Seedlings of Amaranthus caudatus L. var. Pendula were used to study the influence of several treatment: white light, 3,4-dihydroxyphenylalanine (DOPA), kinetin, gibberellic acid (GA3) on betalains biosynthesis. The pigments, betacyanins and betaxanthins, were separated using a Sephadex G-15 column chromatography. Qualitative as well as quantitative differences were observed according to the treatments applied.The amaranthin biosynthesis seemed to be favored in the absence of DOPA. Under the combined effect of kinetin and white light a small quantity of betanin was also synthesized. Adding exogenous DOPA led to a more diversified production which included betacyanins (amaranthin and betanin), betaxanthins (vulgaxanthin and miraxanthin), and even dopachrome. As a general rule, kinetin activated the betalains biosynthesis whereas GA3 inhibited it. The stimulating effect of white light was always much greater than that of kinetin.

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Abscisic acid (ABA) uptake by Amaranthus tricolor cell suspensions was found to include both a nonsaturable component and a saturable part with Km of 3.74 ± 0.43 micromolar and an apparent V., of 1.5 ± 0.12 nanomoles per gram per minute.These kinetic parameters as well as the uptake by intact cells at 0°C or by frozen and thawed cells, are consistent with operation of a saturable carrier. This carrier-mediated ABA uptake was partially energized by ApH: it increased as the extemal pH was lowered to pH 4.0; it decreased after the lowering of the ApH by the proton ionophore carbonylcyanide-m-chlorophenylhydrazone or after the altering of metabolically maintained pH gradient by metabolic inhibitors (KCN, oligomycin). The carrier is specific for ABA among the plant growth regulators tested, is unaffected by (RS)-trans-ABA and was inhibited by (S)-ABA, (R)-ABA, and also by the ABA analog LAB 173711.Transmembrane transport is fundamental to the intercellular transport and the distribution of hormones between intracellular compartments. From the many studies of auxin transport using tissues, cells or vesicle preparations, the available evidence suggests a model that includes permeation of the neutral lipophilic form of the weak acid (IAAH) through the lipid bilayer, a saturable symport of the auxin anion (IAA-) with protons and a passive efflux ofanion via a specific saturable anion channel. Some studies suggest that a saturable binding component may contribute to the total uptake by vesicle system (7). For the other weakly acidic hormones (ABA, GAs) simple diffusion of their hydrophobic neutral species and saturable high affinity uptake carriers have also been described but they have received considerably less attention (1-4, 20 for ABA; 9, 22, 23 for GAs).As far as ABA is concerned, diffusion of the undissociated species was first demonstrated for chloroplasts by Heilmann et al. (12) and later for mesophyll cells by Kaiser and Hartung (13). In addition to the diffusive path, Astle and Rubery (1,2) (17). The purpose of this study was to investigate the ABA transport characteristics in suspension-cultured Amaranthus tricolor L. cells.

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In Amaranthus tricolor seedlings, amaranthin synthesis can be induced by cytokinins and (or) by light . It was found that 5,6-dichloro-l-fl-D-ribofuranosylbenzimidazole (DRB) was a specific inhibitor of the cytokinin response whereas the light response was unchanged . DRB also inhibited the negative response of pigment production to an anticytokinin, 7-(pentylamino)-3-methylpyrazolo(4,3-d) pyrimidine (PAMPP) .DRB can be considered as a specific inhibitor of the physiological responses to cytokinins . The evolution of the inhibition percentage versus cytokinin or anticytokinin concentration shows that DRB is not a `competitor' of cytokinins .The experiments suggest that cytokinins or anticytokinins act as modulators of a fundamental light activated reaction of amaranthin synthesis .Resume . Chez les plantules d'Amaranthus tricolor, la synthese d'amarantine peut titre induite par les cytokinines et (ou) par la lumiere . Le 5,6-dichloro-l-f-D-ribofuranosylbenzimidazole (DRB) inhibe de fagon specifique la reponse aux cytokinines alors qu'il est sans effet sur l'induction photochimique . Ce compose s'oppose aussi a I'effet inhibiteur d'une anticytokinine la 7-(pentylamino)-3-methylpyrazolo(4,3-d) pyrimidine (PAMPP) .Le DRB peut titre considers comme un inhibiteur specifique des reponses physiologiques aux cytokinines . L'evolution du pourcentage d'inhibition en fonction de la concentration en cytokinine ou en anticytokinine montre que le DRB West pas un inhibiteur competitif des cytokinines.Les experiences suggerent que cytokinines ou anticytokinines agissent en modulant une reaction fondamentale de la synthese d'amarantine contrSlse par la lumiere.