Detection of Chlorophyll Breakdown Products in the Senescent Leaves of Higher Plants

The determination of intermediary breakdown products of chlorophylls in senescent leaves of higher plants was performed by high-performance liquid chromatographic technique that had been newly developed to separate and identify the oxidation products of chlorophylls, in particular monopyrrole derivatives [Suzuki et al. (1999) J. Chromatogr. A 839: 85]. In six plants tested, degradation products were detected only in the senescent leaves of plants including barley (Hordeum vulgare), except for radish (Raphanus sativus), in which they were found both in pre- and senescent cotyledons. In the senescent cotyledons of barley, three degradation products, hematinic acid, methyl ethyl maleimide, and the putative degraded C-E-ring derivative, methyl vinyl maleimide dialdehyde, were detected. In addition to above three products, methyl vinyl maleimide was also found in both pre- and senescent cotyledons of radish. These products decreased during senescence with an accumulation of unknown compound(s), probably degraded monopyrrole derivatives. The degradation process and amounts of breakdown products of chlorophylls depend largely on plant species and vary with length of senescence. To conclude, it is likely that chlorophylls are degraded into low-molecular-weight hydrolytic compounds through monopyrroles.