Studies in the physiology of germination in the genus Avena

Drennan, Donald Stewart Hall (1961) Studies in the physiology of germination in the genus Avena. PhD thesis, University of Glasgow.

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Studies in the Physiology of germination in the genus Avena. The germination requirements of grains of Avena sativa, Avena fatua AveMia. ludoviciana have been investigated, and seed dormancy shown to develop with the attainment of ripeness in these species. The degree of dormancy was found to be transitory in A. sativa, and more intense and more persistent in the other two species. Promotion of the subsequent germination was observed when grains of A. sativa were allowed to imbibe for several hours, subjected to a dehydration treatment and a period of dry storage before being returned to germination conditions. This was shown to be largely due to the retention of some of the physical and physiological changes which normally occur within' the early stages of germination. Embryo damage resulted when the same treatment was given to grains with growing embryos, the severity of the damage being related to the degree of morphological development of the embryo at the time of treatment. It was concluded that -there is no initial period of imbibition which can be completely reversed by this treatment, and that there is no distinct lag between the commencement of imbibition and of the changes leading to the onset of growth. The development of amylolytic enzymes in germinating grains of A.sativa has also been studied. Only b-Amylase was present in the dry grain but concurrently with, or shortly after the commencement of embryo growth a-Amylase began to be developed. General similarities were observed in the pattern of Amylase, development in germinating grains of all three species investigated, but dormant brains of A. fatua and A. ludoviciana showed no .increased amylase development. The development of a-Amylase would appear to take place in the endosperm, but the greying embryo appears to play an -essential role in its development. Analyses of grains of A. sativa after 24 hours in germination conditions showed that a Considerable utilisation of seed fats, and of some soluble carbohydrates has Occurred. Starch hydrolysis was not evident until 24.48 hours in germination conditions. Proteolytic activity of dry grains of A. sativa was found to be mainly located in the embryo tissues, and to undergo a several-told increase during the pre-germination period of imbibition. This development took place mainly in the embryo tissues, with diffusion to the endosperm occurring later. Germinating grains of A. fatua and A. ludoviciana showed a similar pattern of increasing proteolytic activity, but dormant grains showed no capacity for increased activity. Since this increased activity is a pre-germination change, and is potentially capable of restricting embryo growth it must be considered as a possible mechanism by which seed dormancy is enforced. The presence of germination inhibiting materials in whole grains, and husks of A.sativa has been confirmed, and their activity shown against seed of A. sativa, Hordeum vulgare, Triticum aestivum, Linum usitatissimum, Brssica oleracea and Trifolium pratense. Previous investigators claimed that the action of these materials was due to their inhibition of the amylase enzymes of the grains, particularly a-Amylase. Tests with amylase preparations from germinated grains of A. sativa, and Barley, and fungal and bacterial a-Amylases failed to confirm this finding. The possibility of retarding germination by inhibiting amylases would appear to be doubtful in the light of our findings on amylase development and starch utilisation. Considerable inhibition of the activity of proteolytic enzymes from grains of A. sativa and Barley was however observed in the extract of A. sativa husks. The same water extracts of whole grains of A, sativa and Ate, fatua were found to be capable of inhibiting the germination of A. eativa grains and promoting the germination of A. fatua grains. The presence, and the amounts of these germination inhibiting and promoting materials in A. fatua could net be correlated with the degree of dormancy in the grains used for extraction.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Alex MM Barrie
Keywords: Plant sciences
Date of Award: 1961
Depositing User: Enlighten Team
Unique ID: glathesis:1961-73667
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56

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