An inverse relation between the multiplication rate and the starch content of the fronds of Spirodela polyrhiza (L.) Schleiden cultivated in the presence or absence of branched-chain amino acids

L-leucine, L-valine and L-isoleucine have been shown to inhibit frond multiplication of Spirodela polyrhiza (L.) Schleiden, if present in axenic cultures of this duckweed in concentrations of approximately 10~5-10“4 M (Borstlap 1970). Growth experiments with this species, cultivated in a medium according to Lacor (1968) plus 1% sucrose, using various concentrations of the inhibitory amino acids, showed that the inhibition of frond multiplication was accompanied by an increase of the dry weights of the fronds (multiplication rate N defined as log —- / t2-tl; Na and Nt2 are number of fronds at time tl and t2 Ntl respectively). By plotting the frond multiplication rates against the frond dry weigths, an inverse relation was found between these two parameters {fig. I). The increase in dry weight of the inhibited plants appeared to be time dependent and largely due to an increase in the carbohydrate content (up till 80 % of the dry weight).