Influence of protein damage and proteasome gene expression on the longevity of recalcitrant Madhuca latifolia Roxb. seeds

Enhanced cellular damage during desiccation is considered to be one of the key factors limiting vigour and viability of seeds. The uncontrolled accumulation of reactive oxygen species and resultant damaging reactions such as the oxidation of lipids and DNA in desiccating seeds of Madhuca latifolia (Roxb.) J. F. Macbr. has already been well characterized. However, hydrolytic and (or) oxidative damage to proteins requires further study. This study investigated the desiccation-induced oxidative damage to proteins and proteolytic systems in recalcitrant M. latifolia seeds during ambient storage. Seeds experienced a significant drop in seed water content [ca. 1.32 to ca. 0.23 g.(g dry mass)(-1)] during storage resulting in complete loss of viability after 35 days of storage. A considerable decline in total protein content (3.0-3.6 fold) and activity (4.8-13.8 fold) in the gene expressions of proteasome subunits (alpha, beta, and E2) were recorded in the embryonic axis of desiccating M. latifolia seeds. In contrast, increases in the level of protein carbonyls (2.46 fold), hydroperoxides (2.31 fold), malondialdehyde- and 4-hydroxy-2-nonenalprotein adducts (1.8 and 3.9 fold), and Amadori and Maillard reaction products, along with proteases (14.5-30.4 fold) were observed in desiccating M. latifoIla seeds. This study revealed that increased oxidation/modification of proteins and proteasome dysfunction are involved in the deterioration of desiccating M. latifolia seeds.