Date of Award:
Master of Science (MS)
Plants, Soils, and Climate
William F. Campbell
Clarification of the bracteole restraint on germination and the development of an improved seed pre-treatment were the objectives of this study. Bracteole cell walls were isolated and hydrolyzed with 72% sulfuric acid followed by dilution and further hydrolysis. Individual monosaccharide yields were monitored with gas chromaixtography and colorimetry. Lignin was determined as the acid insoluble residue . Cell wall composition on a dry weight basis was 17.0% lignin, 32 . 75% glucose, 28.77% xylose, 7.21% arabinose, 1.11% galactose and 0.35% mannose. Linear xylans and glucans represent a large portion of the cell wall . The quantity of lignified tissue is extraordinarily large, resulting in a rigid, impermeable seed case.
Bracteole cell walls were delignified with acid chlorite. A comparison of enzyme catalyzed hydrolysis of the untreated cell walls with delignified cell walls followed. Three commercial enzyme preparations were incubated with the samples separately and in combination treatments: cellulase (EC 3 . 2. 1.4) from Trichoderma viride supplemented with B- D-glucosidase (EC 22.214.171.124); crude-hemicellulase from Aspergillus niger; polygalacturonase (EC 126.96.36.199) from Aspergillus niger. The production of reducing groups was monitored. Enzyme catalyzed hydr olysis of lignified cell walls was limited: cellulase followed by polygalacturonase degraded 14.1% of the lignified cell wall, all other treatments yielded less than 10% degradation. Dramatic improvements in the activity of all enzymes was noted after delignification. Cellulase activity increased to 35%, hemicellulase to 25%, and polygalacturonase to 36% hydrolysis of the sample.
Intact seeds were subjected to delignification with acid chlorite at 35 degrees. Of these seeds, half were treated with cellulase, supplemented as before . The germination percentages of delignified and delignified/enzyme treated seeds were compared with other common germination pre-treatments. Four hundred seeds of each treatment were sown in soil and allowed to germinate with 20 degree days and 15 degree nights. The thirty minute delignification left the seed viable, but still lignified: only 3% germinated as compared with 28.0% for physically scarified seeds, 6% for acid treated seeds, 5.5% for surface sterilized seeds, and 4.0% for cold water leached seeds. Physical scarification proved to be the easiest method of pre-treatment.
Burton, Priscilla Woolley, "Seed Case Studies on Atriplex Gardneri (MOQ) Dietr.: Bracteole Cell Wall Composition and Enzymatic Degradation" (1982). All Graduate Theses and Dissertations. 3467.
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