THE EFFECTS OF LIGHT AND GIBBERELLIN ON LACTUCA SATIVA L. GERMINATION
The time that a seed germinates, and whether or not it actually does germinate, depends on many factors. These factors include; the chemical environment, which must be the right conditions; oxygen must be present, and inhibitory chemicals must not be present. Germination also depends on the physical environment. Temperatures must be suited to the seed, and light quality and quantity must also be suited to the needs of the seed. In some cases, all these conditions are met, and still, the seed fails to germinate. This is because the seed is said to be dormant (Bewley and Black 1985).
Seed dormancy is a short-lived deficiency, or block of an able seed to complete germination under suitable conditions. There are two different types of dormancy, embryo, and coat dormancy (Kucera et al.2005). Embryo dormancy is mostly common in woody species, but can also be found in blossoming plants as well. Coat dormancy is when the tissues that enclose the seed are too tight and the seed cannot overcome the constraint. Seeds can be released from dormancy through being chilled, sometimes for several weeks, or sometimes even months, at temperatures of one to five degrees Celsius. This means that seeds that rely on such ways of dormancy must wait for the cold seasons to pass before they can germinate (Bewley and Black 1985).
Many seeds can germinate with, or without light, but the plants that require light, are called photoblastic, and are controlled by the phytochrome (Kendrick and Russell 1975). Phytochrome has two descriptions, the first one, Phytochrome red (Pr), is transformed by red light, to the second form, phytochrome far red (Pfr). Far red radiation can reverse the whole process. Phytochrome far red absorbs far red light (730nm), and phytochrome red absorbs red light (660nm) (Toyomasu et al. 1997).
Seeds that are grown in darkness don’t germinate unless they are exposed to red...
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