Possibility of Upward Transport ofD-Pinitol in Soybean Plant: Investigation by Petiole Girdling Treatment

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Abstract
In recent years, many investigators have reported the presence of cyclitols in leguminous plants (1–5). However information about the function of cyclitols is limited. STREETER (2) observed a positive relationship between D-pinitol concentrations and C2H2 reduction activities in nodules and "tentatively concluded" that cyclitols are mainly located in the infected region of nodules (6). We inferred that D-pinitol might be associated with the multiplication of nodule tissues (7). But these descriptions are restricted to nodule tissues. There is no clear interpretation ab,out the function of cycIitols in shoots of leguminous plants. In the nodules there are several cyclitols such as D-pinitol, D-chiro-inositol, and myo-inositol, whereas in the stems, D-pinitol is the predominant cyclitol whose content parallels that of sucrose (6, 7). According to our results (7), the pattern of changes of the D-pinitol content was similar to that of sucrose but different from that of glucose or fructose in the stem of soybean through the growth period. Furthermore, its content did not decrease at the leaf-yellowing stage in the stem of soybean., We assume that D-pinitol is not merely a carbon-storing compound in stem. Many workers have analyzed the carbohydrate content in shoots, of legumes (8–13) by various methods, for example, 14C-labeling methods or phloem collection techniques. Results show consistently that sucrose and several amino acids are the transport form in legumes. However the role of cyclitols has not been documented. We carried out a petiole-girdIing experiment by steam to interfere with the phloem transport in soy bean plants and examined the effects of the inhibition of the phloem stream on the carbohydrate contents in the shoots.