Proceedings of the 5th international symposium of parasitic weeds
1991
Thalouarn, P. | Arnaud, M.C. | Rey, L. (Laboratoire de Cytopathologie Vegetale, Nantes (France))
Several aspects of carbon fixation ability were studied in two Striga species: an hemiparasite Striga hermonthica and a nearly achlorophyllous holoparasite S. gesnerioides. In S. hermonthica, leaves, plastids appeared as typically structured chloroplasts. Determination of Rubisco capacity and immunodetection of LSU and SSU in a proteic extract gave results not very different from those obtained with tobacco leaf tissue. Moreover positive hybridizations of total DNA and cpDNA with respectively rbcS and rbcL tobacco gene probes were obtained. Conversely, in S. gesnerioides scale-leaves, plastids showed a less developed thylakoid system and scarce starch inclusions, observations which are consistent with the poor chlorophyll content and the weak Rubisco capacity found in this species. However, like in S. hermonthica, LSU was immunodetected in proteic extracts and the presence of rbcS and rbcL genes in the DNAs was demonstrated by hybridizations. On the other hand a PEPc capacity close to that of a non parasitic C3 type plant was evidenced in both Striga species but, particulary in the case of S. gesnerioides it should not compensate the decrease in RuBPc capacity. Both Striga PEPc showed a lack of homology with that of C4 sorghum and correlatively no hybridizations were obtained between the total DNAs and a sorghum C4 type leaf PEPc gene probe. The unexpected persistence of rbcS and rbcL in S. gesnerioides DNA raises the question of photosynthesis genes expression in such a degraded parasitic flowering plant and possible changes in the sequence of these genes should be considered
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