Translocation of ¹⁴C-Photosynthates in Grafts between the Wild Type and Improved Variety in Ipomoea

Abstract

The purpose of this study is to make clear the effects of sink activities on the translocation of ¹⁴C-photosynthates by using the sample grafts. Four reciprocal grafts were obtained by grafting between the stocks and scions of wild type (Ipomoea trifida (H.B.K.) (Don.) ·T-15) and improved variety (Ipomoea batatas Poiret var. Okinawa No. 100). The fifth leaf of the respective grafts was exposed to ¹⁴CO₂ for 1 hour, and the plants were harvested in the lapse of 24 hours after treatments. The study results obtained are summarized as follows: (1) In case where Okinawa No. 100 was used as stocks, it was observed that the dry weights of whole plants and tuberous roots were greater, and the apparent photosynthetic rate was higher than I. trifida·T-15 was used as stocks. (2) The highest specific radioactivities were observed in cases of leaves, petioles and stems at the position exposed to ¹⁴CO₂. These values gradually decreased according as it became away from them. Generally speaking, the highest values next to those at the position exposed to ¹⁴CO₂ were observed in the undeveloped foliar parts. (3) It was observed that the specific and total radioactivities of stems found in the position lower the leaf blades exposed to ¹⁴CO₂ were greater in case where Okinawa No. 100 was used as stocks than I. Trifida·T-15 was used as stocks, whatever type of scions might be used. (4) When the same type scions was grafted on the stocks, the total radioactivities of the tuberous roots and roots of Okinawa No. 100-stock grafts were greater than those of I. trifida·T-15-stock grafts. (5) From the above mentioned facts, close relationships were observed between the "translocation process of ¹⁴C-photosynthates or the apparent photosynthetic rate of leaf blades" and the "growth of tuberous roots". In this sense, it may safely be said that the sink activity has effect on the translocation of photosynthates and photosynthetic activity.