Cleome, a genus closely related to Arabidopsis, contains species spanning a developmental progression from C(3) to C(4) photosynthesis

C(4) photosynthesis involves alterations to leaf development, cell biology and biochemistry. Different lineages of C(4) plants use varying mechanisms to generate the C(4) pathway. Although the biochemistry of C(4) photosynthesis was described around 20 years ago, the phylogenetic distance between Arabidopsis and the traditional C(4) models has not facilitated the transfer of knowledge from Arabidopsis research to understanding C(4) systems. We show that Cleome, a genus closely related to Arabidopsis, contains species spanning a developmental progression from C(3) to C(4) photosynthesis. The majority of species we assessed are C(3) plants but have increased venation in leaves. Three C(3) species have both increased venation and enlarged bundle sheath cells, and there is also a tendency to accumulate proteins and transcripts needed for C(4) photosynthesis. Cleome gynandra shows all the characteristics needed for efficient C(4) photosynthesis, including alterations to leaf biochemistry, cell biology and development, and belongs to the NAD-dependent malic enzyme subtype. Combined with its phylogenetic proximity to Arabidopsis, the developmental progression from C(3) to C(4) photosynthesis within the genus provides a potentially excellent new model to increase our understanding of C(4) photosynthesis, and provide insights into its evolution.

Differentiation of C4 photosynthesis along a leaf developmental gradient in two Cleome species having different forms of Kranz anatomy

In family Cleomaceae there are NAD-malic enzyme-type C4 species having different forms of leaf anatomy. Leaves of Cleome angustifolia have Glossocardioid-type anatomy with a single complex Kranz unit which surrounds all the veins, while C. gynandra has Atriplicoid anatomy with multiple Kranz units, each surrounding an individual vein. Biochemical and ultrastructural differentiation of mesophyll (M) and bundle sheath (BS) cells were studied along a developmental gradient, from the leaf base (youngest) to the tip (mature). Initially, there is cell-specific expression of certain photosynthetic enzymes, which subsequently increase along with structural differentiation. At the base of the leaf, following division of ground tissue to form M and BS cells which are structurally similar, there is selective localization of Rubisco and glycine decarboxylase to BS cells. Thus, a biochemical C3 default stage, with Rubisco expression in both cell types, does not occur. Additionally, phosphoenolpyruvate carboxylase (PEPC) is selectively expressed in M cells near the base. Surprisingly, in both species, an additional layer of spongy M cells on the abaxial side of the leaf has the same differentiation with PEPC, even though it is not in contact with BS cells. During development along the longitudinal gradient there is structural differentiation of the cells, chloroplasts, and mitochondria, resulting in complete formation of Kranz anatomy. In both species, development of the C4 system occurs similarly, irrespective of having very different types of Kranz anatomy, different ontogenetic origins of BS and M, and independent evolutionary origins of C4 photosynthesis.

Biological activities of an extract from Cleome viscosa L. (Capparaceae)

Electron micrograph examination of the leaf and stem surfaces of Cleome viscosa L (Family Capparaceae) revealed the presence of secretory glandular trichomes with club-cylinder and cylinder morphologies. In the present study, the leaves and stems of C. viscosa were extracted with hexane and the extract was evaluated for the following biological activities: anti-bacterial, anti-fungal, contact insecticidal and nematicidal. The extract was found to be a potent anti-bacterial agent according to the thin layer chromatography autobiographic assay. Activity-directed isolation studies of the anti-bacterially active compounds led to a 14-member ring cembranoid diterpene being identified as one of the effective agents. Minimum inhibitory concentration (MIC) values (microg/spot) of 5.0 microg/spot and 1.0 microg/spot were found for the diterpene on Bacillus subtilis (Gram-positive) and Pseudomonas fluorescens (Gram-negative), respectively. The diterpene did not inhibit the growth of the fungus Cladosporium cucumerinum. The extract demonstrated a pyrethroid type of contact insecticidal activity on adult Cylas formicarius elegantulus Summer (Coleoptera: Curculionidae). The extract also had high nematicidal activity with a percentage Abbott's value of 72.69 on the plant parasitic nematode Meloidogyne incognita Chitwood; however, the extract lost its potency upon subfractionation.