Lecturer: Sakariyawo PhD PCP 101

1. Lecturer: Sakariyawo PhDPCP 101 Department: Plant Physiology and Crop Production College of Plant Science

2. Topic: Homeostasis • A basic Biological Axiom

3. Basic concepts • Homeostasis • Control • Regulation • Growth • Nasty • Tropism • Photomorphogenesis • Thigmotropism • Osmoregulation, • Autopoiesis

4. Learning Objectives • Understanding the concept of homeostasis, regulation and control • Life as organisational homeostasis and its biological implications

5. Homeostasis defined • biological stability Basis for biological stability could be ascribed to circularity observed in living systems. For example interconnectedness and interrelatedness of biochemical pathways forming a coherent unit.

6. Conceptual framework of homeostasis in a biological system

7. Implication of autopoietic model of Humberto Maturana • Organisational invariance • Autonomy • Self-referentiality

8. Dimensions of Biological stability • Physiological • Ecological

9. Physiological stability • Level of physiological activities is within certain limit for it to operate; • All physiological processes operate within certain concentration of solutes, temperature and pH.

10. Ecological stability • Presupposes that there is a certain correspondence; functional and structural between the biological system and its environment. This is evident in the cycle of certain elements in nature, such as water, nitrogen, carbon, phosphorus cycles and the formation of different adaptive mechanisms to various ecological conditions. One vivid example is the formation of different ecotypes of plant depending on their adaptability to available water. • Mesophytes • Hydrophytes • Xerophytes • Halophytes

11. Model of biological stability • Biological stability = Coordination or control

12. Elements of biological control system

13. Elements of Biological control (continue) • Perturbation: Any environmental factor, capable of disrupting system’s stability. These factors are Abiotic and biotic in nature • Sensor: element for detecting difference in status from the system goal. Within the context of a plant, there are different sensors; such as phytochrome, cryptochrome, phototropin and zeaxianthin. • Perceptor: plant organs • Model: The genetic composition of the plant • Goal: homeostasis • Information processing: signalling elements and signal transduction • Decision making: System survivability and senescence • Effector: Plant organ • Action: System’s response, in plant they could take the following forms; growth, nasty, morphogenesis, tropism and thigmotropism

14. Comparative plant and animal homeostasis matrix

15. Topic: Osmoregulation and Methods of Elimination of Waste Materials in Plant • Basic concepts: Osmoregulation, transport, transporters, active and passive transport, primary and secondary transport, symport, antiport

16. Learning objectives: • Water balance in plants and strategies for acclimation and adaptation • Osmoregulation as a mechanism for maintaining water balance in plant • Methods of eliminating waste product in plants • Transport mechanism in plant

17. Osmoregulatory strategies at molecular level towards water balance • Synthesis and accumulation of osmolytes and osmoprotectants • Organic nitrogen-containing • Organic non-nitrogen containing • Uptake of compatible ions • Extrusion, sequestration and compartmentalisation of incompatible ions

18. Nitrogen containing compatible osmolytes • Amino acids e.g. proline, glycine betaine • Amino acids derivatives • Quaternary amino acids

19. Non-Nitrogen containing compatible osmolytes • Sugars • Cyclic and acyclic polyols; mannitol, sorbitol • Fructans • Sulphoniumcompounds

20. Defining compatibility • Accumulation of these substances in the cell will not lead to the disruption of normal metabolic activities

21. Some biological functions of compatible osmolytes • Water balance in cell • Osmoprotectivefunctions such as the protection of the protein stability, scavenging reactive oxygen radical • Adjustment of cellular redox state and membrane stabilisation.

22. Extrusion, sequestration and compartmentalisation • Organs: Vacuole, Golgi bodies and Endoplasmic reticulum, leaf

23. Active mediators of Extrusion, sequestration and compartmentalisation • Channels • Selective (Potassium Inward Regulated Channel, KIRC; Potassium Outward Regulated Channel, KORC, Aquaporin) • Non-Selective • Carriers; High and low affinity carriers • Pumps • Electrogenic (H+/ ATP-ase, H+/PP) • Electroneutral

24. Growth and Development • Definition of growth: • A process of irreversible increase by cell division and enlargement, including synthesis of new cellular material and organization of sub cellular organelles • Process involving conversion of reserve materials into structural materials

25. Measuring growth • Increase in fresh weight • Increase in dry weight • Volume • Length • Height • Surface area

26. Classifying shoot growth • Determinate – flower buds initiate terminally; shoot elongation stops; e.g. bush snap beans • Indeterminate – flower buds born laterally; shoot terminals remain vegetative; e.g. pole beans

27. SHOOT GROWTH PATTERNS • Annuals • Herbaceous (nonwoody) plants • Complete life cycle in one growing season • See life cycle of angiosperm annual

28. SHOOT GROWTH PATTERNS • Biennials • Herbaceous plants • Require two growing seasons to complete their life cycle (not necessarily two full years) • Stem growth limited during first growing season; Note vegetative growth vs. flowering e.g. celery, beets, cabbage, Brussels sprouts

29. SHOOT GROWTH PATTERNS • Perennials • Either herbaceous or woody • Herbaceous roots live indefinitely (shoots can) • Shoot growth resumes in spring from adventitious buds in crown • Many grown as annuals • Woody roots and shoots live indefinitely • Growth varies with annual environment and zone • Pronounced diurnal variation in shoot growth; night greater

30. ROOT GROWTH PATTERNS • Variation in pattern with species and season • Growth peaks in spring, late summer/early fall • Spring growth from previous year’s foods • Fall growth from summer’s accumulated foods • Some species roots grow during winter • Some species have some roots ‘resting’ while, in the same plant, others are growing

31. Development • Definition: • Process of qualitative change in a living system over time

32. Phasic theory of Development • Development is phasic in nature, i.e. progression from one physiological system state of the meristerm to another • Identified are two phases; vegetative and reproductive phases • Plant system possesses the capability of development to progress autonomously • The identifies phases of development are irreversible • Development process is controlled by various environmental and genetic factors, mainly; temperature and photoperiod (G X PX T) • Photoperiod gene and vernalisation genes possesses delaying impact on the process of development • Temperature effect is through Q10 effect on the activities of the enzymes and ultimately on the biochemical reaction

33. PHASE CHANGE: JUVENILITY, MATURATION, SENESCENCE • Phasic development • embryonic growth • juvenility • transition stage • maturity • senescence • death • During maturation, seedlings of many woody perennials differ strikingly in appearance at various stages of development

34. Continues • Juvenility • terminated by flowering and fruiting • may be extensive in certain forest species • Maturity • loss or reduction in ability of cuttings to form adventitious roots • Physiologically related • lower part of plant may be oldest chronologically, yet be youngest physiologically (e.g. some woody plants) • top part of plant may be youngest in days, yet develop into the part that matures and bears flowers and fruit

35. AGING AND SENESCENCE • Life spans among plants differ greatly • range from few months to thousands of years • clones should be able to exist indefinately • Senescence • a physiological aging process in which tissues in an organism deteriorate and finally die • considered to be terminal, irreversible • can be postponed by removing flowers before seeds start to form

36. Comparative evaluation of aging and senescence

37. REPRODUCTIVE GROWTH AND DEVELOPMENT • Phases • Flower induction and initiation • Flower differentiation and development • Pollination • Fertilization • Fruit set and seed formation • Growth and maturation of fruit and seed • Fruit senescence

38. GENETIC FACTORS AFFECTING GROWTH AND DEVELOPMENT • DNA directs growth and differentiation • Enzymes catalyze biochemical reactions • Structural genes • Genes involved in protein synthesis • Operator genes • Regulate structural genes • Regulatory genes • Regulate operator genes

39. What signals trigger these genes? • Believed to include: • Growth regulators • Inorganic ions • Coenzymes • Environmental factors; e.g. temperature, light • Therefore . . . • Genetics directs the final form and size of the plant as altered by the environment

40. Continues • Flower induction and initiation • What causes a plant to flower? • Daylength (photoperiod) • Low temperatures (vernalization) • Neither

41. Photoperiodim • Photoperiodism: Phenomenon of plant response to relative length of day to night • Short-day plants (long-night; need darkness) • Long-day plants (need sufficient light) • Day-neutral plants (flowering unaffected by period) • Change from vegetative to reproductive

42. Effect of low temperature • Low temperature induction • Vernalization • “making ready for spring” • Any temperature treatment that induces or promotes flowering • First observed in winter wheat; many biennials • Temperature and exposure varies among species • Note difference/relationship to dormancy Many plants do not respond to changed daylength or low temperature; agricultural

43. Flower developmet • Flower development • Stimulus from leaves to apical meristem changes vegetative to flowering • Some SDPs require only limited stimulus to induce flowering; e.g. cocklebur – one day (night) • Once changed the process is not reversible • Environmental conditions must be favorable for full flower development

44. Pollination • Pollination • Transfer of pollen from anther to stigma • May be: • Same flower (self-pollination) • Different flowers, but same plant (self-pollination) • Different flowers/plants, same cultivar (self-pollination) • Different flowers, different cultivars (cross-pollination

45. Continues • Self-fertile plant produces fruit and seed with its own pollen • Self-sterile plant requires pollen from another cultivar to set fruit and seed • Often due to incompatibility; pollen will not grow through style to embryo sac • Sometimes cross-pollination incompatibility

46. Continues • Pollen transferred by: • Insects; chiefly honeybees • Bright flowers • Attractive nectar • Wind • Important for plants with inconspicuous flowers • e.g. grasses, cereal grain crops, forest tree species, some fruit and nut crops • Other minor agents – water, snails, slugs, birds, bats

47. Continues • What if pollination and fertilization fail to occur? • Fruit and seed don’t develop • Exception: Parthenocarpy • Formation of fruit without pollination/fertilization • Parthenocarpic fruit are seedless

48. Continues • Fertilization • Angiosperms (flowering plants) • Termed double fertilization • Gymnosperms (cone-bearing plants) • Staminate, pollen-producing cones • Ovulate cones produce “naked” seed on cone scales

49. Fruit setting • Fruit setting • Accessory tissues often involved • e.g. enlarged, fleshy receptacle of apple and pear • True fruit is enlarged ovary • Not all flowers develop into fruit • Certain plant hormones involved • Optimum level of fruit setting • Remove excess by hand, machine, or chemical • Some species self-thinning; Washington Navel Orange • Temperature strongly influences fruit set

50. Fruit growth and development • Fruit growth and development • After set, true fruit and associated tissues begin to grow • Food moves from other plant parts into fruit tissue • Hormones from seeds and fruit affect growth • Auxin relation in strawberry fruits • Gibberellins in grape • Patterns of growth vary with fruits