Graduate Thesis Or Dissertation
 

Acid hydrolases and seed shriveling in triticale seeds

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  • The tissue and substrate degradational enzymes, acid hydrolases, in endosperm were studied in order to discern the mechanism of seed shriveling in triticale (XTriticosecale Wittmack). Acid hydrolases in crude extract of 7-week-old developing endosperm of 2 lines each of triticale with shriveled (6TB,JZBS) and plump seeds (6TA, RBP) were successfully separated into 5 fractions by DEAE-Sephacel column chromatography. Dramatically difference was observed in the run-off fraction which had a 6-fold higher acid phosphatase activity in shriveled seeds than that in plump ones. Fraction III had much higher acid phosphatase, ATPase and phospholipid phosphatase activity in shriveled seeds than that of plump ones. A detection method of enzyme activity on polyacrylamide gel was developed for nucleoside phosphatase in order to monitor the efficiency of purification steps. Using the detection method developed, 2 slow-moving isozymes were found in shriveled seeds to be different from plump ones. Nucleoside phosphatase activity was 1.3- to 2.5-fold higher in shriveled endosperm than in plump ones. In fraction III, 2 pairs each of corresponding acid phosphatase isozymes on gel from RBP and RBS were partially purified and compared for their kinetic properties. RBP-1 and RBS-1, a corresponding pair slower moving on gel (Rm 0.43) and fast-eluted from column (105 mM KC1) were very different in their kinetic properties. Specifically RBS-I had lower Km for p-nitrophenyl phosphate (0.21 mM) than RBP-I (0.57 mM) and 9-fold higher 150 for Pi (32 mM) than RBP-1 (3.6 mM). RBP-II and RBS -II, another corresponding pair fast-moving on gel (Rm 0.61) and slow-eluted from column (140 mM KC1) had similar properties. This study confirms past report that higher acid hydrolase activity was found in genetic lines producing shriveled seeds. The kinetic properties of 2 corresponding pairs of isozymes of endosperm acid phosphatase indicated that slow-moving isozymes in shriveled seeds were able to degrade more substrate, energy compound and activator for starch synthesis, and could function well under high endogenous Pi concentration. Thus the in situ functional difference in enzymatic activity may have resulted in morphological variation of seed conformation.
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