Phytic acid mobilization is an early response to chilling of the embryonic axes from dormant oilseed of hazel (Corylus avellana).

Dormancy of hazel (Corylus avellana L.) seeds is alleviated by a chilling treatment during which cytological, hormonal, and biochemical changes occur. Phytic acid and phosphate mobilization have been examined during this treatment. Phytic acid accounted for 0.7% and up to 3.2% of dry weight in axiferous and cotyledonary tissue, respectively. Phytic acid levels in embryonic axes were reduced by 60% within the first 3 weeks of chilling, with little subsequent change, in contrast to warm-imbibed tissue where levels did not change significantly. In cotyledons, phytic acid was mobilized to a lesser extent. Phosphate levels expressed on a fresh weight basis remained almost unaltered suggesting either the operation of a homeostatic mechanism for intracellular concentration or rapid utilization due to active metabolism. Phytase activity increased during stratification in both axiferous and cotyledonary tissue. The initial rise observed was associated with dormancy alleviation, since it occurred before the realization of full germination potential by the seeds and not in warm-imbibed tissue. Protein bodies were isolated from hazel seeds by non-aqueous density gradients. Phytase activity was closely associated with the purified organelles, where phytic acid was located by light microscopy. Overall, these findings suggest that phytic acid mobilization by phytase and previously described processes associated with protein bodies, such as considerable proteolysis, are early participants in the plethora of events leading to seed dormancy relief and germination in hazel.

Biochemical and molecular characterization of hazelnut (Corylus avellana) seed lipoxygenases.

Plant lipoxygenases (LOXs) are a class of dioxygenases which display diverse functions in several physiological processes such as growth, development and response to biotic and abiotic stresses. Even though LOXs have been characterized from several plant species, the physiological role of seed LOXs is still unclear. With the aim to better clarify the occurrence of LOXs and their influence on hazelnut seed quality, we carried out the biochemical and molecular characterization of the main LOX isoforms expressed during seed development. A genomic clone containing a complete LOX gene was isolated and fully characterized. The 9887 bp sequence reported contains an open reading frame of 5334 bp encoding a putative polypeptide of 99 kDa. Semiquantitative RT-PCR carried out from RNAs extracted from seeds at different maturation stages showed that LOXs are mainly expressed at early developmental stages. These results were confirmed by LOX activity assays. Biochemical characterization of the reaction products of the hazelnut LOX indicated that it is a 9-LOX. Two cDNAs were isolated by RT-PCR carried out on total RNA from immature hazelnut seeds. Sequence analysis indicated that the two cDNAs are highly homologous (91.9% degree of identity) and one of these corresponded exactly to the genomic clone. The deduced amino acid sequences of the hazelnut LOXs showed that they are closely related to a previously reported almond LOX (79.5% identity) and, to a lesser extent, to some LOXs involved in plant responses to pathogens (cotton and tobacco LOXs, 75.5 and 74.6% identity, respectively). The physiological role of hazelnut LOXs and their role in influencing seed quality are also discussed.