Seasonal and spatial variation in carbohydrate content, gene transcription and protein content for key enzymes of carbohydrate metabolism in poplar xylem
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The goal of this study was to determine seasonal and spatial correlation between the carbohydrate levels and gene transcripts of key enzymes involved in carbohydrate metabolism in Populus deltoides xylem and twigs and Populus balsamifera twigs. The seasonal and spatial patterns in the carbohydrate variation was found to be consistent with the need to regulate starch storage so that it does not compete with xylem growth and yet can serve as a reserve for bud growth in the spring in both the species. In the twigs of balsam poplar, a decline in starch during spring was observed to be associated with a lower transcript level for a key enzyme in starch synthesis than when starch levels were high. Low sucrose content was preceded by a low transcript level for a key sucrose synthesis enzyme. Transcripts for sucrose synthase that degrades sucrose for growth processes of the vascular cambium were highest during the summer. However, the transcript level for β-amylase, an enzyme of starch degradation, was not always consistent with starch content. The growth and correlations observed with balsam poplar did not show good synchronization with the environment of Lubbock which could be due to a high degree of variation in the environment relative to its native region, Canada. The growth rings of P.deltoides showed high starch levels in the innermost ring and the starch levels decreased towards the outermost ring. Transcripts for the enzymes showed a positive correlation with that of carbohydrate levels. Since the storage of carbohydrate competes with the developing xylem of the stem via the activity of the vascular cambium during the growing season, regulation was expected. Accordingly, the correlations between the carbohydrates, gene transcripts and protein content of the enzymes were stumpy. Whether the transcript levels of these enzymes are being affected by the regulation of small interfering RNAs was studied by other researchers and it was found that certain miRNAs were discovered to target SPS and SuSy gene transcripts. The eastern cottonwood which originally belonged to north Indiana did grow along well with the environmental changes in Lubbock.