Growth, sucrose synthase, and invertase activities of developing Phaseolus vulgaris L. fruits

Activities of the sucrose-cleaving enzymes, acid and neutral invertase and sucrose synthase, were measured in pods and seeds of developing snap bean (Phaseolus vulgaris L.) fruits, and compared with ¹⁴C-import, elongation and dry weight accumulation. During the first 10 d post-anthesis, pods elongated rapidly with pod dry weight increase lagging behind by several days. The temporal patterns of acid invertase activity and import coincided closely during the first part of pod development, consonant with a central role for this enzyme in converting imported sucrose during pod elongation and early dry weight accumulation. Later, sucrose synthase became the predominant enzyme of dry weight accumulation and was possibly associated with the development of phloem in pod walls. Sucrose synthase activity in seeds showed two peaks, corresponding to two phases of rapid import and dry weight accumulation; hence, sucrose synthase was associated with seed sink growth. Acid invertase activities in seeds were low and did not show a noticeable relationship with import or growth. All neutral invertase activities, during pod and seed development, were too low for it to have a dominant role in sucrose cleavage. Changes in activities of certain sucrose-cleaving enzymes appear to be correlated with certain sink functions, including import, storage of reserves, and biosynthetic activities. The data supports the association of specific sucrose-cleaving enzymes with the specific processes that occur in the developing pods and seeds of snap bean fruits; for example, acid invertase with pod elongation and sucrose synthase with fruit dry matter accumulation.     

九连小檗悬浮培养细胞生理生化特性的研究——Ⅱ.干物质积累与过氧化物酶同工酶和蛋白质的变化

本文报道了九连小檗细胞悬浮培养过程干物质积累与过氧化物酶同工酶和可溶性蛋白质的变化。实验表明在悬浮培养过程中细胞干物质积累可分为四个时期,即延迟期、缓慢增重期、线性增重期和减慢静止期。过氧化物酶同工酶谱的变化与干物质积累相关,在延迟期和减慢静止期的同工酶谱带较少,活力较低,在增重期的同工酶谱带较多,活力较高。蛋白质含量在接种后的第2至5天达到高峰,随后便逐渐降低,这些大分子的变化是在一定条件下基因表达的引发或阻抑的结果。     

Potential Role of Pyrophosphate:Fructose 6-Phosphate Phosphotransferase in Carbohydrate Metabolism of Cold Stored Tubers of Solanum tuberosum cv Bintje

To gain a better understanding of the mechanism of cold induced sweetening, sugar accumulation in potato, Solanum tuberosum cv Bintje, was compared to the maximum activity of inorganic pyrophosphate (PPi):fructose 6-phosphate 1-phosphotransferase (EC 2.7.1.90) and the concentration of two regulatory metabolites. Mature tubers accumulated reducing sugars and sucrose at an almost linear rate of 13.4 and 5.2 micromole per day per gram dry weight at 2°C and 4.5 and 1.3 micromole per day per gram dry weight, respectively, at 4°C. During storage at 8°C sugar accumulation was nil. Sugar accumulation was preceded by a lag phase of about 4 days. The accumulation of reducing sugars persisted for at least 4 weeks, whereas sucrose accumulation declined after 2 weeks of storage. The ratio of glucose:fructose changed concomitantly with sugar increase from 65:35 to equimolarity. The maximum activity of PPi:fructose 6-phosphate 1-phosphotransferase was 2.51 and 2.25 units per gram dry weight during storage at 2 and 8°C, respectively. The temperature coefficient of this enzyme from potatoes kept at 2 or 8°C was 2.12 and 2.48, respectively. The endogenous concentration of fructose 2,6-biphosphate increased from 0.15 to 1 nanomole per gram dry weight during storage at 2 and 4°C but remained the same throughout storage at 8°C. After exposure to 2°C an initial increase in the concentration of PPi was observed from 4.0 to 5.6 nanomoles per gram dry weight. Pyrophosphate concentration did not change during storage at 4°C but decreased slightly at 8°C. All observed changes became annulled after transfer of cold stored tubers to 18°C. These data strongly indicate that PPi:fructose 6-phosphate 1-phosphotransferase can be fully operational in cold stored potato tubers and the lack of increase in PPi concentration supports the functioning of this enzyme during sugar accumulation.     

Interaction of carbon and nitrogen metabolism in the productivity of maize

Five maize (Zea mays L.) hybrids, FS854, B73 × Mo17, B84 × Mo17, B73 × B77, and P3382, grown under field conditions, were sampled at intervals during the grain-filling period. Plants were subdivided into stalks (including sheaths), leaves, and kernels. These parts were assayed for dry weight, reduced nitrogen, and extractable nonstructural carbohydrates. The duration and rates of net nitrate reduction and photosynthesis were approximated by the changes over time in the accumulation of reduced nitrogen and dry weight by the plant (total, above ground), respectively.

Data on the accumulation of reduced nitrogen and dry weight by the plant show that decreases in nitrate reduction preceded (in time and extent for four of the hybrids and in extent for FS854) decreases or cessation of photosynthesis. FS854 continued to accumulate reduced nitrogen and dry matter throughout the grain-filling period.

The patterns of change in stalk carbohydrate and reduced nitrogen during the early stages of ear development show the stalk serves as a storage reservoir and that these reserves were remobilized during the final stages of grain development. The marked increase and maintenance of dry weight and carbohydrate content of stalks until 34 days after anthesis, shows the capacity of the leaves to produce photosynthate through the first half of the grain-filling period exceeds the needs of the ear and/or the transport system. In contrast, stalk nitrogen content shows a slight increase up to 12 days after anthesis and decreases continually thereafter. Leaf nitrogen was lost continuously throughout grain development. The potential capacity of the plant to supply newly reduced nitrogen was inadequate to support initiation and early development of the kernels without remobilization of vegetative nitrogen. Of the two hybrids having delayed leaf senescence, FS854 with its initially higher concentration and content of reduced nitrogen in the stalk, initiated and developed a bigger ear than P3382, which had lower levels of stalk nitrogen.

Three of the five hybrids had `near linear' rates of accumulation of kernel dry weight, whereas none of the hybrids had linear rates of gain in kernel nitrogen. All hybrids had maximum or near maximum rates of gain of kernel nitrogen between 26 and 34 days after anthesis and a marked reduction (41-52%) of rates in the following sampling interval. These decreases are concurrent with decreases in rates of nitrate reduction (nitrogen accumulation) by the whole plant for four of the hybrids and with decreases in remobilization of nitrogen from the vegetation of FS854. Data for the ratio of rates of accumulation of dry weight/reduced nitrogen by the kernels versus time after anthesis, show that the accumulation of dry weight and reduced nitrogen are independent of each other. The variations in the ratio values appear best related to variations in the availability of nitrogen from the vegetation.

     

Kinetics of taxol production, growth, and nutrient uptake in cell suspensions of Taxus cuspidata

Cell culture of Taxus cuspidata may represent an alternative to extraction of bark as a source of taxol and related taxanes. Cell suspensions of a cell line of T. cuspidata were grown for 44 days in shake flasks containing B5C2 medium. Throughout the growth cycle, fresh and dry weight accumulation, taxol yield on a dry weight basis, taxol accumulation in the medium, pH and pigmentation variation in the medium, as well as the uptake of sucrose, glucose, fructose, nitrate, and inorganic phosphate from the culture medium were examined. The results showed that the growth was relatively slow (doubling times of 17 and 20 days for fresh and dry weight, respectively), and taxol accumulation in the cells was non-growth related (higher in the stationary phase) and at relatively low levels (up to 4 mug/g of the extracted dry weight). Taxol concentration in the medium had two peaks: one during the early (0.4mug/mL) and another during the late (0.1-mug/mL) parts of the growth cycle. On a volumetric basis, the average total amount of taxol produced during the stationary phase (day 38) was 0.15 mug/mL, of which approximately 66% was in the medium and 34% was in the cells. Total carbohydrate uptake was closely associated with the increase in dry biomass. Sucrose was apparently extracellularly hydrolyzed after the first 6 days of culture; glucose was used before fructose. Nitrate was assimilated throughout the growth cycle, but phosphate was absorbed within the first week of culture. The pH variation showed an initial drop followed by a trend toward alkalinization for most of the growth period. Dark pigmentation in the medium increased progressively, particularly during the stationary phase. (c) 1994 John Wiley & Sons, Inc.     

GROWTH OF ULVA FENESTRATA (CHLOROPHYTA) IN MICROCOSMS RICH IN ZOSTERA MARINA (ANTHOPHYTA) DETRITUS1,2

In laboratory experiments discs cut from thalli of Ulva fenestrata Postels & Ruprecht grew in diameter and biomass (dry weight and ash-free dry weight) more when dead leaves of Zostera marina L. were present than when absent. A maximum increase in dry weight of 500% in 14 days occurred with Zostera present compared with only a 200% increase with no detritus. When NO^?₃ and PO^3-₄ were added the weight of an Ulva disc increased by over 800% when Zostera was present but by only 400% in controls. In general penicillin G (475 units/ml) caused a reduction in algal growth in cultures containing detritus. It is concluded that bacteria on the detritus may compete with algae for nutrients but by releasing unknown substances the bacteria promote the growth of Ulva.     

Effects of Night-break Treatment on Leaf Area and Leaf Dry Weight in Callistephus chinensis

Plants of Callistephus chinensis were grown in eight hours ofdaylight per day and received either uninterrupted dark periodsor dark periods interrupted by one hour of low-intensity light.The growth in area and the accumulation of dry matter was followedfor leaves at different heights of insertion on the stem. Lightinterruption treatment caused more rapid surface expansion ofindividual leaves. The rate of accumulation of dry matter wasalso increased but less in proportion to the increase in areaso that the area per unit weight of leaf material, i.e. thespecific leaf area, was greater. The final areas and dry weightsof leaves were also considerably greater than in the uninterruptednight treatment. When plants were transferred from uninterruptedto interrupted nights, a similar response was obtained fromthose leaves which began to expand rapidly after the commencementof the treatment. The reciprocal transfer into uninterrupted nights immediatelyretarded the rate of leaf expansion and final leaf areas wereless. The rate of accumulation of dry matter was not affectedso rapidly and the area per unit weight of leaf material fellbelow that recorded from leaves which had always received uninterruptednights. Within any one treatment and on any one occasion thespecific leaf area was almost constant, regardless of heightof insertion and therefore also of leaf size and degree of development. It is postulated that a promotor of leaf growth is producedin the light interruption treatment and that this regulatormay increase cell expansion. Transfer to uninterrupted nightsmay halt the synthesis of this regulator and may also lead tothe production of an inhibitor of leaf expansion. Finally, it is concluded from a survey of the literature, that,in general, where a response to photoperiod exists, leaf areais greater in long days than in short days.     

Sugarcane micropropagation and phenolic excretion

Sugarcane shoot formation was followed using a temporary immersion system. Plant fresh weight, plant dry weight, shoot number and phenolic excretion to the culture medium were recorded during shoot formation. Shoot number increased for 30 days of culture but formation of new shoots was greatly reduced from 31 to 40 days. Phenolic excretion also increased during the first 20 days of culture (gallic acid represented 82% total phenolics) and decreased during the last 10 days (31–40 days of culture). The most intensive period of phenolic excretion (11–20 days) preceded the most intensive period of shoot formation (21–30 days). The same relationship does not seem to exist between the accumulation of fresh and dry weights. Subculture onto fresh medium at the beginning of proliferation (10 days after culture initiation) was detrimental to shoot formation in the subsequent period (11–20 days). However, such a detrimental effect could be avoided if gallic acid was added to the medium. Addition of cysteine to the culture medium reduced both excretion of phenolics and shoot formation but not fresh weight. The use of temporary immersion systems, the increase of culture medium volume per initial explant and the addition of paclobutrazol promoted both phenolic excretion and sugarcane shoot formation. Results presented here indicate a relationship between phenolic excretion and shoot formation but not with accumulation of plant weight. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ontogenetic changes in photosynthetic capacity and dry matter production of flag wheat leaves during the grain filling period

The relationships between photosynthetic capacity and dry matter accumulation during the grain filling period have been studied in flag leaves of Triticum aestivum L., cv. Kolibri grown in Mediterranean field conditions. Particular importance has been given to assimilate accumulation in relation to the onset of senescence. During grain filling, the time course of specific dry weight (SDW) was similar in the blade and in the sheath. Variations in SDW were about six times larger in the sheath than in the blade. Minimum blade SDW values occurred during heading and at anthesis. Maximum blade SDW values were observed two weeks after anthesis. After this, SDW values decreased sharply. The dry matter increase per grain in the period from two weeks after anthesis to the end, was only about 25% of final grain dry weight. The importance of environmental constraints on maximum SDW values are discussed. Maximum SDW values occurred at the beginning of the period of rapid decline in blade net CO₂ assimilation rate and leaf nitrogen content, that is, at the beginning of senescence. On the other hand, the stomatal resistance to CO₂ and the development of senescence are not apparently related. The maximum blade dry weight increase (considering a value of zero at heading) was about 60 mg dry weight per g fresh weight. The possible relationships between dry matter accumulation and senescence onset are discussed.     

Carbon Partitioning among Leaves, Fruits, and Seeds during Development of Phaseolus vulgaris L

Development of vegetative and floral buds was found to be a key factor in establishing the way carbon is distributed among growing leaves and fruits in Phaseolus vulgaris L. plants. Leaves emerged principally during a period 14 to 32 days after planting while flowers were produced during a 10- to 12-day period near the end of leaf emergence. Timing of anthesis established the sigmoidal time course for dry weight accumulated by the composite of all fruits on the plant. During the first 12 days following anthesis, fruit growth mainly consisted of elongation and dry weight accumulation by the pod wall. Thereafter, seed dry weight increased for about 1 week, decreased markedly for several days, and then increased again over the next 2 weeks. Accumulation of imported carbon in individual seeds, measured by steady-state labeling, confirmed the time course for dry weight accumulation observed during seed development. Seed respiration rate initially increased rapidly along with dry weight and then remained nearly steady until seed maturation. A number of developmental events described in the literature coincided with the different phases of diauxic growth. The results demonstrated the feasibility of relating current rates of carbon import in individual seeds measured with tracer ¹⁴C to the rates of conversion of imported sucrose and use of the products for specific developmental processes. The resulting data are useful for evaluating the roles of conversion and utilization of imported sucrose in regulating import by developing seeds.     

Biosynthesis, deposition, and partial characterization of potato suberin phenolics

Alkaline nitrobenzene oxidation of the polymeric materials from wound-healed potato (Solanum tuberosum L. var. White Rose) tuber tissue liberated p-hydroxybenzaldehyde, vanillin, and minor amounts of syringaldehyde as determined by gas chromatography/mass spectrometry. The aromatic aldehydes were derived only from periderm. The amounts of aromatic aldehydes liberated were used as a measure of the deposition of phenolic suberin components. Phenolic deposition began after about 2 days of wound healing; after 8 days the amounts of p-hydroxybenzaldehyde released by nitrobenzene oxidation leveled off at 5 milligrams per gram dry weight and after 12 days vanillin liberation reached a maximum at 7.5 milligrams per gram dry weight. The time course of deposition of the phenolic polymeric material is analogous to that reported for the deposition of the aliphatic components of suberin and therefore these results are consistent with the proposed structure of suberin. Experiments with radiolabeled l-phenylalanine and cinnamic acid indicated that exogenous phenylalanine was less efficient than cinnamic acid as a precursor of suberin phenolics. Nitrobenzene oxidation of radiolabeled suberin preparations gave three major labeled fractions: a diethyl ether-soluble fraction containing aromatic aldehydes ( approximately 20%), an ethyl acetate-soluble fraction containing unknown compounds ( approximately 15%), and a condensed phenolic fraction ( approximately 10%). Thin-layer and gas-liquid chromatographic analysis of the ether fraction showed that the major labeled components were vanillin and p-hydroxybenzaldehyde. The condensed tannin fraction revealed the presence of several labeled macromolecular phenolic fractions. Elution profiles of the condensed tannin fraction from tissues suberized for different periods of time were essentially identical, suggesting qualitative similarity of deposition and polymerization of suberin phenolics throughout the duration of wound healing. Chlorogenic acid accumulation in wound healing potato tuber discs was measured by high-performance liquid chromatography. The level of this compound reached 130 micrograms per disk after 11 days and did not decline even after the deposition of suberin ceased, revealing no precursor role for this acid in suberization.     

Effects of zinc, iron, cobalt, and manganese on Fusarium moniliforme NRRL 13616 growth and fusarin C biosynthesis in submerged cultures.

The influence of zinc, iron, cobalt, and manganese on submerged cultures of Fusarium moniliforme NRRL 13616 was assessed by measuring dry weight accumulation, fusarin C biosynthesis, and ammonia assimilation. Shake flask cultures were grown in a nitrogen-limited defined medium supplemented with various combinations of metal ions according to partial-factorial experimental designs. Zinc (26 to 3,200 ppb [26 to 3,200 ng/ml]) inhibited fusarin C biosynthesis, increased dry weight accumulation, and increased ammonia assimilation. Carbohydrate was found to be the principal component of the increased dry weight in zinc-supplemented cultures. Zinc-deficient cultures synthesized more lipid and lipidlike compounds, such as fusarin C, than did zinc-supplemented cultures. Microscopic examination showed that zinc-deficient hyphae contained numerous lipid globules which were not present in zinc-supplemented cultures. Addition of zinc (3,200 ppb) to 2- and 4-day-old cultures inhibited further fusarin C biosynthesis but did not stimulate additional dry weight accumulation. Iron (10.0 ppm) and cobalt (9.0 ppm) did not affect fusarin C biosynthesis or dry weight accumulation. Manganese (5.1 ppm) did not affect dry weight accumulation but did increase fusarin C biosynthesis in the absence of zinc. Maximum fusarin C levels, 32.3 micrograms/mg (dry weight), were produced when cultures were supplied manganese, whereas minimum fusarin C levels, 0.07 micrograms/mg (dry weight), were produced when zinc, iron, cobalt, and manganese were supplied. These results suggest a multifunctional role for zinc in affecting F. moniliforme metabolism.     

Effects of zinc, iron, cobalt, and manganese on Fusarium moniliforme NRRL 13616 growth and fusarin C biosynthesis in submerged cultures

The influence of zinc, iron, cobalt, and manganese on submerged cultures of Fusarium moniliforme NRRL 13616 was assessed by measuring dry weight accumulation, fusarin C biosynthesis, and ammonia assimilation. Shake flask cultures were grown in a nitrogen-limited defined medium supplemented with various combinations of metal ions according to partial-factorial experimental designs. Zinc (26 to 3,200 ppb [26 to 3,200 ng/ml]) inhibited fusarin C biosynthesis, increased dry weight accumulation, and increased ammonia assimilation. Carbohydrate was found to be the principal component of the increased dry weight in zinc-supplemented cultures. Zinc-deficient cultures synthesized more lipid and lipidlike compounds, such as fusarin C, than did zinc-supplemented cultures. Microscopic examination showed that zinc-deficient hyphae contained numerous lipid globules which were not present in zinc-supplemented cultures. Addition of zinc (3,200 ppb) to 2- and 4-day-old cultures inhibited further fusarin C biosynthesis but did not stimulate additional dry weight accumulation. Iron (10.0 ppm) and cobalt (9.0 ppm) did not affect fusarin C biosynthesis or dry weight accumulation. Manganese (5.1 ppm) did not affect dry weight accumulation but did increase fusarin C biosynthesis in the absence of zinc. Maximum fusarin C levels, 32.3 micrograms/mg (dry weight), were produced when cultures were supplied manganese, whereas minimum fusarin C levels, 0.07 micrograms/mg (dry weight), were produced when zinc, iron, cobalt, and manganese were supplied. These results suggest a multifunctional role for zinc in affecting F. moniliforme metabolism.     

Cell cycle analysis of Taxus suspension cultures at the single cell level as an indicator of culture heterogeneity

Single cell growth and division was measured via flow cytometry in order to characterize the metabolic variability of Taxus cuspidata suspension cultures, which produce the valuable secondary metabolite Taxol. Good agreement was observed between the cell cycle distribution and biomass accumulation over the batch culture period. Specific growth rates of 0.13 days(-1) by fresh weight and 0.15 days(-1) by dry weight were measured. Elicitation with methyl jasmonate (MJ) significantly decreased both cell cycle progression and biomass accumulation, as the specific growth rate decreased to 0.027 days(-1) by fresh and dry weight. Despite the decrease in biomass accumulation for MJ elicited cultures, sucrose utilization was not significantly different from control cultures. MJ elicitation also increased the accumulation of paclitaxel and other taxanes. The accumulation of upstream taxanes (baccatin III and 10-deactylbaccatin III) increased during exponential growth, reached a maximum around day 12, and then declined throughout the stationary phase. The paclitaxel concentration increased during both exponential growth and stationary phase, reaching a maximum around days 20-25. Throughout the culture period, greater than 70% of the cells were in G(0)/G(1) phase of the cell cycle. Studies using bromodeoxyuridine (BrdU) incorporation showed that approximately 65% of the Taxus cells are noncycling, even during exponential growth. Although the role of these cells is currently unknown, the presence of a large, noncycling subpopulation can have a significant impact on the utilization of plant cell culture technology for the large-scale production of paclitaxel. These results demonstrate that there is a high degree of metabolic heterogeneity in Taxus cuspidata suspension cultures. Understanding this heterogeneity is important for the optimization of plant cell cultures, particularly the reduction of production variability.     

氮素营养对小麦根冠协调生长的调控

在植物生长箱通过溶液培养方式,对不同氮素条件下不同抗旱性的小麦品种西农1043和小偃6号的幼苗根苗生长特性进行了研究,结果表明在不同氮素浓度下,氮肥用量的提高对地上部干重和叶片气体交换参数表现为增效效应,当用量增至一定程度时,地上部干重和叶片气体交换参数均呈下降趋势,只是各自的适宜用量存在差异。培养介质氮素浓度低时,有利于小麦根系干重累积,培养介质氮素浓度高时,不利于根系干重累积。西农1043和小偃6号根长分布基本相似,水分利用效率随着根冠比的增大而降低。小麦根冠比的增加并不利于叶片水分利用效率的提高,而叶片光合作用最优的根冠比为0．5左右。     

Effect of increased temperature in apical regions of maize ears on starch-synthesis enzymes and accumulation of sugars and starch

Apical florets of maize (Zea mays L.) ears differentiate later than basal florets and form kernels which have lower dry matter accumulation rates. The purpose of this study was to determine whether increasing the temperature of apical kernels during the dry matter accumulation period would alter the difference in growth rate between apical and basal kernels. Apical regions of field-grown maize (cultivar Cornell 175) ears were heated to 25 ± 3°C from 7 days after pollination to maturity (tip-heated ears) and compared with unheated ears (control). In controls, apical-kernel endosperm had 24% smaller dry weight at maturity, lower concentration of sucrose, and lower activity of ADP-Glc starch synthase than basal-kernel endosperm, whereas ADP-Glc-pyrophosphorylase (ADPG-PPase) activities were similar. In tip-heated ears apical-kernel endosperm had the same growth rate and final weight as basal-kernel endosperm and apical kernels had higher sucrose concentrations, higher ADP-Glc starch synthase activity, and similar ADPG-PPase activity. Total grain weight per ear was not increased by tip-heating because the increase in size of apical kernels was partially offset by a slight decrease in size of the basal- and middle-position kernels. Tip-heating hastened some of the developmental events in apical kernels. ADPG-PPase and ADP-Glc starch synthase activities reached peak levels and starch concentration began rising earlier in apical kernels. However, tip-heating did not shorten the period of starch accumulation in apical kernels. The results indicate that the lower growth rate and smaller size of apical kernels are not solely determined by differences in prepollination floret development.     

Nucleic acid and protein synthesis in discs cut from mature leaves of Nicotiana tabacum L. and cultured on nutrient agar with and without kinetin

The effect of kinetin on aspects of the metabolism of discs cut from mature leaves of Nicotiana tabacum and cultured in the light on agar containing mineral salts and sucrose was studied. In the first few days of culture there was a rapid decline in chlorophyll content. Discs treated with kinetin in the light began to resynthesise chlorophyll after 3–4 days and this was correlated with chloroplast replication. Kinetin promoted chloroplast replication but was not always essential. An increase in fresh weight also occurred, due mainly to cell expansion. Nitrate reductase activity increased rapidly during the first few hours after placing discs on the culture medium but kinetin had no effect on this reponse. Subsequently there were dramatic increases in RNA and protein content which were largely independent of kinetin. Gel electrophoresis showed that cytoplasmic and chloroplast ribosomal RNA and a large amount of soluble RNA were synthesised during culture of the discs. These results are discussed in relation to the role of kinetin in delaying leaf sensescence.     

Is osmotic adjustment required for water stress resistance in the Mediterranean shrub Atriplex halimus L?

The effect of water stress was investigated in plants from two populations of Atriplex halimus L: Tensift issued from a salt-affected coastal area and Kairouan, originating from an inland dried site. Water deficit was applied by withholding water for 22 days. Shoot dry weight (shoot DW), leaf relative water content (RWC), turgid weight to dry weight ratio (TW/DW), osmotic potential (psis), osmotic adjustment (OA), proline, glycinebetaine, and sugar content were determined 1, 8, 15 and 22 days after withholding watering. Water stress induced a decrease in shoot DW, RWC, psis, and TW/DW, but an increase in glycinebetaine and sugar leaf contents. The decrease of psis and TW/DW was more marked in Kairouan than in Tensift. At the end of the stress period, Kairouan showed a greater OA compared with Tensift. However, the contribution of net solute accumulation (OAacc) was similar in both populations in response to stress. Water stress resistance could thus not be associated with higher OA, although the ability of plants to regulate these metabolic and physiological functions could play an important role under harmful conditions. The possible roles of osmolyte accumulations are discussed in relation to the specific physiological strategy of water-stress-resistance in this species.     

Role of transpiration from fruits in phloem transport and fruit growth in tomato fruits

Sink activity of fruits had been suggested to vary depending on transpiration of fruits. In this study, the effect of transpiration on dry matter accumulation was evaluated in tomato ( Lycopersicon esculentum Mill.). Fruits of cv. Saturn at 14 days after anthesis were enclosed in chambers and aerated with dried (<15% RH) or moistened (>90% RH) air. These treatments did not cause any significant differences in fruit fresh weight, dry weight, percentage of dry matter, and concentration of soluble sugars within 5 days of the treatment, or the import of ¹⁴C within 18 h after the application of ¹⁴CO₂ to the source leaves. However, displacement transducer measurement of each fruit showed a 40% reduction in growth rate in response to exchange of moistened air with dried air. When fruits of cv. Momotaro were exposed to transpiration treatments from the beginning of visible fruit enlargement until the ripening stage, the fruits exhibited 20% reduction in growth and lower accumulation of dry matter at harvest following treatment with dried air. These results suggested that higher transpiration reduced both water accumulation and dry matter accumulation. In contrast, when fruit growth was mechanically restricted by enclosing the fruits in a chamber packed with glass beads, and dried or moistened air was passed through the spaces between the glass beads, fruits exhibited higher dry matter accumulation under dried air treatment conditions. The results show that only under artificial conditions would transpiration of fruits potentially drive carbohydrate transport; it does not serve as a limiting step of carbohydrate transport to tomato fruits under normal circumstances.