STUDIES ON POLYAMINES IN SOLANUM-TUBEROSUM IN-VITRO - EFFECTS OF DFMO, DFMA, CHLOROGENIC ACID AND PUTRESCINE ON THE ENDOGENOUS DISTRIBUTIONOF POLYAMINES, TUBERIZATION AND MORPHOLOGY

The effects of inhibitors of putrescine (PUT) biosynthesis, DL-alpha-d ifluoromthylornithine (DFMO) and DL-a-difluoromethylarginine (DFMA), c hlorogenic acid representing phenolic conjugation partners of PAs, and exogenous putrescine (PUT), on the distribution of free and conjugate d PAs were examined in relation to their effects on growth, tuberizati on and morphology in Solanum tuberosum. Changes in the profile of PAs were consistently associated with effects on tuberization. DFMO tot-al ly prevented, but DFMA only decreased, tuberization. Thus, it is concl uded that arginine decarboxylase-activity is low and the PAs required are predominantly generated via the ornithine decarboxylase pathway. D FMO treatment increased the level of free PAs. At 5 mmol/L DFMO the fo rmat-ion of conjugated PAs was strongly reduced, whereas at 1.8 mmol/L conjugated PAs accumulated to a level higher than in untreated contro ls. Chlorogenic acid promoted tuber formation and tuber growth in a co ncentration-dependent manner, involving conjugation with PAs. Exogenou s PUT, in general, caused improved growth of leafy shoots, rooting and loss of tuber dormancy. Tuberization was either promoted or inhibited , depending on the concentration applied. Added to the tuber-inducing control medium, low concentration (0.2 mmol/L) of PUT accelerated tube rization, establishing the PA-profile typical of tuberization. A high concentration (5 mmol/L) prevented full tuberization and disturbed the typical PA-profile. Neither concentration counterbalanced. the impact of DFMO on the distribution of endogenous PAs and tuberization. Howev er, exogenous PUT counteracted the decrease in tuberization due to DFM A treatment and also the delay in tuberization onset caused by chlorog enic acid, which was putatively due to reduced levels of free PAs as a result of conjugation. The results of monitoring the changes in the d istribution of endogenous PAs following treatments that perturb tuberi zation support the conclusion that a specific balance of free and conj ugated PAs is required for optimal progress through tuberization.