Effect of anaerobic environment on germination and growth of rice and wheat: endogenous levels of ABA and IAA

Indoleacetic acid and abscisic acid are present in cereal seeds. It is believed that they play roles in seed maturation and germination. Modification of environmental conditions can inhibit or modify germination and seedling elongation. Our aim is to analyse the role played by IAA and ABA during the anoxia seedlings growth in lack of oxygen comparing rice, Oryza sativa, the only crop plant able to germinate in absence of oxygen, to wheat, Triticum aestivum. Seeds of both, rice and wheat, showed to contain either IAA and ABA stored in free and conjugated forms, the later was predominantly. The examine of the metabolism of the stored IAA and ABA during the first week of rice aerobic germination showed that IAA- and ABA-conjugates were hydrolysed and transported to coleoptiles and roots. During anoxic germination of rice the hydrolysis of IAA conjugates occurred to a reduced low quantity, while ABA stored forms were hydrolysed and rapidly released in the growth medium. Wheat did not germinate in anaerobic conditions, so wheat seedling germinated in air were then transferred to anoxic environment. In this condition the seedling growth was blocked. IAA and ABA, in free form, were present either in coleoptile and root in relevant amount, compared to rice tissues, after 2 days of air germination. Both substances stopped to increase when wheat seedling were transferred to anoxia. No release of ABA in the medium was detected. The results from the comparison between anoxia tolerant and intolerant cereal species give indication that the endogenous level of free IAA is not strictly correlated with anaerobic coleoptile elongation capacity, while the ability to decrease the endogenous level of ABA coupled with the ability to excrete ABA in the growth medium could be seen as an adaptive mechanism to allow elongation of anaerobic rice coleoptile.