Developmental Physiology of Sugar-beet: III. EFFECTS OF DECAPITATION, DEFOLIATION, AND REMOVING PART OF THE ROOT AND SHOOT ON SUBSEQUENT GROWTH OF SUGAR-BEET

Decapitation and subsequent removal of unfolding leaves of sugar-beetplants (Beta vulgaris L.) at 2-, 4-, 14-, and 31-leaf stagesresulted in much greater growth of the remaining leaves, theeffect being more pronounced the less advanced the leaves atthe time of treatment. A two- to three-fold increase in areawas accompanied by a five- to six-fold increase in weight. Bothtreatments caused a transient increase in the rate of growthof the root, the promotive effect being sustained for a longerperiod at the later stages of growth when a greater photo-syntheticsurface was present than earlier. The results suggest that thesepromotive effects came mainly from the availability and distributionof substrates following the retardation of growth processesin the shoot and the removal of the shoot apex acting as a ‘sink’of unknown size. Removal of part of the shoot resulted in proportionately greatergrowth of that remaining, whereas removal of part of the roothad no effect on the shoot unless it was reduced to one quarter.The change in the amount of shoot had no significant effecton the growth of the root, nor was there a compensating effecton the growth of the remaining root after more than one halfof it had been removed. Removal of more than one third of theroot resulted in an appreciable decrease in the net assimilationrate, while removal of part of the shoot of plants with thesame root ‘sink strength’ led to an increased netassimilation rate.