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Photosynthate Partitioning in Pigeonpea in Response to Defoliation and Shading¹

The effect of shading or defoliation on reserve carbohydrate distribution in pigeonpea [Cajanus cajan (L.) Millsp.] plants was investigated and the potential value of vegetative organs as photosynthate reservoirs was assessed. Plants were grown to the pod-filling stage, labeled with ¹⁴CO₂, and nonstructural carbohydrate levels were determined. Glucose, sucrose, and starch were present at low concentrations [less than 30 g (kg dry wt) ^–1 total] in roots, stems, and leaves of control plants. Defoliation reduced glucose plus sucrose levels after 24 h by 44 and 64% in stem and pod wall, respectively. Starch contents in pod walls were reduced by 53%. Shading for 24 h reduced sugar levels in leaves, stems, and pod walls by 43, 35, and 42%, respectively, and reduced starch levels in leaves by 70%. Specific radioactivities after pulse ¹⁴CO₂ labeling were higher in leaves (excluding ¹⁴CO₂-fed leaves) and pod walls following shading or defoliation, consistent with the lower degree dilution from nonradioactive current photosynthate.

Key Words: Reserve carbohydrates • Nonstructural carbohydrates • Glucose • Sucrose • Starch

² Assistant professor, Dep. of Agronomy, Cornell Univ.; and senior lecturer and research assistant, respectively, Dep. of Biological Sciences, the Univ. of the West Indies.

Received for publication June 9, 1983.