Changes in respiration and structure of non-heading Chinese cabbage seeds during gradual artificial aging

The aging of seeds is a major problem in the agricultural sector. It is also a complex biological question that remains unclear for many crop seeds. In this experiment, we investigated how different ageing levels influence seeds germination, storage components, structure, respiration metabolism, and whether respiration is a promising indicator that can non-destructively evaluate seed aging. First, we obtained non-heading Chinese cabbage seeds with varying ageing levels by applying artificial aging treatments over a period of six days (0 d-6 d). Subsequently, respiration related indexes and ultrastructural observations were conducted. Our results showed that the respiratory rate remains low when seeds have a low water content. With the increased water content, the activities of respiratory-related enzymes, phosphohexose isomerase (PGI) and malate dehydrogenase (MDH), reached maximum levels when seeds were aged for two days. Respiration rates peaked one day later, followed by a rapid decline with increasing age. The ageing process consumed a large amount of storage components (e.g. soluble sugar, sucrose, and starch), leading to the degradation of mitochondria, proteasomes, fat bodies and cell nuclei in the aged seeds, which resulted in the reduction of respiratory rates. This, in turn, negatively affected seed germination. When seeds germinated (1 h-6 h, 1 d-6 d) under standard germination condition, the germination rate and respiratory rate showed significant correlation. Especially for 5 h and 6 h, the correlation coefficients reached 0.954 and 0.976 respectively. Measured at those times, respiratory rate should be a promising indicator for seed aging.