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Plant NutritionPlant Responsesto External SignalsSoilTopsoil: mixture of rock particles and living organisms (how break rock?)Teaspoon of topsoil: 5 billion bacteria, fungi, algae, insects, earthworms, nematodes

Humus: decaying organic materials

Important: prudent fertilization, thoughtful irrigation and prevent erosionFertilization: want to use less: smart plants, minor color change when a nutrient is deficient.Erosion: contour tillage (on hilly ground)Soil reclamation: phytoremediation: use some plants to remove soil pollutantsSoil bacteria & nitrogenAtmosphere is 80% nitrogen (gas)

Nitrogen in soil from microbes breaking down organic material

Nitrogen fixing bacteria: convert N2 from atmosphere to NH3 (ammonia)Nitrogenase (catalyst): reduces N2 to NH3

Mutualistic relationshipsSymbiotic nitrogen fixation by bacteria in roots.Rhizobium: root living bacteriaEach plant is associated with a specific species of rhizobium.MycorrhizaeMycorrhizae: modified roots: a mutualistic association of fungi and roots.Fungi increases the surface area of the root.Fungi have hyphae (web like roots)Ectomycorrhizae: hyphae outside rootEndomycorrhize: hyphae poke into root Response to stimuliGrass seedling bends toward light.Plant sensing the direction, quantitiy and color of lightCells in tip of seedling: complex biochem changes that influence the distribution ofchemicals in plant.Unequal distribution of growth-regulating chemicals lead to bending.EtoliationMorphological adaptations for growing in darkness. Ie: potato in darkness, focus on elongation of stem (to break surface)De-etoliation: once out: focus on expand leaves, elongate roots, shoots produce chlorophylCell signalingStimulant = lightResponse = greening

Reception: signal detected by receptors: proteins - conformational change.Photoreceptor in cytoplasm (usu. in cell memb)

TransductionResponseTransductionTransduction: The receptor may perceive very small amount of stim.Transduction will AMPLIFY it.Second messengers: cGMP or Ca++Receptor stim 100s of 2nd messengersThey stim 1,000s of enzyme moleculesProtein kinases (enzymes) add phosphates to 100s of molecules.ResponseUltimately, a signal transduction pathway leads to regulation of cellular activity (by regulating enzymes)1. transcription (regulate creation of enzymes)Transcription factors bind to segment of DNA2. post transcription (reg. function of enzyme)HormonesHormones:Chemicals produced in 1 area of organism that have effect in different area. (transported)Only effect target cellsSmall quantity of hormone: large effectHormonesAuxinStem elongation, root growth, develop fruitGibberellins Seed and bud germinationAbscisic acid Inhibit root growth, close stomataEthylene Fruit ripening

PhotomorphogenesisPhotomorphogenesis is the effects of light on a plant morphologyLight reception allows plants to measure the passage of days and seasons.Most important colors are red and blue because chlorophyll absorbs light in the red or blue portions of the visible spectrum.

Circadian RhythmCircadian rhythm- physiological cycle of 24 hours, present in all eukaryotic organisms, persist in absence of external cues.If organism is kept in constant environment its circadian rhythms deviate from a 24- hour period.These free running periods vary from 21-27 hours depending on the rhythmic response.

Biological clocksA biological clock tells each plant, human, and animal when to sleep, eat, and wake up.Biological clocks help a species to survive.Depending of the phase of sleep the light can advance or delay a circadian rhythm.Much lower light levels are required to reset the clocks in nocturnal rodents than in humans.Light is an important factor to which the clock is set. Disruption of rhythms generally has a negative effect on the body.

PhotoperiodismPhotoperiodism- a physiological response to the photoperiod, the relative lengths of night and day. An example of photoperiodism is flowering.

Factors that control floweringMeristem identity genes- induce the bud to form a flower instead of a vegetative shoot

Plant responses to Environmental Stimuli other than LightGravitropism- a plants response to gravityRoots display positive gravitropism while shoots display negative gravitropism. Gravitropism functions as soon as a seed germinates- the root grows into the soil and the shoot grow towards the sunlight.Statoliths specialized plastids containing dense starch grains, roll to the lower portions of cells. Thigmotropism- A directional growth in response to touch.

An example of how motor organs can cause rapid leaf movements is through the leaf of the Mimosa pudica.When touched, the leaflets fold together This is a result of a rapid loss of turgor by cells. The motor cells suddenly become flaccid after stimulation because they lose potassium, which causes water to leave the cell by osmosis.Rapid leaf movements has a feature of transmitting the stimulus through the plantFrom the point of stimulation, the signal that produces this response travels at a speed of about 1 cm/sec. An electrical impulse, traveling at the same rate, can be detected by attaching electrodes to the leaf. These impulses, called action potentials, resemble nerve impulses in animals, though the action potentials of plants are thousands of times slower.

Plants Response to DroughtIn drought a plant is losing water by transpiration faster than the water can be restored by uptake from the soil.

In response plants can reduce the rate of transpiration simply by closing their stomata, like in cam plants

Water deficit also stimulates increased synthesis and release of abscisic acid in the leaf, and this hormone help keep stomata closed by acting on guard cell membranes.

Plants Response to FloodingBy flooding, plants may suffocate because the soil lacks the air spaces that provide oxygen for cellular respiration in roots.

Plants like the mangroves (trees in marsh area), have roots which are continuous with aerial roots that provide access to oxygen.

Others produce ethylene, which causes some of the cells in the root cortex to undergo a programmed cell death (apoptosis).

Enzymatic destruction of cells creates cell tube that function as "snorkels," providing oxygen to the submerged roots.

Plants Response to Salt StressSalt lowers water potential, reducing water uptake and certain other ions are toxic to plants when concentrations are relatively high.

In response, produce solutes that are well tolerated at high concentrations, mostly inorganic compounds that keep water potentials of cells more negative than that of the soil solution without admitting toxic quantities of salt.

Also, halophytes have salt glands that pump salt out across the leaf epidermis.

Plants Response to TemperatureHeat can denature its enzymes and damage its metabolism.In response, the plants can make heat-shock proteins that is believed to prevent denaturing of the enzymes.

In cold, plants lose its fluidity as the lipids become locked into crystalline structuresIn response, altering lipid composition of membranes helps protect against that.

Plant DefensesPhysical defenses include morphological adaptations such asthorns, chemical defenses such as distasteful or toxic compounds, airborne attractants that bring animals that destroy herbivores.

Defense against pathogens:skin, epidermischemical defense: R genes recognize foreign substances.