From pollination to fertilization in fruit trees

The phase that elapses from pollination to fertilization is re-examined giving special attention to pollen pistil interaction in compatible matings. Pollination induces an activation of the pistil. A number of changes take place in the different tissues of this organ that appear to support male gametophyte development and to assist fertilization. Thus pollination induces stigma secretion, the release of starch from the transmitting tissue and prolongs embryo sac viability. It appears that even those pollen grains that do not achieve fertilization have a synergistic role supporting others to do so. The pistil also has an effect on pollen tube growth. Pollen tube growth along the pistil is not continuous, accelerations and decelerations take place depending on the different tissues they traverse. The fact that pollen tube growth is heterotrophic, at the expenses of the pistil reserves, and that these reserves are not continuously produced confers the pistil with a role controlling pollen tube growth kinetics.Peer reviewe

Genetic Inactivation of European Sea Bass (Dicentrarchus labrax L.) Eggs Using UV-Irradiation: Observations and Perspectives

International audienceAndrogenesis is a form of uniparental reproduction leading to progenies inheriting only the paternal set of chromosomes. Ithas been achieved with variable success in a number of freshwater species and can be attained by artificial fertilization ofgenetically inactivated eggs following exposure to gamma (c), X-ray or UV irradiation (haploid androgenesis) and byrestoration of diploidy by suppression of mitosis using a pressure or thermal shock. The conditions for the geneticinactivation of the maternal genome in the European sea bass (Dicentrarchus labraxL.) were explored using differentcombinations of UV irradiation levels and durations. UV treatments significantly affected embryo survival and generated awide range of developmental abnormalities. Despite the wide range of UV doses tested (from 7.2 to 720 mJ.cm22), only onedose (60 mJ.cm22.min21with 1 min irradiation) resulted in a small percentage (14%) of haploid larvae at hatching in theinitial trials as verified by flow cytometry. Microsatellite marker analyses of three further batches of larvae produced by usingthis UV treatment showed a majority of larvae with variable levels of paternal and maternal contributions and only one larvadisplaying pure paternal inheritance. The results are discussed also in the context of an assessment of the UV-absorbancecharacteristics of egg extracts in this species that revealed the presence of gadusol, a compound structurally related tomycosporine-like amino acids (MAAs) with known UV-screening properties

Ultraviolet-B Wavelengths Regulate Changes in UV Absorption of Cleaner Fish Labroides dimidiatus Mucus

High-energy wavelengths in the ultraviolet-B (UVB, 280-315 nm) and the UVA (315-400-nm) portion of the spectrum are harmful to terrestrial and aquatic organisms. Interestingly, UVA is also involved in the repair of UV induced damage. Organisms living in shallow coral reef environments possess UV absorbing compounds, such as mycosporine-like amino acids, to protect them from UV radiation. While it has been demonstrated that exposure to UV (280-400 nm) affects the UV absorbance of fish mucus, whether the effects of UV exposure vary between UVB and UVA wavelengths is not known. Therefore, we investigated whether the UVB, UVA, or photosynthetically active radiation (PAR, 400-700 nm) portions of the spectrum affected the UV absorbance of epithelial mucus and Fulton's body condition index of the cleaner fish Labroides dimidiatus. We also compared field-measured UV absorbance with laboratory based high-performance liquid chromatography measurements of mycosporine-like amino acid concentrations. After 1 week, we found that the UV absorbance of epithelial mucus was higher in the UVB+UVA+PAR treatment compared with the UVA+PAR and PAR only treatments; after 2 and 3 weeks, however, differences between treatments were not detected. After 3 weeks, Fulton's body condition index was lower for fish in the UVB+UVA+PAR compared with PAR and UVA+PAR treatments; furthermore, all experimentally treated fish had a lower Fulton's body condition index than did freshly caught fish. Finally, we found a decrease with depth in the UV absorbance of mucus of wild-caught fish. This study suggests that the increase in UV absorbance of fish mucus in response to increased overall UV levels is a function of the UVB portion of the spectrum. This has important implications for the ability of cleaner fish and other fishes to adjust their mucus UV protection in response to variations in environmental UV exposure