Dynamics of Nectar Production and Nectar Homeostasis in Male Flowers of Cucurbita pepo L.

Male flowers of Cucurbita pepo L. cv. Alberello di Sarzana produce nectar in the first hours of anthesis (5:00 a.m.–8:00 a.m.). However, nectar production ceases soon after 9:00 a.m. Removal of nectar had no effect on total nectar volume and sugar concentration. Nectar substitution experiments were performed using low (20 μL) and high (100 μL) nectar volumes in combination with low (10%) and high (60%) nectar sugar concentrations. Experiments were performed during the nectar production phase (5:00 a.m.) and after the cessation phase began (10:00 a.m.). In both phases, high-volume treatments tended to reverse the passage of water from the nectary to the nectar. Although reabsorption of water and sugar is more obvious after the commencement of the cessation phase, and especially during high-concentration treatments, it can also occur during the secretory phase, thereby demonstrating that the flowers are able to secrete and reabsorb water and sugar independently throughout the whole of anthesis. This is very important from an ecological point of view, especially for species with an extended period of anthesis, during which nectar may undergo modifications as a result of environmental changes.