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8.6: Shoot Morphology - Biology

8.6: Shoot Morphology - Biology


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Shoots are composed of nodes. Each node has a leaf and an axillary bud, which emerges from the leaf axil. The identity of each organ is determined by its location in the node.

In the diagram below, label the bolded features, as well as the photosynthetic part of the leaf (the blade) and the stem of the leaf (the petiole). Label the bolded features in the diagram below.

Scars and Features of a Woody Shoot

When a leaf or bud falls off, it leaves a scar behind. Leaf scars are crescent shaped and have small, circular bundle scars within them where vascular bundles traversed the plant tissues. A leaf scar will be located below a bud, branch, or bud scar.

Plants that grow in temperate regions generally have a growing season. Each year, the newly emerging growth is within the terminal bud which is protected by terminal bud scales. When these scales fall off as the new growth emerges, they leave a region of terminal bud scale scars behind. Regions between terminal bud scale scars represent one year of growth.

On woody shoots, a layer of bark has replaced the epidermis (more on this in lab 8). To continue to exchange gases with the exterior environment, the bark layer develops small tears called lenticels. These can be small circular or elongated scars.

Label the bolded features in the diagram below. Draw in leaf scars where they are missing!

Leaf Arrangement

As shoots develop, the leaves are arranged in a particular order which can differ from plant to plant. In some plant species, one leaf emerges from the branch at a time (left) so leaves appear to alternate from side to side. This type of leaf arrangement is called alternate. In other plants, two leaves are formed on either side of the stem at the same time. This type of leaf arrangement is called opposite (middle). If three or more leaves are produced at the same region on the stem, the leaf arrangement is whorled (right).

Observe the shoots available in lab and identify the leaf arrangement and age of each. Record your findings in the table below.

Shoot

Leaf Arrangement

Age (years)


Pinus: External Morphology and Different Parts

2. Branches grow spirally and thus the plant gives the appearance of a conical or pyramidal structure.

3. Sporophytic plant body is differentiated into roots, stem and acicular (needle-like) leaves (Fig. 26).

4. A tap root with few root hair is present but it disap­pears soon. Later on many lateral roots develop, which help in absorption and fixation.

5. The ultimate branches of these roots are covered by a covering of fungal hyphae called ectotrophic mycorrhiza.

6. The stem is cylindrical and erect, and remains cov­ered with bark. Branching is monopodial.

7. Two types of branches are present: long shoots and dwarf shoots. These are also known as branches of unlimited and limited growth, respec­tively.

8. Long shoots contain apical bud and grow indefi­nitely. Many scaly leaves are present on the long shoot.

9. Dwarf shoots are devoid of any apical bud and thus are limited in their growth. They arise on the long shoot in the axil of scaly leaves.

10. A dwarf shoot (Fig. 27) has two scaly leaves called prophylls, followed by 5-13 cataphylls arranged in 2/5 phyllotaxy, and 1-5 needles.

11. The leaves are of two types, i.e., foliage and scaly.

12. Scaly leaves are thin, brown-coloured and scale like and develop only on long as well as dwarf shoots.

13. Foliage leaves are present at the apex of the dwarf shoots only.

14. Foliage leaves are large, needle-like, and vary in number from 1 to 5 in different species.

15. A spur (Fig. 28) is called unifoliar if only one leaf is present at the apex of the dwarf shoot, bifoliar if two leaves are present, trifoliar if three leaves are present, and so on.

Some of the species with differ­ent types of spurs are as follows:

(i) Pinus monophylla-unifoliar (having only one needle)

(ii) P. sylvestris-bifoliar (having two needles)

(iii) P. gerardiana-trifoliar (having three needles)

(iv) P. quadrifolia-quadrifoliar (having four needles)

(v) P. wallichiana-pentafoliar (having five needles).

Anatomy of Different Parts of Pinus:

Cut thin sections of different parts of the plant (Young root, old root, young long shoot, old long shoot, T.L.S. wood, R.L.S. wood, young dwarf shoot, old dwarf shoot and needle), stain them separately in a safranin-fast green combination, mount in glycerine and study. Also compare your preparations with the permanent slides shown to you in the laboratory.

1. Outermost layer of the circular roots is thick-walled epiblema with many root hair.

2. Epiblema is followed by many layers of parenchy­matous cortex.

3. Inner to the cortex is present a layer of endodermis and many layers of pericycle.

4. Vascular bundles are radially arranged and diarch to tetrarch with exarch protoxylem.

5. Protoxylem is bifurcated (Y-shaped) towards the periphery, and in between each bifurcation is present a resin cannal (Fig. 29).

6. Phloem is present alternate to the protoxylem.

7. Pith is poorly-developed or absent.

T.S. Old Root Showing Secondary Growth:

1. On the outer side are present a few layers of cork, formed by the meristematic activity of the cork cam­bium.

2. Cork cambium cuts secondary cortex towards inner side.

3. Many resin canals and stone cells are present in the secondary cortex, the cells of which are sepa­rated with the intercellular spaces.

4. Below the phloem patches develop cambium, which cuts secondary phloem towards outer side and sec­ondary xylem towards inner side.

5. Crushed primary phloem is present outside the sec­ondary phloem (Fig. 30).

6. Many uniseriate medullary rays are present in the secondary xylem.

7. Primary xylem is the same as in young roots, i.e., each group is bifurcated (Y-shaped) and a resin canal is present in between the bifurcation.

1. Many leaf bases are present on the stem (Fig. 31), due to which it appears wavy in outline.

2. Outermost single-layered, thick-walled epidermis is heavily cuticularized and followed by multilayered cortex.

3. A few outer layers of cortex are sclerenchymatous, and some inner layers are parenchymatous.

4. In the inner layers of cortex are present many resin canals.

5. The stele is eustelic or polyfascicular endarch siphonostele.

6. Vascular bundles are conjoint, collateral, open and endarch, and resemble greatly with that of a dicot stem. 5-10 vascular bundles are arranged in a ring.

7. Endodermis and pericycle are indistinguishable.

8. Narrow xylem rays connect the cortex and pith.

9. Endarch xylem consists of only tracheids.

10. Phloem is present on the ventral side and consists of sieve cells, sieve plates, phloem parenchyma and some albuminous cells.

11. Intrafascicular cambium is present in between the xylem and phloem.

12. Many leaf traces are also present.

13. A small parenchymatous pith is present in the cen­tre of stem.

1. Secondary growth, similar to that of a dicotyledon­ous stem, is present in the old stem of Pinus.

2. Cork cambium cuts cork towards outer side and a few layers of secondary cortex towards inner side.

3. Many tannin-filled cells and resin canals are dis­tributed in the primary cortex.

4. Cambium cuts secondary phloem towards outer side and secondary xylem towards inner side (Fig. 32).

5. Primary phloem is crushed and pushed towards outer side by the secondary phloem.

6. In the secondary xylem, annual rings of thin-walled spring wood (formed in spring season) and thick- walled autumn wood (formed in autumn season) are present alternately. Such a compact wood is called pycnoxylic (Age of the plant can be calcu­lated by counting the number of these annual rings).

7. Below the secondary xylem are present a few groups of endarch primary xylem.

8. Some of the medullary rays connect the pith with the cortex and called primary medullary rays while the others run in between secondary xylem and secondary phloem and called secondary medullary rays.

9. Central part of the stem is filled with the parenchy­matous pith.

10. Resin canals are present in cortex, secondary xylem, primary xylem and rarely in the pith.

Tangential Longitudinal Section (T.L.S.) of Wood:

In T.L.S. the longitudinal section is cut along the tan­gent of the wood.

Following structures are visible:

1. Bordered pits and medullary rays are present in sectional view.

2. Each border pit is enclosed by a pit chamber bounded by a pit membrane and contains a cen­trally located swollen torus (Fig. 33).

3. Tracheids are composed of rectangular cells. Middle lamella is very clear.

4. Many uniseriate medullary rays are present.

5. In the xylem region medullary rays contain a cen­trally located starch cell surrounded by tracheidial cells.

6. Albuminous cells are also present in medullary rays in phloem region.

Radial Longitudinal Section (R.L.S.) of Wood:

In R.L.S., the stem is cut along the radius, and so the pith is also visible.

Following other details are visible:

1. It is bounded externally by cork, cork cambium, secondary phloem and crushed primary phloem.

2. Bordered pits surrounded by bars of Sanio in trac­heids are seen in surface view.

3. Uniseriate medullary rays run horizontally.

4. In the xylem region thick medullary ray cells are surrounded by ray tracheids (Fig. 34).

5. Thin-walled ray parenchyma is also present.

6. Xylem is separated from phloem with the help of cambium.

7. Albuminous cells are present in medullary ray in the phloem region.

8. Phloem consists of sieve tubes, sieve plates and phloem parenchyma.

It is exactly similar to that of T.S. of young long shoot except following differences:

1. The number of the resin canals present in the cor­tex is not indefinite but generally six (Fig. 35).

Though it is variable in different species.

2. The number of the vascular bundles is also gener­ally six. However, it is also variable in different spe­cies.

3. Pith in dwarf shoot is comparatively smaller than the long shoot.

4. Structure of the vascular bundles is same, i.e., con­joint, collateral, open and endarch.

1. It is also similar to old long shoot in many aspects.

2. Cork, cork cambium and secondary cortex are not normally present, but the epidermis surrounded externally by scaly leaves and followed internally by multilayered cortex is present.

3. Inner to the cortex is crushed primary phloem, sec­ondary phloem, cambium and secondary xylem with medullary rays (Fig. 36). Protoxylem is endarch.

4. A small pith with some tannin cells is present in the centre.

If a section of distal end of dwarf shoot is cut, the needles get separated, each having the same structure. In a bifoliar spur two needles are present while in a trifoliar spur there are present three foliage leaves or needles (Fig. 37).

T.S. Needle (Foliage Leaf):

1. It is circular in outline in Pinus monophylla, semi­circular in P. sylvestris and triangular (Fig. 38) in P. longifolia, P. roxburghii, etc.

2. Outermost layer is epidermis, which consists of thick-walled cells. It is covered by a very strong cuticle.

3. Many sunken stomata are present on the epider­mis (Fig. 38).

4. Each stoma opens internally into a substomatal cavity and externally into a respiratory cavity or vestibule.

5. Below the epidermis are present a few layers of thick-walled sclerenchymatous hypodermis. It is well-developed at ridges.

6. In between the hypodermis and endodermis is present the mesophyll tissue.

7. Cells of the mesophyll are polygonal and filled with chloroplasts. Many peg-like infoldings of cellulose also arise from the inner side of the wall of meso­phyll cells.

8. Few resin canals are present in the mesophyll, adjoining the hypodermis. Their number is vari­able but generally they are two in number.

9. Endodermis is single-layered with barrel-shaped cells and clear casparian strips.

10. Pericycle is multilayered and consists of mainly par­enchymatous cells and some sclerenchymatous cells forming T-shaped girder, which separates two vascular bundles (Fig. 38). Transfusion tissue con­sists of tracheidial cells.

11. Two conjoint and collateral vascular bundles are present in the centre. These are closed but cam­bium may also present in the sections passing through the base of the needle.

12. Xylem lies towards the angular side and the phloem towards the convex side of the needle.

Reproductive Structures of Pinus:

1. Plant body is sporophytic.

2. Pinus is monoecious, and male and female flowers are present in the form of cones or strobili on the separate branches of the same plant.

3. Many male cones are present together in the form of clusters, each of which consists of many microsporophylls. The female cones consist of megasporophylls.

4. The male cones on the plant develop much earlier than the female cones.

Separate a male cone from the cluster, study its struc­ture, cut its longitudinal section, study the structure of a single microsporophyll, and also prepare a slide of pollen grains and study.

1. The male cones develop in clusters (Fig. 39) in the axil of scaly leaves on long shoot.

2. They replace the dwarf shoots of the long shoot.

3. Each male cone is ovoid in shape and ranges from 1.5 to 2.5 cm. in length (Fig. 40).

4. A male cone (Fig. 41) consists of a large number of microsporophylls arranged spirally on the cone axis.

5. Each microsporophyll is small, membranous, brown-coloured structure.

6. A microsporophyll (Fig. 41) is comparable with the stamen of the flower of angiosperms because it consists of a stalk (=filament) with a terminal leafy expansion (= anther), the tip of which is projected upwards and called apophysis.

7. Two pouch-like microsporangia (= pollen sacs) are present on the abaxial or undersurface of each microsporophyll. In each microsporangium are present many microspores (= pollen grains).

8. Each microspore or pollen grain is a rounded and yellow-coloured, light, uninucleate structure with two outer coverings, i.e., thick outer exine and thin inner intine (Fig. 42).

9. The exine protrudes out on two sides in the form of two balloon-shaped wings. Wings help in floating and dispersal of pollen grains.

10. Wings help in floating and dispersal of pollen grains.

11. A few microsporophylls of lower side of cone are sterile. Sporangia are also not present on the adaxial surface of each microsporophyll of the male cone.

Observe the external features and longitudinal sec­tion of a young female cone and also study 1st year, 2nd year and 3rd year female cones.

1. Female cone develops either solitary or in groups of 2 to 4.

2. They also develop in the axil of scaly leaves on long shoots (Fig. 43) like male cones.

3. Each female cone is an ovoid, structure when young but becomes elongated or cylindrical at maturity.

1. In the centre is present a cone axis (Fig. 44).

2. Many megasporophylls are arranged spirally on the cone axis.

3. A few megasporophylls, present at the base and at the apex of strobilus, are sterile.

4. Megasporophylls present in the middle of the stro­bilus are very large and they decrease in size to­wards the base and apex.

5. Each megasporophyll consists of two types of scales, known as bract scales and ovuliferous scales.

6. Bract scales are thin, dry, membranous, brown- coloured structures having fringed upper part. These are also called carpellary scales.

7. An ovuliferous scale is present on the upper sur­face of each bract scale.

8. Each oruliferous scale is woody, bigger and stouter than bract scale and it is triangular in shape. A broad sterile structure, with pointed tip, is present at the apex of these scales. This is called apophy­sis.

9. At the base of upper surface of each ovuliferous scale are present two sessile and naked ovules.

10. Micropyle of each ovule faces towards the cone axis.

11. Each ovule is orthotropous, and it remains sur­rounded by a single integument, consisting of an outer fleshy, a middle stony and an inner fleshy layer. It opens with a mouth opening called micro­pyle.

12. Integument surrounds the megasporangium or nucellus.

13. Just opposite the micropyle is present a pollen chamber.

14. In the endosperm or female gametophyte are present 2 to 5 archegonia.

Female Cone of 1 st Year:

1. It is oval (Fig. 45) in shape.

2. It ranges from 1 to 4 cm. in length.

3. It is green to reddish-green in colour.

4. It is attached with the help of a short stalk on the long shoot.

5. Megasporophylls are arranged very close to each other, and so the cone is a compact structure.

Female Cone of 2nd Year:

1. It is elongated and larger than the first year cone.

2. It ranges from 5 to 15 cm. or more in length.

3. It is red-coloured structure.

5. Megasporophylls are compactly arranged (Fig. 46) but not so compact as in 1st year cone.

6. Seeds are present inside in the later stages (Fig. 46).

Female Cone of 3rd Year:

1. It is elongated or roughly rounded in shape.

2. It is also woody in nature like the 2nd year cone.

3. Megasporophylls (Fig. 47) are loosely arranged.

4. Seeds are dispersed from 3rd year cone.

1. Both the ovules of each ovuliferous scale develop into seeds (Fig. 48).

2. Each seed contains a large membranous wing formed from the ovuliferous scale.

Anatomy of seed shows following (Fig. 48C) details:

1. It is enveloped by a seed coat developed from the middle stony layer of the ovule.

2. Inner fleshy layer may survive in the form a thin membrane. Outer fleshy layer disappears.

3. A thin, membranous and papery structure, called perisperm, develops inner to the seed coat.

4. Well-developed endosperm is present.

5. In the centre is present the embryo consisting of a hypocotyle, radicle, plumule and 2 to 14 or more cotyledons.

(i) Sporophytic plant body differentiated into roots, stem and leaves.

(iv) Phloem lacks companion cells.

(v) Sex organs are present in the form of cones…………. Gymnosperms


8.6: Shoot Morphology - Biology

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Biology and seasonal incidence of the jack shoot and fruit borer, Diaphania caesalis (Walker) (Lepidoptera: Crambidae)

The biology and seasonal incidence of the shoot and fruit borer of jackfruit tree, Diaphania caesalis (Walker) (Lepidoptera: Crambidae) has been studied. The male and female moths completed their life cycle in 30.4 ± 2.3 and 31.8 ± 2.3 days respectively with five larval instars. The mean incubation period of the egg, developmental duration of larva, prepupa and pupa were 4.9 ± 0.6, 17 ± 0.6, 3.6 ± 0.4, 8 ± 0.4 days respectively. The first and last instar larva measured 2.6 ± 0.3 and 22.4 ± 0.4 mm in length respectively. Unfed moths lived significantly shorter duration (6–9 days) than those with access to water (9–12 days), honey (12–14 days), and honey with vitamin supplement (14–17 days). The incidence of D. caesalis was recorded throughout the year during 2013–2016 indicated an overlapping of generations. However, two distinct peaks in the population level were recorded during June–July and October–November. Subsequently, the pest population declined at the beginning of the winter and was at a very low level in summer. Further, analysis of the data with population density and weather parameters revealed that relative humidity, minimum temperature and rainfall were positively correlated, whereas evaporation was negatively correlated with the incidence of D. caesalis.

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Shoot Anatomy and Morphology

This chapter discusses the anatomy and morphology of cacti shoot, focusing primarily on its cellular characteristics and biomechanical properties. The shoot consists of internodes, nodes where leaves are attached, and axillary buds (the spine-producing areoles). The bud scales and leaves of axillary buds are the signature spines of cacti. The ability of cacti to adapt to xeric conditions is due to increases in water-storage tissue, especially in the cortex and wood, thickened cuticles, and the presence of a hypodermis. The fundamental tissue, cortex and pith, carries out two important functions related to xeric adaptations: photosynthesis and water storage.

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Seeds and their Morphological Features (With Diagram)

Gram seed (Fig. 8.2) is a dicot, non-endospermic seed. The seeds are produced within the pods or leguminous fruits.

A gram seed appears conical-pyriform in outline.

It has following parts:

It consists of two layers-outer testa and inner tegmen. Testa is thick and brownish. The tegmen is thin, membranous, and whitish and remains fused with testa. The pointed beak like end of the seed has a minute pore called micropyle. If a soaked seed is gently pressed, a drop of water oozes out of the micropyle. A small oval scar seen near the micropyle is called hilum through which the seed was attached to fruit. Another oval scar present in the middle is called chalaza or strophiole. A distinct ridge called raphe runs from hilum to chalaza.

It presents inner to seed coat. It consists of two circular yellowish cotyledons that are attached to the embryo axis. The part of embryo axis above the point of attachment to the cotyledons is called epicotyle. The tip of epicotyle is called plumule. Similarly, the region of the embryo axis below the point of attachment of cotyledons is called the hypocotyle. The tip of hypocotyle is called radicle. During germination, the radicle comes out first through the micropyle and grows to form a tap root. The plumule gives rise to shoot system.

2. Morphology of Castor Seed (Ricinus communis):

Castor seed is a monocot, endospermic seed. The castor seeds are produced within a schizocarpic fruit called the regma which on maturity breaks up into 3 cocci, each containing a single seed. A castor seed is roughly oblong in outline with distinct convex (dorsal) and flat (ventral) surfaces. A castor seed has following parts (Fig. 8.3)

It is the outer layer of seed coat. It is thick, hard and brittle. The external surface appears smooth, shinning and mottled brown in colour.

It is the inner layer of seed coat that appears dull and papery. Now it is called as perisperm or persistent nucellus.

It is a white spongy bilobed outgrowth present near the narrow end of the seed. If partially covers the hilum (dark scar) and completely covers the micropyle (small pore). Caruncle absorbs water which percolates through the micropyle into the seed.

It is a shallow ridge present on the testa of flat surface of the seed. The distinct bifurcation of raphae represents chalaza.

It is a white oily food storage tissue that is present inner to the perisperm. From this layer castor oil of commerce is extracted.

Embryo lies in the centre of endosperm. It consists of a radicle, a plumule and two lateral cotyledons, all of which are present on a short embryo axis. The cotyledons are thin, semi-transparent and oval in outline. They have palmate venation. The middle costa or rib is more prominent and bears a few lateral veins.

Radicle lies outside the cotyledons towards the micropylar end. It is a knob-like outgrowth. Plumule lies in between the two cotyledons and is quite indistinct. Epicotyl is also indistinct. In between the place of origin of the two cotyledons and the radicle is present a short hypocotyl. Castor-oil seed is dicotyledonous (having two cotyledons), endospermic (with a special food storing tissue called endosperm) and perispermic (having perisperm or persistent nucellus).

3. Morphology of a maize seed (Zea mays):

Maize or Corn seed (Fig. 8.4) is actually a one seeded fruit called caryopsis or grain. It is a monocot endospermic seed.

It consists of following parts:

It is fused with the fruit wall (pericarp). It encloses a kernal which includes embryo and endosperm.

It constitutes 2/3 of the grain. Endosperm consists of outer aleurone layer and inner starchy endosperm.

It lies on one side of the starchy endosperm and appears to be a lighter oval area in the whole seed. Embryo consists of a scutellum and a short embryo axis (tigellum). The scutellum is a shield-shaped cotyledon attached to a node of embryo axis. The surface of scutellum facing endosperm is called epithelial layer. It is both secretory and absorptive in nature. The epithelial layer secretes hormones into the endosperm for the synthesis of enzymes required for solubilisation of food. The solubilised food is absorbed by it and then transferred to the embryo axis.

The embryo axis has plumule (upper end) and radicle (lower end). The plumule contains a few rudimentary leaves and a conical protective sheath called coleoptile. The coleoptile has a termina pore for the emergence of first leaf during germination. The sheath is capable of growth. It assists the future shoot in passing through the soil during germination.

The radicle has two protective sheaths, inner root cap and outer coleorhiza. Roughly in the middle of embryo axis arises a vascular strand. It ramifies into the scutellum. The place of origin of the vascular strand from the embryo axis is called cotyledonary node.

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Morphology of root system

Roots are typically of non-green underground cylindrical structure forming the axis of the plant which gives rise to endogenous and does not possess leaves, nodes or buds.

Characteristics of the root system

  • They normally constituted the descending part of the plant axis.
  • These are the cylindrical structure which is non-green and do not have the distraction of nodes and internodes.
  • Buds and leaves are absent and its functions root is covered by a root cap.
  • Root branches develop from the interior of the parent root such and origin is called endogenous which is in contrast to exogenous or external origin in case of the stem.
  • The roots are neutral or negatively phototrophic and positively hydrotropic and positively geotropic.

Parts of a typical root:

  • It is our thimble-shaped or cap-like parenchymatous multicellular structure which covers the root meristem.
  • The cells of the root cap secret mucilage.
  • The water lubricates the passage of roots through the soil.
  • Without it, the tender route would be unable to penetrate the hard soil.
  • Another function of the root cap is the protection of the root meristem from the friction of the soil particle.
  • Route pockets function at balance in the aquatic plants which is finger glove-like covering at the root apices.
  • These are structurally similar to the root caps but differ from the damaged or lost root pocket are not regenerated.

(2) Growing point Or meristematic zone

  • It is about 1 mm in length.
  • The growing point of the root is determined and lies protected below the root cap.
  • The meristematic reason produces a new cell for the root cap and the based region of the root.
  • Therefore it is essential for the growth of the root.

(3) Region for the zone of elongation

  • It is about 4 to 8 mm in length.
  • It lies behind the growing point.
  • The cells of this region are newly formed cell which loses the power of division.
  • They elongate rapidly.
  • This increase the length of the root.
  • This also causes the power of absorption of water and mineral salt from the soil.

(4) Root hair zone

  • It also represents the zone of differentiation or maturation because a different type of primary tissues differentiates or mature in this reason like xylem and phloem, pericycle, endodermis cortex, epiblema etc.
  • Root hair zone is 126 CM in length.
  • Most of the water absorption occurs in this region.
  • Some of the outer cells of this zone give rise to lateral tabular outgrowth called root hairs.
  • The root hairs increase the exposed surface of the root for absorption.

(5) Region or zone of mature cell

  • It forms the bulk of the route.
  • The cells of this reason do not undergo any further change.
  • The outermost layer of this region has a thick world or impermeable sales.
  • So this region cannot help the root in water absorption.
  • Its only functions to anchor the plant firmly in the soil.

Types of the root system

(1)Taproot system:

  • it is a mass of roots which develop from the radicle of the embryo.
  • it consists of a tap root, secondary roots, tertiary roots and also rootlets.
  • The radical itself grow up directly into the main or primary root.
  • The persistent primary root is known as the taproot.
  • they are formed in acropetal succession and oldest towards the base of the parent Root.
  • Rootlets are the ultimate root branches.
  • They bear root hair for absorption.
  • The root system is of two types:-

(1)Deep feeder

(2)Surface feeder

  • deep feeder tap root which penetrates the deeper layer of the soil.
  • it is mostly found in trees.
  • in surface feeders, the taproot does not elongate very much.
  • the secondary roots spread to a greater extent mostly horizontal near the soil surface.
  • the surface feeder tap root system of some annual plant consists of thin fibrous roots.
  • it may be called a fibrous tap root system.

(2) adventitious root system

  • The root that grows from any part of the plant other than the radicle or its branches is called adventitious roots.
  • The branches like a taproot.
  • a mass of adventitious roots along with their branches constituent and adventitious root system.
  • the plant having adventitious root also developed primary root from the radical.
  • However, it is short-lived and therefore does not produce taproot.
  • fibrous roots are underground root which arises in group weather at the base of the erect steam for the notes of the horizontal stem.
  • the main roots are of equal length.
  • they give off small branches.
  • both the main root and their branches are thin and thread-like.
  • therefore they are called fibrous roots which do not penetrate deep in the soil are hens named as a surface feeder.

Function of roots

Primary or main functions

Roots take part in a succession of the plant and supporting the aerial shoot system.

Roots absorb water from the soil.

Roots absorb mineral salts from the soil.

Roots hold the soil particles firmly to prevent soil erosion.

The taking part in transport to absorb water and mineral to shoot system.

Secondary functions:

  1. Storage:It occurs in fresh roots.Conical-carrots, Napiform-Beat, Tuber-microbilis
  2. Extra or mechanical support: It is provided by several types of roots.Buttress roots- Bombax,Stilt roots- Maize
  3. Climbing: Roots help some of the weak stem plants to cling and hence climb of support.Ex- money plant.
  4. Nitrogen fixation: Nodulated roots of pea, bean, gram, methylation: Prop roots, knee roots
  5. Reproduction: By bearing adventitious buds on both tap roots and adventitious roots.
  6. Floating: By storing air sum of the function of the root as floats.
  7. Photosynthesis: As in propa, Tinospora
  8. Oxidation: The roots of some amphibious plant release Oxygen and oxidize the surrounding environment as for example rice.

Also, you can check the flowering plant characteristics and reproduction in- Study Notes on Sexual reproduction in flowering plants


Exogenous 6-benzyladenine application affects root morphology by altering hormone status and gene expression of developing lateral roots in Malus hupehensis

D. Zhang, College of Horticulture, Northwest Agriculture & Forestry University, Yangling 712100, China.

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

College of Life Science, Northwest Agriculture & Forestry University, Yangling, China

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

Department of Agricultural Sciences, the University of Haripur, Haripur, Pakistan

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

Beijing Ori-Gene Science and Technology Corp., Ltd., Beijing, China

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

College of Life Science, Northwest Agriculture & Forestry University, Yangling, China

College of Horticulture, Northwest Agriculture & Forestry University, Yangling, China

College of Life Science, Northwest Agriculture & Forestry University, Yangling, China

D. Zhang, College of Horticulture, Northwest Agriculture & Forestry University, Yangling 712100, China.

Abstract

  • Malus hupehensis is an extensively used apple rootstock in China. In the current study, M. hupehensis seedlings were treated with exogenous 2.2 µ m 6-benzyladenine (6-BA) so as to investigate the mechanism by which 6-BA affects lateral root development.
  • The results indicate that 6-BA treatment promotes elongation and thickening of both root and shoot in M. hupehensis, but reduces the number of lateral roots, as well as reducing the auxin level after 6-BA treatment. Moreover, MhAHK4, MhRR1 and MhRR2 were also significantly up-regulated in response to 6-BA treatment.
  • Expression levels of auxin synthesis- and transport-related genes, such as MhYUCCA6, MhYUCCA10, MhPIN1 and MhPIN2, were down-regulated, which corresponds with lower auxin levels in the 6-BA-treated seedlings. A negative regulator of auxin, MhIAA3, was induced by 6-BA treatment, leading to reduced expression of MhARF7 and MhARF19 in 6-BA-treated seedlings. As a result, expression of MhWOX11, MhWOX5, MhLBD16 and MhLBD29 was blocked, which in turn inhibited lateral root initiation.
  • In addition, a lower auxin level decreased expression of MhRR7 and MhRR15, which repressed expression of key transcription factors associated with root development, thus inhibiting lateral root development. In contrast, 6-BA treatment promoted secondary growth (thickening) of the root by inducing expression of MhCYCD31 and MhCYCD32. Collectively, the changes in hormone levels and gene expression resulted in a reduced number of lateral roots and thicker roots in 6-BA-treated plants.

Figure S1. Effect of exogenous application of 2.2 µ m 6-BA on relative expression of the cytokinin signal, IAA synthesis, IAA signal transduction, cell cycle and lateral root development-related genes in lateral roots of Malus hupehensis seedlings, using the gene EF-1α for normalization. Values represent mean ± SE of three biological replicates. *significant 0.05 level, **significant at 0.01 level.

Table S1. Formula for 1/2 Hoagland nutrient solution.

Table S2. The gene name (abbreviations and full names) and apple MDP number, as well as species and protein of the homologue on which the apple protein is based.

Table S3. Sequence of primers used for expression analysis. F, forward primer R, reverse primer MDP, number of gene and length of primers.

Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.


Watch the video: Morphology (September 2022).


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