Abstract
The effects of shading on growth and allocation pattern of photosynthate in the seminal root of corn seedlings were studied using 13C as a tracer. Corn seedlings, preshaded for 2 days (light intensity was reduced to 57% or 25% of nonshaded plants), were fed with <13>C-labelled CO2 for 2 h under given light conditions, then allowed to grow for the subsequent 3 days. The extension rate of the seminal axis was not affected by shading. The total number and length of laterals were reduced by shading, while a marked increase of number and length of laterals was observed in the specific region within 10 cm from the apex of shaded plants. The 13C allocation to the laterals of the seminal root was reduced by shading ; in contrast, allocation was increased in the seminal axis. The decrease of 13C allocation to the laterals was associated with the reduction of the development of laterals. The increase of 13C allocation to the seminal axis was due to a marked accumulation of 13C in the root tip and axis within 10 cm from the apex, and this accumulation was strongly associated with the enhancement of the growth of laterals and the extension of the axis that occurred in the same region.
