Inhibition Of Transpiration Research Articles

Decreased Sulfamethoxazole Uptake in Lettuce (Lactuca sativa L.) due to Transpiration Inhibition by Polypropylene Microplastics

Microplastics and antibiotics are emerging contaminants in agricultural soil that can have negative effects on crops. However, limited research has been conducted on the effects of the polypropylene (PP) microplastic and sulfamethoxazole (SMX) co-exposure on crops, specifically regarding the impact of PP microplastics on SMX uptake and transport in crops. In this study, hydroponic experiments were carried out using lettuce (Lactuca sativa L.), PP microplastics (1.0 g L−1), and SMX (0.5 mg L−1 or 2.5 mg L−1) to investigate the individual and co-exposure effects of PP microplastics and SMX on Lettuce growth, explore the uptake and translocation of SMX in lettuce and elucidate the underlying mechanism of PP microplastic impact on SMX uptake. Results demonstrated that co-exposure to 1.0 g L−1 of PP microplastics and 0.5 mg L−1 of SMX resulted in an enhanced toxic effect. However, no intensified toxic effect on the lettuce was observed when 1.0 g L−1 PP microplastics were added in the presence of 2.5 mg L−1 SMX, indicating that the SMX dominated the toxic effect on lettuce at high concentrations. Additionally, the study found that the water absorption process controlled by the aquaporin and transpiration contributed to the uptake and translocation of SMX in lettuce. When exposed to PP microplastics, no impact was observed on the aquaporin contents of the lettuce while the transpiration rate was significantly decreased by 31.6 % - 44.2 % resulting from microplastics adhered to the root surface. Therefore, in the presence of 2.5 mg L−1 SMX, the SMX uptake in the lettuce root was inhibited by 35.9 % (P < 0.05) when exposed to 1.0 g L−1 PP microplastic. This work deepens our understanding of the behaviour of microplastics and antibiotics in the terrestrial environment.

Nanobubbles in vase water inhibit transpiration and prolong the vase life of cut chrysanthemum flowers.

Nanobubble (NB) water has been shown to promote the growth of several types of plants and animals, but the mechanism underlying this promoting effect remains unclear. The present study evaluated the mechanism by which NBs maintain the freshness of cut flowers by keeping cut chrysanthemum (Chrysanthemum morifolium Ramat.) flowers at the bud stage in vase water containing air NBs. The condition of petals and leaves was assessed to determine the vase life of these cut flowers. The NB treatment delayed bud opening and petal senescence of the inflorescences. Water absorption and transpiration by cut flower stems were lower in NB water than in distilled water (DW). Furthermore, when all the leaves were removed from the cut flower stems, no significant difference in vase life was observed between NB water and DW. These findings indicate that the inhibition of transpiration from leaves prolonged the vase life of NB-treated cut chrysanthemum flowers. In the early stage of the treatment, NB treatment significantly reduced transpiration without closing stomata, suggesting that the reduction in transpiration observed in the NB-treated plants might be due to the suppression of cuticular transpiration, defined as water loss through the epidermis. Surface tension, one of the important driving forces of water movement in plants, was not affected by the presence of NBs in water. To our knowledge, this is the first report to show that transpiration from leaves is inhibited by NB treatment.

Inhibition Roles of Calcium in Cadmium Uptake and Translocation in Rice: A Review.

Cadmium (Cd) contamination in rice grains is posing a significant threat to global food security. To restrict the transport of Cd in the soil-rice system, an efficient way is to use the ionomics strategy. Since calcium (Ca) and Cd have similar ionic radii, their uptake and translocation may be linked in multiple aspects in rice. However, the underlying antagonistic mechanisms are still not fully understood. Therefore, we first summarized the current knowledge on the physiological and molecular footprints of Cd translocation in plants and then explored the potential antagonistic points between Ca and Cd in rice, including exchange adsorption on roots, plant cell-wall composition, co-transporter gene expression, and transpiration inhibition. This review provides suggestions for Ca/Cd interaction studies on rice and introduces ionomics research as a means of better controlling the accumulation of Cd in plants.

Enhanced phytotoxicity of 4-chloro-3-methyphenol and lindane under sodium and potassium salt stresses

Investigating the uptake of organic pollutants by plants under salt stress is critical for evaluating crop contamination, understanding the mechanism of plant uptake, and implementing phytoremediation. The uptake of a highly phytotoxic contaminant, 4-Chloro-3-Methyphenol (CMP, 45 mg L−1), from solutions by wheat seedling with or without Na+ and K+ was studied to illustrate the synergistic effect of salt on phytotoxicity of CMP, using uptake kinetics, transpiration, Ca2+ leakage and fatty acid saturation as indicators. The influence of Na+ and K+ on the uptake of lindane, a relatively low toxic contaminant, from soil was also explored. Under CMP-Na+ and CMP-K+ exposure, the concentrations of CMP in both root and shoot were lower than those under CMP exposure, as a result of the inhibition of transpiration caused by Na+ and K+ stresses. Low concentration of CMP did not reveal serious toxicity on cell membrane. No apparent difference of MDA generation in root cells was observed, due to the lethal concentration of CMP. The relatively small variation of Ca2+ leakage and fatty acid saturation degree in the root cell under exposure of CMP, CMP-Na+ and CMP-K+, compared to intracellular CMP content, suggested the enhanced phytotoxicity of CMP induced by salt. Higher MDA concentration in shoot cell under CMP-Na+ and CMP-K+ exposure compared with that under CMP exposure again showed the synergetic toxicity of CMP. High Na+ and K+ concentration significantly facilitated the uptake of lindane by wheat seedlings in soils, indicating that it could boost the permeability of cell membrane, thereby increasing the toxicity of linande to wheat seedlings. The short-term effect of low salt concentration on the uptake of lindane was not obvious, but long-term exposure also led to increased uptake. In conclusion, the presence of salt could amplify the phtotoxicity of organic contaminant via several mechanisms.

Plant waterflow restrictions among sweet corn lines related to limited‐transpiration trait

AbstractWhile partial stomata closure under elevated vapor pressure deficit (VPD), that is, a limited‐transpiration trait resulting in soil water conservation and crop drought resiliency, has been identified in a few lines in all major crop species, the basis for the trait is not resolved. Since changes in stomatal aperture are associated with hydraulic processes, properties influencing waterflow in the plant are candidates associated with expression of limited‐transpiration. In a previous study with leaves of sweet corn (Zea mays L.), limited‐transpiration was only weakly associated with the effect of silver ion, an aquaporin inhibitor, on leaf transpiration rate. The hypothesis was explored that total aquaporin activity rather than only silver‐sensitive aquaporins may be more relevant in the expression of limited transpiration. Leaves were fed potent aquaporin inhibitors of mercury and peroxide which both resulted in greater transpiration inhibition than silver, but there were no differences in response among lines. A second hypothesis was that there may be a major limitation of waterflow in the root system accounting for genotypic variation in expression of the limited‐transpiration trait. No differences in root hydraulic conductance were found among sweet corn lines differing in the limited‐transpiration trait. However, it was discovered that the root conductance decreased during the photoperiod in all tested lines. Measurements of root hydraulic conductance in response to a silver treatment showed differences among lines with an association between the VPD breakpoint for limited transpiration and transpiration sensitivity to the silver treatment.

Activation of the root xylem proton pump by hydraulic signals from leaves under suppressed transpiration.

Long term field observations have revealed that the inhibition of transpiration by heavy rainfall promotes immediate positive shift in the trans-root electric potential (TRP), indicating activation of the xylem proton pump in the tree root system presumably participating in acropetal water transport. This phenomenon is indicative of signal transmission from the aerial part to the root system via change in the xylem hydraulic pressure. To test this hypothesis, we constructed a newdevice that enables the simultaneous recording of artificially applied xylem hydraulic pressure and the change in the TRP of tree saplings. With the application of artificial pressure to the xylem vessels (20-62kPa), TRP shifted towards positive potential by 20-80mV, which indicates the activation of the proton pump in the root xylem. The reaction was observed in 11 tree species, six deciduous and five evergreen, although only during the resting phase of the xylem proton pump (May to October) when the transpiration rates were high. Contrastingly the application of tension (negative pressure) produced no reaction. Simultaneous determination of the two components of the TRP, i.e. Vps (electric membrane potential difference across root surface cell membrane) and Vpx (electric membrane potential difference between root symplast and xylem vessel), are performed using the intra-cellular micro-electrode technique throughout the four seasons. Application of excess xylem hydraulic pressure had no significant effect on Vps, while it brought about hyper-polarisation of Vpx except during the winter season, most significantly during summer when transpiration is vigorous and the xylem pump is in a resting state. Such effect of excess xylem pressure was, however, not observed under anoxia.

Involvement of abscisic acid and other stress indicators in taro (Colocasia esculenta (L.) Schott) response to drought conditions

Taro (Colocasia esculenta (L.) Schott) is a staple food and represents an important food security role in most tropical regions. It is, unfortunately, susceptible to prolonged drought conditions. Abscisic acid (ABA) is a well-documented stress-induced phytohormone that tolerant crops usually accumulate in leaves to induce stomatal closure, preventing water loss through inhibition of transpiration. Hitherto, exists very scarce information regarding the ABA role in taro response to drought. Here, we determined the ABA content in the shoots and corms of taro subjected to seven months of water scarcity and linked ABA to other drought resilience traits, including carbon isotopic discrimination (Δ13C), oxalic acid (OA), chlorophyll content index (CCI), water use efficiency (WUE), and biomass (B). The Δ13C-shoot content showed partially open stomata in all accessions, and significant correlation with Δ13C-corm, CCI, and WUE. The osmotically active OA-shoot decrease seemed not to interfere with the stomatal aperture. The tolerant accessions subjected to drought stress had higher B-corm, ABA-shoot, Δ13C-shoot, CCI, OA, and WUE. However, the observed under drought conditions increase of ABA in the shoots, and its decrease in the corms were not significantly correlated, nor with other traits, suggesting that ABA was not the main regulator of taro physiological processes under stress. The information gained should be considered in breeding programs to predict taro’s response to climate change.

Pearl millet (Pennisetum glaucum) contrasting for the transpiration response to vapour pressure deficit also differ in their dependence on the symplastic and apoplastic water transport pathways.

Genotypic differences in transpiration rate responses to high vapour pressure deficit (VPD) was earlier reported. Here we tested the hypothesis that this limitation could relate to different degrees of dependence on the apoplastic (spaces between cells), and symplastic water transport pathways (through cells via aquaporin-facilitated transport), which are known to have different hydraulic conductivities. The low transpiration rate (Tr) genotype PRLT 2/89/33 either restricted its transpiration under high VPD, or was more sensitive to VPD than H77/833-2, when grown hydroponically or in soil. The slope of the transpiration response to an ascending series of VPD was lower in whole plants than in de-rooted shoots. In addition, the transpiration response of detached leaves to moderately high VPD (2.67kPa), normalised against leaves exposed to constant VPD (1.27kPa), was similar in low and high Tr genotypes. This suggested that roots hydraulics were a substantial limitation to water flow in pearl millet, especially under high VPD. The dependence on the apoplastic and symplastic water transport pathways was investigated by assessing the transpiration response of plants treated with inhibitors specific to the AQP-mediated symplastic pathway (AgNO3 and H2O2) and to the apoplastic pathway (precipitates of Cu(Fe(CN)6) or Cu(CuFe(CN)6)). When CuSO4 alone was used, Cu ions caused an inhibition of transpiration in both genotypes and more so in H77/833-2. The transpiration of high Tr H77/833-2 was decreased more by AQP inhibitors under low VPD (1.8kPa) than in PRLT 2/89/33, whereas under high VPD (4.2kPa), the transpiration of PRLT 2/89/33 was decreased more by AQP inhibitors than in H77/833-2. The transpiration rate of detached leaves from H77/833-2 when treated with AgNO3 decreased more than in PRLT 2/89/33. Although the root hydraulic conductivity of both genotypes was similar, it decreased more upon the application of a symplastic inhibitor in H77/833-2. The transpiration of low Tr PRLT 2/89/33 was decreased more by apoplastic inhibitors under both low and high VPD. Then the hydraulic conductivity decreased more upon the application of an apoplastic inhibitor in PRLT 2/89/33. In conclusion, both pathways contributed to water transport, and their contribution varied with environmental conditions and genotypes. Roots were a main source of hydraulic limitation in these genotypes of pearl millet, although a leaf limitation was not excluded. The similarity between genotypes in root hydraulic conductivity under normal conditions also suggests changes in this conductivity upon changes in the evaporative demand. The low Tr genotype depended more on the apoplastic pathway for water transport, whereas the high Tr genotype depended on both pathway, may be by 'tuning-up' the symplastic pathway under high transpiration demand, very likely via the involvement of aquaporins.

Chickpea Genotypes Contrasting for Vigor and Canopy Conductance Also Differ in Their Dependence on Different Water Transport Pathways.

Lower plant transpiration rate (TR) under high vapor pressure deficit (VPD) conditions and early plant vigor are proposed as major traits influencing the rate of crop water use and possibly the fitness of chickpea lines to specific terminal drought conditions—this being the major constraint limiting chickpea productivity. The physiological mechanisms underlying difference in TR under high VPD and vigor are still unresolved, and so is the link between vigor and TR. Lower TR is hypothesized to relate to hydraulic conductance differences. Experiments were conducted in both soil (Vertisol) and hydroponic culture. The assessment of the TR response to increasing VPD showed that high vigor genotypes had TR restriction under high VPD, and this was confirmed in the early vigor parent and progeny genotype (ICC 4958 and RIL 211) having lower TR than the late vigor parent and progeny genotype (ICC 1882 and RIL 022). Inhibition of water transport pathways [apoplast and symplast (aquaporins)] in intact plants led to a lower transpiration inhibition in the early vigor/low TR genotypes than in the late vigor/high TR genotypes. De-rooted shoot treatment with an aquaporin inhibitor led to a lower transpiration inhibition in the early vigor/low TR genotypes than in the late vigor/high TR genotypes. Early vigor genotypes had lower root hydraulic conductivity than late vigor/high TR genotypes. Under inhibited conditions (apoplast, symplast), root hydraulic conductivity was reduced more in the late vigor/high TR genotypes than in the early vigor/low TR genotypes. We interpret that early vigor/low TR genotypes have a lower involvement of aquaporins in water transport pathways and may also have a smaller apoplastic pathway than high TR genotypes, which could explain the transpiration restriction under high VPD and would be helpful to conserve soil water under high evaporative demand. These findings open an opportunity for breeding to tailor genotypes with different “dosage” of these traits toward adaptation to varying drought-prone environments.

Toxicity of 56 substances to trees.

Toxicity data of substances to higher plants is needed for the purpose of risk assessment, site evaluation, phytoremediation, and plant protection. However, the results from the most common phytotoxicity tests, like the OECD algae and Lemna test, are not necessarily valid for higher terrestrial plants. The willow tree toxicity test uses inhibition of transpiration (aside of growth and water use efficiency) of willow cuttings grown in spiked solutions or soils as end point to quantify toxicity. This overview presents results from 60 studies including 24 new unpublished experiments for 56 different chemicals or substrates. Highest toxicity (EC50<1mg/L) was observed from exposure to heavy metals like copper and cadmium. Also, organotins and free cyanide showed very high toxicity. The toxic effect of chlorophenols on willows was comparable to that on duck weed (Lemna) and green algae, while volatile compounds like chlorinated solvents or benzene, toluene, ethylbenzene, and xylene had less effect on trees than on these aquatic plants, due to volatilization from leaves and test media. In particular low (g/L range) toxicity was observed for tested nanomaterials. Effects of pharmaceuticals (typically weak acids or bases) depended strongly of the solution pH. Like for algae, baseline toxicity was observed for willows, which is related to the water solubility of the compounds, with absolute chemical activity ranging from 0.01 to 0.1, but with several exceptions. We conclude that the willow tree toxicity test is a robust method for relating uptake, accumulation, and metabolism of substances to the toxicity to trees.

Effect of Competition and Treatment with Inhibitor of Ethylene Perception on Growth and Hormone Content of Lettuce Plants

We elucidated the effect of increased planting density (single and grouped competing plants) on concentrations of auxin, abscisic acid, and cytokinins in normal lettuce plants and in those with ethylene perception inhibited by 1-methylcyclopropene (1-MCP). An attempt was made to relate the changes in hormone concentration induced by competition and inhibition of ethylene sensitivity to growth responses of lettuce planting. The results showed changes in concentrations of auxins, cytokinins, and ABA in the response of lettuce to crowding. Accumulation of ABA in shoots was likely to contribute to inhibition of transpiration of the plants grown in the presence of neighbors. This assumption was supported by the results of application of an inhibitor of ABA synthesis (fluridone and carotenoid biosynthesis herbicide) resulting in increased transpiration of grouped, but not single plants. Increased planting density led to the decline in root auxins paralleled by inhibition of root growth. This effect was likely to be due to decreased auxin transport to the roots from the shoots suggested by accumulation of auxins in the shoots and inhibition of root growth by application of the auxin transport inhibitor [N-(1-naphtyl)phtalamic acid (NPA)]. Importance of the changes in hormone concentrations was confirmed by data showing that disturbance of auxin and cytokinin distribution detected in MCP-treated plants was accompanied by corresponding modification of the growth response.

Water relations in plants subjected to heavy metal stresses

Concentrations of heavy metals in soil seldom reach a level sufficient to cause osmotic disturbances in plants. It is likely that water entry to the roots is indirectly governed by other factors which are themselves affected by metals. Decreased elongation of the primary root, impaired secondary growth, increased root dieback, or reduced root hair caused by toxic ions all exert a deleterious effect on the root-absorbing area and water uptake. Moreover, metals are able to decelerate short-distance water transfer both in symplast and apoplast, which in turn reduce the movement of water into the vascular system and affect water supply to the shoot. Long-distance transport is limited also due to decreased hydraulic conductivity in the root, stem and leaf midrib caused by a reduction in the size of vessels and tracheids, and partial blockage of xylem elements by cellular debris or gums. Heavy metals influence water delivery to the shoot due to inhibition of transpiration as they decrease the size of the leaves and the thickness of the lamina, reduce intercellular spaces, affect the density of stomata and decrease their aperture. Stomata closure is induced by direct interaction of toxic metals with guard cells and/or as a consequence of the early effects of metal toxicity on roots and stems. In metal-stressed plants, root-derived ABA or ABA-induced signals might play a role in stomatal movement. Disturbances in water relations trigger differential regulation of aquaporin gene expression, which may contribute to further reductions in water loss.

Impact of leaf retained water on tree transpiration

Water retained on tree leaves after rainfall, dew, or fog impacts transpiration. To determine the impact of leaf retained water (LRW) on the transpiration of trees, the difference between transpiration rates of different species with and without water sprayed on the leaves was measured. Results show that transpiration was inhibited by LRW. Both the inhibition extent and duration of LRW were higher on broadleaf species than on coniferous species. Under conditions of saturated LRW of the tree crown, mean transpiration inhibition rates of the test species were 0.32 (Quercus mongolica Fisch. ex Ledeb.), 0.25 (Acer mono), 0.37 (Tilia amurensis Rupr.), 0.31 (Fraxinus mandshurica Rupr.), 0.22 (Pinus koraiensis Siebold &amp; Zucc.), 0.22 (Abies nephrolepis (Trautv. ex Maxim.) Maxim.), and 0.23 (Picea asperata Mast.). Mean inhibition rate and inhibition time for broadleaf species were 0.31 and 115 min, which were 40% higher and 27 min longer than those for coniferous species, respectively. The transpiration inhibition rate of LRW increased linearly with the LRW amount, and there was a higher transpiration inhibition rate in broadleaf species than in coniferous species for the same amount of LRW. Mean rising velocity of the inhibition with LRW amount for broadleaf species was 0.53%, whereas it was only 0.15% for the coniferous species.

花序からの蒸散の抑制によるアジサイ切り花の花持ちの延長

花序からの蒸散の抑制によるアジサイ切り花の花持ちの延長

Phytotoxicity of Sodium Fluoride and Uptake of Fluoride in Willow Trees

The willow tree (Salix viminalis) toxicity test and a cress seed germination test (Lepidium sativum) were used to determine uptake of F and phytotoxicity of NaF. Concentrations in hydroponic solutions were 0–1000 mg F/L and 0–400 mg F/L in the preliminary and definitive test. A third test was done with soils collected from a fluoride-contaminated site at Fredericia, Denmark. The EC10, EC20 and EC50-values for inhibition of transpiration were determined to 38.0, 59.6 and 128.7 mg F/L, respectively. The toxicity test with soil showed strong inhibition for the sample with the highest fluoride concentration (405 mg free F per kg soil, 75 mg F per L soil solution). The seed germination and root elongation test with cress gave EC10, EC20 and EC50-values of 61.4, 105.0 and 262.8 mg F/L, respectively. At low external concentrations, fluoride was taken up more slowly than water and at high external concentrations at the same velocity. This indicates that an efflux pump becomes overloaded at concentrations above 210 mg F/L. Uptake kinetics were simulated with a non-linear mathematical model, and the Michaelis-Menten parameters were determined to half-saturation constant KM near 2 g F/L and maximum enzymatic removal rate vmax at 9 g/(kg d).

식물 코팅 소재 선발법과 작물들에 대한 콩 오일의 증산 억제 효과

Plants as well as crops are damaged by a combination of the hot and dry winds that has been a major factor in the reduction of crop production. A means to protect them from damaging conditions is to consider a coating material. In this study, we established laboratory screening methods to find a coating material to protect a crop from rapid transpiration caused by various factors. In a test measuring the weight loss of kidney bean seedlings for 6 days, Avion treatments decreased its weight loss (P=0.05). Owing to long-time spend in completing this assay, we performed a more simple method using a cobalt chloride paper strip, which changes from blue to red colors under water condition. Beewax, guagum, paraffin liquid, soybean oil, and PE-635 gave a waterproofing effect above 37 and 43% at 0.5 and 1 h after treatment, respectively. However, these tested materials did not show significant waterproofing results at 2 h. Although the methods produced reasonable results, a screening method to obtain more objective data is needed. An alternative is to use an instrument that can detect the transpiration of crop leaves. In a preliminary test using barley leaves, a portable photosynthesis system showed transpiration inhibition of 2% soybean oil and 10 times-diluted Avion under field conditions. In another test using the leaves of maize seedlings and apricot tree, 2% liquid paraffin and plant oils such as apricot oil, linseed oil, olive oil, and soybean oil showed significant transpiration inhibition (P=0.05). Especially, paraffin liquid and soybean oil selected from above tests gave good transpiration inhibitory effects against rice at 2%. In addition, the mixture of 2% soybean oil and a spreader showed more elevated inhibition results comparing with soybean oil or the spreader alone indicating that the spreader may be attributed to more uniform diffusion of the hydrophobic material onto the leaf surface of maize seedlings. The hydrophobic material coated physically the stomata and cuticle layers on leaf surfaces of rice. These hydrophobic materials screened in this study are expected to be used as plant coating materials.

기능성 필름 포장 및 저장온도에 따른 '부유' 단감의 품질 변화

'부유' 단감의 상품성 유지를 위한 저장온도(상온과 저온)와 포장재(기능성 필름)효과를 구명하기 위해 본 연구를 수행하였다. 단감의 중량 감소는 포장재에 따른 차이가 커서 기능성 필름 포장처리 한 것이 무포장보다 매우 작았으며, 온도에 따라서는 저온저장이 중량감소 정도를 줄이는 것으로 나타났다. 단감의 경도는 온도의 영향을 받아 저온에서 변화 정도가 적었으며, 저온에서 기능성 필름 포장재를 이용한 처리구에서 가장 적게 변하는 것으로 나타났다. 포장 내 가스조성 변화는 <TEX>$CO_2$</TEX> 농도가 저장온도 및 포장재에 따라 차이를 보여, 저온저장에서 기능성 필름을 이용한 처리구에서 적정 <TEX>$CO_2$</TEX> 농도에 근접하는 것으로 나타났다. 단감의 호흡율(<TEX>$CO_2$</TEX> 발생량)은 저장 후 온도에 영향을 받으며, 포장재에 따라 달라졌는데, 저온저장에서 낮아지고 기능성 필름 포장재를 이용한 처리구에서 약간 낮아지는 경향을 보였다. 에틸렌 발생은 온도의 영향이 커서 저온저장에서 감소하였다. Hunter 'b' 값의 황색도는 포장재처리보다는 저장온도에 따른 차이가 큰 것으로 나타났으며, 저온에 저장하는 것이 변색을 지연시켰으나 저장기간이 길어질수록 단감의 변색과 품질저하가 우려되는 것으로 보인다. 따라서 '부유' 단감의 효과적인 상품성 유지를 위하여 저온조건에서 기능성 필름을 이용하는 것이 효과적인 것으로 나타났다. The effect of storage temperatures (<TEX>$0^{\circ}C$</TEX>and <TEX>$20^{\circ}C$</TEX>) and packing functional film for fruit quality were examined in 'Fuyu' persimmon. The fresh weight loss was delay more effectively by the inhibition of transpiration when functional film was used. The firmness was effectively maintained in functional film packages at low temperature (<TEX>$0^{\circ}C$</TEX>), which might result from the beneficial combination of <TEX>$CO_2$</TEX> and <TEX>$O_2$</TEX>. The soluble solid contents was higher with packing of functional film at <TEX>$0^{\circ}C$</TEX> than at room temperature (<TEX>$20^{\circ}C$</TEX>). Highest <TEX>$CO_2$</TEX> production in functional film bags was observed in room temperature storage after one week and thereafter declined sharply whereas lowest in 8 weeks. <TEX>$CO_2$</TEX> concentration regardless of packing slowly increased to <TEX>$5.2{\mu}L{\sim}10.2mL{\cdot}kg^{-1}{\cdot}h^{-1}$</TEX> until 8 weeks of low temperature due to persimmon respiration. Hunter 'b' value changed greatly yellowness according to temperature of storage but there were no significant differences among packaging treatments. Effects of functional film and low temperature in slower softening were consistent. This results suggested that the packing functional film at low temperature resulted in the best retention of quality market.

ARSENATE INDUCES WATER STRESS

The effects of arsenate and arsenite on growth and transpiration were investigated in cucumber plants grown in nutrient solution containing 2, 10, and 100 μM phosphate, respectively. Root and shoot growth decreased by 48–64% compared to the control in all treatments and there was no significant difference between the effects of arsenic As(V) and As(III) except for the lowest phosphate concentration. At 2 μM phosphate As(III) had significantly higher growth inhibition than As(V). The inhibition of transpiration was between 46–68% in all treatments, and As(V) had stronger effect at 10 μM phosphate compared to 100 μM. Arsenic caused fast wilting 2 hours after the commencement of the treatment. However, the formation of adventitious roots prevented the loss of turgor. The hypothesis that aquaporins might be involved in the action of As(V) has been tested by comparison of the effect of As(V) and Hg, the inhibitor of aquaporins. Both treatments resulted in similar inhibition of growth and transpiration, increase in water saturation deficit and decrease in root exudation. Data imply that (i) phosphate reduces arsenate uptake, (ii) arsenate can be at least partially detoxified in cucumber at higher phosphate concentrations, (iii) arsenate may be reduced to arsenite and (iv) As(V) may interfere with the proper functioning of aquaporins.

Stress responses in Salix gracilistyla cuttings subjected to repetitive alternate flooding and drought

To determine the tolerance of Salix gracilistyla to repetitive alternate flooding and drought, we measured leaf stomatal conductance, pre-dawn water potential, osmotic adjustment, and biomass production under greenhouse conditions. We used a control and nine crossed treatments (F1-D1–F3-D3) in which we combined 1-, 2-, or 3-week floodings (F) and droughts (D). Leaf stomatal conductance was lowest in 3 weeks of flooding or drought when the preceding event (flood or drought) was also of a 3-week duration. Leaf pre-dawn water potential was reduced in 3 weeks of drought when preceded by 2 or 3 weeks of flooding. Cuttings had slight osmotic adjustments in repetitions of long floodings and droughts. During longer durations of drought in crossed experiments, plants had low root and shoot mass, few hypertrophic lenticels, and reduced leaf mass; when flooding duration increased in crossed experiments, root mass was reduced, there were more hypertrophic lenticels, and the leaf area was reduced. Cuttings achieved stress tolerance by inhibition of transpiration, osmotic adjustment, reduction of transpiration area, and development of hypertrophic lenticels. Stress tolerance was weak when repetitive 2- or 3-week floodings were combined with 3-week droughts. The duration of flooding and drought periods under which S. gracilistyla achieves stress tolerance may be critical in determining distributions along riverbanks.

Uptake, Removal, Accumulation, and Phytotoxicity of 4-Chlorophenol in Willow Trees

4-chlorophenol (4-CP) is a well-known hazardous chlorinated compound and a precursor for the synthesis of the herbicide 2,4-dichlorophenoxyacetate. The relation between uptake, accumulation, toxicity, and removal of 4-CP in willow trees (Salix viminalis) was determined. In addition, the feasibility of implementing phytoremediation as a treatment method for 4-CP contamination was investigated. Willows were exposed to 4-CP levels < or =79.9 mg/L in hydroponic solution. The transpiration of the trees was used to determine toxic effects. Almost no inhibition of transpiration was detected at concentrations > or =15 mg/L. For concentrations > or =37.3 mg/L, transpiration decreased to < or =50%, and the trees wilted. Trees exposed to 79.9 mg/L wilted and eventually died. For concentrations of 79.9 mg/L, a significantly higher amount of 4-CP remained at the end of experiments in the test system compared with the amount remaining at all other concentrations. The loss of chemical from the system in experiments with trees was high, < or =99.5%. In treeless experiments, the mass loss of 4-CP was only 6% to 10%. The results indicated that degradation in the root zone is the main reason for the removal of 4-CP from the media. Phytoremediation of 4-CP in willow trees seems to be a remediation option, especially at concentrations <37.3 mg/L, at which point degradation of 4-CP is rapid and efficient, and the toxic effects on trees are not lethal.