Towards understanding the basis of desiccation-induced oxidative stress in recalcitrant seeds: The case of Madhuca latifolia Roxb.

Abstract

Approximately 20% of plant species, including Madhuca latifolia Roxb., produce recalcitrant seeds that show sensitivity towards desiccation and, not amenable to conventional seed storage techniques. This sensitivity is attributed to the poor expression of structural, biochemical and molecular mechanisms responsible for tolerance to desiccation in orthodox seeds. Though oxidative stress-induced viability loss during desiccation has been widely reported in recalcitrant seeds, most studies have assayed oxidant/antioxidant activity rather than assessing the underlying genetic basis.This motivated the present study on the effects of desiccation in reactive oxygen species (ROS) generation and lipid peroxidation together with gene expression of a key ROS generating enzyme (NADPH oxidase; NOX), and activities/gene expression of five important enzymatic antioxidants (superoxide dismutase, ascorbate peroxidase, catalase, guaiacol peroxidase and glutathione-S-transferase) in association with an enzyme involved in proline biosynthesis (pyrroline-5-carboxylate synthetase) in the embryonic axis of M. latifolia.Significant increase in ROS, total aldehydes and NOX activity was recorded with advancement of desiccation, which was accompanied with alterations in the activities and expression of key genes involved in ROS quenching and proline biosynthesis.Our findings suggest that dehydration/storage-induced stress provoked an over expression of NOX gene, excessive accumulation of ROS, peroxidation of lipid, together with alterations in the activities/gene expression of antioxidants and multi-functional stress adaptor molecule, proline in the embryonic axis of recalcitrant M. latifolia. Future studies should look at how manipulation of these oxidative stress protective mechanisms at the gene level can improve the desiccation tolerance (storage longevity) of recalcitrant seeds.