Chlorophenoxyacetic acid and chloropyridylphenylurea accelerate translocation of photoassimilates to parthenocarpic and seeded fruits of muskmelon (Cucumis melo)

We compared the effect of p-chlorophenoxyacetic acid (p-CPA) and 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU) on parthenocarpic and seeded muskmelon (Cucumis melo) fruits in regards to fruit development and the transport of photoassimilates from leaves exposed to 14CO2 to the developing fruits. Ten days after anthesis (DAA), the fresh weight, total 14C-radioactivity and contents of 14C-sucrose and 14C-fructose were higher in the CPPU-induced parthenocarpic fruits than in seeded fruits. However, at 35 DAA, fresh weight and sucrose content in mesocarp, placenta and empty seeds of the parthenocarpic fruits were lower than in seeded fruits. Also, total 14C-radioactivity and 14C-sugar content of the parthenocarpic fruits were lower as well as the translocation rate of 14C-photoassimilates into these fruits. Application of p-CPA to the parthenocarpic fruits at 10 and 25 DAA increased fresh weight and sugar content. Moreover, these treatments elevated the total 14C-radioactivity, 14C-sucrose content and the translocation rate of 14C-photoassimilates. The 14C-radioactivity along the translocation pathway from leaf to petiole, stem, lateral shoot and peduncle showed a declining pattern but dramatically increased again in the fruits. These results suggest that the fruit's sink strength was regulated by the seed and enhanced by the application of p-CPA.