Physiological and molecular mechanisms underlying the quality changes of lotus seeds during different ripening periods

Lotus seeds, which are renowned for their unique flavor and medicinal value, have become an important economic crop. Determining the optimal harvesting period is crucial for obtaining high-quality lotus seeds. From the perspectives of appearance and nutritional composition, we described the variations in lotus seeds "Jianxuan 30" during different developmental stages. Furthermore, we employed headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and a transcriptomic analysis to identify the characteristic volatile metabolites and differentially expressed genes in mature lotus seeds. Our findings revealed that the morphological development of lotus seeds is not synchronized with the accumulation of nutrients. During the 15-20-day developmental period, although the rate of morphological change slows, the contents and weights of nutrients increase rapidly. Upon maturation, hexadecanoic acid methyl ester, 1-butanol, 3-methylbutanal, and methylparinarate are released, and their biosynthesis is attributed to the transcriptional activation of lipoxygenase (LOX), alcohol dehydrogenase (ADH), and aldehyde dehydrogenase (ALDH). Consequently, relying on visual appearance to assess the ripeness of lotus seeds is inaccurate. We elucidated the key volatile metabolites produced during the maturation of lotus seeds and the marker genes that promote their biosynthesis, laying a molecular foundation for future applications of Odor scanner to determine the optimal harvesting period for lotus seeds.