Eucalyptus ESTs corresponding to the protoporphyrinogen IX oxidase enzyme related to the synthesis of heme, chlorophyll, and to the action of herbicides

Function of ALA Content in Porphyrin Metabolism Regulation of Ananas comosus var. bracteatus

Chlorophyll and heme are essential molecules for photosynthesis and respiration, which are competing branches of the porphyrin metabolism pathway. Chlorophyll and heme balance regulation is very important for the growth and development of plants. The chimeric leaves of Ananas comosus var. bracteatus were composed of central photosynthetic tissue (PT) and marginal albino tissue (AT), which were ideal materials for the study of porphyrin metabolism mechanisms. In this study, the regulatory function of ALA content on porphyrin metabolism (chlorophyll and heme balance) was revealed by comparing PT and AT, 5-Aminolevulinic Acid (ALA) exogenous supply, and interference of hemA expression. The AT remained similar in porphyrin metabolism flow level to the PT by keeping an equal ALA content in both tissues, which was very important for the normal growth of the chimeric leaves. As the chlorophyll biosynthesis in AT was significantly inhibited, the porphyrin metabolism flow was directed more toward the heme branch. Both tissues had similar Mg2+ contents; however, Fe2+ content was significantly increased in the AT. The chlorophyll biosynthesis inhibition in the white tissue was not due to a lack of Mg2+ and ALA. A 1.5-fold increase in ALA content inhibited chlorophyll biosynthesis while promoting heme biosynthesis and hemA expression. The doubling of ALA content boosted chlorophyll biosynthesis while decreasing hemA expression and heme content. HemA expression interference resulted in a higher ALA content and a lower chlorophyll content, while the heme content remained at a relatively low and stable level. Conclusively, a certain amount of ALA was important for the stability of porphyrin metabolism and the normal growth of plants. The ALA content appears to be able to regulate chlorophyll and heme content by bidirectionally regulating porphyrin metabolism branch direction.

Hemin-induced increase in saponin content contributes to the alleviation of osmotic and cold stress damage to Conyza blinii in a heme oxygenase 1-dependent manner

Hemin can improve the stress resistance of plants through the heme oxygenase system. Additionally, substances contained in plants, such as secondary metabolites, can improve stress resistance. However, few studies have explored the effects of hemin on secondary metabolite content. Therefore, the effects of hemin on saponin synthesis and the mechanism of plant injury relief by hemin in Conyza blinii were investigated in this study. Hemin treatment promoted plant growth and increased the antioxidant enzyme activity and saponin content of C. blinii under osmotic stress and cold stress. Further study showed that hemin could provide sufficient precursors for saponin synthesis by improving the photosynthetic capacity of C. blinii and increasing the gene expression of key enzymes in the saponin synthesis pathway, thus increasing the saponin content. Moreover, the promotion effect of hemin on saponin synthesis is dependent on heme oxygenase-1 and can be reversed by the inhibitor Zn-protoporphyrin-IX (ZnPPIX). This study revealed that hemin can increase the saponin content of C. blinii and alleviate the damage caused by abiotic stress, and it also broadened the understanding of the relationship between hemin and secondary metabolites in plant abiotic stress relief.