Abstract
Removal of root apices from light-grown Phaseolus coccineus seedlings inhibited shoot growth. This inhibition was partially overcome by treatment with gibberellin A
3
. Extracts from control seedlings and seedlings without root apices were purified with G-10 Sephadex, chromatographed on silicic acid partition columns, and tested for GA-like activity with the 'Tan-ginbozu' dwarf rice and barley aleurone α-amylase bioassays. The major GA in control plants was GA
1
; traces of GA
19
were also detected. Removal of root apices resulted in the disappearance of GA
1
and the accumulation of GA
19
in the leaves and apical buds and in the subapical root remnants. Gibberellin A
1
levels in the cotyledons were unaffected by the removal of the root apices.The data are interpreted as indicating that root and shoot GA's are interrelated in that the GA
1
in the shoot originates in the root system. Synthesis of the cotyledon GA
1
appears to be independent of GA metabolism in the roots. A scheme is proposed that involves the recycling of GA's from shoot → root → shoot, with the shoot being the site of synthesis of GA
19
, which moves to the root where it is converted to GA
1
, which in turn is exported to the shoot. An important point in this scheme is that the shoot is the primary site of GA biosynthesis and the root is merely the site of a GA interconversion. Results of other workers indicating that roots are a site of GA biosynthesis are not equivocal and can be equally well interpreted in terms of a GA interconversion system.