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  • Author or Editor: Gary D. Coleman x
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Temperate woody perennials produce proteins in the stem for seasonal nitrogen (N) storage. In Populus species, this seasonal N storage occurs primarily as a 32-kDa Bark Storage Protein (BSP), which can accumulate to 50% of total bark proteins during the winter. Plants of the Populus tremula × Populus alba (clone 717) were transformed with the BSP cDNA in antisense orientation (fused to a constitutive promoter), and regenerated lines were screened. Several independent antisense-BSP (A-BSP) lines were selected, which, after 4 weeks of SD photoperiod, showed 70% to 90% reduction in total BSP accumulation compared to the wild-type (WT). A series of experiments were conducted to compare LD growth of one A-BSP line to that of the WT. A-BSP plants showed reduced growth at both 5 and 50 mM ammonium nitrate fertilization. However, the higher N rate eventually resulted in toxicity in WT, but not in A-BSP plants. A-BSP plants grown hydroponically (0.5x Hoagland1s) showed altered partitioning with reduced stem length and increased leaf area (Leaf:stem dry-weight ratios were 14.8 and 20.9 for ABSP and WT, respectively). Partitioning to the roots was not different between A-BSP and WT. Proposed functions of BSP in seasonal and LD nitrogen metabolism will be discussed.

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In poplar (Populus deltoides) a 32kDa bark storage protein (BSP) accumulates during the fall, and is a major form of stored nitrogen during overwintering. This protein is induced by short-day (SD) photoperiod and may play an important role in nitrogen cycling in the plant. To determine the effect of plant nitrogen status upon BSP gene expression, poplar plants were grown in controlled environmental chambers under either SD or long-day (LD) photoperiods and watered with either 5, 10, 50, and 100 mM NH4NO3 for four weeks. [15N]-NH4NO3 was applied during the first and third weeks. SDS-PAGE and western blot analysis were used to detect the relative amounts of BSP. RNA gel blot analysis was used to determine the changes in BSP gene expression. BSP accumulation was enhanced by increasing levels of nitrogen under both photoperiods, however, SD photoperiod appears to moderate the response. These results indicate that BSP gene expression is dependant upon the nutritional status of the plant. [15N] analysis will also be presented.

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A 32kDa bark storage protein (BSP) which accumulates in the fall and is degraded in the spring has been identified in Populus deltoides bark. The BSP gene has been shown to be regulated by short day (SD) photoperiod (8 h). The physiological condition of the plant and the environmental factors necessary for the degradation and retranslocation of BSP are of considerable interest for determining the role of this protein in the remobilization of nitrogen in trees.

Poplar plants were placed in a SD growth chamber for 4 or 7 weeks to induce growth cessation (bud set) or dormancy, respectively. BSP accumulated to high levels in bark tissues after 3 weeks SD and remained high through 7 weeks SD. Plants in which growth had stopped (4 weeks SD), or in which dormancy (7 weeks SD) was broken with hydrogen cyanamide (0.5 M) or chilling (4 weeks 0C) broke bud within 1 week of being placed into long day (LD) conditions. Dormant plants which were not chilled broke bud after 3 weeks LD. BSP levels decreased around the time of budbreak, suggesting that the degradation of BSP is dependent on the need for a nitrogen sink, ie. budbreak and new shoot growth.

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