The Science of Plants in Agriculture Pl.Sci 102. Getting to Know Plants

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1 The Science of Plants in Agriculture Pl.Sci 102 Getting to Know Plants

2 Growth and Development of Plants Why it s important to have knowledge about plant development. What factors affect plant growth. Cells, cell types and plant tissues. Reproduction and plant propagation. Genotype and phenotype.

3 Why would you want to know what controls the growth and development of plants? Manipulate plant growth, and predict production. Genetically modify plants to increase productivity or quality. Determine the effects of pests and diseases on plant growth to develop natural resistance. Determine how plants grow to discover ways to kill them (herbicides).

4 What does a plant have to do to survive? Produce energy from the sun, photosynthesis Uptake water and nutrients from the roots. CO 2 and O 2 Ability to reproduce, Sexually or A-sexually Defense against pests and stress factors.

5 What has an impact on a plant s ability to grow? Genotype Environment Light, temperature, water, soil. Pests and diseases Insects, diseases, animals (people).

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8 Cell wall: provides protection and structure. Plasma membrane: controls movement of minerals, metabolites and water into and out of the cell. Chloroplast: site of photosynthesis, starch biosynthesis and starch accumulation. Golgi apparatus: site of synthesis of polysaccharides such as hemicellulose needed for cell walls. Mitochondria: site of all biochemical reactions of respiration. Endoplasmic reticulum: site of protein synthesis. Vacuole: site for storage of proteins. Nucleus : site of the majority of the genetic information (DNA) and is the site of transcription

9 Meristem Cells Ground tissues Dermal tissues Vascular tissues

10 Plant Cells Ground tissues Parenchyma Collenchyma Sclerenchyma Vascular tissues Phloem Xylem Dermal tissues Epidermis Stometes Hairs/tricomes

11 Ground Tissues Parenchyma cells Make up the majority of the fruit and vegetables we eat. In leaves they function in photosynthesis (mesophyll), while in stems and roots they function in starch, sugar and oil storage. Adjacent to the xylem or phloem sieve they act as transfer cells.

12 Ground Tissues Collenchyma cells Like parenchyma cells, these are live cells. They are elongated with much thicker cell walls. Just underneath the epidermis and provide mechanical support

13 Ground Tissues Sclerenchyma cells These cells also have a supportive role, but these cells are actually dead cells and have very thick cell walls with lignin. They form fibers that protect the phloem in the stem.

14 Epidermis Dermal Tissues Usually only a cell layer Leaf epidermis has a thick outer cell wall covered with wax Root epidermis has no waxy layer

15 Stometes Dermal Tissues Small holes or pores in leaves and stems that regulate gas exchange. Bordered by two kidney shapes cells called guard cells.

16 Dermal Tissues Hairs Occur on all organs. Root hairs are important for water and mineral uptake. On leaves and seeds (tricomes) often act as defense against insect pests.

17 Vascular Tissues Phloem They transport sugars and amino acids throughout the plant: from leaves to roots, and to developing fruit and seed; and from senescing to growing. Xylem Transports water and minerals from the root to the shoot. Upward flow is caused by evaporation of water from the leaves.

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21 Self-pollinator Pure-line inbred cultivar. Multi-line cultivar. Out-pollinator Out-pollinated population cultivars Hybrid cultivars Synthetic cultivars Clonal cultivars.

22 Certified Seed Grown under strict quality standards Inspected and tagged by state certification authorities. Genetically pure. Free from weeds. Free from seed borne diseases. Better for agriculture, better end product.

23 Land Preparation Adopt an appropriate tillage system. Maintain an appropriate supply of organic matter. Maintain a prober supply and balance of nutrients. Control soil pollution. Maintain proper soil reaction of ph. Control soil degradation.

24 Conventional Tillage Primary tillage. Topsoil is plowed to a depth of 6 to 14 inches (15-36 cm). Aim is to remove crop stubble and control weeds. Implements include: Moldboard plow; Disk plow and Chisel plow.

25 Moldboard Plow

26 Chisel Plow

27 Conventional Tillage Secondary tillage. Aim to maximize seed-soil contact at planting. Includes disc-ing and harrowing. Often associated with application of granular fertilizers and preplant incorporated herbicides.

28 Harrow Cultivators

29 Conventional Tillage Advantages Causes compaction, but can manage soil compaction. Easier to fertilizer and seed, good seedsoil contact. Tilled soil heats quicker in fall and spring for quicker seedling development. Lack of residue on soil surface reduced overwintering of pests (green bridge).

30 Conventional Tillage Disadvantages Erosion, due to lack of surface residue. Soil compaction. Costs, more fuel. Reduced soil organic matter over time. Moisture loss.

31 Conservation tillage Advantages Reduced grower inputs. Reduced fuel emissions. Avoids soil erosion. Improved soil structure. Avoids soil compaction. Improved water holding. More earth worms.

32 Conservation tillage Disadvantages Highly dependant on chemical control, particularly weeds. Can involve high investment costs in seeders. High risk of crop loss due to pests and diseases. High residues can impact seedling establishment Low yield - initially.

33 Seed Treatments Germination enhancement Fungicides Insecticides

34 Factors that influence how plants grow

35 Solar Energy

36 Light Spectrum

37 Light Quality Light affects plant processes in the range of 380 to 800 nm. Photosynthesis requires a narrower band than this. Blue light (440 um) and red light (680 um) are more effective than green light (520 um) As a result green light is reflected more hence green plants.

38 Photomorphogenesis Seed germination in light sensitive seeds. De-etiolation, greening of young seedlings Stem growth in plants that are competing for light with their neighboring plants. Related to plant receptors called phytochrome.

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40 Photoperiodism Plants can be either: Long day plants (LDP), or short night plants. Short day plants (SDP), or long night plants. Day neutral plants (DNP), which are neutral to day (or night) lengths. Day lengths plants have a critical day length (CDL) which must be satisfied in order that the plant will flower.

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42 Temperature All plants have a minimum temperature below which there is no plant growth often below 4 o C (39 o F). Plants also have a maximum temperature limit whereby plants cease to function usually no higher than 50 o C (122 o F).

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44 Gases Atmospheric gasses are composed of 78% nitrogen (N 2 ) = 780,000 ppm. 21% oxygen (O 2 ) = 210,000 ppm % carbon dioxide (CO 2 ) = 350 ppm.

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46 World Sea Temperature Change

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48 Growth Hormones

49 Auxins Cytokinins Gibberellins Ethylene Abscisic acid Brassinosteroids Jamonic acid

50 Phototropism

51 The ratio of auxin to cytokinin in a tissue dictates growth of axillary meristems: High auxin / Low cytokinins = meristem remains dormant; Low auxin / High cytokinins = meristem starts to under go cell division and starts to grow.

52 Auxin:Cytokinin Association IAA Concentration

53 GA 3 Control

54 Ethylene

55 Abscisic Acid Stimulates the closure of stomata (water stress brings about an increase ). Inhibits shoot growth but will not have as much affect on roots or may even promote growth of roots. Induces seeds to synthesize storage proteins.

56 Brassinosteroids Regulate cell expansion and are one of the most important hormones that regulate stature. Without them, plants are tiny dwarves, with reduced vasculature and roots, and are infertile. They also regulate senescence or aging.

57 Jasmonic Acid Major functions is in regulating plant growth including growth inhibition, senescence, and leaf abscission. It has an important role in response to wounding of plants plant resistance. When plants are attacked by insects, they respond by releasing Jasmonic acid, which inhibits the insects' ability to digest protein. It is also responsible for tuber formation in potatoes, yams, and onions.

58 Growth Hormones Auxins: stimulates cell elongation, mediates tropism. Cytokinins: stimulates cell division, in ratio with auxins regulate meristematic cell division. Gibberellins: breaks seed dormancy. Abscisic acid: stimulates the closure of stomata. Ethylene: is associated with fruit ripening. Brassinosteroids: regulate plant stature (height). Jasmonic acid: give a response to wounding of plants and associated with pest resistance.

59 Photosynthesis Conversion of Solar Energy to Chemical Energy by Plants

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61 Photosynthesis in plants converts light energy in the form of photons into chemical energy in the form of ATP and NADPH

62 The energy stored in ATP and NADPH can then be used to convert CO 2 and H 2 O (water) into simple sugars

63 An added bonus of photosynthesis is the production of O 2 (oxygen) by the plant

64 Photosynthesis Light Reaction Dark Reaction

65 Photosynthesis O H H + O H H O 2 H + H + e - e - H + H + e - e -

66 Light H 2 O NADPH & H + Light Reaction ATP O 2

67 Light H 2 O CO 2 Light Reaction NADPH & H + ATP Pi ADP Calvin Cycle NADP+ O 2 C 6 H 12 O 6 = Glucose

68 Photosynthesis light 6CO H 2 O C 6 H 12 O H 2 O + 6O 2 energy

69 C-4 Plants Plant species such as corn, sorghum and sugar cane use a two step version of the photosynthetic system to reduce the loss due to photorespiration by producing a 4 carbon molecule to initially capture atmospheric CO 2

70 Water, Soil and Plant Nutrients

71 Hydrologic Cycle Transpiration Evaporation Uptake Percolation Ground Water

72 Irrigation

73 Water Movement in Vascular Plants

74 Water Movement Water potential controls water movement. potential energy of water per unit volume. typically negative values. denoted by Ψ. Water moves into and through the xylem in the plant by going from regions of high water potential (small negative values) to regions of low water potential (more negative values).

75 Water Potential Water potential Air -95 Leaf -0.8 Stem -0.7 Root -0.6 Soil -0.4

76 Why is soil important for the majority of agricultural crops? Soil is critical as a holding for plants, and supplies water and nutrients that are critical for photosynthesis and plant function.

77 Soil Profile

78 Soil Properties The size of the soil particles (soil texture), size of space between soil particles (soil structure) and the availability of water in the soil influences the ability of a plants roots to extract water from the soil. The texture and structure of a particular soil determines the water-holding capacity of the soil and the tension that water is held to the surface of the soil particles as well the aeration of the soil.

79 Waterlogged Field capacity Dried

80 Soil Texture There are three basic types of soil particles based on size: sand 2 to 0.02 mm in diameter. silt 0.02 to mm in diameter. clay smaller than mm in diameter. The water-holding capacity of a soil is determined by the porosity of the soil and the surface area of the soil particles in the soil.

81 Soil Types

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83 Soil Compaction g/cm 3 g/cm 3 g/cm 3

84 Results of excessive tillage and poor soil structure

85 Soil Testing Most useful with a representative and uniform soil samples. Depth of sample One foot increments. One foot for non-mobile nutrients, such as P & K. Deeper for nitrate nitrogen, depends on field/crop. Sample through the field to avoid sampling effects. Once collected, air-dried to avoid changes in NO 3 - nitrogen as a result of microbial activity. Sample as close to planting as is feasible.

86 Nutrients Macronutrients Nitrogen (N) Phosphorous (P) Potassium (K) Calcium Magnesium Sulfur Micronutrients Boron Iron Copper Nickel Chlorine Zinc Manganese

87 Next Class Test #2 Wednesday, October 22nd, :30-11:20