COURSE OBJECTIVES: to gain knowledge about

1. COURSE OBJECTIVES: to gain knowledge about - plantresponses to environmental stress (physiological, biochemical, genetic) - research approaches for study of environmental stresses. • biochemical, genetic and molecular on one hand mechanisms responsible for environmental stress tolerance on the other hand the factors causing injury during stress. • integrateconcepts from related disciplines

2. Environmental stimuli that affect plant growth Plant response to environmental stimuli involves perception, transduction, adaptation Sensing changes in the surrounding environment Responding to gravity and direction of light, etc. Adjusting their growth pattern and development Control systems in plants involve adaptations, adaptations, adaptations Plants need to monitor everything in order to optimize growth (i.e. to adapt)toenvironmental conditions, endogenous present & future

3. Plants have to exploit their immediate environment to maximum effect. Their inability to move means that the best way of dealing with stress is by physiological or morphological changes. Abiotic stresses, and ways to adapt to them are numerous and interlinked there’s more than one way to skin a cat

4. Abiotic Water Oxygen Nutrients Temperature Salt stress Pollutants excess or deficit Biotic Insects Weeds Pathogens Plant competition mutations In biology, stress is the driving force behind the process of adaptation and evolution

5. Resistance to drought and salt stresses is interlinked

6. Example of elucidating stress responses SIGNAL TRANSDUCTION Inputs for ionic and osmotic signaling pathways are ionic (excess Na+) and osmotic (turgor) changes. The output of ionic and osmotic signaling is cellular and plant homeostasis. Annual Review of Plant Biology 53: 247

7. Na+ UPTAKE/EXTRUSION IN THE PLANT CELL Plasma Membrane Na+ Na+ PPi H+ K+ H+ High-affinity K+ transporters V-PPase H+ Na+ Na+/H+ antiport Vacuole Na+ Na+ Tonoplast V-ATPase K+ K+/Na+ selectiveVICs H+ ATP ATP K+/Na+ ratio H+ P-ATPase Adapted from Mansour et al. 2003

8. Water STRESS stress Temperature Light Nutrients time The Four Elements of Abiotic Stress in general, performance below optimal genetic potential is indicative of stress

9. Plant Responses to Stress Mechanical concept of stress Stress is a force per unit area Strain is a change in dimension in response to stress(in other words, deformation of a physical body under the action of applied forces) Failure of a material occurs when the material cannot strain sufficiently to resist stress

10. Plant Responses to Stress Biological concept of stress Abiotic (physical or chemical) or biotic factor adversely affecting an organism Measured as effect on growth rate and productivity

11. average losses  Crop  record yield*  average yield*  disease  insect  weed  other (abiotic)  corn  19,300  4,600  750  691  511  12,700  wheat  14,500  1,880  336  134  256  11,900  soybean  7,390  1,610  269  67  330  5,120  sorghum  20,000  2,830  314  314  423  16,200  oats  10,600  1,720  465  107  352  7,960  barley  11,400  2,050  377  108  280  8,590 potatoes  94,100  28,300  8,000  5,900  875  50,900  sugar beets  121,000  42,600  6,700  6,700  3,700  61,300 % of record yield  21.6%  4.1%  2.6%  2.6%  69.1% A comparison of the record yields and the average yields indicates that mostly crops are only reaching 20% of their genetic potentialdue tobioticcategories: disease, insect and weeds. The major reduction in yield (~ 70%)is due to abiotic stress.The most significant abiotic stress is water stress, both deficit stress (drought) and excess stress (flooding, anoxia).

13. Factors that determine plant stress responses

14. Strategies of stress tolerance in plants • Susceptibility -slowed growth--senescence--death • Avoidance -deep rooting -short life cycle -leaf modifications • Resistance -ex. can survive desiccation of protoplasm “resurrection plants” constitutive deep roots constitutive succulent If plants can induce stress resisting genes  Why these genes are not constitutively on? induced freezing toleranceresistance Drought avoidance

15. I. Important concepts of stress physiology • Stress– external factor that is disadvantageous to plants; survival, growth, development, yield • Acclimated (Hardened)- increased stress tolerance as a result of prior exposureto a stress condition • Cross Resistance- tolerance to a stress based on exposure to a previous stress event of a different nature • Adaptation- is a genetically determined level of resistance acquired by a process of selection over many generations

16. Plants respond to stress on a cellular and on the whole plant levels link between biotic and abiotic stress signal transduction and plant development Responses to Biotic and Abiotic stresses are connected genetically: bon1 are miniature at 22oC but like wild-type at 28oC growth regulation by BON1 is mediated through defense responses. BON1 is a negative regulator of a Resistance (R) gene SNC1. The bon1-1 loss-of-function mutation activates SNC1, leading to constitutive defense responses and, consequently, reduced cell growth

17. Plant Response to Stress • Plants adapt to changing environmental conditions through changes in expression patternsof numerous genes. • There is a group of genes whose expression confers resistance to a given stress. • There is a common core of defense genes, which responds to several different stresses (general stress-response genes) versus stress-specific genes. • Increase in expression of protective genes is co-regulated and is correlated with resistance to oxidative stress.

18. Methods to study stress resistance • Biochemical Approach • control vs. resistant plants • control vs. induced conditions • The Genetic Approach • identify mutants with altered response • suppressor mutations • Comparative approach: complementation in yeast • The Genomic Approach • The Metabolomic Approach • The Ionomic Approach • Discovery vs. Hypothesis-Driven Science

19. II. PLANT RESPONSES TO HORMONES Hormone = A compound produced by one part of an organism that is transported to other parts where it triggers a response in target cells and tissues. B. Plant hormones help coordinate growth, development, and responses to environmental stimuli 1) By affecting division, elongation, and differentiation of cells 2) Effects depend on site of action, stage of plant growth and hormone concentration 3) The hormone signal is amplified, perhaps by affecting gene expression, enzyme activity, or membrane properties 4) Reaction to hormones depends on hormonal balance 5) Five classes of plant hormones: (1) Auxin (such as IAA). (2) Cytokinins (such as zeatin) (3) Gibberellins (such as GA3) (4) Abscisic acid (5) Ethylene

20. hormones are chemical signals that are produced in one part of the body, transported to other parts, bind to specific receptors, and trigger responses in targets cells and tissues. • Only minute quantities of hormones are necessary to induce substantial change in an organism. • Often the response of a plant is governed by the interaction of two or more hormones.

21. Plant hormones are produced at low concentration • Signal transduction pathways amplify the hormonal signal many fold and connect it to a cell’s specific responses. • These include altering the expression of genes, by affecting the activity of existing enzymes, or changing the properties of membranes. • Response to a hormone usually depends not so much on its absolute concentration as on its relative concentration compared to other hormones

22. Stress physiology... Biological membranes are the primary target of many environmental stresses. Membranes are made of phospholipids and proteins. ~50:50 %, thus not just a barrier phospholipid hydrophobic interior phospholipid hydrophilic exterior