Harpin Hpa1 promotes flower development in Impatiens and Parochetus plants

BACKGROUND: The harpin protein Hpa1 has multiple beneficial effects in plants, promoting plant growth and development, increasing crop yield, and inducing plant resistance to pathogens and insect pests. In these effects, the 10–40 residue fragment (Hpa1(10–42)) isolated from the Hpa1 sequence is 1.3 to 7.5-fold more effective than the full length. RESULTS: This study extends the beneficial effects of Hpa1 and Hpa1(10–42) to flower development in three species of the garden balsam Impatiens and the garden scoparius Parochetus communis plant. The external application of Hpa1 or Hpa1(10–42) to the four ornamental plants had three effects, i.e., promoting flower growth, retarding senescence of fully expanded flowers, and increasing anthocyanin concentrations in those flowers and therefore improving their ornamental visages. Based on quantitative comparisons, Hpa1(10–42) was at least 17 and 42 % more effective than Hpa1 to increase anthocyanin concentrations and to promote the growth of flowers or delay their senescence. CONCLUSION: Our results suggest that Hpa1 and especially Hpa1(10–42) have a great potential of horticultural application to increase ornamental merits of the different garden plants.