Distribution of Total Non‐Structural Carbohydrates in Soybean Plants Having Increased Reproductive Load1

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Abstract
The purpose of these experiments was to compare the distribution of total non‐structural carbohydrate (TNC) in soybean (Glycine max (L.) Merr.) plants with “normal” and with an increased reproductive load. This study included a comparison of methods for extraction and analysis of carbohydrates in soybean plant organs. Extraction with commercially available hydrolytic enzymes (“Clarase”) and analysis of extracts with ferricyanide method were chosen based on superior precision, accuracy, and recovery of standard added to samples.Number of fruits and seed weight/plant were increased 30% or more by placing aluminum foil reflectors in plots for 2 weeks near the end of flowering. Beginning with the 2nd week of the reflector treatment period, plants were sampled twice weekly for analysis of TNC. Height, number of nodes, leaf blade dry weight, and stem + petiole dry weight of control and reflector‐treated plants were similar.The initial effect of reflectors was to increase TNC concentration in all vegetative tissues. After reflectors had been removed for several weeks and throughout the period of rapid seed development, TNC concentration in pods and stems + petioles was almost always lower for reflector‐treated than control plants. There was a four‐fold decline in TNC concentration of pods and stems + petioles during seed development. However, leaf blades showed relatively little decline in TNC concentration during seed development, and senescent Ieaf blades contained 9% or more TNC. Also, increasing reproductive load by 30% appeared to have little effect on leaf blade TNC.Based on this and other recent work, it is concluded that pods, stems, and petioles serve as major sources of stored carbohydrate for developing seeds while stored carbohydrate in leaf blades is relatively unavailable for supporting seed development. From the standpoint of TNC content, the soybean plant appears capable of maintaining higher reproductive loads.