Profiles of small polar metabolites from aspen (Populus tremuloides Michx.) leaves spanning the sink-to-source transition zone were compared. Approximately 25% of 250 to 300 routinely resolved peaks were identified, with carbohydrates, organic acids, and amino acids being most abundant. Two-thirds of identified metabolites exhibited greater than 4-fold changes in abundance during leaf ontogeny. In the context of photosynthetic and respiratory measurements, profile data yielded information consistent with expected developmental trends in carbon-heterotrophic and carbon-autotrophic metabolism. Suc concentration increased throughout leaf expansion, while hexose sugar concentrations peaked at mid-expansion and decreased sharply thereafter. Amino acid contents generally decreased during leaf expansion, but an early increase in Phe and a later one in Gly and Ser reflected growing commitments to secondary metabolism and photorespiration, respectively. The assimilation of nitrate and utilization of stored Asn appeared to be marked by sequential changes in malate concentration and Asn transaminase activity. Principal component and hierarchical clustering analysis facilitated the grouping of cell wall maturation (pectins, hemicelluloses, and oxalate) and membrane biogenesis markers in relation to developmental changes in carbon and nitrogen assimilation. Metabolite profiling will facilitate investigation of nitrogen use and cellular development in Populus sp. varying widely in their growth and pattern of carbon allocation during sink-to-source development and in response to stress.Quaking aspen (Populus tremuloides Michx.) is an ecological keystone species, an important component of the wood products industry, and a useful experimental model system for the study of woody plant development (Bradshaw et al., 2000). We are interested in using metabolic profiling to characterize the sink-to-source transition in developing aspen leaves. The approach is expected to provide a basis for more extended studies analyzing the effects of various carbon sinks on aspen development and growth. An illustrative example is the regulation of phenolic sinks in leaves of aspen and close relatives in the genera Populus and Salix (Orians and Fritz, 1995;Lindroth and Hwang, 1996;Kao et al., 2002). Phenolic deposition is very characteristic of these species, exhibits wide genetic variation, can begin early during aspen leaf expansion (Kleiner et al., 1999;Kao et al., 2002), and can reach levels that negatively affect aspen stem and branch growth (Lindroth and Hwang, 1996). The allocation of metabolic carbon into such sinks is influenced by plant nutrient status and photosynthesis rate (Bryant et al., 1983;Hemming and Lindroth, 1999;Mansfield et al., 1999) and in young leaves, therefore, may be linked to metabolic development.Metabolic profiling of plants is generally geared toward the extraction of a broad spectrum of biochemical information from multiple sample types by relatively direct analytical means (for review, see Fiehn and Weckwerth, 200...

Regulation of leaf condensed tannins (CT) and salicylate-derived phenolic glycosides (PG) in fast- and slow-growing cottonwood backcrosses was analyzed by metabolic profiling and cDNA microarray hybridization. Seven hybrid lines of Populus fremontii L. and P. angustifolia James exhibiting growth/CT-PG phenotypes ranging from fast/low (Lines 18 and 1979) to slow/high (Lines 1012 and RL2) and intermediate (Lines NUL, 3200 and RM5) were investigated. Methanol-extractable leaf metabolites were analyzed by gas chromatography-mass spectrometry, and the results evaluated by principal component analysis. The hybrid lines formed separate clusters based on their primary metabolite profiles, with cluster arrangement also reflecting differences in CT-PG phenotype. Nitrogen (N) supply was manipulated to alter CT-PG partitioning and to obtain molecular insights into how primary metabolism interfaces with CT-PG accumulation. Three backcross lines (RM5, 1012, 18) exhibiting differential CT-PG responses to a 10-day hydroponic N-deprivation treatment were chosen for metabolite and gene expression analyses. The fast- growing Line 18 showed a minimal CT-PG response to N deprivation, and a reduction in photosynthetic gene expression. Line 1012 exhibited a strong phenylpropanoid response to N deprivation, including a doubling in phenylalanine ammonia-lyase (PAL) gene expression, and a shift from CT accumulation in the absence of stress toward PG accumulation under N-deprivation conditions. Amino acid concentrations were depressed in Lines 18 and 1012, as was expression of nitrate-sensitive genes coding for transketolase (TK), and malate dehydrogenase (MDH). Genes associated with protein synthesis and fate were down-regulated in Line 1012 but not in Line 18. Line RM5 exhibited a comparatively large increase in CT in response to N deprivation, but did not sustain decreases in amino acid concentrations, or changes in PAL, TK or MDH gene expression. Molecular characterization of the variable CT-PG responses shows promise for the identification and future testing of candidate genes for CT-PG trait selection or manipulation.

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Algal growth studies of Chlorella strains were conducted in a batch mode with bench type experiments. Carbon dioxide fixation rates of the following green microalgae were determined: Chlorella sp. H84, Chlorella sp. A2, Chlorella sorokiniana UTEX 1230, Chlorella vulgaris, and Chlorella pyrenoidosa. C. vulgaris, among other strains of microalgae, showed the highest growth rate (1.17 optical density/5 days). Cultivating conditions for C. vulgaris that produced the highest growth rate were at concentrations of 243 µg CO 2 /mL, 10 mM ammonia, and 1 mM phosphate, with an initial pH range of 7-8.