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PubMed2002

The Distance to Which Wound Effects Influence the Structure of Secondary Xylem of Decapitated Pinus pinea.

Decapitation of stems of annuals and trees for the study of vascular and fiber differentiation with or without hormonal application is a common procedure. There is controversy about whether wound effects play a role in such experiments, and to what distance from the point of decapitation. To examine this question, the distance from the point of decapitation at which apparent wound effects are obvious developmentally, was studied in decapitated 4-year-old Pinus pinea plants. The wound effects just below the cut included differentiation of many traumatic resin ducts, a parenchyma band instead of tracheids, more tracheid files, and a higher proportion of late wood. The increase in the number of resin ducts was still considerable and statistically significant 10 cm below the point of decapitation compared with the nondecapitated control. These results indicate that in pines, wound effects in the first 5 cm below the decapitation point (a common point for tissue examination) cannot be ignored in experiments on the regulation of vascular differentiation.

Journal Article↗
PubMed2004

Salt stress enhances xylem development and expression of S-adenosyl-L-methionine synthase in lignifying tissues of tomato plants.

S-Adenosyl-L-methionine synthase (SAM; ATP: L-methionine adenosyltransferase, EC 2.5.1.6) catalyzes the biosynthesis of S-adenosyl-L-methionine (AdoMet), a universal methyl-group donor. This enzyme is induced by salinity stress in tomato (Lycopersicon esculentum Mill.). To elucidate the role of SAM and AdoMet in the adaptation of plants to a saline environment, the expression pattern and histological distribution of SAM was investigated in control and salt-stressed tomato plants. Immunohistochemical analysis showed that SAM proteins were expressed in all cell types and plant organs, albeit with preferential accumulation in lignified tissues. Lignin deposition was estimated by histochemical tests and the extent of tissue lignification in response to salinity was quantified by image analysis. The average number of lignified cells in vascular bundles was significantly greater in plants under salt stress, with a maximal expansion of the lignified area found in the root vasculature. Accordingly, the greatest abundance of SAM gene transcripts and proteins occurred in roots. These results indicate that increased SAM activity correlated with a greater deposition of lignin in the vascular tissues of plants under salinity stress. A model is proposed in which an increased number of lignified tracheary elements in tomato roots under salt stress may enhance the cell-to-cell pathway for water transport, which would impart greater selectivity and reduced ion uptake, and compensate for diminished bulk flow of water and solutes along the apoplastic pathway.

Environment↗
PubMed2001

Cambial history of Scots pine trees (Pinus Sylvestris) prior and after the Chernobyl accident as encoded in the xylem.

Studies were carried out on wood samples collected in October 1997 from breast height of Scots pine trees (Pinus sylvestris) from site located 5 km south from the Chernobyl nuclear power plant. The radioactive contamination at the site was 3.7x10(5) kBq m(-2). These samples of secondary wood were used as an archive of information about the dynamics of a meristematic tissue cambium affected by ionising radiation from the Chernobyl reactor accident. The results show that frequency of the cambial cells events like anticlinal divisions, intrusive growth and cells elimination, was after the Chernobyl accident, about three times higher in comparison to preceding years. The most interesting finding was that after irradiation the length of tracheids increased. This increase is interpreted as an effect of intracambial competition among cells in the initial layer.

Journal Article↗
PubMed2006

Uptake and xylem transport of fipronil in sunflower.

The phenylpyrazole insecticide, fipronil, is used in seed coating against Agriotes larvae, which infest mainly corn and sunflower. Coating the seeds of the cultivated plants with fipronil has proven its effectiveness against Agriotes populations. In the case of sunflower or even corn, the possible root uptake of this insecticide may lead to a toxic effect against pollinators such as honeybees. In the present report, the uptake and transport of fipronil inside the sunflower seedling was studied in the laboratory. In a first study, sunflower was cultivated on an aqueous medium containing fipronil. An intense root uptake of fipronil occurred, leading to a transport into leaves depending upon transpiration. In a second study, plants were cultivated on a soil in which fipronil was uniformly distributed. Under our soil conditions (20% organic carbon), the partition coefficient between soil and water (K(d)) was found to be equal to 386 +/- 30. The average rate of fipronil transfer from soil water to seedlings was from 2 to 2.6 times lower than water transfer. During the 3 week experiment, 55% of recovered labeled compounds was in the parent form and 35% had been converted to lipophilic metabolites, with either a 4-CF(3)-SO(2) or 4-CF(3)-S substituant, which are also very potent lipophilic insecticides. This paper suggests that the possible uptake of fipronil by sunflower seedlings under agronomic conditions is mainly controlled by the physicochemical characteristics of the seed-coating mixture.

Biological Transport↗
PubMed1995

Arabinogalactan proteins in maize coleoptiles: developmental relationship to cell death during xylem differentiation but not to extension growth.

The spatial and temporal expression of arabinogalactan proteins (AGPs) in the coleoptile of maize seedlings was investigated with monoclonal antibodies (MAC207, JIM13, JIM14) raised against particular AGP epitopes in carrot. MAC207 binds to a buffer-soluble AGP fraction of 90-210 kDa that also reacts with beta-glucosyl Yariv reagent and the lectin RCA120. Immunogold-labelling showed that the MAC207 epitope is exclusively localized in the plasma membrane. JIM13 binds to a 120 kDa component of the buffer-soluble AGP fraction localized in the plasma membrane of future sclerenchyma cells and secondary-wall thickenings of future tracheids of vascular bundles. JIM14 binds to a 50 kDa component of the salt-extractable fraction from cell walls localized in the innermost wall layer of sclerenchyma cells. These AGP epitopes demonstrate different temporal expression patterns which do not correlate with extension growth. Auxin had no effect on the amount of soluble AGP from coleoptile sections, containing the growth-controlling epidermis but no vascular bundles, as measured by crossed electrophoresis. Moreover, incorporation of radioactive arabinose, galactose or proline into this fraction was not stimulated by auxin. These results contradict the hypothesis that AGPs function as wall-loosening agents in auxin-mediated extension growth. The results are compatible with the notion that AGPs serve as developmental markers defining particular features of future cell differentiation. The specific association of the epitopes recognized by JIM13 and JIM14 with disintegrating cells suggests that the related AGPs identify those cells of the coleoptile which are committed to programmed cell death.

Cell Death↗
PubMed2004

Variation in xylem structure from tropics to tundra: evidence from vestured pits.

Bordered pits play an important role in permitting water flow among adjacent tracheary elements in flowering plants. Variation in the bordered pit structure is suggested to be adaptive in optimally balancing the conflict between hydraulic efficiency (conductivity) and safety from air entry at the pit membrane (air seeding). The possible function of vestured pits, which are bordered pits with protuberances from the secondary cell wall of the pit chamber, could be increased hydraulic resistance or minimized vulnerability to air seeding. These functional hypotheses have to be harmonized with the notion that the vestured or nonvestured nature of pits contains strong phylogenetic signals (i.e., often characterize large species-rich clades with broad ecological ranges). A literature survey of 11,843 species covering 6,428 genera from diverse climates indicates that the incidence of vestured pits considerably decreases from tropics to tundra. The highest frequencies of vestured pits occur in deserts and tropical seasonal woodlands. Moreover, a distinctly developed network of branched vestures is mainly restricted to warm habitats in both mesic and dry (sub)tropical lowlands, whereas vestures in woody plants from cold and boreal arctic environments are usually minute and simple. A similar survey of the frequency of exclusively scalariform perforation plates illustrates that the major ecological trend of this feature is opposite that of vestured pits. These findings provide previously undescribed insights suggesting that vessels with vestured pits and simple perforation plates function as an efficient hydraulic system in plants growing in warm environments with periodical or continuous drought stress.

Cold Climate↗