Studies On The Physiological And Molecular Mechanism Of Parthenocarpy Induced By CPPU In Lagenaria Leucantha

Flower abortion under unfavorable weather conditions is a serious problem in commercial production of cucurbitaceous crops in spite of artificial pollination, since the plant produces almost all female flowers with a few male flowers during the fall (from December to February) and spring (from March to May). In addition, a low fruit set has also been a serious problem during the rainy season because of the sluggish activity of pollinating insects. In this study, the effects of NAA (naphthaleneacetic acid), GAs (gibberellic acid) and CPPU (A^-(2-chloro-4-pyridyl)-Ar'-phenylurea) on fruit set and development in unpollinated and pollinated ovaries of Chinese white-flowered gourd (Lagenaria leucanthd) were determined with the aim of increasing fruit set and development. On the base of that, the mechanism of CPPU in inducing fruit development was studied. Full-length cDNA for two D cyclin genes and one Acid Invertase gene were also sequenced from young ovary of Lagenaria leucantha.1. Unpollinated ovaries could not growth. NAA and GA induced parthenocarpic fruit set in 36.4% and 63.6% of treated ovaries respectively, however, they could not induce parthenocarpic fruits of normal size. CPPU not only showed high activity in inducing parthenocarpy, the parthenocarpy set was as high as 100%, but also promoted the fruit development. NAA and GAa increased the fruit set in pollinated ovary but had no effect on the fresh weight per fruit and the fruit length. CPPU, however, increased both the fruit set and fruit growth of pollinated ovaries. Treating all ovaries on a plant or alternate ovaries increased fruit yield, but reduced fruit size.2. Treating ovary with CPPU significantly increased fruit yield especially the early yield in Lagenaria leucantha. As compared with control, fruit harvesting was ahead of about 20 days and the total fruit yield was increased by 46%. CPPU treatment also decreased the source/sink ratio of the plants. Leaf dry weight was reduced by 30%, while the fruit dry weight increased by 43%. The total biomass remained almost unchanged. Net photosynthetic rate and the export ratio from the labeled leaf and allocation of 14C -assimilate to fruits were all increased by CPPU treatment. CPPU strengthened sink activity and accelerated the translocation of assimilate to the fruits.3. Treating ovary with CPPU significantly increased the fruit yield, especially the early yield, in Lagenaria leucantha. The effect of CPPU was enhanced with the elevated COz concentration, and lOOOuL/L COa produced more significant effect than 2000uL/L CO2. Fruit yield for control plant seems to be less affected byenrichment. Leaf net photosynthetic rate was increased by COi-enrichment, and was much more apparent in CPPU-treated plant. All these results were related to the improved sink activity.4. NAA and GA} showed no significant effectiveness in reactiving cell division, which occurred during the first 4 days after anthesis. CPPU stimulated both cell division and expansion. Cell number, cell area in inner pericarp in cross-section and fruit weight are significantly larger in pathenocarpic fruit formed by CPPU induction, as compared with unpollinatecd ovaries and pollinated fruits.5. IAA and r-zeatin concentrations in pollinated or unpollinated fruit increased with fruit growth and reached their maximum values 9d after anthesis (DAA). IAA levels in CPPU-treated fruit, however, declined gradually during fruit development, and were much lower than in pollinated fruits. The /-zeatin concentration in CPPU-treated fruit was peaked at 3DAA then declined gradually.6. Full-length cDNA clones for two D cyclin genes were isolated from young ovary of Lagenaria kucantha. They were classified as D3 cyclins by sequence similarities and phylogenetic analysis, and named as LlCycD3;l and LlCycD3;2, respectively. The deduced amino acid sequences for LICycDS contained a retinoblastoma-binding motif and a PEST-destruction motif. Pollination induced an active cell division, accompanied with a high incre...