Basipetal Direction Research Articles

Leaf age-dependent differences in sulphur assimilation and allocation in poplar (Populus tremula x P. alba) leaves.

35S-sulphate was flap-fed to poplar leaves of different leaf development stages - young developing, expanding, mature, and old mature poplar leaves. (35)S-sulphate was taken up independent of the leaf development stage. Whereas young development leaves did not export the (35)S taken up, export increased with increasing leaf development stage. Expanding leaves allocated the exported (35)S mainly into apical tree parts (73-87%) and only to a minor extent (13-27%) in basipetal direction. Neither lower trunk sections nor the roots were sinks for the exported (35)S. Expanding and developing leaves, but not the shoot apex, were the main sinks for the (35)S allocated in apical direction. In contrast, mature and old mature leaves exported the (35)S taken up mainly in basipetal direction (65-82%) with the roots constituting the main sinks. The (35)S allocated into apical tree parts was found in expanding and developing leaves, but only to a minor extent in the shoot apex. Apical allocated (35)S was identified as sulphate. Apparently the demand of young developing leaves for reduced sulphur was not fulfilled by mature leaves. Therefore, reduced sulphur for growth and development of young developing leaves must be supplied from other sources. In vitro activity of enzymes involved in assimilatory sulphate reduction was measured to investigate whether demand for reduced sulphur by young leaves is met by their own sulphate reduction. ATP sulphurylase and APS reductase activities were not significantly lower in developing than in mature leaves. Sulphite reductase and serine acetyltransferase activities were highest in developing leaves; O:-acetylserine (thiol) lyase activity was similar in all leaf developing stages. Apparently, young developing poplar leaves are able to produce their own reduced sulphur for growth and development. Whether other sources such as storage tissues and/or roots are involved in reduced sulphur supply to developing leaves remains to be elucidated.

The geometry of light interception by shoots of Heteromeles arbutifolia: morphological and physiological consequences for individual leaves.

The influence of leaf orientation and position within shoots on individual leaf light environments, carbon gain, and susceptibility to photoinhibition was studied in the California chaparral shrub Heteromeles arbutifolia with measurements of gas exchange and chlorophyll fluorescence, and by application of a three-dimensional canopy architecture model. Simulations of light absorption and photosynthesis revealed a complex pattern of leaf light environments and resulting leaf carbon gain within the shoots. Upper, south-facing leaves were potentially the most productive because they intercepted greater daily photon flux density (PFD) than leaves of any other orientation. North-facing leaves intercepted less PFD but of this, more was received on the abaxial surface because of the steep leaf angles. Leaves differed in their response to abaxial versus adaxial illumination depending on their orientation. While most had lower photosynthetic rates when illuminated on their abaxial as compared to adaxial surface, the photosynthetic rates of north-facing leaves were independent of the surface of illumination. Because of the increasing self-shading, there were strong decreases in absorbed PFD and daily carbon gain in the basipetal direction. Leaf nitrogen per unit mass also decreased in the basipetal direction but on a per unit area basis was nearly constant along the shoot. The decrease in leaf N per unit mass was accounted for by an increase in leaf mass per unit area (LMA) rather than by movement of N from older to younger leaves during shoot growth. The increased LMA of older lower leaves may have contributed directly to their lower photosynthetic capacities by increasing the limitations to diffusion of CO2 within the leaf to the sites of carboxylation. There was no evidence for sun/shade acclimation along the shoot. Upper leaves and especially south-facing upper leaves had a potential risk for photoinhibition as demonstrated by the high PFDs received and the diurnal decreases in the fluorescence ratio F v/F m. Predawn F v/F m ratios remained high (>0.8) indicating that when in their normal orientations leaves sustained no photoinhibition. Reorientation of the leaves to horizontal induced a strong sustained decrease in F v/F m and CO2 exchange that slowly recovered over the next 10-15 days. If leaves were also inverted so that the abaxial surface received the increased PFDs, then the reduction in F v/F m and CO2 assimilation was much greater with no evidence for recovery. The heterogeneity of responses was due to a combination of differences between leaves of different orientation, differences between responses on their abaxial versus adaxial surfaces, and differences along the shoot due to leaf age and self-shading effects.

Monoterpene composition of essential oil from peppermint (Mentha x piperita L.) with regard to leaf position using solid-phase microextraction and gas chromatography/mass spectrometry analysis.

Monoterpene compounds of leaf pairs and flowers of Mentha x piperita have been studied by direct headspace sampling using solid-phase microextraction coupled with gas chromatography/mass spectrometry (SPME-GC/MS). The content of peppermint-characteristic compounds such as menthol, menthyl acetate, and neomenthol increased in a basipetal direction (older plant parts), whereas menthone and isomenthone showed higher levels in the acropetal direction (younger plant parts). Higher levels of menthofuran were found in peppermint flowers in contrast to the leaves. SPME sampling resulted in relatively higher amounts of high-volatile monoterpenes and lower detection of less volatile compounds such as menthol and menthone, compared to solvent-based samples from essential oil distillation.

A Statistical Approach to Biological Factors of Safety: Bending and Shearing inPsilotumAxes

A method is presented to calculate the factor of safety (based on any criterion of failure) for populations of equivalent biological structures that normally sustain mechanical loads (e.g. stems of the same order of branching). The method uses the empirically determined mean and standard deviation of the actual loads and the load capabilities provided that both types of loads are normally distributed in the population. The factor of safetySis calculated from the formulaS⩾1+α(sd2ω+sd2η)1/2/Aβfχ L, where α and β are determined from regression analyses,sddenotes standard deviation,ωis load capability (the maximum load a structure can sustain before it mechanically fails), χ is the actual load (the load the structure normally sustains), χL is the mean actual load determined for the population, andAfis the area under the frequency distribution curve for whichω-η<0. The method was used to computeSfor the axes drawn from different orders of branching in the aerial trusses ofPsilotum nudum, a taxonomically problematic pteridophyte. Failure in bending and failure in twisting were used as two criteria of mechanical failure. The actual loads, load capabilities, and the difference between the two loads measured in bending and twisting for representative axes in each branch level were normally distributed. Based on the area of overlap between the frequency distribution curves of the two kinds of loads, the standard deviations of the loads, and the mean actual loads for the axes drawn from each level of branching, the factor of safety in bending and twisting was found to decrease in a basipetal direction: distal axes had the highest factors of safety, while the most proximal axes in trusses had the lowest factors of safety. The data indicated that axes from all levels of branching had factors of safety greater than unity, and thus all axes were mechanically reliable load-bearing members. The limitations and benefits of the method for computingSare discussed in the specific context ofP. nudumand for the vertical stems of vascular plants in general. The principal limitation of the method is the assumption that actual loads and load capabilities have normal frequency distributions; the main benefit of the method is that factors of safety are numerically indexed in an objective way based on the distribution of mechanical properties of a population of otherwise similar organic structures.

Interactive effects of elevated atmospheric CO2, mycorrhization and drought on long‐distance transport of reduced sulphur in young pedunculate oak trees (Quercus robur L.)

Pedunculate oak (Quercus robur L.) was germinated and grown under nutrient non‐limiting conditions for a total of 10–15 weeks at ambient CO2 concentration and 1100 μmol mol–1 CO2 either in the presence or the absence of the mycorrhizal fungus Laccaria laccata. Half of the oak trees of these treatments were exposed to drought during final growth by suspending the water supply for 21 d. Mycorrhization and elevated atmospheric CO2 each enhanced total plant biomass per tree. Whereas additional biomass accumulation of trees grown under elevated CO2 was mainly attributed to increased growth of lateral roots, mycorrhization promoted shoot growth. Water deficiency reduced biomass accumulation without affecting relative water content, but this effect was more pronounced in mycorrhizal as compared to non‐mycorrhizal trees. Elevated CO2 partially prevented the development of drought stress, as indicated by leaf water potential, but did not counteract the negative effects of water deficiency on growth during the time studied. Enhanced biomass accumulation requires adaption in protein synthesis and, as a consequence, enhanced allocation of reduced sulphur produced in the leaves to growing tissues. Therefore, allocation of reduced sulphur from oak leaves was studied by flap‐feeding radiolabelled GSH, the main long‐distance transport form of reduced sulphur, to mature oak leaves. Export of radiolabel proceeded almost exclusively in basipetal direction to the roots. The rate of export of radioactivity out of the fed leaves was significantly enhanced under elevated CO2, irrespective of mycorrhization. A higher proportion of the exported GSH was transported to the roots than to basipetal stem sections under elevated CO2 as compared to ambient CO2. Mycorrhization did not affect 35S export out of the fed leaves, but the distribution of radiolabel between stem and roots was altered in preference of the stem. Trees exposed to drought did not show appreciable export of the 35S radioactivity fed to the leaves when grown under ambient CO2. Apparently, drought inhibited basipetal transport of reduced sulphur at the level of phloem loading and/or phloem transport. Elevated CO2 seemed to counteract this effect of drought stress to some extent, since higher leaf water potentials and improved 35S export out of the fed leaves was observed in oak trees exposed to drought and elevated CO2 as compared to trees exposed to drought and ambient CO2.

Basipetal Gradient of Axillary Bud Inhibition Along a Rose (Rosa hybridaL.) Stem: Growth Potential of Primary Buds and their Two Most Basal Secondary Buds as Affected by Position and Age

Abstract In Rosa hybrida L. cv. Ruidriko ‘Vivaldi’®, the effect of position on growth and development potentials of axillary buds was investigated by single internode cuttings excised along the floral stem and its bearing shoot. The experiments were carried out in both glasshouses and in a phytotron. The study firstly concerned the development of the primary shoot from the onset of bud growth until anthesis. The primary shoot was then bent horizontally to promote the growth of the two most proximal secondary buds, the collateral buds, already differentiated inside the primary bud. They gave rise to basal shoots. In the basipetal direction, the axillary buds along the floral stem exhibited both an increase in the lag time before bud growth and a decrease in bud growth percentage, demonstrating the existence of a physiological basipetal gradient of inhibition intrinsic to the buds or due to short range correlations. The same basipetal gradient of inhibition was observed along the floral stem and its bearing shoot, demonstrating that the age of the bud was not a major factor in determining the rate of bud growth. After bending the primary shoot, the percentage of collateral bud growth was also affected by the cutting position. The more proximal the cutting, the lower the sprouting ability of collateral buds. The growth potential of these buds appeared to be already determined inside the main bud before cutting excision.

High levels of inter-ramet water translocation in two rhizomatous Carex species, as quantified by deuterium labelling.

We studied water trnaslocation between interconnected mother and daughter ramets in two rhizomatous Carex species, using a newly developed quantitative method based on deuterium tracing. Under homogeneous conditions, in which both ramets were subjected either to wet or dry soil, little water was exchanged between the ramets. When the ramet pair was exposed to a heterogeneous water supply, water translocation became unidirectional and strongly increased to a level at which 30-60% of the water acquired by the wet ramet was exported towards the dry ramet. The quantity of water translocated was unrelated to the difference in water potential between the ramets, but highly correlated to the difference in leaf area. In both species, the transpiration of the entire plant was similar under heterogeneous and homogeneous wet conditions. This was a direct result of an increase in water uptake by the wet ramet in response to the dry conditions experienced by the interconnected ramet. In C. hirta, the costs and benefits of integration in terms of ramet biomass paralleled the responses of water consumption. This species achieved a similar whole-plant biomass in heterogeneous and homogeneous wet treatments, and water translocation was equally effective in the acropetal and basipetal directions. In C. flacca, responses of biomass and water consumption did not match and, under some conditions, water translocation imposed costs rather than benefits to the plants of this species. It is concluded that enhanced resource acquisition by donor ramets may be of critical importance for the net benefits of physiological integration in clonal plants.

Interactive effects of mycorrhization and elevated atmospheric CO2 on sulphur nutrition of young pedunculate oak (Quercus robur L.) trees

ABSTRACTPedunculate oak (Quercus robur L.) was germinated and grown at ambient CO2 concentration and 650 μmol mol−1 CO2 in the presence and absence of the ectomycorrhizal fungus Laccaria laccata for a total of 22 weeks under nonlimiting nutrient conditions. Sulphate uptake, xylem loading and exudation were analysed in excised roots. Despite a relatively high affinity for sulphate (KM= 1.6 mmol m−3), the rates of sulphate uptake by excised lateral roots of mycorrhizal oak trees were low as compared to herbaceous plants. Rates of sulphate uptake were similar in mycorrhizal and non‐mycorrhizal roots and were not affected by growth of the trees at elevated CO2. However, the total uptake of sulphate per plant was enhanced by elevated CO2 and further enhanced by elevated CO2 and mycorrhization. Sulphate uptake seemed to be closely correlated with biomass accumulation under the conditions applied.The percentage of the sulphate taken up by mycorrhizal oak roots that was loaded into the xylem was an order of magnitude lower than previously observed for herbaceous plants. The rate of xylem loading was enhanced by mycorrhization and, in roots of mycorrhizal trees only, by growth at elevated CO2. On a whole‐plant basis this increase in xylem loading could only partially be explained by the increased growth of the trees. Elevated CO2 and mycorrhization appeared to increase greatly the sulphate supply of the shoot at the level of xylem loading. For all treatments, calculated rates of sulphate exudation were significantly lower than the corresponding rates of xylem loading of sulphate. Radiolabelled sulphate loaded into the xylem therefore seems to be readily diluted by unlabelled sulphate during xylem transport.Allocation of reduced sulphur from oak leaves was studied by flap‐feeding radiolabelled GSH to mature oak leaves. The rate of export of radioactivity from the fed leaves was 4–5 times higher in mycorrhizal oak trees grown at elevated CO2 than in those grown at ambient CO2. Export of radiolabel proceeded almost exclusively in a basipetal direction to the roots. From these experiments it can be concluded that, in mycorrhizal oak trees grown at elevated CO2, the transport of sulphate to the shoot is increased at the level of xylem loading to enable increased sulphate reduction in the leaves. Increased sulphate reduction seems to be required for the enhanced allocation of reduced sulphur to the roots which is observed in trees grown at elevated CO2. These changes in sulphate and reduced sulphur allocation may be a prerequisite for the positive effect of elevated CO2 on growth of oak trees previously observed.

The mechanism of resistance to paraquat is strongly temperature dependent in resistant Hordeum leporinum Link and H. glaucum Steud.

Paraquat-resistant biotypes of the closely-related weed species Hordeum leporinum Link and H. glaucum Steud. are highly resistant to paraquat when grown during the normal winter growing season. However, when grown and treated with paraquat in summer, these biotypes are markedly less resistant to paraquat. This reduced resistance to paraquat in summer is primarily a result of increased temperature following herbicide treatment. The mechanism governing this decrease in resistance at high temperature was examined in H. leporinum. No differences were observed between susceptible and resistant biotypes in the interaction of paraquat with isolated thylakoids when assayed at 15, 25, or 35 °C. About 98 and 65% of applied paraquat was absorbed through the leaf cuticle of both biotypes at 15 and 30 °C, respectively. Following application to leaves, more herbicide was translocated in a basipetal direction in the susceptible biotype compared to the resistant biotype at 15 °C. However, at 30 °C more paraquat was translocated in a basipetal direction in the resistant biotype. Photosynthetic activity of young leaf tissue from within the leaf sheath which had not been directly exposed to paraquat was measured 24 h after treatment of plants with para. quat. This activity was inhibited in the susceptible biotype when plants were maintained at either 15 °C or 30 °C after treatment. In contrast, photosynthetic activity of such tissue of the resistant biotype was not inhibited when plants were maintained at 15 °C after treatment, but was inhibited at 30 °C. The mechanism of resistance in this biotype of H. leporinum correlates with decreased translocation of paraquat and decreased penetration to the active site. This mechanism is temperature sensitive and breaks down at higher temperatures.

The three-dimensional structure of vascular tissues in Agrobacterium tumefaciens-induced crown galls and in the host stems of Ricinus communis L.

The three-dimensional pattern of phloem and xylem in 10-d-to two-month-old tumors induced by Agrobacterium tumefaciens (C58) and in adjacent Ricinus communis L. stem tissues was studied in thick sections by clearing with lactic acid and by staining with lacmoid. The crown galls contained two types of vascular strands: treelike branched bundles, which developed towards the tumor surface in fast-growing regions, and globular bundles in the slowly developing parts. Both types of vascular bundles contained xylem and phloem and were continuous with the vascular system of the host plant. The tumor bundles were interconnected by a dense net of phloem anastomoses, consisting of sieve tubes but no vessels. These vascular patterns reflect the apparent synthesis sites, concentration gradients and flow pathways of the plant hormones additionally produced in the tumors upon expression of the T-DNA-encoded genes. The A. tumefaciens-induced crown gall affected vascular differentiation in the host stem. In the basipetal direction, the tumor induced more xylem differentiation directly below it, where the crown-gall bundles joined the vascular system of the host. In the centripetal direction, the crown gall caused the development of pathologic xylem characterized by narrow vessels, giant rays and absence of fibers. On the other hand, most probably as a consequence of its gibberellic acid content, the host plant stimulated a local differentiation of regenerative phloem and xylem fibers with unique ramifications, only at the base of the tumor. However, fibers were absent from the main body of the crown gall. The study shows that A. tumefaciens-induced crown galls are characterized by a sophisticated network of vascular tissues in the tumor and are accompanied by a perturbated vessel system in the host. The hormonal mechanisms controlling vascular differentiation in the tumor and neighboring host tissues are discussed. In addition, the “gall constriction hypothesis” is proposed for explaining the mechanism which gives priority in water supply to the growing gall over the host shoot.

Long‐distance transport of 35S‐sulphur in 3‐year‐old beech trees (Fagus sylvatica)

35S‐L‐cysteine was fed to a mature leaf of 3‐year‐old beech trees via a flap. After 1 to 4 h the distribution of 35S‐radioactivity was analysed in the leaves as well as the bark and wood of the trunk and the main root. Transport of 35S out of the fed leaf amounted to 0.3–1.2% of the total 35S taken up. The branches of the trees did not act as sink organs for the exported radioactivity. The main portion of the 35S‐radioactivity transported out of the fed leaf was found in basipetal parts of the trunk. Only a small portion of 35S‐radioactivity was transported in acropetal direction. The distribution of the 35S‐radioactivity within the trunk showed a higher portion of 35S in the bark than in the wood. In both tissues, bark (70 to 80%) and wood (60 to 70%), the 35S was predominantly found in the HCl soluble fraction. However, 35S‐cysteine, the compound fed to the leaves was not exported out of the fed leaf. Along the trunk 35S‐cysteine was neither determined in bark nor in wood sections. The only low molecular mass S‐compounds found was 35S‐glutathione (GSH). The 35S‐sulphate detected in bark and wood origined from cysteine oxidation in the leaf tissue and from contamination of the 35S‐cysteine feeding solution. The ratio of GSH to sulphate decreased with increasing distance from the fed leaf. Apparently, 35S‐radioactivity was transported as sulphate and GSH in the phloem in basipetal direction, but GSH was removed preferentially out of the phloem along the transport path. 35S‐radioactivity exported out of the phloem and transported into the wood of the trunk was not retranslocated in the xylem. It may therefore be assumed that part of the 35S translocated was stored in ray cells, medullary sheath cells and/or pith parenchyma cells. Girdling experiments in which the bark of the trunk was peeled off basipetal to the branch containing the fed leaf support these assumptions.

Dimethomorph Activity Against Oomycete Fungal Plant Pathogens

Dimethomorph (DMM) was effective in controlling late blight in potato and tomato caused by either metalaxyl-sensitive (MS) or metalaxyl-resistant (MR) field isolates of Phytophthora infestans and downy mildew in cucumbers and melons caused by MS or MR isolates of Pseudoperonospora cubensis. The fungicide did not affect zoospore discharge from sporangia of P. infestans but strongly inhibited zoospore encystment, cystospore germination, and mycelial growth in vitro. DMM showed translaminar activity and local systemic activity in intact plants but failed to translocate from one leaf to another in either acropetal or basipetal direction. DMM applied as a soil drench strongly protected tomatoes against late blight but failed to protect cucumbers against downy mildew. When applied in lanolin paste to the stem surface, but not when applied to the hypocotyl, it provided excellent control of both diseases in the foliage. DMM applied 1 day postinoculation partially protected potato against late blight and cucumber against downy mildew, and in both systems reduced sporulation of the pathogen. DMM diminished the sporulation of P. infestans and P. cubensis when applied to normally developed infected tissue. In P cubensis it induced enhanced callose-encasement of haustoria. It showed a remarkable persistence on foliage subsequent to excessive washing with water as well as a high residual activity lasting for 9 days. DMM seems to be a good candidate for the control of oomycete diseases in the field especially in growing areas where phenylamide-resistant fungal populations prevail.

Maize Internode Elongation Patterns

During maize (Zea mays L.) growth, the stalk elongates in a sigmoidal pattern. This overall pattern arises from the variable growth rates of individual internodes comprising the maize stalk. To discern differences in growth rate among internodes of the stalk, individual elongation rates and patterns were determined in a single‐cross hybrid. When each of 12 aboveground internodes (7 through 18) of growth‐chamber‐grown plants reached approximately 10 mm in length, they were dotted along their lengths with black acrylic paint at 1‐mm intervals and photographed daily over 35 d. Full‐scale photographs documented that all internodes elongated sigmoidally, in a basipetal direction. Elongation began slowly and uniformly throughout the length of the undeveloped internode during the first 2 to 3 d, increased in rate and shifted basipetally from the upper internode region toward the middle, and later, toward the basal region of the enlarging internode. Elongation decelerated in the intercalary meristem region during the final days of internode lengthening. Internodes 8 through 12 elongated similarly with the greatest dally growth rates. Internodes 13 and 14, which supported developing ears, had the longest elongation periods but slower growth rates and shorter final lengths than other internodes. Internode 15 had a rapid rate of growth like I8 through 12, but an elongation pattern similar to I13 and 14. Evidence from this study indicates that the relative position of internodes in the emerging stalk hierarchy and the functional role of internodes in stalk development influences individual internode growth rate, elongation period, and developmental pattern.

Indole‐3‐butyric acid in plants: occurrence, synthesis, metabolism and transport

Indole‐3‐butyric acid (IBA) was recently identified by GC/MS analysis as an endogenous constituent of various plants. Plant tissues contained 9 ng g−1 fresh weight of free IBA and 37 ng g−1 fresh weight of total IBA, compared to 26 ng g−1 and 52 ng g−1 fresh weight of free and total indole‐3‐acetic acid (IAA), respectively. IBA level was found to increase during plant development, but never reached the level of IAA. It is generally assumed that the greater ability of IBA as compared with IAA to promote rooting is due to its relatively higher stability. Indeed, the concentrations of IAA and IBA in autoclaved medium were reduced by 40% and 20%, respectively, compared with filter sterilized controls. In liquid medium, IAA was more sensitive than IBA to non‐biological degradation. However, in all plant tissues tested, both auxins were found to be metabolized rapidly and conjugated at the same rate with amino acids or sugar.Studies of auxin transport showed that IAA was transported faster than IBA. The velocities of some of the auxins tested were 7. 5 mm h−1 for IAA, 6. 7 mm h−1 for naphthaleneacetic acid (NAA) and only 3. 2 mm h−1 for IBA. Like IAA, IBA was transported predominantly in a basipetal direction (polar transport). After application of 3H‐IBA to cuttings of various plants, most of the label remained in the bases of the cuttings. Easy‐to‐root cultivars were found to absorb more of the auxin and transport more of it to the leaves.It has been postulated that easy‐to‐root, as opposed to the difficult‐to‐root cultivars, have the ability to hydrolyze auxin conjugates at the appropriate time to release free auxin which may promote root initiation. This theory is supported by reports on increased levels of free auxin in the bases of cuttings prior to rooting. The auxin conjugate probably acts as a ‘slow‐release’ hormone in the tissues. Easy‐to‐root cultivars were also able to convert IBA to IAA which accumulated in the cutting bases prior to rooting. IAA conjugates, but not IBA conjugates, were subject to oxidation, and thus deactivation. The efficiency of the two auxins in root induction therefore seems to depend on the stability of their conjugates. The higher rooting promotion of IBA was also ascribed to the fact that its level remained elevated longer than that of IAA, even though IBA was metabolized in the tissue.IAA was converted to IBA by seedlings of corn and Arabidopsis. The Km value for IBA formation was low (approximately 20 μM), indicating high affinity for the substrate. That means that small amounts of IAA (only a fraction of the total IAA in the plant tissues) can be converted to IBA. It was suggested that IBA is formed by the acetylation of IAA with acetyl‐CoA in the carboxyl position via a biosynthetic pathway analogous to the primary steps of fatty acid biosynthesis, where acetyl moieties are transferred to an acceptor molecule. Incubation of the soluble enzyme fraction from Arabidopsis with 3H‐IBA, IBA and UDP‐glucose resulted in a product that was identified tentatively as IBA glucose (IBGIc). IBGIc was detected only during the first 30 min of incubation, showing that it might be converted rapidly to another conjugate.

Distribution of Imported Glyphosate in Quackgrass (Elytrigia repens) Rhizomes in Relation to Assimilate Accumulation

The fact that quackgrass may occasionally escape control by the herbicide glyphosate is thought to result from the wide range in growth rate and sink activity among rhizome buds, especially in older portions of the rhizome. To study growth of rhizome structures, we supplied whole plants with14CO2throughout a 10-h light period and determined the amount of labeled carbon accumulated by the end of the subsequent 14-h night. Growth of rhizome structures during this 24-h period was estimated by determining their growth rate coefficients: the amount of labeled carbon accumulated per unit of carbon present in the structure. Growth rate coefficients generally were high for the rhizome tip that is enclosed in a sheath and the adjacent bud and rhizome segment, with values decreasing rapidly in a basipetal direction. However, extensive differences in the level and pattern of assimilate accumulation among rhizome structures were observed as rhizome development continued. Glyphosate accumulation generally paralleled the level of assimilate accumulation even though the range among rhizome structures for both increased with rhizome age. As a result of the increased variability among buds, some of the older buds will accumulate only a small, perhaps sublethal, amount of glyphosate and this may explain the tendency of the buds in older regions to escape control by glyphosate.

Taxonomic Studies on Ceramieae (Ceramiales, Rhodophyta) with Predominantly Basipetal Growth of Corticating Filaments

Ceramieae, the Ceramiaceae that have corticating filaments applied on axes at junctions of monosiphonous filaments, have species in which corticating filaments remain only at the nodes or cover the axis by growing mostly in an acropetal (Ceramium) or a basipetal direction (Centroceras). Those species with mostly basipetal growth of corticating filaments have either three or four primary corticating filaments from each pericentral cell. Some species having three primary corticating filaments from each pericentral cell have two placed distally and one in a proximal position. Only acropetal growth occurs in one of the distal filaments, producing only a 2-3-celled filament. Basipetal growth occurs on the other distal filament which may also produce a 1-few-celled acropetal filament

Effect of ethylene treatment on transport and metabolism of indole-3-butyric acid in citrus leaf midribs

Transport and metabolism of radiolabeled indole-3-butyric acid (IBA) were studied in midrib sections of Cleopatra mandarin (Citrus reticulata Blanco) and compared to that of indole-3-acetic acid (IAA). Exogenous IBA was metabolized by the midribs to a polar compound, probably an ester conjugate. Ethylene pretreatment of the midribs reduced their capacity to metabolize IBA by ca. 70% as compared to air pretreatment. IBA transport capacity in the leaf midribs was ca. two times greater in the basipetal direction than the acropetal. The basipetal transport capacity of 3H-IBA was lower than that of 14C-IAA (ca. 24% and 39% of the uptake, respectively). While ethylene treatment reduced basipetal transport of IAA by ca. 70% it did not affect the transport of IBA. Most of the transported label was found as free IBA, but the reduction of IBA conjugation by ethylene treatment did not affect the transport capacity.

Uptake and Transport of Thiamin (Vitamin B 1) by Barley and Soybean

Plant roots have been shown to absorb a variety of organic substances. The uptake of vitamins, however, has been little investigated, although under natural conditions roots are in contact with various vitamins present in the soil. We investigated the uptake of thiamin (vitamin B1) by germinating barley (Hordeum vulgare L. “Atos”) seeds and soybean (Glycine max. Merr., L. “Maple arrow”). The germinating barley seeds and soybean seedlings readily absorbed thiamin and transported it to their leaves. Uptake of 14C-thiamin by soybean roots was a linear function of thiamin concentration in the uptake solution (0.01-100 mmol L-1) and a nonlinear function of time. Increase in root temperature from 5 to 35°C increased 14C-thiamin uptake and transport to the tops. The Q10 for the uptake was, however, less than two. Aeration of the rooting media with nitrogen gas or the addition of 2,4-DNP decreased the uptake of 14C-thiamin. Aeration with nitrogen gas as compared with air increased the partitioning of thiamin to the plant tops. Partitioning of root-absorbed thiamin between plant roots and tops was affected by thiamin concentration and the oxygen supply in the rooting media. Leaf-applied 14C-thiamin was transported in both acropetal and basipetal directions. It is concluded that the uptake of thiamin by plants, in contrast to its uptake by animal tissues, does not require metabolic energy. Whether uptake of thiamin by plant roots would play any significant role in the thiamin budget of the plant tissues or for the growth of roots under natural conditions is not clear. Since thiamin is considered to be a growth factor for plant roots, it is postulated that if, at some stages of plant development or under certain soil or environmental conditions, the synthesis of thiamin in the leaves and/or its transport to the roots is reduced to insufficient levels, then any uptake of this vitamin by the plant roots from soil containing this vitamin may be beneficial for the plant growth.

Site of (2RS, 3RS)-pacIobutrazol promotion of axillary flower initiation in pear cv. Doyenne du Comice

The aim of this work was to examine how localized treatment of pear shoot tips with (2RS, 3RS) paclobutrazol is able to stimulate flower initiation throughout the tree. The chemical was applied locally on three occasions during June and July, before floral induction, to the tips or the bases of vigorous vertical new shoots of cv. Doyenne du Comice. Basal treatment stimulated flower initiation without inhibiting shoot extension. Small amounts of the chemical, as measured by combined gas chromatography mass-spectrometry, were found to have moved rapidly between the shoot tip and basal nodes in both the acropetal and basipetal directions, and to persist for several months. Paclobutrazol was also found in axillary vegetative and floral buds sampled in October from the tip- or basally-treated shoots; the floral buds in both containing twice as much. Much less chemical appeared to be required to promote flowering than to inhibit shoot growth, the amounts freely mobile within the shoot apparently being sufficien...

Propagated fluctuations of the electric potential in the apoplasm of Lepidium sativum L. roots

The electric potential on the surface of the Lepidium sativum L. root apex was recorded by means of six non-polarizable electrodes. Nonevoked fluctuations of the potential with amplitudes below 0.1 mV were observed. The fluctuations could be reversibly inhibited either by ether vapor or by anoxia caused by N2. They did not occur in killed roots. Cross-correlation analysis of the fluctuations from six electrodes located one above another along the 3-mm apical region showed a pattern of time delay which indicates that the fluctuations may be the consequence of signals propagated in the root with a velocity of 3-9 mm · s(-1) in a basipetal direction from the root cap. We hypothesize that the fluctuations are due to signals of an unknown nature propagated along an intrasymplasmic continuous system, the "symreticulum", composed of the cortical ER of individual cells and desmotubules passing through the plasmodesmata.