DYNAMIC DISTRIBUTION OF CALCIUM IN THE STIGMA AND STYLE OF LILY AFTER POLLINATION

Lilies are ornamental plants of global importance, yet cross incompatibility remains a major problem in breeding programmes. Calcium plays an essential role in the sexual reproduction of flowering plants. However, the regulatory mechanisms of calcium distribution during the fertilization process are unclear at present. An accurate assessment of calcium ions in pollinated styles can help to substantiate the role of calcium in pollination. In the current study, Lilium pumilum DC. and two Asiatic Lilium cultivars ('Pollyanna' and 'Prato') were used for crossing. Three cross combinations with different compatibilities were selected. The style of the female parent was collected before and after pollination at different stages. The amount of exudate in the stylar canal was estimated at the same time points. The style was cut into four different segments using an ultramicrotome and calcium ions were localized using potassium pyroantimonate. Calcium precipitates were examined and photographed using transmission electron microscopy. The results showed that the amount of exudate in the style increased prominently following pollination in compatible crosses ('Prato' x 'Pollyanna'). The amount of calcium in the stigma increased after pollination, particularly significantly so in incompatible crosses ('Prato' x L. pumilum). The amount of calcium in the canal cells and vascular bundles of the style was greater than in the adjacent parenchyma cells. In the style of compatible crosses, calcium was obviously transferred from the top to the base in the canal cells and vascular bundles, and a rising calcium gradient was ultimately formed. It is speculated that a rapid increase and high concentration of calcium in the stigma of the female parent could negatively impact pollen tube growth. Instead, abundant calcium in the style appears to promote the growth of the pollen tube towards the ovary.