PHYTOCHROME-MEDIATED GERMINATION CONTROL OF DATURA-STRAMONIUM L. SEEDS AFTER SEED BURIAL

A series of experiments investigated the light sensitivity of buried w eed seeds both within and outside the soil gas microenvironment. Light sensitivity of Datura stramonium L. seeds was found to be increased m arkedly by a period of soil burial; seeds showed a pronounced germinat ion response even in far-red light (724 nm). Despite this elevated lig ht sensitivity (even to less than 0.01% of incident light), soil overl ying buried seeds was sufficient to neutralize the germination trigger . Furthermore, in situ irradiation of buried seeds was found to be vir tually ineffective as a germination trigger, showing that the gaseous environment surrounding buried seeds may represent the main obstacle t o germination. It is suggested in this study that the soil environment restricts the removal of the germination-inhibiting products of ferme ntation metabolism. This suggestion is supported by the finding that g as exchange within the seed:soil complex, achieved by flushing with ni trogen, partially restores seed light sensitivity. In addition, it was found that with increasing sowing depth, the germination response was attenuated and also became less dependent on seed phytochrome photoeq uilibrium conditions. This demonstrates that the phenomenon of germina tion photoinduction can be reversed by other environmental factors tha t reduce or eliminate phytochrome physiological activity. Finally, it was shown that seed very low fluence response (VLFR) is triggered only when gas exchange around buried seeds co-occurs with light exposure.