Bacteria filled leaf nodules can be found on some plant species within the
genus Pavetta. The identity of the bacterial endophytes within leaf nodules
has been described for certain leaf nodulated plant species such as
Psychotria kirkii and Pavetta schumanniana. These bacteria were found to
belong to the genus Burkholderia. The bacterial endophyte population within
the leaves of three Pavetta spp. indigenous to South Africa, viz. P.
lanceolata, P. edentula and P. schumanniana, was investigated in this study
with a focus on the species of bacterial endophytes that form the nodules on
the leaves of these plants. To achieve this, a combination of culturing and
Denaturing Gradient Gel Electrophoresis (DGGE) was used. The bacterial
endophyte population within the leaves was found to be different between
the three plant species but harboured bacterial genera that have been found
in other plants. The nodule-forming bacterial endophyte in P. edentula and P. schumanniana was found to be related to those Burkholderia spp. previously
described. The nodule forming bacterial endophyte in P. lanceolata
specimens growing in pots was found to be a different species, i.e. from the
family Bradyrhizobiaceae. This was compared to P. lanceolata specimens
that were growing in open soil where a bacterium belonging to the genus
Burkholderia was identified within the nodules. Further sampling and
experimentation is necessary to determine if this finding is a rare incident
and why the bacterial species within the leaf nodules of P. lanceolata differed
between the two sites.
Leaf nodule development and morphology has been well documented within
the Psychotria, another plant genus that includes leaf nodulated species.
The leaf nodule development in Pavetta spp. has not been documented.
With the aid of electron microscopy, leaf nodule development was studied in
the three indigenous Pavetta spp. Differences such as the number of
bacteria at various leaf nodule ages and the shape of the bacteria were
noted between the three plant species. The most notable difference was
between the leaf nodules of P. edentula and P. schumanniana which were
shown to be colonized by Burkholderia spp. in comparison to the P.
lanceolata leaf nodules that were filled with a bacterium from the
Bradyrhizobiaceae. Once again further analysis is required to determine if
this difference in nodule morphology is due to the nodule-forming bacterial
species or the species of Pavetta.
The presence of the nodule-forming bacteria has been observed within the
leaf nodules and on rare occasions within the flowers and seeds of some
Pavetta spp. but their presence within stem tissue and deciduous hosts
during winter has not been reported. With the use of Burkholderia specific
primers the presence of the nodule-forming bacterial endophyte was
investigated in different tissue types of P. schumanniana in winter and
summer and within P. edentula. A Burkholderia sp. was detected within the
older leaf buds of both winter and summer samples of P. schumanniana as
well as in the flowers. No Burkholderia spp. were detected in the stem tissue
of either plant species or the leaf buds of P. edentula.