25 February, 2022

Pollen tube growth in Calotropis procera is controlled by environmental changes: does it have an impact on delayed fertilization?

 by Adina Mishal and Dan Eisikowitch


   Open flower of Calotropis procera, Ein Gedi Israel.
Calotropis procera belongs to the Apocynaceae family. Nectar in Calotropis has two functions: it serves as a reward for the pollinators and as medium for pollen germination. The optimal range of nectar concentration for pollen germination is between 20% and 40% sucrose equivalents.

The genus Calotropis grows in Israel in extremely hot and dry weather, which causes nectar concentration to fluctuate greatly throughout the day, sometimes beyond the range at which pollen is capable of germination. The nectaries are not exposed as in “normal” flowers, but concealed within the flower body in the stigmatic chamber, and the nectar flows via a capillary system to outer reservoirs (cucully).

The aim of this study was to elucidate the effects of the natural fluctuations of nectar concentration on pollen germination and pollen tube growth, and their possible role in delaying fertilization in Calotropis procera.

In a series of lab experiments we showed that the optimal concentration for pollen germination is 20%. However, if the concentration
of nectar is higher for several hours, pollen tube growth of already germinated pollen is stopped. Pollen tubes restart elongation when the medium is less concentrated afterwards. 

This phenomenon can delay the fertilization of Calotropis and enables the plant to thrive under extreme desert conditions.

Read the scientific publication in JPE.