Changes in free polyamine titers and expression of polyamine biosynthetic genes during growth of peach in vitro callus

In the present paper, correlation between free polyamines and growth of peach (Prunus persica cv. Yuzora) in vitro callus was investigated. Growth of the callus was divided into three phases based on measurement of fresh weight. Free polyamines, putrescine (Put), spermidine (Spd), and spermine (Spm), could be detected during peach callus growth. Changes in free Put titers followed the callus growth rate, as shown by low and stable levels in the first stage, quick increase at the beginning of the second phase, and slow increase in the last phase, whereas fluctuations of Spd and Spm titers were aberrant from that of Put at early stage. Expressions of five key genes involved in polyamine biosynthesis were characterized, in which only the genes leading to Put synthesis, ADC (arginine decarboxylase) and ODC (ornithine decarboxylase), agreed with callus growth and fluctuation of Put titers. Treatment of the callus with D-arginine, an inhibitor of ADC, led to significant growth inhibition and enormous reduction of endogenous Put, coupled with obvious decrease of mRNA levels of ADC and ODC. Exogenous application of Put partially restored the callus growth, along with resumption of endogenous Put and expression levels of ADC and ODC. Spd and Spm titers experienced minor change in comparison to Put. The data presented here suggested that free Put played an important part in peach callus growth. Putative mechanisms or mode of action underlying the role of Put in peach callus growth and different expression patterns of the genes responsible for polyamine biosynthesis are also discussed.