Cell Sap pH Research Articles

Effects of exogenous calcium on the drought response of the tea plant (Camellia sinensis (L.) Kuntze).

Drought is one of the major factors reducing the yield of many crops worldwide, including the tea crop (Camellia sinensis (L.) Kuntze). Calcium participates in most of cellular signaling processes, and its important role in stress detection and triggering a response has been shown in many crops. The aim of this study was to evaluate possible effects of calcium on the tea plant response to drought. Experiments were conducted using 3-year-old potted tea plants of the best local cultivar Kolkhida. Application of ammonium nitrate (control treatment) or calcium nitrate (Ca treatment) to the soil was performed before drought induction. Next, a 7-day drought was induced in both groups of plants. The following physiological parameters were measured: relative electrical conductivity, pH of cell sap, and concentrations of cations, sugars, and amino acids. In addition, relative expression levels of 40 stress-related and crop quality-related genes were analyzed. Under drought stress, leaf electrolyte leakage differed significantly, indicating greater damage to cell membranes in control plants than in Ca-treated plants. Calcium application resulted in greater pH of cell sap; higher accumulation of tyrosine, methionine, and valine; and a greater Mg2+ content as compared to control plants. Drought stress downregulated most of the quality-related genes in both groups of tea plants. By contrast, significant upregulation of some genes was observed, namely CRK45, NAC26, TPS11, LOX1, LOX6, Hydrolase22, DREB26, SWEET2, GS, ADC, DHN2, GOLS1, GOLS3, and RHL41. Among them, three genes (LOX1, RHL41, and GOLS1) showed 2-3 times greater expression in Ca-treated plants than in control plants. Based on these results, it can be speculated that calcium affects galactinol biosynthesis and participates in the regulation of stomatal aperture not only through activation of abscisic-acid signaling but also through jasmonic-acid pathway activation. These findings clarify calcium-mediated mechanisms of drought defense in tree crops. Thus, calcium improves the drought response in the tea tree.

Anticipated Performance and Air Pollution Tolerance Indices for the Establishment of Green Belt Development in an Industrial Area

Background: To identify the plant species tolerance levels in an industrial area by assessing Anticipated Performance Index (API) and Air Pollution Tolerance Index (APTI) to establish a green belt in the industrial area. Methods: A survey on local species was conducted in and around the study areas. Seventeen plant species were chosen for an evaluation of tolerant species based on their occurrence and dominance in the study areas. Standard methods were applied for estimation of biochemical parameters such as Cell Sap pH, Relative Water Content (RWC), Total Chlorophyll Content (TCC), and Ascorbic Acid (AA) and were used to compute the APTI. API is assessed based on socioeconomic and biological characteristics. Correlation coefficient test was performed to gain the information about relationship between variables. Findings: The results revealed that APTI positively correlated with biochemical parameters in control, negatively correlated with in industrial samples and except ascorbic acid. Ascorbic acid is one of the critical elements in biochemical parameters. It changes plant species sensitivity to tolerance. In API, based on social, biological, and physical characteristics (+, -) codes were used to classify poor, moderate, good, very good, best, and excellent. In the present study Ficus benghalensis as excellent (87.25%) in the control area and best (93.75%) in industrial area; Syzygium cumini species best (93.75%) in control and excellent (87.25%) in industrial areas. In comparison, Mimusops elengi reported moderate (56.25%) to the poor (50) in control and the industrial areas. Novelty: This study was carried out to determine the impact of air pollution on plant species which exhibit either sensitivity or tolerance depend on their endurance level. The identified list of the tree species helps to minimize air pollution levels in theindustrial area and can be used to establish green belt development. Keywords: Anticipated Performance Index (API); Air Pollution Tolerance Index (APTI); Tolerance; Green Belt; Biochemical Parameters

AIR POLLUTION TOLERANCE INDEX OF WHEAT AND RICE IN THE PROXIMITY OF GAS BASED POWER PLANT

The study aimed to identify the tolerance level of rice and wheat due to air pollutants around the gas-based power plant. Ten sites were selected around 10km radius of gas based power plant. Major air pollutants like NOx, SOx, ozone, and PM10 were monitored in ten sites during the growth of rice and wheat. The Air Quality Index (AQI) of villages falls mostly in the category of moderately polluted sites. Air Pollution Tolerance Index (APTI) is a tool applied for categorizing sensitive or tolerant plants towards air pollution and is calculated by using four biochemical parameters like total chlorophyll content, ascorbic acid, pH, and relative water content of rice and wheat. Results indicated that the pH of cell sap of both the crops was acidic to neutral pH (3.5-6.9) at polluted sites while neutral to slightly alkaline (7.0-7.9) at less polluted sites. Ascorbic acid content was high at polluted sites since ascorbic acid shows a defense mechanism against air pollution. Chlorophyll content (up to 0.61mg/g) and relative water content have shown a significant decrease at most polluted sites. As per APTI values (APTI<11), both the crops were sensitive to air pollution in the selected area. APTI might be beneficial in the selection of crop species in the polluted area which shows that a higher concentration of air pollutants can damage crops severely. APTI was found to be positively correlated with pH, total chlorophyll content, and relative water content and negatively correlated with ascorbic acid.

Metabolomics Analysis Reveals the Role of Cyanidin Metabolism in Plumbago auriculata Flower Color

Blue flowers, which are rare, have long been a focus for researchers engaged in colored flower breeding. In this study, Plumbago auriculata, a plant with blue flowers, and its white flower forma Plumbago auriculata f. alba were used as research materials. Flower color quantification, environmental scanning electron microscopy (ESEM) observation of petal epidermal cells, and determination of the cell sap pH were carried out; moreover, metabolomic analysis was used to analyze the flavonoid metabolites of both types of petals. The results showed that the flower color of P. auriculata was bluish violet, and there was no significant difference in the epidermal cell distribution of the white and blue petals. The key substance that determined the bluish violet flower color was cyanidin-3-O-(6″-p-coumaroylglucoside) (Cy3-pC·G). Compared to the white petal cells, the blue petal cells exhibited up to 40 upregulated flavonoid compounds that were copigments. Together with the significantly increased pH (5.92 ± 0.12) of the petal cell sap, these copigments affected the color presentation of Cy3-pC·G, causing the final petal color of P. auriculata to be bluish violet. The results of this study indicate that cyanidin is an important anthocyanidin in blue flowers, which provides new insights into the breeding of blue flowers.

Factors Affecting the Color of Herbaceous Peony

Herbaceous peony (Paeonia lactiflora Pall.) is a well-known ornamental plant with abundant flower colors. However, our understanding of the underlying mechanisms of flower color formation is limited. In this study, a wild sample of herbaceous peony (collected from Heze, China) and eight cultivars with different colors were selected for experimental investigation. The Royal Horticultural Society Color Chart was used to determine flower color, and the anatomic structure; cell sap pH value; moisture content (MC); condensed tannin content (Ct); soluble sugar and soluble protein content of the petals; and content and composition of anthocyanin, flavonoids, and carotenoids in the petals were examined. 1) In the white, pinkish white, pale purple, purplish pink, and reddish purple cultivars, deeper color was associated with greater total amounts of anthocyanin (TA). Hypochromic effects were observed for kaempferol-7-O-glucoside (Km7G), myricetin-3-rhamnoside (My3R), and luteolin-7-O-glucoside (Lu7G). The accumulation of quercetin-3-O-glucoside (Qu3G) and lutein affected yellow color formation in the petals. 2) There are papillate epidermal cells in the petals of the wild P. lactiflora sample, ‘Lanyucangjin’, and ‘Dongjingnvlang’. 3) Cell sap pH and MC of the petals of white, pinkish white, pale purple, and purplish pink cultivars were greater than those of the purplish red and most of the reddish purple cultivars. 4) The Ct was greatest in the purplish red cultivars, whereas no condensed tannins were detected in the white, pinkish white, and pale purple cultivars. 5) There were no significant correlations among soluble sugar content, soluble protein content, and the other physiological indications.

Nanosilver and sucrose delay the senescence of cut snapdragon flowers

Abstract Snapdragon (Antirrhinum majus L.) is one of the most important annuals grown for cut flowers, but its vase life in water is relatively short. In this study, the effects of nanosilver (NS) on the vase life of cut snapdragon and effects on physiology, biochemical and morphology levels were investigated. Xylem vessel blockages started to appear soon after harvest. NS prevented tylose formation, but not the blockages caused by bacteria. Cut flowers treated with 1 mg L−1 NS with 2 % sucrose had a longer vase life than those held in water or in NS alone, and improved flower opening, coloration and higher relative water content of flowers in the lower (older) part of the spike. Carbohydrate accumulated in flowers in the NS solution. NS limited increased electric conductivity, and with sucrose decreased the pH of cell sap. NS also limited the increase in the malondialdehyde content, especially in the upper (younger) part of spikes where also the hydrogen peroxide content was much lower than in flowers from the lower spike parts. The activities of antioxidative enzymes were higher in the NS-treated flowers, especially when the NS solution was supplemented with sucrose, and the nuclei and epidermis degradation was delayed. It is evident that the presence of NS in the holding solution, especially when supplemented with sucrose, delays and reduces the severity of all senescence symptoms, thereby extending the useful vase life of snapdragon.

Anatomical and biochemical analyses reveal the mechanism of double-color formation in Paeonia suffruticosa 'Shima Nishiki'.

Paeonia suffruticosa 'Shima Nishiki' is a very precious double-color cultivar because of its distinctive and colorful flowers. However, our understanding of the underlying mechanisms of its double-color formation is limited. The present study investigated the soluble sugar content, cell sap pH value and anatomical structure, anthocyanin composition and content and expression patterns of genes related to anthocyanin biosynthesis in the red and pink petals of the 'Shima Nishiki' cultivar. Here, we found that soluble sugar content, cell sap pH and the shape of outer epidermal cells were not the key factors that determine double-color formation. Five different anthocyanins were detected in both the red and pink petals, and the pelargonidin-3,5-di-O-glucoside (Pg3G5G) and pelargonidin-3-O-glucoside (Pg3G) contents in the red petals were significantly higher than those in the pink petals at every developmental stage. In addition, these gene expression patterns suggested that the significant differential expression of the dihydroflavonol 4-reductase gene (PsDFR) gene might play a key role in double-color formation. These results will provide a valuable resource for further studies unraveling the underlying genetic mechanisms of double-color formation in P. suffruticosa 'Shima Nishiki'.

Morphological and Biochemical Studies of the Yellow and Purple–red Petal Pigmentation in Paeonia delavayi

Paeonia delavayi is a species endemic to Southwest China and an important genetic resource for flower color breeding of tree peonies. The mechanisms underlying the flower coloration of this plant have not been fully elucidated. In this article, the petals of yellow-colored individual (Pl) and purple–red-colored individual (Pd) of P. delavayi were studied. And anatomical observations revealed that a large amount of yellow protoplasts and a small amount of colorless protoplasts were located in the yellow-colored Pl petals, whereas a mixture of purple, red, and pink protoplasts were observed in the purple–red-colored Pd petals. The Pl cells were subrotund and flat, whereas the Pd cells were irregularly polygon-shaped and bulging. Chemical analyses were performed, and the results indicated that significant differences occurred between the cell sap pH of the Pl and Pd flowers and large differences occurred in the contents of Fe and Al between Pl and Pd. Cyanidin- and peonidin-based anthocyanins with flavones and flavonols as copigments determined the Pd flower color, whereas chalcone 2 ′G with apigenin 7-O-neohesperidoside and chrysoeriol 7-O-glucoside as copigments determined the yellow color of Pl. Correspondingly, the genes dihydroflavonol 4-reductase (DFR) and anthocyanidin synthase (ANS) were significantly highly expressed in Pd, whereas chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavone synthase (FNS), flavonol synthase (FLS), flavonoid 7-O-glycosyltransferase (7GT), and 2′4′6′4-tetrahydroxychalcone 2′-glucosyltransferase (THC) had high transcript levels in Pl relative to Pd. The results indicate that the color variation of P. delavayi petals may be related to a delicately controlled balance of the aforementioned factors.

High Temperature Induced Anthocyanin Inhibition and Active Degradation in Malus profusion.

The red fleshed fruits of Malus profusion represent gradual color loss during high temperature in summer, potentially due to active degradation of anthocyanin. The objective of this study was to examine both physiological and molecular evidence of anthocyanin degradation. Malus crabapple fruits were exposed to either room temperature (RT = 18 ± 2°C: 25 ± 2°C) or high temperature (HT = 33 ± 2°C: 25 ± 2°C) regimens (12 h: 12 h) under hypoxic (2%) or normoxic (21%) oxygen levels. The results showed that the concentration of cyanidin 3-galactoside (cy-3-gal) was dramatically reduced following HT treatments due to a significant down-regulation of anthocyanin biosynthetic genes (MpCHS, MpDFR, MpLDOX, MpUFGT, and MpMYB10). Among other repressor MYBs, MpMYB15 expression was high following HT treatment of the fruit. HT led to the generation of a substantial concentration of H2O2 due to enhanced activities of superoxide dismutase (SOD), methane dicarboxylic aldehyde (MDA) content and cell sap pH value. Similarly, transcript levels of MpVHA-B1 and MpVHA-B2 were reduced which are involved in the vacuolar transportation of anthocyanin. The enzymatic degradation of anthocyanin was eventually enhanced coupled with the oxidative activities of peroxidase (POD) and H2O2. Conversely, the RT treatments potentially enhanced anthocyanin content by stabilizing physiological attributes (such as MDA, H2O2, and pH, among others) and sustaining sufficient biosynthetic gene expression levels. Quantitative real-time PCR analysis indicated that the transcription of MpPOD1, MpPOD8 and MpPOD9 genes in fruit tissues was up-regulated due to HT treatment and that hypoxic conditions seems more compatible with the responsible POD isoenzymes involved in active anthocyanin degradation. The results of the current study could be useful for understanding as well as elucidating the physiological phenomenon and molecular signaling cascade underlying active anthocyanin degradation in Malus crops.

Identification and comparative profiling of miRNAs in herbaceous peony (Paeonia lactiflora Pall.) with red/yellow bicoloured flowers

Herbaceous peony (Paeonia lactiflora Pall.) is popular worldwide because of its gorgeous flower colour, and the yellow flower is the rarest. However, its mechanism of yellow formation is still unexplored from the post-translational level. In this study, the anatomy of the petal, cell sap pH and metal elements were investigated in bicoloured flower cultivar ‘Jinhui’ with red outer-petal and yellow inner-petal, and the yellow formation was influenced by the anatomy of petal, while not by the cell sap pH and metal elements. Subsequently, microRNAs sequencing (miRNA-seq) was used to identify small RNAs (sRNAs). A total of 4,172,810 and 3,565,152 specific unique sRNAs were obtained, 207 and 204 conserved miRNAs and 38 and 42 novel miRNAs were identified from red outer-petal and yellow inner-petal, respectively, which were confirmed by subcloning. Among these miRNAs, 163 conserved and 28 novel miRNAs were differentially expressed in two wheel of petals. And 5 differentially expressed miRNAs and their corresponding target genes related to yellow formation were screened, and their dynamic expression patterns confirmed that the yellow formation might be under the regulation of miR156e-3p-targeted squamosa promoter binding protein-like gene (SPL1). These results improve the understanding of miRNA regulation of the yellow formation in P. lactiflora.

Anatomical and biochemical analysis reveal the role of anthocyanins in flower coloration of herbaceous peony

Herbaceous peony (Paeonia lactiflora Pall.) is particularly appreciated because of its elegant and gorgeous flower color, but little is known about the underlying mechanisms of flower coloration. In this study, three P. lactiflora cultivars ‘Xuefeng’, ‘Fenyulou’ and ‘Dahonglou’ with white, pink and red flower were selected as the materials. Their anatomical structures, cell sap pH and metal elements were investigated, and the colored pigment mainly distributed in palisade mesophyll was only found in ‘Fenyulou’ and ‘Dahonglou’, and their shape of epidermal cells, cell sap pH and metal elements were not the key factors deciding phenotype color. Moreover, the qualitative and quantitative analysis of flavonoids were performed, their total anthocyanin, anthoxanthin and flavonoid contents were decreased during flower development, and only anthocyanin content in ‘Dahonglou’ was always higher than that in ‘Xuefeng’ and ‘Fenyulou’. Subsequently, three anthocyanin compositions were found, and peonidin 3,5-di-O-glucoside (Pn3G5G) was identified as the main anthocyanin composition. In addition, the full-length of flavonol synthase gene (FLS) was isolated with the GenBank accession number KM259902, and the expression patterns of eight flavonoid biosynthetic genes showed that only PlDFR and PlANS basically had the highest levels in ‘Dahonglou’ and the lowest levels in ‘Xuefeng’, and they basically displayed a descended trend during flower development especially PlDFR, suggesting that these two genes might play a key role in the anthocyanin biosynthesis which resulted in the shift from white to pink and red in flowers. These results would contribute to understand the underlying molecular mechanisms of flower coloration in P. lactiflora.

COMPARISON OF PECTIN BIOSYNTHESIS IN LOCAL APPLE CULTIVAR 'AZAYESH' AND SOME COMMERCIAL CULTIVARS AS AFFECTED BY PH AND CARBOHYDRATES CONTENT

In order to study the characteristics of commercial apple cultivars grown under climatic conditions in Karaj 32 different characters were evaluated in 30 native Iranian and introduced cultivars based on Apple Descriptor during 2008. Some of the important pomological characteristics such as: weight, shape, skin and flesh color and other physicochemical characteristic including: pectin content, carbohydrates, pH, TSS, TA, flesh firmness of 'Golden Delicious', 'Red Delicious', 'Granny Smith' and a very dwarf native Iranian crab 'Azayesh' were measured. All of the pomological evaluations were done at the fruit ripening phase. The results of mean comparison obtained from the collected data related to measurements of physicochemical variables under experiment showed that 'Granny Smith' and 'Azayesh' had the highest levels of pectin compared with 'Golden Delicious' and 'Red Delicious'. Further analyses confirmed that cultivars containing more pectin biosynthesis capacity present lower pH values, the difference showed to be statistically significant among cultivars. There was in fact significant difference between 'Golden Delicious' and 'Red Delicious'. Supplementary studies showed that pectin biosynthesis is positively correlated with lower pH of cell sap. Consequently, a pectin biosynthesis increase was always accompanied with a pH decrease. Contrarily, pectin biosynthesis was positively correlated with carbohydrates content. In fact, total carbohydrate measurements confirmed a higher content of carbohydrates in 'Azayesh', while the other cultivars show a low pectin producing capacity in contest of genetic variability. It is clearly known that the high economic value of 'Granny Smith' in the fresh consumption market is a limiting factor for being used as pectin source, while pectin may be abundantly extracted from 'Azayesh' because other researches showed the high fruit set percent in Karaj climatic conditions. 'Azayesh' is a well known dwarf rootstock, adapted to the typical compact and calcareous soils of Iran. Demonstrating its potential in pectin biosynthesis in this research, makes it more valuable and could be also recognized as a new cultivar to be used for pectin extraction.

Greenish blue flower colour of Strongylodon macrobotrys

The flower colour of Strongyledon macrobotrys is luminous blue green and attracts bats for pollination. The chemical basis for development of the flower colour was investigated. The flower contained an anthocyanin (malvin) and a flavone (saponarin), approximately 1:9 (malvin: saponarin) in molar ratio. The pH of the pigmented epidermal cell sap of the jade vine petal was exceptionally high, 7.90, while the pH value of the colourless inner tissue was 5.60. Copigmentation test using the mixtures of malvin and saponarin (1:9 M ratio) at various pH values revealed that the characteristic blue green colour of the jade vine is developed by copigmentation of malvin with saponarin in slightly alkaline cell sap, pH 7.9. In the copigmentation in slightly alkaline condition, saponarin shows a strong yellow colour, which gives a greenish tone to the flower colour.

Color and Phenolic Content Changes during Flower Development in Groundcover Rose

In the present study, the chemical and morphological status of eight cultivars of groundcover rose (Rosa ×hybrida) with a range of flower colors was investigated. From the methanolic extracts of rose petals collected from flowers at four developmental stages, several phenolic compounds were identified via high-performance liquid chromatography/mass spectrometry, including five anthocyanins, which are especially important for the visual attributes of rose flowers. Colorimetric parameters were also measured and correlated with total anthocyanins and cell sap pH levels. During flower development from bud to senescent stage, a significant trend was detected; lightness (L*) increased, b* decreased in all analyzed roses, and a* decreased in pink and red cultivars. Cell sap pH level increased from bud to senescent petals; fresh weight, dry weight, and water content increased to fully open stage and were then reduced in senescent petals. Total anthocyanin and quercetin content increased from bud stage to fully open flowers, and was decreased in senescent ones. However, the highest content of total phenolics was measured in buds and partially opened flowers, respectively. Three distinct groups were formed according to the content of total anthocyanins and quercetins; white cultivars were most distant from the red ones, which were similar to the pink and light red cultivars.

Carbonate extraction process for the metabolic, isozymic and proteomic profiling of rose‐scented geranium (Pelargonium sp.), a hyper‐acidic plant

Rose-scented geranium (Pelargonium sp.) is a valuable monoterpene-yielding plant. It has been well characterised phytochemically through the isolation of >270 secondary metabolites, however, there is hardly any biochemical or metabolic information concerning this plant. Initial attempts to investigate its metabolism failed to produce any enzyme activity in the tissue extracts prepared in routine extraction buffers owing to the intrinsic properties of the tissue matrix. It was recognised that cellular hyper-acidity (cell sap pH approximately 3.0) gave rise to very low protein levels in the extracts, thus prohibiting detection of activities of even primary metabolic enzymes that are usually abundantly present in plants. Tissue extraction in Tris solution without pH adjustment (as used for studies involving citrus and banana) led to little or no improvement. Therefore, a novel approach using sodium carbonate solution as an efficient extraction system for enzymes and proteins from the plant was studied. Functionality of the carbonate extraction has been demonstrated through its effectiveness, a several-fold superior performance, in yielding protein, monitoring primary metabolism and secondary metabolic enzymes, and isozymic and polypeptide profiling. The process may also be helpful in the reliable analysis of other acidic plant tissues.

Utilisation de quelques tests physiologiques sur la sélection de variétés de roses coupées

We have observed that the evolution of the senescence in vase can be appreciated by the measures of pH, conductivity, or osmolarity of the petal cell sap of a rose variety. We wanted to check whether these physiological tests could be used to select the post-harvest quality of varieties in process of evaluation. Whereas the measures of pH and osmolarity do not seem to be correlated with the flower's vase life, those of conductivity seem to be linked to it ( r = − 0.74 ). As far as the pH is concerned, when the correlation is tested on varieties grouped in colours (white, yellow and ochre; pink and red; multicoloured) and not on the whole mixed varieties, then the correlation seems to be satisfactory, being characterized by r coefficients between −0.78 and −0.91. To cite this article: S. Gudin et al., C. R. Biologies 330 (2007).

低酸素条件下の根のエタノール，乳酸およびリンゴ酸代謝と細胞液ｐＨにおけるトマトとキュウリ間の差異

Plant growth in nutrient solution with a low dissolved oxygen concentration (DO) of 1 ppm is greatly inhibited in tomato (Lycopersicon esculentum Mill.), but almost normal in cucumber (Cucumis sativus L.)(Guo·Tachibana, 1997). To elucidate the mechanisms for the high tolerance of cucumber to root-zone hypoxia, the metabolisms of ethanol, lactate and malate, and the cell sap pH in intact and excised roots under hypoxia were compared between tomato 'Hausu-Momotaro' and cucumber 'Sharp I'. In intact roots of tomato, concentrations of ethanol and lactate as well as the activity of alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH) were markedly increased on exposure to 1 ppm DO for 3 and 6 days compared to 4 ppm DO. Similar results were obtained with excised tomato roots incubated at 0, 1, and 4 ppm DOs for 24 and 48 hr. Concentrations of malate decreased at low DOs in both intact and excised tomato roots. Contrarily, in cucumber the increase in ethanol concentrations and ADH activity at low DOs was slight in intact roots and did not occur in excised roots. Lactate concentrations and LDH activity did not increase in both types of hypoxic roots, except that excised roots incubated at 0 ppm DO exhibited a slight increase in lactate concentrations but to a much lesser extent than tomato roots. On the other hand, malate concentrations were greatly increased in both intact and excised roots at 1 ppm DO ; excised roots, incubated at 0 ppm DO, showed no increase in malate concentrations. The cell sap pH of intact tomato roots grown 3 days at 1 ppm DO fell from 5.70 to 5.51 and that at 0 ppm DO to 5.22. However, in intact cucumber roots it did not change significantly at 1 ppm DO and arose markedly from 5.98 to 6.33 after 3 days at 0 ppm DO. The results strongly suggest that the metabolic properties of roots to stimulate synthesis of malate in response to low O2 in the root tissue and consequently prevent cytoplasmic acidosis because of lactate accumulation are responsible for the high tolerance of cucumber to root-zone hypoxia.

Modulation by weak bases or weak acids of the pH of cell sap and phosphoenolpyruvate carboxylase activity in leaf discs of C4 plants

When leaf discs of a C4 species, Alternanthera pungens (L.) H.B. and K. or Amaranthus hypochondriacus L., were preincubated in 7.5 mM NH4Cl, the pH of the cell sap increased by nearly 0.3 unit, while the activity of phosphoenolpyruvate carboxylase (PEPC) about doubled compared to the cell sap from control leaf discs (preincubated in 5 mM Tricine‐KOH, pH 8.5). The sensitivity of PEPC to L‐malate (a feedback inhibitor) decreased marginally as a result of cytosolic alkalization. The pH of the cell sap and PEPC activity decreased by nearly 0.4 unit and 50%, respectively, when leaf discs were incubated in weak organic acids such as propionic, butyric or salicylic acid. Thus, our results demonstrate a marked modulation in vivo of cell sap pH and PEPC activity in leaf discs from C4 plants by external alkalizing or acidifying reagents. The rise in PEPC activity due to alkalization of leaf discs was not sensitive to cycloheximide, implying that cytosolic protein synthesis was not involved in the activation of PEPC. Despite the marked increase in the PEPC activity due to the base‐loading of leaf discs, the change in malate sensitivity of the enzyme was only marginal, indicating that there was no significant increase in the extent of PEPC‐phosphorylation. Besides the physiological significance, the technique of acid/ base‐loading may be an important tool for studying the regulation of PEPC in leaf discs of C4 species, since the activity of PEPC could be enhanced apparently without phosphorylation of the enzyme.

Changes in Bent-neck, Neck Strength, and Water Balance According to Cultivars and Preservative Solutions of Cut Rose Flowers

Rose (Rosa hybrida) cvs. Red Velvet, First Red, Sonia, and Saphir stems harvested at bud stage were kept in deionized water or preservative solution (3% sucrose + 200 ppm HQS + 0.1 mM ethionine) at 21°C under continuous light (1200 lux). Vase life of `First Red' and `Saphir' was much longer than those of `Red Velvet' and `Sonia' held in deionized water. Severe bent-neck was observed in `Red Velvet' flowers held in deionized water in 8 days after harvest. Rose flowers held in preservative solution resulted in extended vase life and inhibited senescence and bent-neck in four cultivars. Neck strength of `First Red' and `Saphir' rose flowers having no bent-neck and long vase life was stronger than `Red Velvet' and `Sonia' having frequent bent-neck and short vase life. Neck strength was also increased by preservative solution. Faster changes of water balance to minus value were detected in the rose flowers held in deionized water than those held in preservative solution. `Red Velvet' flowers having much absorption of water but more transpiration caused a fast change to a minus value in water balance and early bent-neck. Cell sap pH gradually increased in petal and stem of rose cultivars during senescence. Cell sap pH of flowers held in distilled water were higher than those held in preservative solution. Increased cell sap pH of rose flowers caused rapid change to blueing and yellowing of petals.

Role for the Vacuolar H+-ATPase in Regulating the Cytoplasmic pH: An in Vivo Study Carried out in chl1, an Arabidopsis thaliana Mutant Impaired in NO-3 Transport

The effects of the growth in a medium containing NH4NO3 as nitrogen source were studied on cell sap pH, cytoplasmic pH and malate content in chll, an Arabidopsis thaliana mutant impaired in chlorate and nitrate transport. In all the conditions tested the pH of the cytoplasm in chll was more alkaline, and that of the vacuole was more acidic as compared with those measured in wt. Treatment with bafilomycin Al, a specific inhibitor of the vacuolar H+ATPase, induced a small alkalinization of the vacuole, and a significant acidification of the cytoplasm, these effects being greater in chll than in wt. The greater response of the mutant to bafilomycin Al suggests that, in the absence of the inhibitor, the activity of the tonoplast H+-ATPase in chll is higher than in wt, this diversity being a possible reason for the differences in intracellular pH detected between the two strains. A possible role for the vacuolar H+-ATPase in regulating the cytoplasmic pH is discussed.