Acclimation of potato plants to polyethylene glycol-induced water deficit II. Contents and subcellular distribution of organic solutes

Potato plants (Solanum tuberosum cv. Désirée) were grown hydroponically and subjected to water deficit induced by addition of 10% (w/v) PEG 6000. The potato plants were able to grow under water deficit by accumulating organic solutes (osmoregulation). Osmoregulation occurred in two phases. During the initial 2d hexoses were accumulated, and after 7 d of PEG treatment osmotic adjustment was mostly due to the accumulation of amino acids, especially proline, which accumulated up to 150 times the control content. Sucrose contents remained unchanged in leaves of PEG-treated plants compared with controls, whereas the starch content decreased during PEG treatment.In control leaves, the hexoses and malate were compartmented in the vacuole and sucrose was found in the cytosol and vacuole. Amino acids were distributed between the cytosol and stroma, but only minor amounts of amino acids could be detected in the vacuole. Under water deficit the subcellular distribution of hexoses, malate and sucrose remained unchanged. Most amino acids showed a slight to moderate higher concentration in the vacuole under water deficit. Proline, the metabolite contributing mainly to osmoregulation, was concentrated mostly in the chloroplast and the cytosol. This underlines the important role of proline as the osmolyte under water deficit.     

Adaptation versus shock response to polyethylene glycol-induced low water potential in cultured potato cells

We compared long-term adaptation versus short-term or shock response of potato ( Solanum tuberosum ) cells to polyethylene glycol (PEG)-induced low water potential. Potato cells, which were allowed to adapt gradually to a decreasing water potential, were able to grow actively in a medium containing 20% PEG. In contrast, no appreciable gain in dry weight was observed in potato cells shocked by abrupt transfer to the same medium. PEG-adapted cells were also salt-tolerant, as they were able to proliferate in a medium supplemented with 200 m M NaCl. No visible ultrastructural changes of mitochondria or proplastids were observed in adapted cells at values of low water potential (about −2.0 MPa), which caused membrane disruption and appearance of lipid droplets in unadapted cells. ABA cellular content increased 5-fold in PEG-shocked cells but no significant increase was found in PEG-adapted cells. The intracellular content of free proline increased 12.5 times over the basal level in PEG-adapted cells and 6.5 times in PEG-shocked cells. As shown by in vivo protein labeling, shock conditions strongly inhibited protein synthesis, which was completely recovered in PEG-adapted cells. Osmotin, a protein associated with salt adaptation in tobacco, was constitutively expressed at a high level in PEG-adapted cells and accumulated in PEG-shocked cells only three days after the transfer in a medium supplemented with 20% PEG. Proline and osmotin accumulation were coincident with the increase in cellular ABA content in PEG-shocked cells, but not in PEG-adapted cells. These data suggest that this hormone is mainly involved in shock response rather than long-term adaptation.     

Acclimation to low water potential in potato cell suspension cultures leads to changes in putrescine metabolism

Changes in levels and biosynthesis of di- and polyamines are associated with stress responses in plant cells. The involvement of these molecules was investigated here in cultured potato (Solanum tuberosum L.) cells grown in medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) and kinetin, and acclimated or not to low water potential. The diamine (putrescine) and polyamine (spermidine and spermine) status in cells gradually acclimated to increasing concentrations (up to 20 %, w/v) of polyethylene glycol (PEG) Mr 8000, was compared with that of unacclimated cells abruptly exposed (shocked) or not (controls) to 20 % (w/v) PEG. After a 72-h subculture, the free and perchloric acid (PCA)-soluble conjugated di- and polyamine pattern in acclimated cells was not dramatically different from that of controls, but PCA-insoluble conjugated putrescine was 14-fold higher than in controls. In shocked cells, a strong reduction in free putrescine and spermidine/spermine titres occurred. Arginine (ADC, EC 4.1.1.19) and ornithine (ODC, EC 4.1.1.17) decarboxylase activities were not substantially altered in shocked cells compared with controls, while in PEG-acclimated cell populations they increased about 3-fold, both in the soluble and particulate fractions. S-Adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.21) and diamine oxidase (DAO, EC 1.4.3.6) activities followed a similar pattern to each other in that their activities were enhanced 2- and 3-fold, respectively, in acclimated cells over unacclimated controls. Ethylene production was also enhanced in acclimated cells. These results indicate that, with respect to di- and polyamines, acquired tolerance to low water potential in potato cells leads principally to changes in putrescine biosynthesis and conjugation which may be involved in ensuring cell survival.     

Regulation of sucrose and starch metabolism in potato tubers in response to short-term water deficit

To investigate the effect of water stress on carbon metabolism in growing potato tubers (Solanum tuberosum L.), freshly cut and washed discs were incubated in a range of mannitol concentrations corresponding to external water potential between 0 and −1.2 MPa. (i) Incorporation of [¹⁴C]glucose into starch was inhibited in water-stressed discs, and labeling of sucrose was increased. High glucose overrode the changes at low water stress (up to −0.5 MPa) but not at high water stress. (ii) Although [¹⁴C]sucrose uptake increased in water-stressed discs, less of the absorbed [¹⁴C]sucrose was metabolised. (iii) Analysis of the sucrose content of the discs confirmed that increasing water deficit leads to a switch, from net sucrose degradation to net sucrose synthesis. (iv) In parallel incubations containing identical concentrations of sugars but differing in which sugar was labeled, degradation of [¹⁴C]sucrose and labeling of sucrose from [¹⁴C]glucose and fructose was found at each mannitol concentration. This shows that there is a cycle of sucrose degradation and resynthesis in these tuber discs. Increasing the extent of water stress changed the relation between sucrose breakdown and sucrose synthesis, in favour of synthesis. (v) Analysis of metabolites showed a biphasic response to increasing water deficit. Moderate water stress (0–200 mM mannitol) led to a decrease of the phosphorylated intermediates, especially 3-phosphoglycerate (3PGA). The decrease of metabolites at moderate water stress was not seen when high concentrations of glucose were supplied to the discs. More extreme water stress (300–500 mM mannitol) was accompanied by an accumulation of metabolites at low and high glucose. (vi) Moderate water stress led to an activation of sucrose phosphate synthase (SPS) in discs, and in intact tubers. The stimulation involved a change in the kinetic properties of SPS, and was blocked␣by protein phosphatase inhibitors. (vii) The amount of ADP-glucose (ADPGlc) decreased when discs were incubated on 100 or 200 mM mannitol. There was a strong correlation between the in vivo levels of ADPGlc and 3PGA when discs were subjected to moderate water stress, and when the sugar supply was varied. (viii) The level of ADPGlc increased and starch synthesis was further inhibited when discs were incubated in 300–500 mM mannitol. (ix) It is proposed that moderate water stress leads to an activation of SPS and stimulates sucrose synthesis. The resulting decline of 3PGA leads to a partial inhibition of ADP-glucose pyrophosphorylase and starch synthesis. More-extreme water stress leads to a further alteration of partitioning, because it inhibits the activities of one or more of the enzymes involved in the terminal reactions of starch synthesis. Received: 26 August 1996 / Accepted: 5 November 1996     

Clonal variation for tolerance to polyethylene glycol-induced water stress in cultured tomato cells

Cell clones were isolated from a population of cultured tomato (Lycopersicon esculentum Mill cv VFNT-cherry) cells and their tolerance to polyethylene glycol (PEG)-induced water stress was measured. Considerable variation for tolerance among the clones was found. Tolerance differences between clones appeared to be spontaneous and were different from tolerance differences between adapted and unadapted cells. Unlike adapted (selected by exposure to PEG) cells, cell clones retained their relative tolerance for many generations in the absence of selection pressure, and tolerance of both relatively tolerant and intolerant clones was very dependent on growth cycle stage and inoculum density. Analysis of subclones isolated from relatively tolerant and intolerant parent clones revealed that each parent clone gives rise to progeny with tolerances near the mean tolerance of both parents. However, progeny populations of both tolerant and intolerant parents are enriched with individuals with phenotypes nearer the mean response of their respective parent populations. When exposed to PEG, relatively tolerant and intolerant clones alike become adapted to the level of PEG to which they are exposed, and have the same phenotypic level of tolerance. Thus, selection by exposure to stress is unable to discriminate (on the basis of growth) between the innately tolerant and intolerant cell types within the population. This is indicated also by the fact that clones isolated from a population of cells adjusted to growth on 25% PEG do not show an enriched frequency of tolerant phenotypes when grown in the absence of PEG compared to the nonselected normal cell population which has never been adjusted to growth on PEG.     

Acclimation to long-term water deficit in the leaves of two sunflower hybrids: photosynthesis, electron transport and carbon metabolism

The influence of long-term water deficit on photosynthesis, electron transport and carbon metabolism of sunflower leaves has been examined. Water deficit was imposed from flower bud formation up to the stage of full flowering in the field on two sunflower hybrids with different drought tolerance. CO2 assimilation and stomatal conductance of the intact leaves, determined at atmospheric CO2 and full sunlight (1500-2000 mol quanta m^-2 s^-1), decreased with water deficit. Maximum quantum efficiency of PSII (Fy/Fm) and relative quantum yield of PSII (II) determined under similar experimental conditions, did not change significantly in severely stressed leaves. The strong inhibition of the plateau region of the light response curve, determined at high CO2 (5%) in water-deficient sunflower leaves, indicates that photosynthesis is also limited by non-stomatal factors. The decreased slope and the plateau of the CO2 response curves show that the capacity of carboxylation and RuBP regeneration decreased in severely stressed intact leaves. Rubisco specific activity decreased in severely stressed leaves, but Rubisco content increased under prolonged drought. The increase of Rubisco content was significantly higher in leaves of the drought-tolerant sunflower hybrid indicating that a higher Rubisco content could be one factor in conferring better acclimation and higher drought tolerance.     

The effect of polyethylene glycol-induced water stress on the maize root apex

Following a 24-h exposure to a solution of polyethylene glycol 4 000 of a —12.66 bar osmotic potential the roots of maize ceased growing. The inhibition of growth was conditioned by the inhibition of cell elongation and division. The elongation of cells was substituted by their radial enlargement which took place both in the peripheral and central root parts. The cells either did not divide at all, or sporadic mitoses still occurred in the roots. The meristematic cells treated were highly vacuolized, chromatin condensation being observed in their nuclei. In contrast to growth processes, differentiation was stimulated: the formation of the secondary wall in protoxylem elements occurred at a shorter distance,i.e. 1 500–2 400 µm from the apex, in comparison with 4000–5 000 µm in the control, this evidently being caused not only by the inhibition of growth, but also by the capacity of cells to differentiate more rapidly. The changes induced by a 24-h exposure to water stress were of a reversible nature; however, a 48-h treatment brought about irreversible changes.     

Cell membrane stability and biochemical response of cultured cells of groundnut under polyethylene glycol-induced water stress

Cell membrane stability (CMS) in suspension cultures of two groundnut cultivars was studied under polyethylene glycol(PEG)-induced water stress. There was a negative relationship between PEG concentration in the medium and membrane stability measured as electrolyte leakage. The CMS values in the cell cultures correlated well with the whole plant tissue and permitted the differentiation of cultivars based on their known response to drought stress. The cell membrane stability was lower (more electrolyte leakage) when cells were grown in culture as compared to the intact plant tissue. Kadiri-3, the drought tolerant cultivar maintained higher CMS than JL-24, the drought susceptible one. With increasing PEG levels the concentration of Potassium in cultured cells declined in both cultivars. However, Kadiri-3 maintained higher K values than JL-24 accompanied with greater cell membrane stability. Total soluble sugars also increased with increasing stress in both cultivars; the increase being higher in Kadiri-3. There was no significant change in the total free amino acids but proline accumulated markedly in both varieties. However, no relationship was found between proline levels and CMS. The results demonstrated that CMS test can also be used under in vitro conditions to differentiate the drought tolerant and susceptible cultivars and the cellular K level has a positive relationship with membrane stability.     

Dynamic Model of Leaf Photosynthesis with Acclimation to Light and Nitrogen

A simple model of photosynthesis in a mature C₃leaf is described,based on a non-rectangular hyperbola: the model allows the high-lightasymptote of that equation (P_max) to respond dynamically tolight and nitrogen. This causes the leaf light response equationto acclimate continuously to the current conditions of lightand N nutrition, which can vary greatly within a crop canopy,and through a growing season, with important consequences forgross production. Predictions are presented for the dynamicsof acclimation, acclimated and non-acclimated photosyntheticrates are compared, and the dependence of leaf properties onlight and N availability is explored. There is good correspondenceof predictions with experimental results at the leaf level.The model also provides a mechanism for a down regulation ofphotosynthesis in response to increased carbon dioxide concentrations,whose magnitude will depend on conditions, particularly of nitrogennutrition.Copyright 1998 Annals of Botany Company Leaf, photosynthesis, hyperbola, model, C₃, acclimation, light, nitrogen.     

飞机草和兰花菊三七光合作用对生长光强的适应

测定了干季不同光强下生长的飞机草和兰花菊三七叶片最大净光合速率(Pmax)、荧光动力学参数、叶绿素含量和比叶重(LMA),研究了两种植物适应光环境的策略,探讨了其与入侵性的关系.100%光强下,两种植物主要通过降低捕光色素复合体Ⅱ的含量减少光能吸收,提高Pmax增加光能利用维持叶片能量平衡,而它们的热耗散能力并不强,均显著低于其它光强下的值.100%光强下,提高类胡萝卜素含量是飞机草耗散过剩能量的有效策略,而兰花菊三七可能有其它耗散途径.4.5%光强下仅飞机草能够存活,它通过降低LMA、维持很低的日间热耗散和较高的光合系统Ⅱ非环式电子传递效率适应了弱光环境.推测对强光环境较强的适应能力是入侵植物的共性之一,但这种能力强不一定入侵性大.     

Chlorophyll Fluorescence Analysis of Cyanobacterial Photosynthesis and Acclimation

Cyanobacteria are ecologically important photosynthetic prokaryotes that also serve as popular model organisms for studies of photosynthesis and gene regulation. Both molecular and ecological studies of cyanobacteria benefit from real-time information on photosynthesis and acclimation. Monitoring in vivo chlorophyll fluorescence can provide noninvasive measures of photosynthetic physiology in a wide range of cyanobacteria and cyanolichens and requires only small samples. Cyanobacterial fluorescence patterns are distinct from those of plants, because of key structural and functional properties of cyanobacteria. These include significant fluorescence emission from the light-harvesting phycobiliproteins; large and rapid changes in fluorescence yield (state transitions) which depend on metabolic and environmental conditions; and flexible, overlapping respiratory and photosynthetic electron transport chains. The fluorescence parameters F_V/F_M, F_V′/F_M′,q_p,q_N, NPQ, and PS II were originally developed to extract information from the fluorescence signals of higher plants. In this review, we consider how the special properties of cyanobacteria can be accommodated and used to extract biologically useful information from cyanobacterial in vivo chlorophyll fluorescence signals. We describe how the pattern of fluorescence yield versus light intensity can be used to predict the acclimated light level for a cyanobacterial population, giving information valuable for both laboratory and field studies of acclimation processes. The size of the change in fluorescence yield during dark-to-light transitions can provide information on respiration and the iron status of the cyanobacteria. Finally, fluorescence parameters can be used to estimate the electron transport rate at the acclimated growth light intensity.     

Polyethylene glycol-induced mammalian cell hybridization: effect of polyethylene glycol molecular weight and concentration.

The effects of polyethylene glycol (PEG) molecular weight and concentration on mammalian cell hybridization were studied. The peak hybridization-inducing activity with all grades of PEG from 400-6000 was found to occur in the concentration range of 50-55%. However, changes in concentration were seen to have different quantitative effects with different grades of PEG. For monolayer fusions, PEG 1000 at 50% seems to be the optimal combination of PEG molecular weight and concentration, in terms of both efficiency of hybridization and relative insensitivity to dilution effects.     

Acclimation and adaptive responses of woody plants to environmental stresses

The predominant emphasis on harmful effects of environmental stresses on growth of woody plants has obscured some very beneficial effects of such stresses. Slowly increasing stresses may induce physiological adjustment that protects plants from the growth inhibition and/or injury that follow when environmental stresses are abruptly imposed. In addition, short exposures of woody plants to extreme environmental conditions at critical times in their development often improve growth. Furthermore, maintaining harvested seedlings and plant products at very low temperatures extends their longevity. Drought tolerance: Seedlings previously exposed to water stress often undergo less inhibition of growth and other processes following transplanting than do seedlings not previously exposed to such stress. Controlled wetting and drying cycles often promote early budset, dormancy, and drought tolerance. In many species increased drought tolerance following such cycles is associated with osmotic adjustment that involves accumulation of osmotically active substances. Maintenance of leaf turgor often is linked to osmotic adjustment. A reduction in osmotic volume at full turgor also results in reduced osmotic potential, even in the absence of solute accumulation. Changes in tissue elasticity may be important for turgor maintenance and drought tolerance of plants that do not adjust osmotically. Water deficits and nutrient deficiencies promote greater relative allocation of photosynthate to root growth, ultimately resulting in plants that have higher root:shoot ratios and greater capacity to absorb water and minerals relative to the shoots that must be supported. At the molecular level, plants respond to water stress by synthesis of certain new proteins and increased levels of synthesis of some proteins produced under well-watered conditions. Evidence has been obtained for enhanced synthesis under water stress of water-channel proteins and other proteins that may protect membranes and other important macromolecules from damage and denaturation as cells dehydrate. Flood tolerance: Both artificial and natural flooding sometimes benefit woody plants. Flooding of orchard soils has been an essential management practice for centuries to increase fruit yields and improve fruit quality. Also, annual advances and recessions of floods are crucial for maintaining valuable riparian forests. Intermittent flooding protects bottomland forests by increasing groundwater supplies, transporting sediments necessary for creating favorable seedbeds, and regulating decomposition of organic matter. Major adaptations for flood tolerance of some woody plants include high capacity for producing adventitious roots that compensate physiologically for decay of original roots under soil anaerobiosis, facilitation of oxygen uptake through stomata and newly formed lenticels, and metabolic adjustments. Halophytes can adapt to saline water by salt tolerance, salt avoidance, or both. Cold hardiness: Environmental stresses that inhibit plant growth, including low temperature, drought, short days, and combinations of these, induce cold hardening and hardiness in many species. Cold hardiness develops in two stages: at temperatures between 10° and 20°C in the autumn, when carbohydrates and lipids accumulate; and at subsequent freezing temperatures. The sum of many biochemical processes determines the degree of cold tolerance. Some of these processes are hormone dependent and induced by short days; others that are linked to activity of enzyme systems are temperature dependent. Short days are important for development of cold hardiness in species that set buds or respond strongly to photoperiod. Nursery managers often expose tree seedlings to moderate water stress at or near the end of the growing season. This accelerates budset, induces early dormancy, and increases cold hardiness. Pollution tolerance: Absorption of gaseous air pollutants varies with resistance to flow along the pollutant’s diffusion path. Hence, the amount of pollutant absorbed by leaves depends on stomatal aperture, stomatal size, and stomatal frequency. Pollution tolerance is increased when drought, dry air, or flooding of soil close stomatal pores. Heat tolerance: Exposure to sublethal high temperature can increase the thermotolerance of plants. Potential mechanisms of response include synthesis of heat-shock proteins and isoprene and antioxidant production to protect the photosynthetic apparatus and cellular metabolism. Breaking of dormancy: Seed dormancy can be broken by cold or heat. Embryo dormancy is broken by prolonged exposure of most seeds to temperatures of 1° to 15°C. The efficiency of treatment depends on interactions between temperature and seed moisture content. Germination can be postponed by partially dehydrating seeds or altering the temperature during seed stratification. Seed-coat dormancy can be broken by fires that rupture seed coats or melt seedcoat waxes, hence promoting water uptake. Seeds with both embryo dormancy and seed-coat dormancy may require exposure to both high and low temperatures to break dormancy. Exposure to smoke itself can also serve as a germination cue in breaking seed dormancy in some species. Bud dormancy of temperate-zone trees is broken by winter cold. The specific chilling requirement varies widely with species and genotype, type of bud (e.g., vegetative or floral bud), depth of dormancy, temperature, duration of chilling, stage of plant development, and daylength. Interruption of a cold regime by high temperature may negate the effect of sustained chilling or breaking of bud dormancy. Near-lethal heat stress may release buds from both endodormancy and ecodormancy. Pollen shedding: Dehiscence of anthers and release of pollen result from dehydration of walls of anther sacs. Both seasonal and diurnal pollen shedding are commonly associated with shrinkage and rupture of anther walls by low relative humidity. Pollen shedding typically is maximal near midday (low relative humidity) and low at night (high relative humidity). Pollen shedding is low or negligible during rainy periods. Seed dispersal: Gymnosperm cones typically dehydrate before opening. The cones open and shed seeds because of differential shrinkage between the adaxial and abaxial tissues of cone scales. Once opened, cones may close and reopen with changes in relative humidity. Both dehydration and heat are necessary for seed dispersal from serotinous (late-to-open) cones. Seeds are stored in serotinous cones because resinous bonds of scales prevent cone opening. After fire melts the resinous material, the cone scales can open on drying. Fires also stimulate germination of seeds of some species. Some heath plants require fire to open their serotinous follicles and shed seeds. Fire destroys the resin at the valves of follicles, and the valves then reflex to release the seeds. Following fire the follicles of some species require alternate wetting and drying for efficient seed dispersal. Stimulation of reproductive growth: Vegetative and reproductive growth of woody plants are negatively correlated. A heavy crop of fruits, cones, and seeds is associated with reduced vegetative growth in the same or following year (or even years). Subjecting trees to drought during early stages of fruit development to inhibit vegetative growth, followed by normal irrigation, sometimes favors reproductive growth. Short periods of drought at critical times not only induce formation of flower buds but also break dormancy of flower buds in some species. Water deficits may induce flowering directly or by inhibiting shoot flushing, thereby limiting the capacity of young leaves to inhibit floral induction. Postharvest water stress often results in abundant return bloom over that in well-irrigated plants. Fruit yields of some species are not reduced or are increased by withholding irrigation during the period of shoot elongation. In several species, osmotic adjustment occurs during deficit irrigation. In other species, increased fruit growth by imposed drought is not associated largely with osmotic adjustment and maintenance of leaf turgor. Seedling storage: Tree seedlings typically are stored at temperatures just above or below freezing. Growth and survival of cold-stored seedlings depend on such factors as: date of lifting from the nursery; species and genotype; storage temperature, humidity, and illumination; duration of storage; and handling of planting stock after storage. Seedlings to be stored over winter should be lifted from the nursery as late as possible. Dehydration of seedlings before, during, and after storage adversely affects growth of outplanted seedlings. Long-term storage of seedlings may result in depletion of stored carbohydrates by respiration and decrease of root growth potential. Although many seedlings are stored in darkness, a daily photoperiod during cold storage may stimulate subsequent growth and increase survival of outplanted seedlings. For some species, rapid thawing may decrease respiratory consumption of carbohydrates (over slowly thawed seedlings) and decrease development of molds. Pollen storage: Preservation of pollen is necessary for insurance against poor flowering years, for gene conservation, and for physiological and biochemical studies. Storage temperature and pollen moisture content largely determine longevity of stored pollen. Pollen can be stored successfully for many years in deep freezers at temperatures near −15°C or in liquid nitrogen (−196°C). Cryopreservation of pollen with a high moisture content is difficult because ice crystals may destroy the cells. Pollens of many species do not survive at temperatures below −40°C if their moisture contents exceed 20–30%. Pollen generally is air dried, vacuum dried, or freeze dried before it is stored. To preserve the germination capacity of stored pollen, rehydration at high humidity often is necessary. Seed storage: Seeds are routinely stored to provide a seed supply during years of poor seed production, to maintain genetic diversity, and to breed plants. For a long time, seeds were classified as either orthodox (relatively long-lived, with capacity for dehydration to very low moisture contents without losing viability) or recalcitrant (short-lived and requiring a high moisture content for retention of viability). More recently, some seeds have been reclassified as suborthodox or intermediate because they retain viability when carefully dried. True orthodox seeds are preserved much more easily than are nonorthodox seeds. Orthodox seeds can be stored for a long time at temperatures between 2° and −20°C, with temperatures below −5°C preferable. Some orthodox seeds have been stored at superlow temperatures, although temperatures of −40°, −70°, or −196°C have not been appreciably better than −20°C for storage of seeds of a number of species. Only relatively short-term storage protocols have been developed for nonorthodox seeds. These treatments typically extend seed viability to as much as a year. The methods often require cryopreservation of excised embryos. Responses to cryopreservation of nonorthodox seeds or embryos vary with species and genotype, rate of drying, use of cryoprotectants, rates of freezing and thawing, and rate of rehydration. Fruit storage: Storing fruits at low temperatures above freezing, increasing the CO₂ concentration, and lowering the O₂ concentration of fruit storage delays senescence of fruits and prolongs their life. Fruits continue to senesce and decay while in storage and become increasingly susceptible to diseases. Both temperate-zone and tropical fruits may develop chilling injury characterized by lesions, internal discoloration, greater susceptibility to decay, and shortened storage life. Chilling injury can be controlled by chemicals, temperature conditioning, and intermittent warming during storage. Stored fruits may become increasingly susceptible to disease organisms. Fruit diseases can be controlled by cold, which inhibits growth of microorganisms and maintains host resistance. Exposure of fruits to high CO₂ and low O₂ during storage directly suppresses disease-causing fungi. Pathogens also can be controlled by exposing fruits to heat before, during, and after storage. Scald that often develops during low-temperature storage can be controlled by chemicals and by heat treatments.     

Photosynthesis and chlorophyll fluorescence responses of Populus sibirica to water deficit in a desertification area in Mongolia

In the present study, photosynthetic traits and chlorophyll (Chl) fluorescence parameters of Populus sibirica grown under different irrigation regimes were investigated to estimate seedling growth and vitality for reforestation of a desertification area. According to our results, photosynthesis and Chl fluorescence were significantly affected by water deficit only under severe drought conditions.     

Morphogenesis of potato plants in vitro. I. Effect of light quality and hormones

Stem cuttings of potato plants (Solanum tuberosum L., cv. Miranda) were cultured in vitro on MS medium with sucrose either without or with addition of indole-3-acetic acid (IAA) or kinetin (K) under red light (R) or blue light (B). Plants on medium without hormones under R were thin, long, with very small leaves, and produced no or only a few microtubers (after longer-lasting cultivations). In B, plants remained short, thick, with large, wellde-veloped leaves and produced a significant amount of microtubers. Darkening of both roots and shoots strongly promoted tuber formation; the tubers were formed on the darkened part of the plant. IAA had no pronounced effect on plant development in B except for slight lengthening of the stem, and, in longer cultivations, slightly enhanced tuber formation as well. In R, IAA brought about several significant effects: stem reduction and induction of tuber formation being the most significant. Kinetin in R increased tuber formation slightly. In B, kinetin not only strongly stimulated tuber formation, but also increased the total fresh weight and root (+ stolons)/shoot ratio. Results are discussed with regard to the possible role of auxins and/or cytokinins in mediating the morphogenetic effects of light.     

Alterations in growth and metabolism of potato plants by calcium deficiency

Summary Experiment in water culture was conducted to evaluate the calcium deficiency symptoms and their cause inSolanum tuberosum L. var. Chandramukhi. Meristematic regions at stem and roots were severely affected and ultimately ceased to grow. Plants remained stunted with few and smaller tubers. Reducing sugar, non-reducing sugar and starch accumulated more in the leaves and stems and less in roots and tubers of calcium deficient plants. Deficiency caused decrease in protein nitrogen, RNA, DNA and increase in soluble nitrogen in all the plant parts. Potassium, phosphorus, calcium and sodium contents were lower and magnesium content higher in the deficient plant, than that of the healthy ones. Morphological symptoms of calcium deficiency can be established by ionic balance and accumulation of oxalic acid in potato plants.     

The isolation of potato virus S from the leaves of potato plants using precipitation by polyethylene glycol

A purified potato virus S was prepared using precipitation by the solution of 35% polyethylene glycol 4000 in the presence of an electrolyte. The mixture for precipitation of the potato virus S had to contain 11% polyethylene glycol and 0·25m NaCl. The S virus was extracted by 0·01m phosphate buffer, pH 7·5, from the precipitation separated by centrifugation. One part of the extract was further purified by means of differential centrifugation and the other by means of gel filtration on Sephadex G-100. The ultraviolet absorption measurements of both preparations showed that the differential centrifugation gave a purer preparation than the gel filtration.