Effects of pollination and N-(2-chloro-4-pyridyl)-N-phenylurea on the expression of acid invertase in ovaries of Lagenaria leucantha

Acid invertase is responsible for the hydrolysis of sucrose to glucose and fructose and is thought to play a central role in determining sink strength of developing plant organs. This process is greatly regulated by plant growth substances. A cDNA encoding acid invertase was cloned from ovaries of Lagenaria leucantha and its nucleotide sequence was determined. The cloned cDNA was 2164 base pairs ( bp) long and contained an open reading frame of 1992 bp, which encoded a polypeptide of 663 amino acids. It was classified as vacuolar acid invertase by sequence similarities and phylogenetic analysis, and nominated L. leucantha acid invertase (LlAI). In unpollinated ovaries, the expression of LlAI gene was decreased together with ovary abortion. Pollination/ fertilization induced an active fruit growth and cell enlargement accompanied by substantial increases in the activity of acid invertase in the first 4 days after anthesis and high increases in the transcript levels of LlAI in young fruits. Treating unpollinated ovaries with N-(2-chloro-4-pyridyl)-N'-phenylurea, a synthetic cytokinin, induced a parthenocarpic fruit growth together with similar changes in cell enlargement, acid invertase activity and LIAI gene transcription to those of pollinated fruit.