Biosynthesis profile and endogenous titers of polyamines differ in totipotent and recalcitrant plant protoplasts

The expression of totipotency in plant protoplasts is a complex developmental phenomenon and is affected by genetic and physiological factors. Polyamines (PAs) are known to be involved in a variety of growth and developmental processes in higher plants, as well as in adaptation to stresses. In this study, we present the homeostatic characteristics of the endogenous PA putrescine (Put), spermidine (Spd), and spermine (Spm) in totipotent (T) and non-totipotent (NT) tobacco protoplasts and in recalcitrant (R) grapevine protoplasts. T-tobacco protoplasts, with high division rates, have the highest level of endogenous PAs. In these protoplasts, the soluble-hydrolyzed fraction predominates and increases, and the insoluble-hydrolyzed fraction also increases, whereas soluble (S) PAs decrease rapidly during culture. The isolation process contributes to the increased Put levels, which are higher in freshly isolated NT-tobacco protoplasts than in T-protoplasts. During culture, total Put predominates over Spd and Spm, and the highest accumulation is found in T-protoplasts. Ornithine decarboxylase and arginase activities both increase in T-protoplasts, whereas arginine decarboxylase activity causes Put accumulation in NT-tobacco protoplasts. R-grapevine protoplasts show a different PA profile, mostly due to the lower PA content, the higher S-fraction, and the higher ratio of Spm to total PAs. The data suggest that the levels and metabolism of the intracellular PAs could be related to the expression of totipotency of plant protoplasts.