WHMF121 Session Five. Plant Morphology Part II Roots

Transcription

1 WHMF121 Session Five Plant Morphology Part II Roots Celeriac ( r/file:celeriac_j2.jpg)

2 Todays Botany Topics o Roots and root development o Root cap o Root modifications o Functions of roots o Vascular Tissue

3 Roots o Roots are normally underground structures which are distinguished from stems by the absence of nodes, buds and chlorophyll. o When a seed germinates, the embryo inside starts to grow in two directions. (

4 Roots o First the radicle (embryonic root) grows downwards towards the centre of the earth in response to gravity. o Later the plumule (embryonic shoot) grows towards the light. ( aba)_seed_germination.jpg)

5 Roots o The first tiny root that grows is the primary root. o In Dicots the primary root becomes the tap root (eg., carrot) with lateral roots developing from it as it grows downwards into the soil. o This forms a tap root system. o NB: Tap roots are not always obvious like carrots. Note the distinctive taproot of Taraxacum officinal or you might know it from its common name Dandelion.

6 Roots o Some taproots become very swollen and are much larger than the many lateral roots whereas in other species such as Achillea millefolium (Yarrow) the taproot is about the same size as the laterals. o The important thing to remember is that the tap root develops from the radicle, which is the embryonic root. Maca root; Lepedium meyenii Beetroot: Beta vulgaris

7 o In Monocots, the primary root doesn t develop into a tap root. o Instead a network of evenly sized roots develops from adventitious roots growing from the base of the stem. o This forms a fibrous root system. (e.g. grass roots) Roots From the family Amaryllidaceae comes Allium sativum, or common garlic, showing a fibrous root system (

8 Roots o As they have not originated from preexisting roots and are not radicles they are called adventitious roots o Adventitious roots increase the root systems capacity for absorption and transportation of water and nutrients (Mauseth, 2014) Banyan Tree (

9 Roots o Fibrous root systems consist of many roots, which are not derived from a radicle but originated in the stem tissue. o The radicle dies during or straight after germination and then the first stage of the fibrous roots are formed. o Some dicots can also form adventitious roots i.e. those with stolons and rhizomes. (Mauseth, 2014) ( ponically-grown_plant.jpg)

10 Roots o The root system of a plant constantly provides the stems and leaves with water and dissolved minerals. o In order to accomplish this, the roots must grow into new areas of the soil. o The growth and metabolism of the plant root system is supported by the process of photosynthesis occurring in the leaves o Other dicots which normally don t produce adventitious roots naturally, but they do so if cut. o This is useful when it comes to asexual propagation or cloning. (Mauseth, 2014)

11 Roots o Both root systems (tap and fibrous) have feeder roots that actively absorb water and nutrients. o Most feeder roots are found in the uppermost 15cm of soil where the richest organic matter is found. These fine roots extend out to where the water falls under the tree's outermost foliage. o Nutrients are concentrated in the area beneath the tree's branches, just cm below the soil surface. As organic matter breaks down on the soil surface, fine feeder roots recycle the nutrients back to the tree.

12 Roots Mangrove roots

13 Roots o Tap root systems can penetrate deeper into the soil so do not rely on surface moisture but they hold the soil in place and prevent soil erosion. o However plants with fibrous roots systems are better for erosion control, because the mass of roots cling to soil particles.

14 Roots o Roots will generally grow in any direction where the correct environment of air, minerals, nutrients and water exists to meet the plant's needs. o Roots will not grow in dry soil. Over time, given the right conditions, roots can crack foundations, snap water lines, and lift sidewalks.

15 Image credit: Wikipedia, viewed 8 January

16 Roots o Tap and fibrous root systems have basically the same structures. o Lateral roots grow from a central core through the root s outer skin (epidermis).

17 Roots o The tip is covered in specialised cells (the root cap). o The section of dense root hairs are responsible for absorption of water and nutrients. o The growing tip is covered by a layer of cells called the root cap.

18 Root Cap o The root cap is where longitudinal growth occurs and unlike animals where all parts of the body grow at the same time, only small sections of the root and stem can grow at the one time. o Because the root is in the soil it is impossible for the whole root body to push its way through. o Only the tip can push its way through the soil. o As the cap is forced through the soil ahead of the body, it is being worn away and therefore needs to be renewed constantly. (Mauseth, 2014) 18

19 Root Cap The root cap helps the root grow through the soil in 3 ways: 1. By protecting the root. As the root grows the cells behind the root cap divide pushing the cap forward first. The cells of the root cap provide a physical barrier around the tender growing tip.

20 Root Cap 2. Lubricating its passage. The cells at the edge of the root cap get old and die, slough off and become slimy, making a mucilaginous coating around the root that lubricates the tip as it moves through the soil. 3. Directing it s growth Roots grow mostly downwards i.e. they exhibit geotropism or gravitropism. Geotropism is growth directed by gravity. The cells of the root cap initiate this.

21 Geotropism o A "tropism" is a plant movement triggered by stimuli. o The mechanism involves little gravity sensors that can move within the cells of the root cap. o If a root begins to grow upwards or sideways, the gravity sensors will move to another part of the cell. o This movement triggers a hormone called auxin that inhibits elongation of the root on the lower side. o The upper side grows normally while the lower side grows less. o The end result is that the root tip points downwards. (Read Capon, B. pp )

22 Geotropism in a Corn Kernel (Monocot) (

23 Root Hair o Behind the tip of the root is an area which can is often called the maturation or root hair zone. o It contains a dense band of root hairs". o Root hairs are tubular outgrowths of the epidermal cells of the root. o Water (and minerals dissolved within it) seep into the root hairs from the soil and are carried to special vessels in the middle of the root (xylem). (Mauseth, 2014)

24 Roots o Xylem are vascular tissue that transports water and nutrients absorbed by the root hairs to the rest of the plant. o The word xylem comes from the Greek meaning wood. o Water is moved in the xylem by a suction like mechanism and only moves upwards throughout the stem and leaves. o Apart from transportation of water and nutrients, the xylem is also used to replace water lost during transpiration and photosynthesis. (Mauseth, 2014)

25 Roots o Many dicots are perennial (live longer than 2 yrs) and undergo secondary growth. This results in an increase in healthy xylem in both the roots and stem. This then also increases the number of leaves and fine new roots. o In monocots there is no secondary growth, once the stem is formed and all of the connective tissue has been established. (Mauseth, 2014)

26 Roots o Extra leaves and an ever increasing tap root system cannot be supplied with water or nutrients. However some monocots do increase their size via stolons or rhizomes o These stolons or rhizomes produce their own adventitious roots. o Because they have arisen from new stem tissue, the water and nutrients are transported directly into them and are not affected by the old shoots. o By this method monocot shoots can grow larger as long as they stay close to the original body of the plant. (Mauseth, 2014)

27 Roots _cross-section.jpg Campanula spp.

28 Roots Think of Cymbopogon citratus (Lemongrass) ( 28

29 Functions of Roots 1. Anchorage and support Roots anchor the plant in the soil, they usually spread under the ground at least as much as branches spread above the ground. (

30 Functions of Roots 2. Absorption of water and nutrients Roots have special adaptations for this, i.e. root hairs. Absorption is vital for plant survival and there must be correct balance between the surface area of the roots (for absorption) and the surface area of the leaves (for photosynthesis). Young plants need a higher surface area ratio of root to leaf than older plants because they are growing more rapidly.

31 Functions of Roots 3. Hormone production The aerial parts of plants depend on plant growth hormones. A number of these are synthesised in the roots, especially: cytokinins (that stimulate cell division) gibberellins (that stimulate stem elongation).

32 Functions of Roots o Lack of the plant hormone auxin can cause abnormal growth. o Which plant do you think lacks the auxin? (

33 4. Storage Functions of Roots Some roots have certain cells adapted for starch storage (e.g. carrot Daucus carota and beetroot Beta vulgaris) Food that has been made in the leaves is transported down to the roots for storage until it is needed. It may be used by the root or returned to the rest of the plant. Many biennial plants store excess food as starch during the first year. This is then used by the plant during the second year when flowering and fruit production occurs. (Tan, 2013)

34 Roots What type of roots are these? Daucus carota (Carrot) from Apiaceae family ( ors.jpg) Roystonea regia palm (Arecales) stems showing secondary root growth

35 Root Modifications o Most roots grow in the soil but in some plants aerial roots have evolved. o Aerial roots are mostly adventitious roots i.e., they grow from the stem rather than from another root. o Adventitious or Modified roots can be; Prop roots Aerial roots Pneumatophores Buttress roots

36 Prop Root o A prop root is an example of an aerial root. o The stem of a monocot becomes wider and then produces these roots which go down to the soil. Common in grasses o In some larger monocots the roots can take months growing through the air until they reach the soil. o Prop roots support the stem and also absorb water and nutrients from underground as well as stabilising the plant.

37 Prop Root e.g. Zea mays- corn plant. 37

38 Climbing Root o Another example of an aerial root is a climbing root. o Climbing roots grow away from light and into cracks. o They support climbing stems like Ivy (Hedera helix) on vertical surfaces (observe the picture to the right) (Tan, 2013) 38 ( penburg_efeu.jpg)

39 Climbing Roots ( 39

40 Aerial Roots o Another example of plants with aerial roots are epiphytes, such as orchids and bromeliads o Epiphytic plants use photosynthesis for energy and obtain moisture from the air or from dampness (rain and cloud moisture) on the surface of their hosts. They are not the same as parasitic plants, they do not kill the host. (

41 Epiphytes on a tree near Santa Elena in Costa Rica (

42 Aerial Roots o Roots may develop primarily for attachment, and specialised structures (e.g. cups and scales) may be used to collect or hold moisture. o The green aerial roots of these plants carry out photosynthesis. Tillandsia spp. happy growing on telephone wires Bolivia dsia_sp._telephone_line_%28codiferous%29.jpg 42

43 Pneumatophores o Pneumatophores are another example of aerial roots. o Pneumatophores have evolved to absorb air as well as water. o Roots need oxygen for respiration, therefore most plants can t survive in water logged soil because there are no air spaces. o Pneumatophores are not adventitious roots because they grow from roots, not other parts of the plant. (Tan, 2013)

44 Arial roots (Pneumatophores) of the grey mangrove Avicennia marina var resinifera - Barker Inlet, South Australia (

45 Pneumatophores o Plants like mangrove dwellers have adapted to swampy habitats by growing extensions of their roots that poke up out of the water and absorb air allowing the roots to breathe. 45

46 Pneumatophores

47 Buttress Roots o Common in rainforest trees. o Large roots all around a shallowly rooted tree o Buttress roots of adjoining trees may emesh overtime, creating an ecosystem of support o What is seen above ground may also be reflected below ground. o Can grow up to 9 metres high o Involved in collecting nutrients for the tree

48 Buttress Roots o How do you think this might be of advantage in rainforests? (

49 Vascular Tissue o Plants are composed of specific cells arranged in roots, leaves and stems these are called vascular tissues. o These tissues perform specialised activities, for example: Xylem from the Greek meaning wood Xylem moves water and nutrients in an upwards direction from the roots Phloem from the Greek mean bark Phloem moves sugars from photosynthesis in a downward direction to the roots (Capon, 2010)

50 Xylem o Xylem is vascular tissue in the middle of the plant stem and root. o Xyleum enables water to move in an upward direction from the roots, therefore transporting it along with nutrients that had been absorbed by the root hairs, to the rest of the plant. o The main cells in the xylem have thickened walls and specifically adapted long thin cells placed end to end that allow water to pass through easily.

51 Phloem o Phloem is the vascular tissue that carries organic nutrients, particularly sucrose, down to all parts of the plant where needed. o The phloem is concerned mainly with the transport of soluble organic material made during photosynthesis. o These cells are especially adapted to enhance flow, but to minimise leakage if damaged. o When a plant stem is damaged phloem cells produce mucilage and resin forming substances that block up the holes and stop sap leaking out. 51 (Capon, 2010)

52 Phloem is Inner Bark Pic: Juha Kamarainen &redlink=1

53 Phloem o Fluid moves around in the phloem according to supply and demand or a source-sink mechanism. o Because phloem tube cells sit on the outside of the xylem in most plants, a tree or other plant can be effectively killed by stripping away the bark in a ring on the trunk or stem. o With the phloem destroyed, nutrients cannot reach the roots and the tree/plant will die. (Mauseth, 2014) 53

54 Cross Section of Root Stem Notice the different representation of the vascular bundles in a stem, which will typically be similarly represented in the roots. Via conduction, these vessels transport all the water and nutrients the plant needs 54

55 Cross Section Apium graveloens Cross section of celery stalk, showing vascular bundles, which include both phloem and xylem (

56 Tutorial Session o Practical: Check on your monocotyledon and dicotyledon seeds germinating in the cottonwool and notice the changes since last week o Be confident that you can draw and label both the fibrous and tap root systems

57 Tutorial Option o Watch a TED video: o Check out Crash Course in Biology Khan Acadamy o

58 Next Week o Preparation: Read through the slides for session 7 stems Read the chapter in your textbook on stems

59 Suggested Readings Tan, E. (2013). Botany of the flowering plants (4 th ed.). (pp ). VIC: Northern Melbourne Institute of TAFE. Chen, R., Rosen, E., & Masson, P. (1999). Plant physiology, 120(2), pp doi: dx. doi. org/ / pp Have a read to learn more about the theory of geotropism. Clarke, I., & Lee, H. (1987). Name that flower: The identification of flowering plants. (pp ). VIC: Melbourne University Press. (Discusses roots and vascular systems.) Mauseth, J. (2014). Botany: An introduction to plant biology. (5 th ed.). (pp ). Jones & Bartlett Publishers. MASS: Raven, J. A., & Edwards, D. (2001). Roots: Evolutionary origins & biogeochemical significance. Journal of Experimental Botany 52(suppl_1), pp doi.org/ /jexbot/52.suppl_1.381 (Read through and focus upon the topics covered in class, but do not concern yourself over the chemical information discussed.)

60 References Capon, B. (2010). Botany for gardeners (3 rd ed.). Portland, OR: Timber Press. Clarke, I., & Lee, H. (1987). Name that flower: The identification of flowering plants. Melbourne, VIC: Brown Prior Anderson for Melbourne University Press. Mauseth, J. (2014). Botany: An introduction to plant biology (5 th ed.). MASS: Jones & Bartlett Publishers. Tan, E. (2004). Herbal preparations laboratory manual. Victoria, Australia: Northern Melbourne Institute of TAFE. Tan, E. (2013). Botany of the flowering plants (4 th ed.). VIC: Northern Melbourne Institute of TAFE. Wohlmuth, H. (1992). An introduction to botany and plant identification (2 nd ed.). Lismore, NSW: MacPlatypus Productions.

61 COMMONWEALTH OF AUSTRALIA Copyright Regulations 1969 COMMONWEALTH OF AUSTRALIA Copyright Regulations 1969 WARNING This material has been reproduced and communicated to you by or on behalf of the Australian College of Natural Medicine Pty Ltd (ACNM) trading as Endeavour College of Natural Health, FIAFitnation, College of Natural Beauty, Wellnation - Pursuant Part VB of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice.