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Articles

Incorporation of ¹⁴C-Photosynthate into Protein during Leaf Development in Young Populus Plants ¹

^a Department of Forestry, Iowa State University, Ames, Iowa 50010

Gas exchange and protein metabolism were studied in expanding, mature, and near-senescent leaves of young clonal Populus x euramericana cv. Wisconsin-5 plants. Dark respiration, CO₂ evolution in the light, and CO₂ compensation concentrations were highest in unexpanded leaves but declined markedly as leaves matured and aged. Net photosynthesis was highest in nearly mature leaves. Fresh weight continued to increase after leaf expansion was complete, whereas soluble protein levels declined. Changes in the distribution of photosynthetically incorporated ¹⁴C indicated that a high level of protein synthesis and rapid formation of structural components occurred only in expanding leaves. Protein turnover was slight in expanding leaves but was substantial after leaves were mature. Expanding leaves synthesized predominantly fraction I protein (ribulose diphosphate carboxylase). However, formation of this protein from photosynthate was slight once leaves matured.

¹ Journal Paper No. J-7885 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 1872. Research was supported in part by funds from the Iowa State University Research Grants Committee.