Chloroplast Biogenesis 60

Abstract

In higher plants, most Photobiology, ABL, University of Illinois, Urbana, monocarboxylic biosynthetic route is not as preponderant as the DV monocarboxylic route, the DV and MV monocarboxylic routes were found to be weakly interconnected (15,17). From in vitro investigations, the DV and MV monocarboxylic routes did not appear to be interconnected at the level of Pchlide, either in etiolated barley or in etiolated cucumber (15,17). Indeed, although it is firmly believed that DV Pchlide is convertible to MV Pchlide in higher plants (5) by conversion of the vinyl group at position 4 of the macrocycle to an ethyl group (Fig. 1), this hypothesis has not yet been corroborated by experimental evidence (15, 17). During ongoing investigations of the regulation of the MV and DV Chl monocarboxylic biosynthetic routes in higher plants, preliminary experimental evidence suggested that in some plant species, DV Pchlide may be convertible to MV Pchlide, under certain conditions.In this work, it is shown that during the transition from the DV Pchlide to the MV Pchlide biosynthetic state, DV Pchlide can be partially converted to MV Pchlide in barley, a DMV/ LDV plant species. Under similar incubation conditions, the conversion of DV Pchlide to MV Pchlide did not appear to take place in cucumber, a DDV/LDV plant species. The discovery of the ubiquitous occurrence of DV3 and MV Pchlides in higher plants (1, 3) has led to a reevaluation of the Chl biosynthetic pathway (14). Protochlorophyllide is the main precursor of Chl in green plants. Considerable experimental evidence now indicates that, in higher plants, MV and DV Pchlides are formed from MV and DV Proto, respectively. via two parallel MV and DV monocarboxylic Chl biosynthetic routes (15,17).Furthermore, on the basis of the MV or DV monocarboxylic biosynthetic routes that predominate at night or in daylight, higher plants have been observed to fall into one of four greening groups (3, 4, 15), namely: dark divinylllight divinyl (DDV/LDV), dark monovinyl/light monovinyl (DMV/LMV), DMV/LDV, and DDV/ LMV. It has also been demonstrated that in etiolated DMV/ LDV plant species such as barley, which are poised in the MV Pchlide biosynthetic mode (3, 4), the DV and MV monocarboxylic biosynthetic routes are strongly interconnected prior to DV Pchlide formation (15, 17). On the other hand, in etiolated DDV/LDV plant species such as cucumber in which the MV '

Tetrapyrrole Metabolism inArabidopsis thaliana

“…By using an in vivo method with isolated cucumber etioplast membranes, Parham and Rebeiz (1995) also report that DV-Chlide a can be readily converted to MV-Chlide. The rate of this conversion is estimated to be 50-to 300-fold higher than that of the activity to convert DV-Pchlide to MV-Pchlide in isolated barley etioplasts (Tripathy and Rebeiz 1988). Although the activity within cucumber and barley etioplasts in these experiments cannot be directly compared, these results are consistent with the hypothesis that DVR prefers DV-Chlide to DV-Pchlide.…”

Monovinyl and Divinyl Protochlorophyllide Pools in Etiolated Tissues of Higher Plants

“…The polyethylene-column HPLC used in this study is par (11). The contents of DV-Pchlide in leaf mustard and cucumber are strongly dependent on their age and decrease rapidly as shown below (see Fig.…”

“…Tripathy and Rebeiz (10) reported that in higher plants, MV-and DV-Pchlides were formed from MV-and DV-protoporphyrin via MV-and DV-monocarboxylic biosynthetic routes, respectively. They also described four types of greening groups in higher plants on the basis of MV-or DV-monocarboxylic biosynthetic routes that predominate at night or in daylight (11 All plants seeds were purchased from a local market. Seeds of each plant were germinated in wet cotton at 250C in the dark for 1 to 10 d.…”

“…atives have been accomplished mainly by fluorescence spectroscopy at low temperature (1,10) or by TLC using polyethylene as a support (11). We previously developed a separation technique for the mixture of MV-and DV-pigment derivatives by HPLC using a polyethylene column and simple elution with aqueous acetone (6).…”

Identification of a Vinyl Reductase Gene for Chlorophyll Synthesis in Arabidopsis thaliana and Implications for the Evolution of Prochlorococcus Species

“…It was reported that divinyl chlorophyllide was efficiently converted to monovinyl chlorophyllide by membrane fraction from cucumber (Parham and Rebeiz, 1992), whereas divinyl protochlorophyllide was not. Another report indicated that the 8-vinyl group of protochlorophyllide was reduced by intact chloroplasts (Tripathy and Rebeiz, 1988). These reports indicated that there are multiple enzymes for the vinyl reduction.…”