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Plumbago auriculata Lam., a typical distylous plant, undergoes heteromorphic self-incompatibility (HetSI). The use of in vitro flowering allows the early identification of a plant's style morphology, and this process can be used to increase the efficiency of the breeding process and expedite research on the flowering mechanisms of P. auriculata. Here, we used seeds of P. auriculata as explants; obtained plantlets; and assessed the effects of temperature, thermoperiod, photoperiod, and light intensity on the in vitro flowering of the plants. The optimum temperature treatment was a diurnal alternation of 35 °C for 12 h and 25 °C for 12 h. Under these conditions, flower bud formation occurred within approximately 33 d, and the flowering percentage was as high as 91%. A photoperiod of 16 h and a light intensity of 200 µmol m−2 s−1 also promoted in vitro flowering. Under these conditions, flower buds formed within approximately 33 d, and the flowering percentage was approximately 90%. However, relatively long photoperiods and high light intensity suppressed flower bud development, reduced flowering, and shortened flower lifespan. The in vitro flowers had a lighter colour and smaller petals than did the in vivo flowers, although their floral structures (including their reproductive structures) were intact. This work demonstrates a stable system for the induction of in vitro flowering in P. auriculata and describes suitable temperature (35 °C/25 °C) and light (16 h photoperiod and 200 µmol m−2 s−1) conditions for rapid in vitro flowering. This system allows the efficient identification of long and short P. auriculata morphs and allows the formulation of a reasonable cultivation plan. The methods described here provide technical support for the development, utilization, and rapid propagation of excellent new P. auriculata varieties.

Heteromorphic self-incompatibility (HetSI), which is regulated by sporophytes, occurs in some species as a strategy to promote cross-pollination. This research aimed to reveal metabolic changes occurring in HetSI. We used fluorescence microscopy as a tool to compare growth behavior in self-incompatible (SI) and self-compatible (SC) pollination in both pin and thrum flowers of Plumbago auriculata and to identify the ideal timepoint for sample collection for subsequent experiments. We also employed scanning electron microscopy (SEM) to evaluate intermorph structural differences in the pollen grains and stigmas in relation to HetSI. Importantly, UPLC-MS/MS was applied in this study to identify metabolites, compare metabolic differences between pin and thrum styles and monitor metabolic changes in SC and SI pollinations in the two types of flowers. The metabolites mainly included amino acids/peptides, flavonoids, glycosides/sugars, phenols, other organic acids, fatty acids (derivatives)/lipids, amines, aldehydes, alkaloids, alcohols and other compounds. Surprisingly, energy-related nutrients such as amino acids/peptides and tricarboxylic acid cycle-related metabolites were found at higher levels in SI pollinations than in SC pollinations. This result indicates that physiological changes in pollen-stigma interactions differ in pin and thrum styles and SC and SI pollinations and that energy deficiency is not one of the reasons for HetSI.

A natural compound plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone) was isolated from the leaves of Plumbago auriculata and found to inhibit the enzyme, 8-amino-7-oxononanoate synthase (AONS, also known as 7-keto-8-aminopelargonate synthase, KAPAS) an IC 50 of 2.1 μM in vitro . Biotin supplement significantly rescued the plant injury caused by the plumbagin treatment, and this result confirmed the target site, AONS. Foliar application of 1000 ∼ 2000 μg/mL plumbagin in a greenhouse condition showed lethal activity against eight species of weeds, containing three grass species of Sorghum bicolor , Echinochloa crus-galli , Digitaria sanguinalis and five broad leaf species of Solanum nigrum , Aeschynomene indica , Abutilon avicennae , Xanthium strumarium , Calystegia japonica . Field trial of foliar application with plumbagin 2000 μg/mL have successfully controlled 10 ∼ 15 leaf-stages and 2 ∼ 3 m vine lengths of Sicyos angulatus at the natural habitats around riparian zone in the Nam-Han River in Korea. Visual symptom of desiccation might be induced by the physiological cellular leakage which was significantly dose dependent on the plumbagin treatment regardless of light.

Plants with hermaphrodite flowers risk conflict between male and female sexual function due to close proximity of sexual organs. Heterostyly, a genetic floral polymorphism characterized mainly by reciprocal herkogamy, may reduce this sexual conflict by increasing the precision of pollen transfer between morphs. This sexual organ reciprocity is often associated with various ancillary characters and a heteromorphic incompatibility system. Here we describe the morphometrics associated with heterostyly and ancillary characters in Plumbago auriculata. Using controlled pollination experiments, we show that this species has a heteromorphic incompatibility system. We also document the fauna of long-proboscid fly and butterfly pollinators in a P. auriculata population in KwaZulu-Natal, South Africa. © 2009 SAAB. Published by Elsevier B.V. All rights reserved.

Dichloromethane and 90% methanol extracts from 51 South African medicinal plants were evaluated for potential genotoxic effects using the bacterial Ames and VITOTOX® tests with and without metabolic activation. Dichloromethane extracts from bulbs of Crinum macowanii showed mutagenicity in strain TA98 with and without metabolic activation, whereas extracts from leaves of Chaetacme aristata and foliage of Plumbago auriculata showed mutagenicity and/or toxicity. Extracts from the leaves of Catharanthus roseus and twigs of Combretum mkhzense were mutagenic with metabolic activation only. The only 90% methanol extracts that were mutagenic in strain TA98 were from the leaves of C. roseus and Ziziphus mucronata in the presence of metabolic activation. No genotoxic effects were found in strain TA100 or in the VITOTOX® test.

The main aim of this study was to develop a rapid and cheap bioassay to identify germination inhibitory compounds directly from plant crude extracts. Extracts of Plumbago auriculata and Carya illinoinensis as well as their previously identified allelopathic compounds, plumbagin and juglone, respectively, were developed on TLC plates. The plates were covered with a thin layer of agar (2–4 mm) and Lactuca sativa (lettuce) and Arabidopsis thaliana seeds placed onto it. After incubation of the plates for three days complete germination inhibition correlating to specific compounds in the extract was clearly visible. Plumbagin and juglone inhibited the growth of the seeds completely while a second compound in the P. auriculata extract also showed inhibition. This compound was identified through chemical synthesis as plumbagin epoxide. This is the first report of its presence in P. auriculata . By using this bioassay on TLC, plant extracts can be tested cheaply and rapidly and the compounds responsible for germination inhibition be identified.