Protein metabolism during natural ageing in desiccating recalcitrant seeds of Shorea robusta

Seeds of Shorea robusta (sal) are recalcitrant owing to its high desiccation sensitivity. Germinability in sal seed was lost rapidly from 100 to 0 % within 8 days. Protein oxidation examined separately in axis and cotyledon of ageing sal seeds by monitoring the levels of carbonyls, hydroperoxide, malondialdehyde and 4-hydroxy-2-nonenal adducts with protein, Amadori and Maillard reaction products. Changes in protease and proteasome activity were also estimated. The levels of all the modified proteins and activities of protease and proteasome were similar in axis and cotyledons. The amounts of carbonyls (5.5 fold in axis and 3.9 fold in cotyledons) and hydroperoxides (13.5 fold in axis and 12 fold in cotyledons) increased significantly as the seeds became non-viable. Similarly, the levels of malondialdehyde and 4-hydroxy-2-nonenal adducts promoted as the storage period advanced and reached tenfold both in the axis and cotyledons in non-viable seeds. The ageing also promoted levels of reducing sugar along with rapid enhancement in the levels of Amadori and Maillard reaction products, respectively, by 4.4 and 1.8 fold in 5 days sal seeds. Substantial promotion in protease activity both in the axis (sevenfold) and cotyledons (tenfold) of absolutely aged seeds was discernible. The activity of proteasome exhibited steady decline from 0.767 to 0.170 nmol min(-1) g(-1) DM in axis and 0.20-0.086 nmol min(-1) g(-1) DM in cotyledons of ageing sal seeds. Changes in the ROS and protein catabolism/oxidation have been discussed to establish loss of germinability in desiccating recalcitrant sal seeds.