Root growth of Lolium Perenne L.

Abstract

The suppression of root elongation of Lolium perenne plants alter defoliation to 25 mm above the base of the shoot was accompanied by a decrease in soluble carbohydrates in the roots. The addition of .sugar to the root medium largely countered the suppression of root elongation, indicating that the depletion of soluble carbohydrates in the roots was the prime cause of the suppression. Placing undefoliated plants in the dark produced a similar effect to defoliating to 25 mm, indicating that the photosynthetic function of the shoot was more important than the storage function in promoting root elongation. The level of soluble carbohydrates in the roots of plants harvested when elongation of most roots had ceased was found to be comparable with that which supported normal root elongation in other experiments. That under such circumstances the application of sugar to the root medium largely countered the suppression of elongation indicates a shortage of soluble carbohydrates at the root apex, i.e., a failure of translocation from elsewhere in the roots. Such a mechanism which results in the suppression of root elongation before the soluble carbohydrates in the roots are exhausted would aid in the survival of grazed plants through increasing the amount of soluble carbohydrates available for regrowth of the shoot. No explanation was found for the partial suppression of root elongation which still occurred when sugar was supplied to the root medium after defoliation.