Wow! What's wrong with the plant?!

Three important hormones for plant growth and their functions: 

I. Auxin 

Auxin

Auxin has several important roles, such as development of the embryo leaf formation, phototropism, gravitropism, apical dominance, fruit development, abscission root initiation and development of the shade-avoidance effect. Auxin is produced in the plant tip, which controls vertical growth in shoots and lateral growth in roots. When the plant needs more water and minerals, Auxin would build up and cause lateral growth in the root system, which allows the plant to receive more nutrients. Furthermore, as we known, plants need light to be able to do photosynthesis. Thus, plants would release Auxin to control their growth. Auxin in the shoot tip is transported to the shady or dark side of the plant, causing that side to grow and therefore bend the plant towards the light or other stimulus (such as gravity). On the other hand, Information regarding auxin metabolism will most likely lead to genetic and chemical manipulation of endogenous hormone levels resulting in desirable growth and differentiation of important crop species. Ultimately, the possibility exists to regulate plant growth without the use of hazardous herbicides and fertilizers (Davies, 1995; Salisbury and Ross, 1992).

Functions of Auxin

• Stimulates cell elongation
• Stimulates cell division inthe cambium and, in combination with cytokinins in tissue culture
• Stimulates differentiation of phloem and xylem
• Stimulates root initiation on stem cuttings and lateral root development in tissue culture
• Mediates the tropistic response of bending in response to gravity and light 
• The auxin supply from the apical bud suppresses growth of lateral buds 
• Delays leaf senescence 
• Can inhibit or promote (via ethylene stimulation) leaf and fruit abscission 
• Can induce fruit setting and growth in some plants 
• Involved in assimilate movement toward auxin possibly by an effect on phloem transport 
• Delays fruit ripening 
• Promotes flowering in Bromeliads 
• Stimulates growth of flower parts 
• Promotes (via ethylene production) femaleness in dioecious flowers 
• Stimulates the production of ethylene at high concentrations

(Davies, 1995; Mauseth, 1991; Raven, 1992; Salisbury and Ross, 1992).

Auxin controlling the growth of plant, towards the light

The effect of auxin on strawberry development.
The achenes produce auxin.
When removed the strawberry does not develop (Raven, 1992).

Additional links: 

http://www.plant-hormones.info/auxins.htm
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/Auxin.html

II. Abscisic acid (ABA)

Abscisic acid (ABA) 

Abscisic acid (ABA) is an interesting hormone. It is a single, naturally occuring compound in plants unlike the auxins, gibberellins, and cytokinins. It was called "abscisin II" originally because it was thought to play a major role in abscission of fruits. However, at about the same time another group was calling it "dormin" because they thought it had a major role in bud dormancy. The name abscisic acid (ABA) was coined by a compromise between the two groups. Though ABA generally is thought to play mostly inhibitory roles, it has many promoting functions as well(Arteca, 1996; Mauseth, 1991; Raven, 1992; Salisbury and Ross, 1992). Furthermore, Abscisic acid in maple and birch buds causes the change from long-day to short-day conditions a marked increase in the activity of dormin (=ABA) and consequently stops the  growth of buds.

ABA is a sesquiterpenoid (15-carbon) which is partially produced via the mevalonic pathway in chloroplasts and other plastids. Because it is sythesized partially in the chloroplasts, it makes sense that biosynthesis primarily occurs in the leaves. The production of ABA is accentuated by stresses such as water loss and freezing temperatures. It is believed that biosynthesis occurs indirectly through the production of carotenoids. Carotenoids are pigments produced by the chloroplast which have 40 carbons. On the other hand, the transport of ABA can occur in both xylem and phloem tissues. It can also be translocated through paranchyma cells. The movement of abscisic acid in plants does not exhibit polarity like auxins. ABA is capable of moving both up and down the stem (Walton and Li, 1995; Salisbury and Ross).

Functions of Abscisic acid

• Stimulates the closure of stomata (water stress brings about an increase in ABA synthesis). 
• 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. 
• Inhibits the affect of gibberellins on stimulating de novo synthesis of a-amylase. 
• Has some effect on induction and maintanance of dormancy. 
• Induces gene transcription especially for proteinase inhibitors in response to wounding which may explain an apparent role in pathogen defense.

(Davies, 1995; Mauseth, 1991; Raven, 1992; Salisbury and Ross, 1992).
Additional links:
http://www.biologie.uni-hamburg.de/b-online/e31/31e.htm
http://www.plant-hormones.info/abscisicacid.htm

ABA!

III. Ethylene

Ethylene is a gaseous hormone. Like abscisic acid, it is the only member of its class. Of all the known plant growth substance, ethylene has the simplest structure. It is produced in all higher plants and is usually associated with fruit ripening and the tripple response (Arteca, 1996; Mauseth, 1991; Raven, 1992; Salisbury and Ross, 1992). Ethylene is a small hydrocarbon gas. It is naturally occurring, but it can also occur as a result of combustion and other processes. You can't see or smell it. Some fruit will produce ethylene as ripening begins. Ethylene is responsible for the changes in texture, softening, color, and other processes involved in ripening. Fruits such as cherries and blueberries do not produce much ethylene and it doesn't influence their ripening. Ethylene is thought of as the aging hormone in plants. In addition of causing fruit to ripen, it can cause plants to die. It can be produced when plants are injured, either mechanically or by disease. Ethylene will cause a wide range of effects in plants, depending on the age of the plant and how sensitive the plant is to ethylene. Ethylene effects include fruit ripening, loss of chlorophyll, abortion of plant parts, stem shortening, abscission of plant parts, and epinasty (bending of stems). 

Ethylene can be either good or bad, depending on what commodity you work with. It is used in a positive manner in fruit ripening. However, it can also cause damage in crops. These damages might include yellowing of vegetables, bud damage in dormant nursery stock, and abscission in ornamentals (leaves, flowers drop off). Often two of the important items to know are 1) if a crop naturally produces a lot of ethylene and 2) if it is responsive to ethylene. The Responsiveness to ethylene will depend on 1) the crop, 2) the stage of plant development, 3) the temperature, 4) the concentration of ethylene, and 5) the duration of exposure.

Ethylene is produced in all higher plants and is produced from methionine in essentially all tissues. Production of ethylene varies with the type of tissue, the plant species, and also the stage of development. The mechanism by which ethylene is produced from methionine is a 3 step process (McKeon et al., 1995; Salisbury and Ross, 1992).
ATP is an essential component in the synthesis of ethylene from methionine. ATP and water are added to methionine resulting in loss of the three phosphates and S-adenosyl methionine.
1-amino-cyclopropane-1-carboxylic acid synthase (ACC-synthase) facilitates the production of ACC from SAM. Oxygen is then needed in order ro oxidize ACC and produce ethylene. This reaction is catalyzed by an oxidative enzyme called ethylene forming enzyme (Klee and Lanahan, 1995).

Additional links:

http://postharvest.tfrec.wsu.edu/pages/PC2000F
http://www.plant-hormones.info/ethylene.htm