Monica A. Madore

Stachyose and mannitol transport in olive (Olea europaea L.)

Source leaves of Olea europea L. (olive) were photosynthetically labelled with 14CO2 and then transferred to 20 mM EDTA solutions to allow exudation of phloem sap. Label in phloem sap was recovered predominantly as stachyose (50–60% of the total label) while only small amounts of label were recovered in the sugar alcohol mannitol (less than 5%). In contrast, in leaf tissues stachyose accounted for only 5% of the total leaf label while mannitol accounted for 30%. Vacuum-infiltration of exuding leaves with 1 mM p-chloromercuriphenylsulfonic acid had no effect on subsequent exudation or on the distribution of label in stachyose or mannitol in either leaf tissues or phloem exudates. In contrast, a similar treatment inhibited the uptake of exogenously supplied [14C]stachyose and [14C]sucrose into leaf discs. Following short-term pulse-chase experiments with 14CO2 (15s pulse, 5 s-20 min chase), sucrose, mannitol and galactinol were rapidly labelled within the first 2 min following the pulse. Stachyose and raffinose, on the other hand, were not appreciably labelled until 10 min after the pulse. Taken together, the data indicate that phloem loading of raffinose oligosaccharides or of mannitol may not require an apoplastic step. Additionally, it appears that there may be a spatial separation of the synthesis of these sugars within the leaf, with mannitol synthesis occurring within the photosynthetic mesophyll tissues and raffinose oligosaccharide synthesis occurring closer to, and probably within, the minor veins.

Plant virus-induced changes in aphid population development and temporal fluctuations in plant nutrients.

Cucurbita pepo plants were infected with zucchini yellow mosaic virus or maintained noninfected.Aphis gossypii, which transmits the virus, lived longer and produced more offspring on infected than on noninfected plants. On infected plants, the intrinsic rate of natural increase forA. gossypii increased with time after inoculation. In a similar experiment, concentrations of phloem sap nutrients, including free amino acids, total protein, and sugars from infected and noninfected plants were compared for 37 days after inoculation. Significant differences in levels of individual amino acids from phloem exudate between infected and noninfected plants were found, yet the concentration of total amino acids was not substantially different between infected and noninfected plants. Beginning four days after inoculation, the total protein content of phloem exudate generally was lower in infected plants than noninfected plants. Likewise, the total sugar content of phloem exudate from infected plants was lower than that of noninfected plants beginning nine days after inoculation. In contrast with the results from analyses of phloem exudate, foliage from infected plants had higher levels of almost all amino acids than noninfected foliage beginning nine days after inoculation. Concentrations of individual and total amino acids in infected foliage increased throughout the experimental period. Although no temporal effects were observed in the foliage sugar content for either individual or total sugars, starch content decreased with time in infected plants, while in noninfected plants, starch content remained level.

Significance of minor-vein anatomy to carbohydrate transport

Plant species which translocate distinct combinations of carbohydrates in the phloem were investigated to assess whether differences in minor-vein anatomy were associated with differences in carbohydrate composition of the phloem sap. In Vicia faba L., a species in which the minor-vein companion cells are modified into transfer cells, sucrose alone was found to be the translocated form of carbohydrate. In Vicia, phloem transport of sucrose was inhibited by pretreatment of leaves with p-chloromercuribenzenesulfonic acid (PCMBS), a known inhibitor of the sucrose carrier. In contrast, in Ocimum basilicum L., a species in which the minor-vein companion cells are of the symplasmically linked intermediary cell type, both sucrose- and raffinose-family oligosaccharides were exported in the phloem. In this species, no PCMBS sensitivity was observed for phloem transport of either sucrose- or raffinose-family oligosaccharides, although a PCMBS-sensitive sucrose carrier was detected in leaf tissues. This carrier did not appear to be involved in phloem loading, rather, it appeared that phloem loading occurred via the symplasm in this species. In the polyoltranslocating species Petroselinum crispum L., the same insensitivity to PCMBS was seen, suggesting that symplasmic phloem loading also occurred. The companion cells were symplasmically connected to the surrounding bundle-sheath cells by numerous “H”-shaped plasmodesmata but were not intermediary cells, and no raffinose oligosaccharides were exported by Petroselinum. Taken together, the data indicate that apoplasmic transport may be responsible for phloem loading in species in which sucrose alone is exported. However, in those plant species in which a combination of sucrose and any other carbohydrate, including the polyols, is translocated, symplasmic phloem loading may predominate.

Root-Zone Salinity Alters Raffinose Oligosaccharide Metabolism and Transport in Coleus.

Exposure of variegated coleus (Coleus blumei Benth.) plants to a saline root-zone environment (60 mM NaCl:12 mM CaCl2) resulted in a significant decline in elongation growth rate over the 30-d experimental period. During the initial 5 to 10 d of exposure, mature source leaves showed strongly diminished rates of photosynthesis, which gradually recovered to close to the control rates by the end of the experiment. In green leaf tissues, starch levels showed the same transient decline and recovery pattern. Low starch levels were accompanied by the appearance of several novel carbohydrates, including high-molecular-weight raffinose family oligosaccharides (RFOs) with a degree of polymerization (DP) of 5 to 8, and an O-methylated inositol (OMI). New enzyme activities, including galactan:galactan galactosyltransferase, for the synthesis of high-DP RFOs and myo-inositol 6-O-methyltransferase for O-methylation of myo-inositol, were induced by salinity stress. Phloem-sap analysis showed that in the stressed condition substantially more sucrose than RFO was exported, as was the OMI. In white sink tissues these phloem sugars were used to synthesize high-DP RFOs but not OMIs. In sink tissues galactan:galactan galactosyltransferase but not myo-inositol 6-O-methyltransferase was induced by salinity stress. Models reflecting the changes in carbohydrate metabolism in source and sink tissues in response to salinity stress are presented.

Effect of urea fertilizer application on soluble protein and free amino acid content of cotton petioles in relation to silverleaf whitefly (Bemisia argentifolii) populations.

The impact of urea nitrogen fertilization on silverleaf whitefly, Bemisia argentifolii Bellows & Perring, population dynamics was examined in field-grown cotton (Gossypium hirsutum L.). Five urea nitrogen treatments were tested, consisting of soil applications of 0, 112, 168, and 224 kg nitrogen per hectare, and a combined soil–foliar application of 112:17 kg nitrogen per hectare. A positive response was observed between N application rates and the measured levels of nitrate N in petioles from mature cotton leaves. Similarly, a positive response was observed between N application rates and the numbers of adult and immature whiteflies appearing during population peaks. To determine whether these positive responses were related, we measured the levels of dietary N compounds (proteins and free amino acids) that would be available for insect nutrition in cotton petioles at the different N application rates. Sampling dates and N application treatments affected levels of soluble proteins in cotton petioles, and interactions between sampling dates and treatments were significant. Across all sampling dates, the relationship between N application rates and levels of soluble proteins was linear. Sampling dates also affected levels of total and individual free amino acids. Fertilizer treatments only affected levels of total amino acids, aspartate, asparagine, and arginine plus threonine. Levels of aspartate or asparagine and the N application rates were linearly correlated. No significant correlations were observed between levels of dietary N compounds in cotton petioles and numbers of whiteflies, either adults or immatures, on the cotton plants.

Formaldehyde exposure affects growth and metabolism of common bean

Recent state and federal directives have slated a substantial increase in the use of methanol as an alternative to gasoline in both fleet and private vehicles in the coming decade. The incomplete combustion of methanol produces formaldehyde vapor, and catalytic converter technology that completely oxidizes formaldehyde has yet to be developed. The approach of this study was to use a range of methanol concentrations encompassing levels currently found or that may occur in the future in the ambient air of some heavily polluted areas to test the potential phytotoxicity of formaldehyde. The study had the following objectives: (1) design and build a formaldehyde vapor generator with sufficient capacity for long-term plant fumigations; (2) determine growth response of common bean to formaldehyde; (3) evaluate physiological and biochemical changes of bean plants associated with formaldehyde exposures. 20 refs., 2 figs., 2 tabs.

Nocturnal stachyose metabolism in leaf tissues of Xerosicyos danguyi H. Humb.

Leaf discs obtained from mature leaves of Xerosicyos danguyi were found to contain appreciable levels of stachyose throughout an 8-h nocturnal period during which this plant performs Crassulacean acid metabolism (CAM). In contrast, in mesophyll tissues obtained from paradermal sections of these same leaf discs and which were devoid of vascular tissues, stachyose pools were rapidly depleted during the nocturnal phase. The pattern of this depletion followed closely the depletion pattern observed for starch, indicating that mesophyll stachyose was possibly involved in nocturnal CAM processes and was not necessarily being used for export. Pulse-labelling of intact X. danguyi leaves prior to excision of leaf discs and mesophyll samples also indicated that, while labelled stachyose had turned-over completely in the mesophyll tissues by the end of the nocturnal period, substantial levels of labelled stachyose were always recovered from the leaf discs from which these mesophyll samples were derived. The data indicate the existence of two separate pools of stachyose in the X. danguyi leaf, one a mesophyll pool which turns over rapidly at night and which may be involved to a small extent in nocturnal CAM processes, and the other a pool associated with and possibly synthesized by the vascular tissues and which presumably represents the phloem-transport pool.

Role of α-galactosidase in cell wall metabolism of date palm (Phoenix dactylifera) endosperm

SummaryThe endosperm of developing date palm (Phoenix dactylifera) seeds was sampled at regular intervals from pollination to mature fruit. The galactose content of the cell wall mannans was assessed. Accumulation of α-galactosidase, a cell wall hydrolase, during endosperm development was analyzed by isoelectric focusing, sodium dodecyl sulfate polyacrylamide gel electrophoresis in combination with Western blotting and immunolocalization on tissue sections. N-terminal amino acid sequence of the first 15 amino acids showed homology with amino acids 71 to 85 of the sequence reported for the mature guar protein. Four forms of the enzyme with isoelectric points ranging from 4.4 to 5.2 appeared by 11 weeks after pollination, and all forms remained until maturity. A major band of 41 kDa and several lower Mr, lightly staining bands cross reacted with the anti-α-galactosidase antiserum. The major band remained until maturity while the lightly staining bands gradually disappeared. In the mobilizing endosperm of germinated seeds, two darkly staining bands were observed at 41 and 40 kDa. At 9 weeks after pollination, the endosperm was cellular and the silver enhanced gold label localizing α-galactosidase occurred predominantly in the cell periphery. By 11 weeks, the label was present in the cytoplasm, but lacking on the thickening cell wall. α-Galactosidase accumulated in the protein bodies along with the storage protein. At 13 to 17 weeks, the label accumulated and then was lost in a centrifugal pattern (from the middle lamella inward) from the cell walls as they matured and was lost in the cytoplasm. The mature endosperm cells had intense label present only over the protein bodies and over the inner cell wall. These observations suggest that α-galactosidase is synthesized during endosperm development and unique forms of the enzyme are associated with cell wall maturation and cell wall mobilization in this species.

Effect of mannose on the plasma membrane ATPase from sugar beet (Beta vulgaris L.) leaves

Abstract Experiments were conducted to determine if the observed reduced influx of sugars following mannose treatment could be attributed to changes in ATPase activity. Mannose was supplied to Beta vulgaris L. (sugar beet) leaves via the transpiration stream for either a 16- or 24-h light period. The plasma membrane was then isolated using the aqueous polymer two-phase partitioning technique. Analysis of ATP hydrolytic activity showed that mannose pretreatment had a progressive inhibitory effect on the H+-ATPase activity. These results are consistent with previous reports that mannose can dramatically influence membrane transport events in sugar beet leaves. Measurement of Mg ATP-dependent, pH-gradient formation by plasma-membrane vesicles indicated that mannose pretreatment shifted the maximal initial rate of proton pumping to more alkaline regions compared with control membranes. At pH 6.5, mannose pretreatment also inhibited the total quench. We cannot attribute this to increased leakage of protons out of the vesicles as mannose pretreatment had no effect on the passive backflow of protons out of the vesicles. Mannose appears to elicit a general perturbation of membrane transport processes which is not limited to sugars and amino acids. Collectively, these studies indicate that mannose may inhibit sugar transport, at least in part, by affecting the activity of the plasma-membrane ATPase.