Characteristics of histological alterations and hormone-variations in floral tissues of edible daylily (Hemerocallis citrina) buds during postharvest senescence

Abstract

Daylily (Hemerocallis citrina Baroni.) buds suffer rapid senescence after harvest. In order to understand morphological and physiological changes of daylily buds during postharvest senescence, histological alterations and hormonal variations of different floral organs (receptacles, sepals, petals, stamens and pistils) were characterized during ambient storage (21 ± 1 °C). The external tissues (receptacles, sepals) turned yellowing and crimpling, while the internal tissues (petals, stamens) get autolyzed and collapsed in advance. Ultrastructural observations suggested that the rapid disassembly of cell walls, dismission of cell organelles (in particular, chloroplasts, mitochondrial, vacuoles), and disruption of cytoplasm occurred in floral segments. Results from biochemical measurements revealed variations of phytohormones including abscisic acid (ABA), salicylic acid, gibberellin, indole-3-acetic acid, 1-aminocyclopropane-1-carboxylic acid, jasmonic acid, and brassinosteroids in different floral organs. Hierarchical clustering analysis revealed associations of variations of these phytohormones with the senescence of different floral organs. ABA was found as the most abundant phytohormone and mostly positively corelated with the senescence of daylily buds. Pearson correlation analysis further unraveled that hormone-crosstalking co-works on the regulation of the senescence of daylily buds. The fundamental understanding on the postharvest senescence would help to establish novel postharvest strategies to maintain quality of daylily flower buds and extend shelf life.