The ultrastructure of synergids which extend through the micropyle as haustoria and lie against 'the ovary wall are described in <em>Cortaderia selloana</em> and its F<sub>l</sub> hybrid with <em>C. araucana</em>. These haustoria bear typical transfer cell wall invaginations closely associated with the plasma membrane and with mitochondria. Their function seems to be one involved in the absorption and conduction of nutrients to the synergids which are atypical in their highly vacuolate structure, degenerate nuclei and few organelles. The synergids appear to act as repositories of nutrients which are, readily accessible to the central cell by virtue of deep intrusions made into them by the central cell cytoplasm. Enzymatic secretion could also be a function of the distal end of the haustorial synergids, both in facilitating tissue peneration during its outward growth and in directing pollen tube growth. At anfhesis, the haustorium - synergid complex appears to be past its peak of absorption and transport activity, and to be involved in a seeretory or degenerative phase.
Ethylene signaling modulates tomato pollen tube growth, through modifications of cell wall remodeling and calcium gradient
