Active polymerization regions of G and S monolignols show different temporal and spatial change patterns in the multicellular space during lignification and its inhibition of the fruit flesh.

introductionSome fruits are vulnerable to chilling lignification during cold storage. However, the active polymerization cell regions of guaiacyl (G) and sinapyl (S) lignin units in fruit flesh during lignification and their dynamic change patterns are unclear. We have visualized G-unit lignin in fruit flesh cells, but there is no method for imaging the active polymerization regions of S monolignol.

objectiveThis work aims to understand the cell dynamics mechanism of newly synthesized G- and S-unit lignin in fruit flesh during postharvest lignification from both accumulation and inhibition perspectives.

methodsA bioorthogonal chemical labeling method to label S-unit lignin in fruit flesh cells was established. Then, using loquat fruit as the research object, and the newly synthesized G- and S-unit lignin in loquat fruit flesh during postharvest lignification was visualized. Moreover, for the inhibition study, we prepared methyl jasmonate (MeJA) hydrogel beads that could continuously inhibit the lignification during postharvest storage.

resultsThe polymerization of G monolignol tended to be active in the middle lamella of the parenchyma cells during early storage, whereas the polymerization of S monolignol tended to be active in the cell corner during late storage. Besides, the change patterns of vascular bundles and lignified cells were different from the parenchyma cells. Furthermore, a hydrogel bead capable of continuously releasing MeJA was prepared and used to inhibit the lignification. Results demonstrated that the inhibitory effects on G- and S-unit lignin were concentrated on the parenchyma cells, and there were also spatiotemporally specific, whereas the effects on vascular bundles and lignified cells were limited.

conclusionThe newly synthesized S-unit lignin in fruit flesh was visualized for the first time. Distinct spatiotemporal polymerization patterns of G- and S-unit lignin were found during postharvest lignification and its inhibition, and the corresponding cellular model was proposed.