Studies on the cytokinin physiology of senescent and nonsenescent grain sorghum cultivars /
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| Other Authors: | , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1988.
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| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| Abstract: | Nonsenescent sorghums have characteristics that resemble cytokinin responses; therefore, their cytokinin physiology was compared with that of senescent sorghums. First, effects of kinetin on chlorophyll retention of disks from mature leaves placed in the dark for 5 days were studied. Two nonsenescent sorghums, 'Tx2817' (tropically-adapted) and 'SC599-6' (late-season drought resistant), had maximal retention at lower concentrations than did senescent 'RTx7000' and 'BTx378' and in some cases had greater responses to 10^-8 M kinetin and to 10^-5 M gibberellic acid. SC599-6 had high initial chlorophyll content and low loss of chlorophyll without kinetin; RTx7000 and Tx2817 showed characteristics opposite of this, and BTx378 was intermediate. Second, xylem sap from Tx2817 and RTx7000 was analyzed for cytokinins using high-performance liquid chromatography (HPLC). Bioassay studies on HPLC-fractionated sap from vegetative plants indicated that zeatin (Z), zeatin riboside (ZR), and a substance eluting similar to ZR 5'-monophosphate were probably responsible for most of the eell-division type of cytokinin activity. HPLC analyses showed that zeatin riboside, zeatin, and isopentenyl adenosine were present in sap from mature plants. The amount of Z + ZR was 51% higher for Tx2817 than that of RTx7000 on a shoot dry weight basis but only 17% higher on green leaf dry weight basis. For vegetative plants grown with solution culture, Z + ZR amounts in sap per g shoot fresh weight were consistent between duplicates. When RTx7000 and Tx2817 were grown with high N and high light, they had nearly the same Z + ZR amounts. However, they differed greatly with moderately suboptimal treatments of 10% N and 50% light for 7 or 8 days. Suboptimal N caused Z + ZR to be 30% and 59% of the control for RTx7000 and Tx28I7, respectively. Suboptimal light decreased Z + ZR for RTx7000 to 55% of the control but increased that of Tx2817 to 136%. The results with suboptimal light may indicate that Tx2817 has high cytokinin production under carbohydrate shortage, a phenomenon which could delay senescence and enhance resistance to adverse conditions. The results are consistent with the hypothesis that nonsenescence in sorghum is associated with enhanced cytokinin levels. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Plant Physiology." |
| Physical Description: | xiv, 289 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references (leaves 159-186). |