Effects of growth retardant PP333 on in vitro growth of Vitis thunbergii var. taiwaniana

To study the effects of paclobutrazol (PP333) on the growth of Vitis thunbergii Sieb. & Zucc. var. taiwaniana Lu., an in vitro culture system using single-node segment was established in this study. In addition to Vitis thunbergii, sweet potato, tobacco and stevia were also used to examine the effects of PP333. Plantlets derived from single-node cuttings grown in PP333-containing media showed apparent alteration of phenotype, such as stunted shoot, shortened internodes, small leaves with dark color. Besides, PP333 also caused the reduction of root length and increase in root thickness. Unlike the other three species tested, the branching roots of Vitis thunbergii were brittle and easily detached from major roots. Gibberellic acid ( GA3 ) and indole-3-acetic acid ( IAA ) were tested for the resumption effect against the action of PP333. Exogenous GA3 could partially alleviate the root thickening, but could not abolish the inhibitory effects of PP333 on shoot growth in V. thunbergii, while IAA had no effect. Root growth of PP333-treated sweet potato and tobacco could be completely restored by application of GA3, and shoot growth did not. According to the results of anatomical analysis, root thickening caused by PP333 treatment could be attributed to increases in stele diameter, cortical cell layers and cell size. GA3 application could partially reverse the effect of PP333 on cortical cell layers and cell size, but could not alter the brittle property of branch roots. Our results also showed that the strong inhibition of 1 mg/L PP333 on in vitro growth of V. thunbergii var. taiwaniana was gradually alleviated during the period of prolonged culture. And it is suggested that including PP333 in medium can be applied to in vitro germplasm conservation of V. thunbergii var. taiwaniana in order to saving labor work of subculture.