A high trans-zeatin nucleoside concentration in corms may promote the multileaf growth of Amorphophallus muelleri

Abstract

Amorphophallus muelleri has a multileaf growth pattern different from that of other konjacs; however, the hormonal mechanism underlying this phenomenon is not clear. In this study, the levels of hormones closely related to the sprouting of the axillary bud, including five types of cytokinins, indole-3-acetic acid (IAA) and abscisic acid (ABA) were measured. In the second leaf sprouting stage, the content of trans-zeatin riboside (tZR) in corms increased more than 5000-fold over that in the dormancy period. Surprisingly, although the expression of CYP735A1 and CYP735A2, which synthesize the precursors for tZR was elevated at the second leaf sprouting stage, the expression of IPTs, which have key roles in cytokinin biosynthesis, did not change significantly. In addition, most cytokinin contents in leaves during the same period were significantly lower than those in corms. We speculate that the high cytokinin contents in the corms may not biosynthesized de novo in corms. In addition, the IAA content in the corms also considerably increased during the second leaf sprouting stage. Indole-3-acetaldehyde oxidase (AO1) and auxin efflux carrier PIN1A, presented relatively high expression levels in the same period. In contrast, ABA content, and the expression of NCED1, a rate-limiting enzyme in ABA biosynthesis, were suppressed at the second leaf sprouting stage. It is worth mentioning that N6-(Δ2-isopentenyl) adenosine (iP)-type cytokinins have a high content in corms in the dormant period that significantly decreases after the first leaf sprouting stage, which is completely different from the trend of tZR. By treating dormant corms with iP, the percentage of multibud plants increased, and the growth performance in terms of bud and root length was significantly higher than those of the control. This implies that iP-type cytokinins tend to play a role in promoting first seedling sprouting. Furthermore, there was a remarkable increase of the IAA content in both corms and roots under iP treatment but an inhibitory effect in buds. We speculate that the increase in the IAA content induced by iP is tissue specific. These results will assist in the understanding of the role of hormones, especially cytokinins, in the multileaf growth type of konjac.

Interaction of Phytohormones and External Environmental Factors in the Regulation of the Bud Dormancy in Woody Plants

“…In Arabidopsis, the inhibition of CTK synthesis by auxin is rapid and dependent on the AXR1 gene-mediated auxin signaling pathway. Similarly, in pea, auxin can decrease CTK levels by down-regulating the expression of IPTs and up-regulating the degradation gene CKX2 [62]. On the other hand, CTK exerts a regulatory effect on the polar transport of auxin.…”

Comparative metabolomics analysis reveals dynamic changes in carbohydrate profiles of corms during the “relay growth” of konjac (Amorphophallus muelleri)

“…As leaves grow, the mother corm gradually shrinks, and as the first leaf reaches maturity, the base of the petiole swells to form the daughter corm. At the second leaf sprouting stage, the new larger daughter corm replaces the mother corm, thereby completing the turnover process ( Xue et al., 2022 ).…”

Different Response Mechanisms of Rhizosphere Microbial Communities in Two Species of Amorphophallus to Pectobacterium carotovorum subsp. carotovorum Infection

“…Therefore, the utilization of disease-resistant varieties is considered one of the most promising strategies for preventing soft rot. A. muelleri is a species that can be propagated by seeding (triploid apomixis 2n = 39) and has a high reproduction factor, high yield, and high resistance to soft rot compared to the traditionally cultivated species A. konjac and A. albus (Xue et al, 2022). Previous studies have elaborated the molecular mechanisms of defense against soft rot in Amorphophallus spp.…”