Allocation of Photosynthate to Individual Tubers ofSolanum tuberosumL.

Abstract

Potato plants (Solanum tuberosum L.) were grown in water culture in a controlled environment. The growth rates of individual tubers were closely reflected by their ¹⁴C-content 20 h after ¹⁴CO₂ had been applied to the aerial parts of the shoot for 4 h. The ¹⁴C-content of the tuber (sink strength) was significantly correlated to the ¹⁴C-concentration of the tuber tissue (¹⁴C g⁻¹ fr. wt.=sink activity). The sink activity, which differed between individual tubers by up to a factor of 10, was also closely related to the conversion rates of ¹⁴C into the starch and the remainder as well as to the ¹⁴C-content in the ethanol soluble fraction. This indicates the simultaneous use of photosynthate for growth and storage in the growing tubers. No preference of photosynthate utilization for either of these processes could be detected in relation to the sink activity of the tubers. Tubers with high sink activity imported ¹⁴C-labelled photosynthate at higher rates although their tissue contained higher concentrations of reducing sugars and sucrose than the tissue of tubers with low sink activity. Despite the close relationship between sink activity and the rate of starch synthesis (¹⁴C-conversion into starch), no significant correlation was found between sink activity and the actual starch concentration of the tissue. The application of zeatin riboside directly onto individual tubers increased their growth rates in comparison to non-treated tubers of the same plant. The results indicate the importance of both growth and storage processes for the regulation of sink activity in young potato tubers.