Anatomy and morphology of female flowers of 'Serr' walnuts (Juglans regia L.), with and without pistillate flower abortion (PFA)

Pistillate flowers abortion (PFA) is a syndrome that occurs early during fruit development in several species. Probably due to an overproduction of ethylene induced by a high load of pollen on the stigma during pollination. In order to determine how pollen load contributes to PFA, we studied the anatomy and morphology of manually pollinated female flowers of 'Serr', treated with different pollen amounts. To do this, flowers with and without PFA symptoms were collected, fixed in FAA and hand-sectioned or sectioned with a microtome, stained with Toluidine Blue-O (for anatomical studies) or with Aniline Blue-O (to observe pollen tube growth). Flowers with symptoms of abortion showed vascular system interrupted in the bundles of the perianth and the involucre, but not on the ventral bundles, which differentiate from the perianth a little above the line of abscission. Flowers with symptoms of PFA showed that part of the pollen deposited on stigmas were able to emit several pollen tubes, while in flowers not showing symptoms of PFA, scarce pollen tubes were observed in the style, which may suggest that pollen tubes, rather than the pollen itself, trigger ethylene production.