Change in Free Polyamine Contents and Expression Profiles of Two Polyamine Biosynthetic Genes in Citrus Embryogenic Callus under Abiotic Stresses

Citrus industry usually encounters a series of adverse environment factors. Polyamines have been shown to play key roles in plant response to a wide range of abiotic stresses. Herein efforts were made to identify the change of free polyamines and expressions of two important polyamine biosynthetic genes, arginine decarboxylase (ADC) and S-adenosylmethionine decarboxylase (SAMDC), in Newhall navel orange (Citrus sinensis) embryogenic callus under high salinity, low and high temperature. Our results showed the three most widely present polyamines, putrescine, spermidine and spermine, could be detected in the callus. Under the aforementioned stresses, the three kinds of polyamines showed accumulation to different extent, in which spermine exhibited the most prominent increase. ADC and SAMDC were induced by the stressful conditions. However, a close correlation between the free polyamine contents and the expression of the two genes could not be fully established. Our data revealed that abiotic stresses led to alteration of free polyamine contents and transcriptional change of the biosynthetic genes in citrus.