One of the Big 5. The "stress hormone", or "universal hormone". Antagonistic to GA. Inhibited by cytokinins and ethylene. Boosts its own production, but cannot initiate its production without a stressor, and is not sufficient to maintain its own synthesis without a stressor. A dynamic, sensitive system.

Involved in seed maturation and dormancy, and drought responses and recovery. Delay growth until environmental conditions are favourable. Helps plants survive freezing and salt stresses. Despite its name, does not cause abscission. Syntheiszed in all cells, in plastids.

During seed development, it promotes tolerance to desiccation, accumulation of seed storage proteins, and keeps the embryo dormant: levels peak during late embryogenesis then plummet to allow for GA sensitivity in the dormant seed. Inhibits seed germination.

Increases in plants during drought stress: increases water conductivity of roots, and the root/shoot ratio. Produced in dryign roots, and moves through the xylem to leaves. In the leaves, it causes stomatal closure and low transpiration. Causes K⁺ and other anions to leaves guard cells, causing water to leave and stomatal closure. Has the same effect on leaves whether sprayed on or delivered from roots, depending on the species.

Abscisic acid mutants do not perceive drought stress, and include cpk10, vp1, abi, aba, and notabilis.

Abscisic acid is used in greenhouse production of flowers to reduce drought impact.

Produced in animal pancreas cells by a different biosynthesis pathway, involved in calcium-based responses in animals.

Fruit drop

Once fruit drops tot he ground, it has a short shelf life. GA can be used to prevent fruit drop by synchronizing ripening for easy harvest. Abscission is not a growth resonse; it is a specific response to the balance of ABA and GA. A change in the ratio causes some cells to die.

Aminocycloprompate carboxylic acid

An intermediate in ethylene synthesis.

Malus sp.

A woody plant with a juvenile period of 4 - 8 years.

Never pull down on an apple, you will damage the bud so that it cannot produce next year. Instead, pull upwards.

Cytokinin is applied at flowering, to increase floral number, and revive old buds. Cytokinin is not normally found at high levels during this time; it is made in seeds. Cytokinin is added only to older trees; younger trees do not need it.

One of the Big 5.  Found at highest concentration at the tips of the root and shoot. Inhibited by cytokinins. Concentrations rise and fall with GA; promoted by GA, and promotes GA in vegetative parts. Promotes production of ethylene. Polar transport; flows only downwards, and cannot affect organs above its source. Establishes polarity in the plant body and cell.

Has two forms: IAA^- and IAAH. Targets Aux/IAA proteins for destruction, activating ARFs, controlling gene transcription.

Has roles in many parts of plant growth and development. Increase shoot growth. Has a different effect on roots. Has roles in phototropic and gravitropic growth, patterning in embryo and shoot/apical meristems, vascular development, wound repair, lateral shoot formation, apical dominance, meristem proliferation, and leaf senescence.

In phototropism, auxin accumulates on the shaded side of the shoot, and the lit side of the root. Causes more growth to one side, and bending of the plant.

In wounding, auxin accumulates in the apoplastic spaces, and the plant redistributes transport, based on the change in auxin flow.

In leaf senescence, it promotes ethylene production, promoting senescence in old leaves, but is itslef a negative regulator of leaf senescence. There is high auxin in young leaves, reducing their sensitivity to ethylene in the abscission zone.

One of the Big 5.

Involved in photomorphogenesis and germination reponses to light. Positive regulators for senescence. Acts as a global regulator of leaf development.

Application accelerates senescence, and BR-deficient mutants have delayed senescence. BR-insensitive Arabidopsis mutants have prolonged life span. Mutants include bri1 - 5.

Citris sp.

A woody plant with a juvenile period of 5 - 8. The plants have a pleasing smell.

A key component in the regulatory pathway that promotes flowering in Arabidopsis in long days, affected by photoperiod and the circadian clock. Encodes a zinc finger transcription factor. Expressed mostly in phloem companion cells in leaf veins. Expression is controlled by the circadian clock, with a peak in mRNA 12 hours after dawn. The CO protein is degraded in the dark, and stable in light. When expression coincides with light, CO accumulates, inducing long-day flowering in Arabidopsis. Promotes expression of FT by directly activating gene expression in the leaf.

Mutants are incapable of photoperiodic flowering response, and have late flowering in long-day conditions (inductive).

Monoecious plants. Originated in Central America. Modern corn is the product of thousands of years of selection by Native Americans. Commits all of its energy into one shoot. Modern corn grown in higher latitudes needs to be less dependeng on photoperiod to induce flower; evolved from short-day plant into a day-neutral plant.

There are over 70,000 varieties of corn, each adapted to local photoperiod conditions. Two very similar-looking varieties can differ by up to 50% of their genomes.

Sometiems seeds can germinate on the ear without a vp1 mutation, if the ear is wet. We have selected for plants that germinate easily for agronomic reasons.

GA deficient mutant corn generally produces anthers in the normally femal flowers of the ear; ther eis no separation of male and female flowers. Application of GA to wild-type corn causes female flowers to form in the normally male flowers of the tassel. Sometimes deformed flowers like this can form in tillers, half tassel and half ear.

Flowers after a certain number of leaves have formed, but if you remove the SAM at this point and graft it to a shorter plant, it won't flower until all the leaves have formed again.

One of the Big 5. Found at highest concentration at the tips of the root and shoot. Inhibits GA, ABA, and auxin. Promotes GA 2 oxidase. Promotes ethylene. Cytokinin receptors are a multi-gene family; there are three genes in Arabidopsis. Derived from adenine nucleotide precursors, catalized by IPT. Levels are controlled by feedback mechanisms. An inactive form is stored in the plant for rapid responses.

The most applied plant hormone in agriculture; very valuable. Used to increase cell mass in calluses, allowing for other hormones to function. Most species need added cytokinin to produce a callus.

Stimulates cell division. Has roles in SAM formation, leaf senescence, apical dominance, root nodule formation, and lateral root formation. Its presence in tissues causes the tissue to be a nutrient sink.

Delays leaf senescence. Levels decrease in mature leaves, or leaves severed from plants. Exogenous application to leaves causes "green islands". Can be applied to leaf crops such as tobacco or lettuce to keep leaves green longer. This response is universal in all plants.

In root nodule formation, it causes root hairs to grow and become infected with bacteria.

Inhibits lateral root formation directly and indirectly.

Excess CK increases cell division in the floral meristem.

Cytokinin mutants are dwarfs.

Production mutant

Can be rescued. A mutant where production of a hormone is affected. Adding exogenous hormone rescues the mutant and restores wild-type phenotype. Mutant phenotype depends on the step of the proess which is mutated.

Developmental pathway

Includes plant size and age. Size is indicated by the physical size of the plant, and the nutrients available to the plant. Includes the autonomous pathways and the GA pathway.

Hedera helix

A woody plant with a juvenile period of 5 - 10 years. Produces leaves with different shape when it reaches reproductive phase.

Quercus robur

A woody plant with a juvenile period of 25 - 30 years.

One of the Big 5. A small molecule. A gaseous hormone with rapid diffusion. Found at highest concentration at ground level. Levels fluctuate in circadian rhythm. Autocatalytic production: positive feedback loop, with addition of ethylene leading to increased production of ethylene. Promotes production of ACS, producing this positive feedback loop. Synthesized from methionine. Oppositional to GA. Inhibits ABA. Activity is antagonized by auxin. Tomatoes release ethylene. Used in grocery stores to ripen fruit.

Involved in fruit ripening, senescence, and abscission, root hair development, promoting germination, and leaf abscission. There is a threshold for ethylene sensitivity.

In leaf abscission, lower auxin in older leaves leads to higher ethylene, inducing cell wall degradation enzymes in the abscission layer.

Fagus sylvatica

A woody plant with a juvenile period of 30 - 40 years.

Floral inductive signal

Originates in the leaves, and targets the SAM. The floral stimulus is induced in response to environmental and/or genetic factors.

Gibberella fujikuroi

A fungal disease in rice, that lead to the discovery of gibberellin. There is increased growth in seedlings.

ga1 mutants

A mutant in biosynthesis of GA1. A mutation in GA 3 oxidase. Can be rescued by adding GA.

Gibberellic acid

One of the Big 5. A large group of chemically related compounds. Most forms in plants are inactive intermediates of GA synthesis. Discovered in Foolish seedling fungal disease. Found at highest concentration at ground level. Absent from the SAM, but there is some inactive GA in the SAM. Most is synthesized in apical tissues. Light can regulate biosynthesis. Transported in the phloem if made in the shoot (non-polar). Transported in the xylem if made in the root. Inhibits ABA. Inhibited by CK. Promotes auxins. Oppositional to ethylene.

Involved in stem growth (cell elongation), seed dormancy and germination, flowering time, flower development, fruit set, and leaf senescence.

Inhibits seed dormancy, and promotes seed germination. Light induced germination activates GA production. Exogenous GA can activate seed germination in the dark. Has stand-alone activity in flowering in germination.

Represses senescence; active forms decline in leaves as they developmentally age.

Applying GA to plants can increase yield.

Vitis sp.

A woody plant with a juvenile period of 1 year. ABA is added to make grapes a deep red colour.

Parenchyma

Differentiates into a procambial cell.

Isopentyl transferase

Inserted by the Ti plasmid of Agrobacterium tumefaciens. Encodes an enzyme that catalyzes the first step in the CK synthesis form nucleotide precursors. Leads to cell division, causing tumour formation. Plant cells grow into a callus. Cytokinin inhibits its activity. Has a negative feedback loop with CKX. A quadruple ipt loss-of-function mutant has reduced CK levels to less than 20% of the wild-type, and there is dramatically reduced shoot apical meristem and shoot growth, and enhanced root growth.

1742 - 1832

A German poet and natural scientist. First speculated that floral organs were highly modified leaves.

Asian gooseberry

The word "kiwi" was developed for marketing. The plant is a C gene mutant, with flowers that produce only petals and sepals. The fruit develosp from parthenocarpy and lacks seeds.

Auxin accumulates on the lower side of roots; inhibiting cell elongation, causing the roto to bedn downwards.

1. Auxin is produced at the growing apex.

2. Stimulus of light or gravity indicates orientation.

3. Auxin is redistributed laterally.

Sprouted seeds

Used in beer making. Gaseous GA is used to induce aleurone cells in the seeds to express hydrolases, which break down starches and proteins. The applied GA synchronizes germination, to maximize enzyme levels when it is added to the beer. Starch is broken into sugars by the enzymes, and the sugars are converted into alcohol by yeast.

Ipomea nil

An obligate short day plant. Takes only one short day to induce flowering. You can cover the plant with an opaque tarp to induce flowering.

Auxin response factor 5

A transcription factor. Phosphorylates PIN1, giving it energy for transport.

EIR1

Mutants have no sense of gravity. If you rotate the plant, there is no response.

Gynoecium

One of the primary floral whorls. The female organs of the flower. Contains ovaries.

Growth regulators

The "brain" of the plant. Some hormones are taxa-specific. All plant hormones are unique to plants, and evolved as plants became multicellular. The relative balance of hormones controls cell differentiation, division, and elongation. Usually act in combination with other hormones, and affect each other's expression. Interactions are complex, and much is still unknown. Synthesized in one part of the plant, and move or are transported to another part to affect development changes or responses to environmental signals. Allows for long distance signalling between plant parts to coordinate growth. Interactions produce problem solving and reactions to stimuli, adaptation to the environment, and preparation for the future. Includes the Big 5. 

Sequoia sempervirens

A woody plant with a juvenile period of 5 - 15 years.

Rosa sp.

A woody plant with a juvenile period of 20 - 30 days. Some commercial varieties have C gene mutations, so the flower forms only sepals and petals.

"Mouth"

Present in all land plants. Even the earliest land plants had stomata. Arrangement and size depends on species.

Acer pseudoplanatus

A woody plant with a juvenile period of 15 - 20 years.

Vessel elements

Xylem cells that facilitate water and solute transport. Thick secondary cell walls. Undergo programmed cell death resulting in continuous system of adjoining hollow cells. Includes protoxylem and metaxylem tracheary elements.

Tracheophytes

Adapted to a variety of environments. Over 250,000 species.