The Relationship between Sucrose and Starch during 'Dark' Export from Leaves of Uniculm Barley |
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Authors: | GORDON, A. J. RYLE, G. J. A. WEBB, GILLIAN |
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Abstract: | Uniculm barley plants were grown in 8 h photoperiods at a quantumflux density of 655 µE m2 s1. Groups ofplants were transferred to four different light environmentsfor one 8 h photoperiod (106, 270, 665, and 975 µE m2s1) and harvested at intervals throughout the succeedingdark period for subsequent carbohydrate analysis of the youngestmature leaf. Sucrose was the predominant carbohydrate in the leaves (attaininga level of c. 100 mg dm2 after 8 h at 975 µE m2s1) but starch was also of significance (20 mg dm2after 8 h at 975 µE m2 s1). During the dark period, following a photoperiod at the threehighest light levels (270, 665, and 975 µE m2 s1),sucrose was exported first while the starch level remained fairlyconstant. When the-sucrose level fell to 1520 mg dm2starch degradation began. This critical sucrose level was reachedearlier in those plants subjected to lower quantum flux densitiesduring the preceding photoperiod. The delay in the remobilizationof starch suggests an important regulatory mechanism which maybe dependent upon the sucrose level. At 106 µE m2s1 the sucrose level rose to only 10 mg dm2. Herethere was no discernible delay in the depletion of sucrose orstarch. |
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