Effects of simulated acid rain on germination, seedling growth and oxidative metabolism of recalcitrant-seeded Trichilia dregeana grown in its natural seed bank

Increased air pollution in a number of developing African countries, together with the reports of vegetation damage typically associated with acid precipitation in commercial forests in South Africa, has raised concerns over the potential impacts of acid rain on natural vegetation in these countries. Recalcitrant (i.e. desiccation sensitive) seeds of many indigenous African species, e.g. must germinate shortly after shedding and hence, may not be able to avoid exposure to acid rain in polluted areas. This study investigated the effects of simulated acid rain (rainwater with pH adjusted to pH 3.0 and 4.5 with 70:30, H2 SO4 :HNO3 ) on germination, seedling growth and oxidative metabolism in a recalcitrant-seeded African tree species Trichilia dregeana Sond., growing in its natural seed bank. The results suggest that acid rain did not compromise T. dregeana seed germination and seedling establishment significantly, relative to the control (non-acidified rainwater). However, pH 3.0 treated seedlings exhibited signs of stress typically associated with acid rain: leaf tip necrosis, abnormal bilobed leaf tips, leaf necrotic spots and chlorosis, reduced leaf chlorophyll concentration, increased stomatal density and indications of oxidative stress. This may explain why total and root biomass of pH 3.0 treated seedlings were significantly lower than the control. Acid rain also induced changes in the species composition and relative abundance of the different life forms emerging from T. dregeana's natural seed bank and in this way could indirectly impact on T. dregeana seedling establishment success.

Preparation of activated carbon by microwave heating of langsat (Lansium domesticum) empty fruit bunch waste

The feasibility of langsat empty fruit bunch waste for preparation of activated carbon (EFBLAC) by microwave-induced activation was explored. Activation with NaOH at the IR ratio of 1.25, microwave power of 600 W for 6 min produced EFBLAC with a carbon yield of 81.31% and adsorption uptake for MB of 302.48 mg/g. Pore structural analysis, scanning electron microscopy and Fourier transform infrared spectroscopy demonstrated the physical and chemical characteristics of EFBLAC. Equilibrium data were best described by the Langmuir isotherm, with a monolayer adsorption capacity of 402.06 mg/g, and the adsorption kinetics was well fitted to the pseudo-second-order equation. The findings revealed the potential to prepare high quality activated carbon from langsat empty fruit bunch waste by microwave irradiation.

Cadmium accumulation and tolerance of mahogany (Swietenia macrophylla) seedlings for phytoextraction applications

Mahogany, a high biomass fast-growing tropical tree, has recently garnered considerable interest for potential use in heavy metal phytoremediation. This study performed hydroponic experiments with Cd concentration gradients at concentrations of 0, 7.5, 15, and 30 mg L(-1) to identify Cd accumulation and tolerance of mahogany (Swietenia macrophylla) seedlings as well as their potential for phytoextraction. Experimental results indicate that Cd inhibited mahogany seedling growth at the highest Cd exposure concentration (30 mg L(-1)). Nevertheless, this woody species demonstrated great potential for phytoextraction at Cd concentrations of 7.5 and 15 mg L(-1). The roots, twigs, and leaves had extremely large bioaccumulation factors at 10.3-65.1, indicating that the plant extracted large amounts of Cd from hydroponic solutions. Mahogany seedlings accumulated up to 154 mg kg(-1) Cd in twigs at a Cd concentration of 15 mg L(-1). Although Cd concentrations in leaves were <100 mg kg(-1), these concentrations markedly exceed the normal ranges for other plants. Due to the high biomass production and Cd uptake capacity of mahogany shoots, this plant is a potential candidate for remediating Cd-contaminated sites in tropical regions.

Herbicide risk assessment for non-target aquatic plants: sulfosulfuron--a case study

Herbicides entering the aquatic environment by spray drift, run-off and leaching to field drains may cause adverse effects on non-target aquatic vegetation. The potential for such effects has typically been evaluated from tests with floating, monocotyledonous Lemna sp. However, concern has been expressed as to whether this species could be used to indicate potential effects on other vegetation types, particularly rooted, submerged, emergent or dicotyledonous species. In 1997, the Centre for Aquatic Plant Management undertook development of new tests based on the additional species, Glyceria maxima (Hartm) Holmb, Lagarosiphon major (Ridl) Moss and Myriophyllum spicatum L. The resulting methodology was used to assess the effects of the sulfonylurea herbicide, sulfosulfuron on these species. Data presented here demonstrate that exposure to initial sulfosulfuron concentrations of 3.33 microg litre(-1) for up to 21 days was tolerated by these species and that adverse effects were observed only when plants were exposed to initial concentrations of 3.33 and 10 microg litre(-1) for 70 days. As the occurrence of such high initial concentrations for long periods is unlikely in the aquatic environment, sulfosulfuron is not expected to have adverse effects on the growth of these species. This study has also demonstrated that G maxima, L major and M spicatum grown in small outdoor tanks can be used successfully to assess the effects of crop-protection products on non-target aquatic flora.

Exploring the use of DMSO and ascorbic acid to promote shoot development by excised embryonic axes of recalcitrant seeds

Seeds of Trichilia dregeana, T. emetica and Protorhus longifolia are recalcitrant (desiccation-sensitive), hence cryopreservation is the only ex situ means feasible for long-term conservation of these germplasm. For cryopreservation of these species, the excised embryonic axis is the explant of choice due to their small size and higher tolerance to desiccation. However, for many species with seeds having fleshy cotyledons, shoot development fails to occur after excision, which has been attributed to a reactive oxygen species (ROS) burst during excision wounding. This is a critical limiting step in developing cryopreservation protocols for such species. In embryos of T. dregeana, T. emetica and P. longifolia, the cotyledonary insertions are in close proximity to the shoot apical meristem and oxidative stress upon excision of the axis from cotyledons has been consistently associated with shoot tip necrosis, which precludes shoot development. This study tested the effects of dimethyl sulphoxide (DMSO) pre-culture prior to complete removal of the cotyledons, and post-excision soaking in DMSO or in the antioxidant, ascorbic acid, on shoot development by axes of T. dregeana and P. longifolia. These treatments had a significant (P < 0.05) positive effect on shoot production with a 6 h DMSO pre-culture combined with a DMSO post-excision soak being optimal for promoting shoot production in 70 percent of the axes of T. dregeana and 60 percent of those of P. longifolia. Embryonic axes of T. emetica responded best to a 6 h DMSO pre-culture alone, with 55 percent of axes producing shoots. It was further shown that two different post-harvest developmental stages of T. dregeana axes differed significantly initially (P < 0.05) in their response to DMSO and ascorbic acid treatments.

Leaf structural traits of tropical woody species resistant to cement dust

Cement industries located nearby limestone outcrops in Brazil have contributed to the coating of cement dust over native plant species. However, little is known about the extent of the response of tropical woody plants to such environmental pollutant particularly during the first stages of plant development and establishment. This work focused on the investigation of possible alterations in leaf structural and ultrastructural traits of 5-month-old Guazuma ulmifolia Lam. (Malvaceae), 6-month-old Myracrodruon urundeuva Allemão (Anacardiaceae), and 9-month-old Trichilia hirta L. (Meliaceae) challenged superficially with cement dust during new leaf development. Leaf surface of plants, the soil or both (leaf plus soil), were treated (or not) for 60 days, under controlled conditions, with cement dust at 2.5 or 5.0 mg cm(-2). After exposure, no significant structural changes were observed in plant leaves. Also, no plant death was recorded by the end of the experiment. There was also some evidence of localized leaf necrosis in G. ulmifolia and T. hirta, leaf curling in M. urundeuva and T. hirta, and bulges formation on epidermal surface of T. hirta, after cement dust contact with plant shoots. All species studied exhibited stomata obliteration while T. hirta, in particular, presented early leaf abscission, changes in cellular relief, and organization and content of midrib cells. No significant ultrastructural alterations were detected under the experimental conditions studied. Indeed, mesophyll cells presented plastids with intact membrane systems. The high plant survival rates, together with mild morphoanatomic traits alterations in leaves, indicate that G. ulmifolia is more resistant to cement dust pollutant, followed by M. urundeuva and T. hirta. Thus, the three plant species are promising for being used to revegetate areas impacted by cement industries activities.

[In vitro propagation of mahogany tree (Swietenia macrophylla King) from axillary buds]

The mahogany tree (Swietenia macrophylla King) is a forest tree with a great commercial value mainly due to its wood quality. Unfortunately, this species is being threatened by the effect of intensive timber exploitation, its low capacity to regenerate, and the attack of the Meliaceae shoot borer (Hypsipylla grandella Zeller) (Lepidoptera Pyralidae). To increase population, large-scale propagation of mahogany by in vitro culture was developed. To obtain plantlets, nodal segments were cultured in a half-strength MS medium supplemented with different combinations of naphthaleneacetic acid (NAA) and 6-benzyladenine (BA), specified by the Central Compositional Rotable Statistical Design Method, within a range of 0-3 mg/L for both hormones. Favourable incubation conditions were: 16 h light, and 40-45 micromol x m(-2) x s(-1) at 25 degrees C. The derived response surface showed an optimal axillary bud elongation on a medium containing 1.94 mg BA/L and 0.38 mg NAA/L. No significant differences were found neither applying Orellana Method nor modified Orellana method. Mahogany plantlets obtained were successfully acclimated.