Pith

About: Pith is a research topic. Over the lifetime, 2011 publications have been published within this topic receiving 32791 citations.

Tracheary Element Differentiation

Abstract: Vascular plants, which are adapted for life on land, first appeared in the late Silurian period, some 400 million years ago. Since then they have evolved to fill a diverse range of habitats all over the earth. The vascular systems of land plants are composed of specialized conducting tissues, the xylem and the phloem, which provide both a pathway for water and nutrient transport and mechanical support for slender plants. The vascular system is also an important conduit for signal-transducing molecules. Tracheary elements (TEs), which are the distinctive cells of the xylem, are characterized by the formation of a secondary cell wall with annular, spiral, reticulate, or pitted wall thickenings. In the primary xylem, TEs differentiate from procambial cells, whereas in the secondary xylem, they arise from cells produced by the vascular cambium. As they mature, TEs lose their nuclei and cell contents, leaving hollow dead cells that form vessels or tracheids. The final stage of TE differentiation represents a typical example of programmed cell death in higher plants (see Pennell and Lamb, 1997, in this issue). TEs can also be induced to form in vitro from various types of cells, including cells of the phloem parenchyma and the cortex in roots, the pith parenchyma in shoots, the tuber parenchyma, and the mesophyll and epidermis in leaves (Roberts et al., 1988; Fukuda, 1992). In Zinnia elegans cell cultures, single mesophyll cells transdifferentiate directly into TEs without cell division in response to phytohormones (Fukuda and Komamine, 1980). The Zinnia system has proven to be particularly useful for studies of the sequence of events during TE differentiation. This is largely because differentiation occurs at a high frequency in Zinnia cultures and because the process can be followed in single cells (Chasan, 1994; Fukuda, 1994, 1996). Recently, I presented a general overview of xylogenesis (Fukuda, 1996). In this article, I focus on efforts to elucidate the molecular mechanisms underlying the in vitro differentiation of parenchyma cells into TEs.

Wound-induced deposition of polyphenols in transgenic plants overexpressing peroxidase

Abstract: Tobacco (Nicotiana tabacum) plants transformed with a chimeric tobacco anionic peroxidase gene have previously been shown to synthesize high levels of peroxidase in all tissues throughout the plant. One of several distinguishable phenotypes of transformed plants is the rapid browning of pith tissue upon wounding. Pith tissue from plants expressing high levels of peroxidase browned within 24 hours of wounding, while tissue from control plants did not brown as late as 7 days after wounding. A correlation between peroxidase activity and wound-induced browning was observed, whereas no relationship between polyphenol oxidase activity and browning was found. The purified tobacco anionic peroxidase was subjected to kinetic analysis with substrates which resemble the precursors of lignin or polyphenolic acid. The purified enzyme was found to readily polymerize phenolic acids in the presence of H2O2 via a modified ping-pong mechanism. The percentage of lignin and lignin-related polymers in cell walls was nearly twofold greater in pith tissue isolated from peroxidase-overproducer plants compared to control plants. Lignin deposition in wounded pith tissue from control plants closely followed the induction of peroxidase activity. However, wound-induced lignification occurred 24 to 48 hours sooner in plants overexpressing the anionic peroxidase. This suggests that the availability of peroxidase rather than substrate may delay polyphenol deposition in wounded tissue.

Temporal patterns of crop-raiding by primates: linking food availability in croplands and adjacent forest

Abstract: Summary Primates dominate lists of pests that damage crops around African parks and reserves. Beyond creating management problems, crop foraging is integral to the ecology of primates inhabiting forest—agriculture ecotones. Twenty-three months of data from four villages around Kibale National Park, Uganda, revealed that redtail monkeys Cercopithecus ascanius, olive baboons Papio cynocephalus and chimpanzees Pan troglodytes selected different crops or plant parts. Baboons took root and tuber crops ignored by other primates, and fed on the greatest variety of crops. All three species preferred maize and/or bananas. Redtails ate only banana fruit, baboons ate banana fruit more frequently than pith, and chimpanzees raided pith and fruit in equal proportions. Each primate showed a distinct monthly pattern of crop foraging, significantly non-random for baboons and redtail monkeys, weakly for chimpanzees. Large inter-monthly variation was observed for all three primates, but was least pronounced in redtails. Raiding frequency on maize peaked approximately 8 weeks after the onset of rains and was strongly correlated between the three primate species. Abundant forest fruit did not diminish primate appetite for maize. Raiding frequency on bananas varied considerably despite continuous availability of fruit and pith. Peaks in banana consumption were unrelated to rainfall or maize raiding, but were associated instead with forest fruit shortages, specifically Mimusops bagshawei. Chimpanzees consumed banana pith more frequently when forest fruits were scarce, whereas baboons targeted more banana fruits. The use of banana pith by chimpanzees supports the suggestion that energy-rich pith is crucial to chimpanzees during fruit scarcity. Conservation of Mimusops bagshawei and other key forest fruit trees may lessen primate raiding intensity on perennial crops, e.g. bananas. Maize raiding appears unaffected by forest fruit abundance. Such highly palatable crops are best planted > 500 m from the forest edge. Planting agroforestry buffers along park edges creates ideal habitat for crop-raiders. This management strategy is appropriate where human population density is low and crop raiding species are legal game. When dangerous or destructive wildlife species forage amidst densely settled subsistence farmland, managers are challenged to separate forests from agriculture using non-palatable plant barriers or electric fences.

A kinetic study of dye sorption by biosorbent waste product pith

Abstract: The sorption of two dyes, namely, Basic Red 22 and Acid Red 114 onto pith has been studied in terms of pseudo-second-order, pseudo-first-order sorption and intraparticle diffusion processes thus comparing chemical sorption and diffusion sorption processes. The pseudo-second-order model, based on the assumption of a pseudo-second-order mechanism, has been developed to predict the rate constant of sorption, the equilibrium capacity and initial sorption rate as a function of the effect of initial dye concentration, pith particle size, pith dose and temperature.