Comparative study of the morphological, physiological and molecular characteristics between diploid and tetraploid radish (Raphunas sativus L.)

Abstract

Polyploidization has been widely used in breeding novel verities in crops and vegetables, since the polyploid plants have many advantages and better performance than their relative diploids. As one of the most favorite diploid vegetable crops cultivated worldwide, there were very limited reports about the induction of radish (Raphunas sativas) tetraploid. Moreover, premature-bolting has become the major limitation factor impacting the radish production and quality. Previous studies suggested that phytohormones play essential roles in the regulation of bolting and flowering. However, the morphological, physiological and biochemical features, as well as the relationship between endogenous phytohormones, flowering genes and bolting in tetraploid radish have not been extensively reported. In this study, we used colchicine to successfully induce tetraploid carmine radish plants, evidenced by flow cytometric quantification of DNA content and the cytological observations of stomata numbers and chloroplasts in pollen mother cells. The tetraploid plants displayed “gigas” effect, including greater size of both vegetative and reproductive organs. Furthermore, the physiological characterization demonstrated that tetraploid radish has improved antioxidant enzyme activity, soluble contents and better quality. Importantly, quantification of endogenous phytohormone levels showed that multiple phytohormones, including GAs, JAs, CTKs, and SA are negatively, whereas ABA and IAA are positively associated with the delayed bolting and flowering in tetraploid, which are contrast to that in diploid plants. Moreover, qRT-PCR analysis suggested that the gene negatively associated with flowering and bolting, FLC1.1, was highly expressed in tetraploid plants at flowering stage, whereas the expression levels of genes positively associated with flowering and bolting were much lower in tetraploid compared to diploid radish, at flowering and bolting stages. These data will provide evidences for breeding late-bolting radish variety through induction of tetraploids.