Despite increasing knowledge of allantoin as a phytochemical involved in rice, relatively little is known about its distribution and function in rice grains. In this study, allantoin was quantified in 15 Chinese rice grains, and its contents varied with grain fraction, cultivar, and genotype. Bran always had the highest allantoin level, followed by brown rice and milled rice. Hull contained the lowest allantoin content. Allantoin in japonica bran ranged from 70 to 171 μg/g but rarely exceeded 100 μg/g in indica bran. There was a positive relationship between allantoin level in grains and seedling survival in seedbeds under low temperature or water deficit. Exogenous allantoin stimulated plant growth, increased soluble sugar and free proline contents, and decreased malondialdehyde content in rice seedlings. However, allantoin did not show any antioxidant activity through free radical-scavenging capacity, reducing power, linoleic acid peroxidation inhibition, and chelating activity. The results suggest that allantoin in rice grains may play some roles in providing plant stress protection but not serving as a beneficial health antioxidant.

Distribution and function of allantoin (5-ureidohydantoin) in rice grains.

Allantoin (5-ureidohydantoin) plays an essential role in the assimilation, metabolism, transport, and storage of nitrogen in numerous higher plants, but its ecological implications are largely unknown. In this study allantoin was found in tissues of 11 rice (Oryza sativa) varieties tested, and its structure was characterised by X-ray diffraction analysis to confirm the fact that allantoin was actually obtained from the rice plants. Furthermore, the endogenous allantoin was exuded from the rice roots into the rhizosphere soils and had a great diversity of biological effects on associated weeds and microbes by soil interactions once released. However, allantoin levels in tissues or soils could not be distinguished between the allelopathic and non-allelopathic rice varieties. Field experiments showed that levels of allantoin released from rice varieties varied with their growth stages and reached the maximal levels at the stem elongation or panicle initiation to booting stages and then decreased dramatically. Allantoin could significantly stimulate the germination and growth of Echinochloa crus-galli and populations of soil bacteria and actinomycetes at selected test concentrations (30–500 μg/g), but had no effect on soil fungi. The half-life (t
 1/2
 ) of allantoin in autoclaved soil (20.2 ± 2.5 h, r
 2 = 0.95) was almost three-times longer than in non-autoclaved soil (7.3 ± 1.9 h, r
 2 = 0.92), indicating that rapid biodegradation or transformation of allantoin occurs in paddy soil. The results suggest that not only may allantoin play a role in the transport and storage of nitrogen in rice tissues but it may also participate in species interactions between rice and other organisms in paddy soil.

Allantoin involved in species interactions with rice and other organisms in paddy soil

The Cerrado (the Brazilian savanna) is one of the vegetation formations of great biodiversity in Brazil and it has experienced strong deforestation and fragmentation. The Cerrado must contain at least 12,000 higher plant species. We discuss the ecological relevance of phytochemical studies carried out on plants from the Cerrado, including examples of phytotoxicity, antifungal, insecticidal and antibacterial activities. The results have been classified according to activity and plant family. The most active compounds have been highlighted and other activities are discussed. A large number of complex biochemical interactions occur in this system. However, only a small fraction of the species has been studied from the phytochemical viewpoint to identify the metabolites responsible for these interactions.

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Ecological phytochemistry of Cerrado (Brazilian savanna) plants

Rice (Oryza sativa L.) may release allantoin into paddy soil. Currently, little attention has been paid to the effects of allantoin on soil microbial diversity and community. In this study, the diversity indices for the microbial community in rice soil and the allantoin-induced shifts in the microbial community composition across moisture regimes versus incubation times were examined by looking at phospholipid fatty acid (PLFA) profiles and PCR-denaturing gradient gel electrophoresis (DGGE) patterns. The total PLFA concentration increased with the amount of allantoin applied during incubation. A similar trend occurred for microbial biomass carbon (MBC) and pH. Furthermore, applying allantoin resulted in an increased ratio of anaerobe: aerobe and bacteria: fungi but decreased the ratio of Gram-negative bacteria: Gram-positive bacteria (GN: GP) and fungal marker 18:2ω6,9c under flooded rice soil. A stepwise discriminant analysis of the PLFA pattern clearly separated allantoin-treated samples from non-treated samples. There was also a clear split between different incubation times. Moisture treatments differed in the ratios of anaerobe: aerobe and GN: GP but showed similar trends in total PLFA concentrations and the bacteria: fungi ratio during incubation. These results suggest that application of allantoin stimulates shifts in microbial community composition and increases microbial diversity as well as living microbial biomass in rice soil.

Allantoin-induced changes of microbial diversity and community in rice soil

Antioxidant, anti-rheumatic and anti-inflammatory investigation of extract and dicentrinone from Duguetia furfuracea (A. St.-Hil.) Benth. & Hook. f.

Memora peregrina (local name: 'ciganinha' - Bignoniaceae) is a weed that often invades pastures in the Brazilian state of Mato Grosso do Sul From its leaves and subterranean parts, the following compounds were isolated: allantoin (207 w/w in subterranean parts), the iridoid 6b-hydroxyipolamiide, hyperin, 3'-O-methylhyperin, 4-hydroxy-N-methylproline, b-sitosterol, a-amirin and b-amirin, and lupeol Allantoin exhibited an activity of inducing germination in seeds of Lactuca sativa used as a biological model, and the iridoid showed moderate activity in the larval development of Anagasta kuehniella These results, associated with this plant's behavior, are suggestive of the occurrence of adaptive and competitive strategies in relation to other plant species

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Elayne de Oliveira Tulli

Papers

Estudo fitoquímico e avaliação alelopática de Memora peregrina - "ciganinha" - Bignoniaceae, uma espécie invasora de pastagens em Mato Grosso do Sul