutions that lacked individual elements. Review Figure 25.2 and Working with Data 25.1
• Soils supply plants with mechanical support, water and dissolved ions, air, and the services of other organisms. Review Figure 25.3
• Protons take the place of mineral nutrient cations bound to clay particles in soil in a process called ion exchange. Review Figure 25.4
• Farmers may use shifting agriculture or fertilizer to make up for nutrient deficiencies in soil.

Concept 25.2 Soil Organisms Contribute to Plant Nutrition

• Signaling molecules called strigolactones induce the hyphae of arbuscular mycorrhizal fungi to invade root cortical cells and form arbuscules, which serve as sites of nutrient exchange between fungus and plant. Review Figure 25.5A
• Legumes signal nitrogen-fixing bacteria (rhizobia) to form bacteroids within nodules that form on their roots. Review Figure 25.5B
• In nitrogen fixation, nitrogen gas (N2) is reduced to ammonia in a reaction catalyzed by nitrogenase. Review Figure 25.6
• Carnivorous plants supplement their nutrient supplies by trapping and digesting arthropods. Parasitic plants obtain minerals, water, or products of photosynthesis from other plants.

Concept 25.3 Water and Solutes Are Transported in the Xylem by Transpiration–Cohesion–Tension

• Water moves through biological membranes by osmosis, always moving toward regions with a more negative water potential. The water potential (Ψ) of a cell or solution is the sum of its solute potential (Ψs) and its pressure potential(Ψp). Review Figure 25.8 and INTERACTIVE TUTORIAL 25.1
• The physical structure of many plants is maintained by the positive pressure potential of their cells (turgor pressure); if the pressure potential drops, the plant wilts.
• Water moves into root cells by osmosis through aquaporins. Mineral ions move into root cells through ion channels, by facilitated diffusion, and by secondary active transport. Review Figure 25.10
• Water and ions may pass from the soil into the root by way of the apoplast or the symplast, but they must pass through the symplast to cross the endodermis and enter the xylem. The Casparian strip in the endodermis blocks the movement of water and ions through the apoplast. Review Figure 25.11 and WEB ACTIVITY 25.1
• Water is transported in the xylem by the transpiration–cohesion–tension Evaporation from the leaf produces tension in the mesophyll, which pulls a column of water—held together by cohesion—up through the xylem from the root. Review Figure 25.12 and ANIMATED TUTORIAL 25.2
• Stomata allow a balance between water retention and CO2 Their opening and closing is regulated by guard cells. Review Figure 25.13

concept 25.4 Solutes Are Transported in the Phloem by Pressure Flow

• Translocation is the movement of the products of photosyn–thesis, as well as some other small molecules, through sieve tubes in the phloem. The solutes move from sources to sinks.
• Translocation is explained by the pressure flow model: the difference in solute potential between sources and sinks creates a difference in pressure potential that pushes phloem sap along the sieve tubes. Review Figure 25.14 and ANIMATED TUTORIAL 25.3

 

Concept 26.1 Plants Develop in Response to the Environment

 

• Plant development is regulated by environmental cues, receptors, hormones, and the plant’s genome.
• Seed dormancy, which has adaptive advantages, is maintained by a variety of mechanisms. When dormancy ends, the seed imbibes water, germinates, and develops into a seedling. Review Figure 26.1 and WEB ACTIVITY 26.1 and WEB ACTIVITY 26.2
• Hormones and photoreceptors act through signal transduction pathways to regulate plant growth and development.
• Genetic screens using the model organism Arabidopsis thaliana have contributed greatly to our understanding of signal transduction pathways in plants. Review Figure 26.2

concept 26.2 Gibberellins and Auxin Have Diverse Effects but a Similar Mechanism of Action

• Gibberellins stimulate growth of stems and fruits as well as mobilization of seed reserves in cereal crops. Review Figure 26.4 and WEB ACTIVITY 26.3
• Auxin is made in cells at the shoot apex and moves down to the growing region in a polar Review Figure 26.5
• Lateral movement of auxin, mediated by auxin efflux carriers, is responsible for phototropism and gravitropism. Review Figure 26.6 and ANIMATED TUTORIAL 26.1
• Auxin plays roles in lateral root formation, leaf abscission, and apical dominance.
• The acid growth hypothesis explains how auxin promotes cell expansion by increasing proton pumps in the plasma membrane, which loosens the cell wall. Review Figure 26.7 and ANIMATED TUTORIAL 26.2
• Both auxin and gibberellins act by binding to their respective receptors, which then bind to a transcriptional repressor, leading to the repressor’s breakdown in the proteasome. Review Figure 26.8

concept 26.3 Other Plant Hormones Have Diverse Effects on Plant Development

• Cytokinins are adenine derivatives that often interact with auxin. They promote plant cell division, promote seed germination in some species, and inhibit stem elongation, among other activities.
• Cytokinins act on plant cells through a two-component signal transduction pathway. Review Figure 26.9
• A balance between auxin and ethylene controls leaf abscission. Ethylene promotes senescence and fruit It causes the stems of eudicot seedlings to form a protective apical hook. In stems, it inhibits elongation, promotes lateral swelling, and decreases sensitivity to gravitropic stimulation.
• Brassinosteroids promote cell elongation, pollen tube elongation, and vascular tissue differentiation but inhibit root elongation. Unlike animal steroids, these hormones act at a plasma membrane receptor.
• Abscisic acid inhibits seed germination, promotes dormancy, and stimulates stomatal closing in response to dry conditions in the environment.

Concept 26.4 Photoreceptors Initiate Developmental Responses to Light

• Phototropin is a blue-light receptor protein involved in phototropism. Zeaxanthin acts in conjunction with phototropin to mediate the light-induced opening of stomata. Cryptochromes are blue-light receptors that affect seedling development and flowering and inhibit cell elongation. Review Figure 26.10
• Phytochrome is a photoreceptor that exists in the cytosol in two interconvertible isoforms, Pr and Pfr. The relative amounts of these two isoforms are a function of the ratio of red to far-red light. Phytochrome plays a number of roles in photomorphogenesis. Review Figure 26.11
• The phytochrome signal transduction pathway affects transcription in two ways: the Pfr isoform interacts directly with some transcription factors and influences transcription indirectly by phosphorylating other proteins. Review Figure 26.12
• Circadian rhythms are changes that occur on a daily cycle. Light can entrain circadian rhythms through photoreceptors such as phytochrome.

 

Concept 27.1 Most Angiosperms Reproduce Sexually

 

• Sexual reproduction promotes genetic diversity in a population. The flower is an angiosperm’s structure for sexual reproduction.
• Flowering plants have microscopic gametophytes. The megagametophyte is the embryo sac, which typically contains eight nuclei in seven cells. The microgametophyte is the two-celled pollen grain. Review Figure 27.2
• Following pollination, the pollen grain delivers sperm cells to the embryo sac by means of a pollen tube.
• Angiosperms exhibit double fertilization, forming a diploid zygote that becomes the embryo and a triploid endosperm that stores reserves. Review Figure 27.4 and ANIMATED TUTORIAL 27.1

concept 27.2 Hormones and Signaling Determine the Transition from the Vegetative to the Reproductive State

• In annuals and biennials, flowering and seed formation are followed by the death of the rest of the plant. Perennials live longer and reproduce repeatedly.
• For a vegetatively growing plant to flower, a shoot apical meristem must become an inflorescence meristem, which in turn must give rise to one or more floral meristems. These events are determined by specific genes. Review Figure 27.6
• Some plants flower in response to photoperiod. Short-day plants (SDPs) flower when nights are longer than a critical length specific to each species; long-day plants (LDPs) flower when nights are shorter than a critical length. Review Figure 27.7 and Figure 27.8 and ANIMATED TUTORIAL 27.2
• The mechanism of photoperiodic control of flowering involves phytochromes and a diffusible protein signal, florigen (FT), which is formed in the leaf and is translocated to the shoot apical meristem. Review Figure 27.9 and Figure 27.10
• In some angiosperms, exposure to cold—called vernalization—is required for flowering. In others, internal signals (such as gibberellin) induce flowering. All of these stimuli converge on the meristem identity genes.

Concept 27.3 Angiosperms Can Reproduce Asexually

• Asexual reproduction allows rapid multiplication of organisms that are well suited to their environment.
• Vegetative reproduction involves the modification of a vegetative organ for reproduction. Review Figure 27.12
• Some plant species produce seeds asexually by apomixis. Review Figure 27.13
• Woody plants can be propagated asexually by grafting.

 

Concept 28.1 Plants Have Constitutive and Induced Responses to Pathogens

 

• Plants and pathogens have evolved together in a continuing “arms race”: pathogens have evolved mechanisms for attacking plants, and plants have evolved mechanisms for defending themselves against those attacks.
• Some of the responses by which plants fight off pathogens are constitutive—always present in the plant—whereas others are induced—produced in reaction to the presence of a pathogen. Review Figure 28.1 and ANIMATED TUTORIAL 28.1
• Plants use physical barriers to block pathogen entry and seal off infected regions.
• Gene-for-gene resistance depends on a match between a plant’s resistance (R) genes and a pathogen’s avirulence (Avr)genes. Review Figure 28.2
• In the hypersensitive response to infection, cells produce phytoalexins and pathogenesis-related (PR) proteins, and the plant isolates the area of infection by forming necrotic lesions.
• The hypersensitive response may be followed by another defensive reaction, systemic acquired resistance, in which salicylic acid activates further synthesis of defensive compounds throughout the plant.

Concept 28.2 Plants Have Mechanical and Chemical Defenses against Herbivores

• Physical structures such as spines and thick cell walls deter some herbivores.
• Plants produce secondary metabolites as defenses against herbivores. Review Table 28.1, Figure 28.5, and Working with Data 28.1
• Hormones, including jasmonate, participate in signaling pathways leading to the production of defensive compounds. Review Figure 28.6
• Plants protect themselves against their own toxic defensive chemicals by compartmentalizing those chemicals, by storing their precursors separately, or through modifications of their own proteins.

Concept 28.3 Plants Adapt to Environmental Stresses

• Xerophytes are plants adapted to dry environments. Their structural adaptations include thickened cuticles, specialized trichomes, stomatal crypts, succulence, and long taproots.
• Some plants accumulate solutes in their cells, which lowers their water potential so they can more easily take up water.
• Adaptations to water-saturated habitats include pneumatophores, extensions of roots that allow oxygen uptake from the air, and aerenchyma, tissue in which oxygen can be stored and can diffuse throughout the plant. Review Figure 28.11
• A signaling pathway involving abscisic acid initiates a plant’s response to drought stress. Review Figure 28.12
• Plants respond to high temperatures by producing heat shock proteins. Low temperatures can result in cold-hardening.
• Plants that are adapted for survival in saline soils are called halophytes. Most halophytes accumulate salt. Some have salt glands that excrete salt to the leaf
• Some plants living in soils that are rich in heavy metals are hyper-accumulators that take up and store large amounts of those metals into their tissues.
• Phytoremediation is the use of hyperaccumulating plants or their genes to clean up environmental pollution in soils.