Effect of decreased rate of water absorption on water balance of leaf tissue

The influence of decrease of water absorption rate on the transpiration rate and the development of water saturation deficit (WSD) was studied on the leaf segments of kale. Solutions of polyethyleneglycol (0-25m, 0-50m, O-75m and 1-00m) and mannitol (0-50m) were used as osmotic agents. The rate of water absorption decreased to zero when the concentration of polyethyleneglycol was 0-25m. At a concentration higher than 0-50m, water from the tissue diluted the external solution. The transpiration rate of samples affected by polyethyleneglycol or mannitol was only a little lower than that of control samples. WSD was noticeably increased only in the absorbing part of segment; in the adjoining, transporting part of segment WSD was practically the same in all variants. WSD in the transpiring part was slightly increased only in some cases. Due to decrease of osmotic potential of the external solution also the gradient of water potential changed. In the case of absorption from pure water, water potential gradually decreased from the absorbing to the transpiring part. Under the influence of polyethyleneglycol or mannitol solution the highest water potential was in the transporting part and from this point water potential decreased to both opposite sides.     

Effects of Extended Periods of Osmotic Stress on Water Relationships of Pepper

Pepper plants grown to uniform size in a controlled environment were subjected to an osmotic stress for periods of 1 to 10 days. Polyethylene glycol 400 was used as the osmotic agent. Leaf area of the plants, grown under uniform conditions, was proportional to the weight of the plants. This relationship was not altered by reduction in rate of growth due to a decrease in osmotic potential of the nutrient solution. The rate of transpiration of the pepper plants decreased as the osmotic potential of the nutrient solution was decreased. The reduction in rate of transpiration was most rapid when the osmotic potential was reduced from ?0.5 to ?7.5 bars. There was continued reduction in the rate of transpiration with change in potential to ?12.5 bar but this change was less than that at the higher potentials. The rate of transpiration remained at a reduced rate for as long as the plants were growing in the solution with low osmotic potential. Alternating the osmotic potential of the nutrient solution between ?0.5 and ?5.0 bar did not change the response to the ?5.0 tension. The reduction in rate of transpiration resulting from the lowering of the osmotic potential by addition of NaCl was similar to that produced by addition of polyethylene glycol. Water potential, osmotic potential, relative water content and stomatal movement were all in dynamic equilibrium with the water content of the leaves. The water content of the leaves was regulated by the supply and demand. In these investigations the demand remained constant. The supply was altered by decreasing the difference in water potential between leaf and substrate and by an increase in resistance to flow of water in the roots as a result of the decrease in osmotic potential of the nutrient solution.     

Mineral nutrition and the water relations of plants

Summary When young tomato plants were transferred from nutrient solution to mineral-free water, reductions in transpiration, water content of the shoots and stomatal aperture were not accompanied by a reduction in the relative water content or an increase in the suction pressure of the leaves. The relative water content of the leaves was increased and the suction pressure was little affected.Following transfer of the plants to mineral-free water, the mineral content of the shoots and the osmotic pressure of expressed leaf sap were reduced. It was concluded that mineral salts were necessary for maintaining the osmotic pressure of the leaf cell sap and that this was achieved, at least in part, by maintaining the mineral concentration of the sap. The amount of water that could be taken up by leaves and their turgor pressure were related to the osmotic pressure of the sap and calculations of turgor pressure showed that it was less in the leaves of plants with their roots in mineral-free water than in the leaves of plants in nutrient solution.Evidence was obtained that in leaflets detached from plants with their roots in mineral-free water, stomatal closure could occur at a higher water content than in leaflets detached from plants in nutrient solution, indicating a further role of minerals in leaf water relations. It is suggested that this role may be related to the properties of the cell walls.     

The Role of Hormones in Fast Growth Responses of Wheat Plants to Osmotic and Cold Shocks

The effects of nutrient-solution cooling and PEG addition to the nutrient solution on the phytohormone content, the rate of leaf growth, leaf extensibility under the influence of external mechanical action, osmotic potential, and transpiration were studied in seven-day-old wheat plants. Leaf growth rapidly ceased, and the transpiration rate was reduced in both treatments. Growth cessation induced by PEG was transient, and growth resumption was preceded by an increase in the leaf extensibility. The functional role of auxin accumulation in plant shoots in the control of extensibility as well as the relationship between the ABA accumulation and a decrease in the cytokinin content, on the one hand, and reduced transpiration, on the other hand, under stress conditions are discussed.     

The Relationship between Transpiration and the Absorption of Inorganic Ions by Intact Plants

The relationship between the rate at which water and the rubidiumand phosphate ions are absorbed by intact plants, and transferredto their shoots has been investigated in water culture undervarying conditions of transpiration and nutrient supply. When the external concentration and the nutrient status of theplants are sufficient low, wide variations in the rate of transpirationhave little effect on the transfer of nutrients to shoots; whenlittle water is being lost by transpiration the concentrationin the transpiration stream may exceed that in the externalmedium by factors exceeding 100. In contrast when the externalconcenration and the nutrient status of the plants are highthe rate of transfer of ions to shoots may vary closely withthe rate of transpiration and the concentration in the transpirationstream may be similar to, or less then, that in the externalmedium. The occurrence of concentrations of ions in the roots is transpirationstream which greatly exceed those in the medium external tothe roots is regarded as evidence that ions not transferredpassively across the roots of intact plants to a significantextent.     

Quantitative Determinations of the Effect of Excision on Transpiration

The temporary transpiration increase which normally occurs when a shoot or a part of a shoot is cut off in the air was studied qnantitatively in young wheat plants by the aid of the corona-hygrometer. The temporary transpiration increase can be characterized by the maximum increase in transpiration rate after the cutting, or by the total time of the temporary transpiration increase, or by the quantity of water given off by the shoot due to the temporary transpiration increase. The influences of the water vapour pressure, the speed of the air stream, and the light intensity on the temporary transpiration increase were determined. It is important to pay attention to the climate in the chamber where the shoot transpires. The maximum temporary transpiration increase was reduced more or less lineary with increasing water vaponr pressure of the air surrounding the shoot and increased with increasing speed of the air stream through the transpiration chamber. The reduction of the maximum temporary transpiration increase at higher light intensities was mainly due to the higher water vapour pressure in the chamber. The total time of the temporary transpiration increase was very little influenced by the water vapour pressure but was reduced more or less lineary with the logarithm of increasing light intensity. When the shoot was cut off in the water, there was normally no temporary transpiration increase. Only at low light intensities there could occur temporary transpiration increases similar to those found when the shoot was cut off in the air. Some hypotheses which could explain the temporary transpiration increase are discussed. The results in this investigation seem to favour the hypothesis that the temporary transpiration increase is due to a sudden reduced water transport up into the leaf, which can bring about a passive opening of the stomata.     

Changes in Transpiration, Net Carbon Dioxide Assimilation and Leaf Water Potential Resulting from Application of Hydrostatic Pressure to Roots of Intact Pepper Plants

Hydrostatic pressures varying from 0 to 6.0 bar were applied to roots of intact Capsicum annuum L. cv. California Wonder plants growing in nutrient solution and the rates of transpiration, and net CO₂ assimilation, apparent compensation point and leaf water potential measured. Increasing the pressure on the roots of plants with roots in solution with either -0.5 or -5.0 bar osmotic potential with 1 bar increments resulted in a decrease in transpiration. With the application of 1 or 2 bar pressure the rate of transpiration returned to near or above the original rate. An application of 3 or 4 bar pressure reduced the rate of transpiration of all plants. The transpiration of plants with roots in solution with -0.5 bar osmotic potential remained at the reduced rate for as long as these pressures were maintained. The transpiration of plants with roots in solution with -5.0 bar was only temporarily suppressed at these pressures. Changing the applied pressure from 3 or 4 bar to 0 resulted in a rapid increase in transpiration which lasted approximately 15 minutes. This was followed by a decrease in transpiration to a rate lower than before the pressure was applied. The pattern of response was similar for plants at low or high light intensity or at normal or low CO₂ concentrations. When leaf diffusive resistance was 6.0 s cm^?1 or greater, changes in net CO₂ assimilation were similar to those of transpiration. The apparent CO₂ compensation point increased as pressure was applied and decreased with a release in pressure. Leaf water potential increased with an increase in pressure and decreased with a decrease in pressure. The changes in leaf water potential were frequently but not always proportional to changes in pressure. It is postulated that the respouses noted were due to changes in resistance to flow of water from xylem terminals through the mesophyll cells and stomatal cavities to the atmosphere.     

Effects of turgor potential on 1-aminocyclopropane-1-carboxylic acid uptake into the vacuolar compartment and ethylene production in tomato pericarp slices

While solute transport and ethylene production by plant tissue are sensitive to the osmotic concentration of the solution bathing the tissue, the influence of tissue water relations and specifically tissue turgor potential on the kinetics of 1-aminocyclopropane-1-carboxylic acid (ACC) uptake into the vacuolar compartment and ethylene production have not been examined. 1-Aminocyclopropane-1-carboxylic acid transport and ethylene production were examined in tomato (Lycopersicon esculentum Mill. cv. Liberty) pericarp slices incubated in solutions having a range of mannitol, polyethylene glycol 3350 and ethylene glycol concentrations known to affect tissue water relations. Tissue osmotic and turgor potentials were derived from osmolality measurements of cell saps recovered by freeze-thawing and corrected for the contribution of the free-space solution. When relatively nonpermeable (mannitol or polyethylene glycol 3350) osmotica were used, both ACC uptake and ethylene production were greatest at a solution osmolality of 230 milliosmolal where tissue turgor potential ranged between 120 and 140 kPa. At higher and lower turgor potentials, the high-affinity saturating component of ACC uptake and ethylene production were inhibited, and ACC efflux from the vacuolar compartment was increased. The inhibition of ACC uptake was evident as a decrease in V_max with no effect on K_m. Turgor potential changes caused by adjusting solution osmolality with mannitol or polyethylene glycol 3350 were accompanied by changes in the osmotic potential and water potential of the tissue. The effects of turgor potential vs the osmotic and water potentials of tomato pericarp slices were differentiated by comparing responses to nonpermeable osmotica and mixtures of nonpermeable and permeable osmotica. Ethylene glycol-mannitol mixtures had effects on the osmotic potential and water potential of the tissue similar to those of nonpermeable osmotica but had less effect on tissue turgor, ACC transport and ethylene production. Incubating tissue in solutions without nonpermeable osmotica osmotically shocked the tissue. Increasing solution osmolality with ethylene glycol in the absence of nonpermeable osmotica increased tissue turgor and ethylene production. The present study indicates that tissue turgor is an important factor affecting the kinetics of ACC uptake into the vacuolar compartment and ethylene production in tomato pericarp slices.     

Osmotic Behavior of Oat Coleoptile Tissue in Relation to Growth

Efforts were made to estimate the water potential difference that is required, between rapidly growing oat coleoptile cylinders and dilute medium, to support the rate of water uptake involved in elongation, (a) by the traditional method of determining the concentration of mannitol in which the tissue neither gains nor loses water, and (b) by measuring the rates of osmotic exchanges induced by treating the tissue with different hypotonic mannitol concentrations. Both methods indicated large water potential differences (3 to 10 atm), in some cases approaching the osmotic pressure of the cells. However, indication was obtained that the rates of osmotic exchanges induced by mannitol solutions, and presumably also the equilibrium response sought in (a), are governed by the rate of diffusional exchange of mannitol with the free space rather than by the permeability of the tissue to water. Osmotic swelling of the tissue measured by immersing it in water after its turgor pressure had been reduced by evaporation, was at least two to four times more rapid than when mannitol was involved. The permeability to water estimated by the evaporation-immersion method indicated that rapidly elongating cylinders have water potentials between -0.8 and -2.5 atm, or between 10 and 25 per cent of their osmotic pressure.     

How do salinity and water stress affect transport of water,assimilates and ions to tomato fruits?

The study was conducted in order to determine whether water stress affects the accumulation of dry matter in tomato fruits similarly to salinity, and whether the increase in fruit dry matter content is solely a result of the decrease in water content. Although the rate of water transport to tomato fruits decreased throughout the entire season in saline water irrigated plants, accumulation rates of dry matter increased significantly. Phloem water transport contributed 80–85% of the total water transport in the control and water-stressed plants, and over 90% under salinity. The concentration of organic compounds in the phloem sap was increased by 40% by salinity. The rate of ions transported via the xylem was also significantly increased by salinity, but their contribution to fruit osmotic adjustment was less. The rate of fruit transpiration was also markedly reduced by salinity. Water stress also decreased the rate of water transport to the tomato fruit and increased the rate of dry matter accumulation, but much less than salinity. The similar changes, 10–15%, indicate that the rise in dry matter accumulation was a result of the decrease in water transport. Other parameters such as fruit transpiration rates, phloem and xylem sap concentration, relative transport via phloem and xylem, solutes contributing to osmotic adjustment of fruits and leaves, were only slightly affected by water stress. The smaller response of these parameters to water stress as compared to salinity could not be attributed to milder stress intensity, as leaf water potential was found to be more negative. Measuring fruit growth of girdled trusses, in which phloem flow was inactive, and comparing it with ungirdled trusses validated the mechanistic model. The relative transport of girdled as compared to ungirdled fruits resembled the calculated values of xylem transport.     

Water stress effects on leaf elongation,leaf water potential,transpiration, and nutrient uptake of rice,maize, and soybean

A pot experiment was conducted in the greenhouse to determine and compare the responses of rice (Oryza sativa L. var, IR 36), maize (Zea mays L. var. DMR-2), and soybean (Glycine max [L.] Merr. var. Clark 63) to soil water stress. Leaf elongation, dawn leaf water potential, transpiration rate, and nutrient uptake in stressed rice declined earlier than in maize and soybean. Maize and soybean, compared with rice, maintained high dawn leaf water potential for a longer period of water stress before leaf water potential. Nutrient uptake under water stress conditions was influenced more by the capacity of the roots to absorb nutrients than by transpiration. Transport of nutrients to the shoots may occur even at reduced transpiration rate It is concluded that the ability of maize and soybean to grow better than rice under water stress conditions may be due to their ability to maintain turgor as a result of the slow decline in leaf water potential brought about by low, transpiration rate and continued uptake of nutrient, especially K, which must have allowed osmotic adjustment to occur.     

Uptake and transport of lead by perennial ryegrass from flowing solution culture with a controlled concentration of lead

Summary Perennial ryegrass was grown in flowing solution culture in a glasshouse, and during February lead was added to the nutrient solution and held at a constant concentration; uptake and transport of lead were followed in conditions of low intensity daylight or higher intensity artificial light. Uptake of lead by the roots was most rapid during the first 4 days after addition to the nutrient solution. After this time there was a steady increase in uptake per g dry weight of root with plants grown in artificial light having a much higher rate of uptake than plants grown in daylight. Roots always contained more lead than the corresponding shoots and concentration was always greater in the roots than in the shoots. The concentration in both roots and shoots increased with time but that in plants grown in artificial light was higher than that in plants grown in daylight. Two phases of uptake were identified, an initial rapid phase which is probably an exchange phenomenon, and a slow sustained phase which may be under metabolic control. A lower proportion of the total lead taken up remained in the roots of plants grown in artificial light than in those grown in daylight. This difference may have resulted from differences in (i) the production of organic carriers and/or (ii) transpiration. re]19750930     

Silicon decreases chloride transport in rice (Oryza sativa L.) in saline conditions

Silicon can alleviate salt damage to plants, although the mechanism(s) still remains to be elucidated. In this paper, we report the effect of silicon on chloride transport in rice (Oryza sativa L.) seedlings in saline conditions. In the absence of salinity, silicon enhanced the growth of shoots, but not roots in three cultivars (cv. GR4, IR36, and CSR10). Salinity reduced the growth of both shoots and roots in all three genotypes. In saline conditions, addition of silicon to the culture solution again improved the growth of shoots, but not of roots. Under these saline conditions, the concentrations of chloride in the shoot were markedly decreased by adding silicon and the ratio of K⁺/Cl⁻ was significantly increased, while the concentration of chloride in the roots was unchanged. The decrease in chloride concentration in the shoot was correlated with the decrease in transpirational bypass flow in rice, as shown by the transport of the apoplastic tracer trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS). Addition of silicon increased the net photosynthetic rate, stomata conductance, and transpiration of salt-stressed plants in cv. IR36, indicating that the reduction of chloride (and sodium) uptake by silicon was not through a reduction in transpiration rate. Silicon addition also increased the instantaneous water use efficiency of salt-stressed plants, while it did not change the relative growth rate of shoots. The results suggest that silicon addition decreased transpirational bypass flow in the roots, and therefore decreased the transport of chloride to the shoot.     

The Effect of Root Temperatures on Water and Sulphate Absorption in Intact Sunflower Plants

The effect of 15, 25, and 35°C root temperature on waterabsorption, transpiration, and sulphate uptake by the rootsand transport to the shoots of intact sunflower plants has beenstudied using 0.5, 5.0, and 50.0 mM sulphate concentrationsat two rates of transpiration induced (1) by light and low relativehumidity and (2) by darkness and high relative humidity. Root temperatures and sulphate concentrations did not significantlyaffect the water absorption and transpiration and both theseprocesses were approximately similar at the different treatments.There was a nearly twofold increase in water absorption andtranspiration in the light and low relative humidity as comparedto the dark and high relative humidity irrespective of the roottemperatures and sulphate concentrations. The A.F.S. uptake in the roots was found to be independent ofthe root temperatures, sulphate concentrations, and transpirationrates, and amounted to 15 to 21 per cent based on the root weight.Sulphate accumulation in the roots was not significantly influencedby the root temperatures at 0.5 and 5.0 mM sulphate concentrations,but nearly doubled with temperature at 50.0 mM sulphate concentrationof the external solution. The slow nature of accumulation ofsulphate, the high sulphate status of the experimental plants,and the short duration of the experiments are considered aslikely reasons for the absence of a clear effect of temperatureson accumulation of sulphate at the two lower concentrationsof the external solution. Effects of high concentration on permeabilityand metabolism of the cells are suggested as the reasons forthe decreased accumulation with an increase in temperature at50.0 mM sulphate concentration. Accumulation of sulphate inthe roots was not significantly influenced by the transpirationrates. Unlike root accumulation, sulphate transport to the shoots increasedwith increasing transpiration. However, a major part of thesulphate transport (70 to 75 per cent at 0.5 and 5.0 mM sulphateconcentrations and 80 to 85 per cent at 50.0 mM sulphate concentration)appeared to have occurred at the low transpiration. The similarityof this transport to the accumulation of sulphate in the rootsindicates that it was due to an active transport process sensitiveto root temperatures and sulphate concentrations. A low concentrationof sulphate in the xylem and an increased permeability of theroot cells to ion movement induced by an increased suction inthe xylem are considered as reasons for a small increase inthe sulphate transport at high transpiration rate. The evidencefor the existence of a barrier—probably endodermis—preventingthe passive diffusion of sulphate and sensitivity of the TranspirationStream Concentration to root temperatures and sulphate concentrationsfavour that the increased transport with increased transpirationwas due to an active process.     

Root cooling strongly affects diel leaf growth dynamics,water and carbohydrate relations in Ricinus communis

In laboratory and greenhouse experiments with potted plants, shoots and roots are exposed to temperature regimes throughout a 24 h (diel) cycle that can differ strongly from the regime under which these plants have evolved. In the field, roots are often exposed to lower temperatures than shoots. When the root‐zone temperature in Ricinus communis was decreased below a threshold value, leaf growth occurred preferentially at night and was strongly inhibited during the day. Overall, leaf expansion, shoot biomass growth, root elongation and ramification decreased rapidly, carbon fluxes from shoot to root were diminished and carbohydrate contents of both root and shoot increased. Further, transpiration rate was not affected, yet hydrostatic tensions in shoot xylem increased. When root temperature was increased again, xylem tension reduced, leaf growth recovered rapidly, carbon fluxes from shoot to root increased, and carbohydrate pools were depleted. We hypothesize that the decreased uptake of water in cool roots diminishes the growth potential of the entire plant – especially diurnally, when the growing leaf loses water via transpiration. As a consequence, leaf growth and metabolite concentrations can vary enormously, depending on root‐zone temperature and its heterogeneity inside pots.     

Osmotic adjustment,water relations and growth attributes of the xero-halophyte <Emphasis Type="Italic">Reaumuria vermiculata</Emphasis> L. (Tamaricaceae) in response to salt stress

Reaumuria vermiculata (L.), a perennial dwarf shrub in the family of Tamaricaceae, is a salt-secreting xero-halophyte found widely in arid areas of Tunisia. In the present study, physiological attributes of R. vermiculata were investigated under salt stress. Four-month-old plants were subjected to various salinity levels (0, 100, 200, 300, 400 or 600 mM NaCl) for 30 days under greenhouse conditions. Results showed that plants grew optimally when treated with standard nutrient solution without NaCl supply. However, increasing osmolality of nutrient solutions caused a significant reduction in biomass production and relative growth rate. This reduction was more pronounced in roots than in shoots. In addition, this species was able to maintain its shoot water content at 30% of the control even when subjected to the highest salt level, whereas root water content seemed to be unaffected by salt. Shoot water potential declined significantly as osmotic potential of watering solutions was lowered and the more negative values were reached at 600 mM NaCl (−3.4 MPa). Concentrations of Na⁺ and Cl⁻ in the shoots of R. vermiculata were markedly increased with increasing osmolality of nutrient solutions, whereas concentration of K⁺ was not affected by NaCl supply. Salt excretion is an efficient mechanism of Na⁺ exclusion from the shoots of this species exhibiting high K⁺/Na⁺ selectivity ratio over a wide range of NaCl salinity. Proline accumulation in shoots was significantly increased with increase in salt level and may play a role in osmoregulation.     

The Comparative Drought Resistance of Landraces of Sorghum and Millet From Dry and Humid Regions

It may be that land-races of sorghum (Sorghum sp.) and millet[Pennisetum americanum (L.) Leeke] which evolved along geographicalgradients of rainfall in Africa and India, differ in their droughtresistance. Any physiological attributes found to be correlatedwith low rainfall might be important and effective characteristicsfor crop production in dry regions. Twenty land-races were chosen which evolved along geographicalgradients of rainfall, seven millets from India, six sorghumsfrom Mali, and seven sorghums from the Sudan. Races were evaluatedfor their growth potential and plant water relations under hydroponicsconditions in a growth chamber. A water stress treatment wasimposed by adding polyethylene glycol-8000 to the nutrient solution,giving a solute water potential of -0.5 MPa, compared with acontrol solution at 003 MPa. Drought resistance, in terms of relatively less growth inhibitionunder stress, was higher in races from dry regions than in racesfrom humid regions. Of all the physiological variables measured[carbon exchange rate, (CER), transpiration, transpiration ratio(CER/transpiration), leaf diffusive resistance, leaf water potentialand osmotic adjustment], only osmotic adjustment under stresswas generally correlated with average rainfall at each race'sorigin, indicating greater osmotic adjustment in land-racesfrom drier regions. Races with a greater capacity for osmoticadjustment were characterized by smaller plants with high ratesof transpiration and low rates of leaf senescence under stress. The carbon exchange rate per unit leaf area increased as liveleaf area decreased under stress due to leaf senescence. Thus,drought resistant races under stress tended to have lower CERper unit live leaf area (but not per plant) than susceptibleraces. Transpiration ratios under stress were lower in resistantthan in susceptible races, mainly because resistant races hadhigher transpiration. The results for the measured variables showed a general trendfor greater drought resistance in sorghum than in millet, indicatingthat the commonly observed adapation of the millets to dry environmentsmay be due to other factors, such as drought escape or heattolerance. Sorghum sp. Pennisetum americanum L. (Leeke), water stress, osmotic adjustment, photosynthesis, transpiration, evolution, drought resistance     

The Dependence of Calcium Transport and Leaf Tipburn in Strawberry on Relative Humidity and Nutrient Solution Concentration

Strawberry plants were grown in controlled-environment cabinetswith different day-and-night relative humidities, in nutrientsolutions of different osmotic potential and different calciumconcentrations. Leaf calcium (% d. wt.) depended strongly on leaf age and waslowest and very sensitive to environment when the leaf was emergingfrom the bud. Calcium in the emergent leaf was greatest andtipburn least when plants were grown in humid nights (VPD usually< 100 Pa) and weak nutrient solutions (osmotic potentialabout –25 kPa). Such plants guttated freely. In contrastplants grown in dry nights (VPD, c. 600 Pa) never guttated,had small concentrations of calcium in emergent leaves and sufferedtipburn. The behaviour of plants transferred between humiditytreatments rapidly reflected the new conditions. Increasingthe osmotic potential of the nutrient increased tipburn anddecreased calcium in emergent leaves even though the nutrientcontained more calcium. When the calcium concentration in the emergent leaf exceeded0.07 per cent of d. wt, tipburn was never seen; below 0.05 percent tipburn was usually severe. These results suggest that pre-emerged, and therefore non-transpiring,leaves depend for their calcium on water flow arising from rootpressure at night. After leaf emergence, calcium intake intoleaves was promoted by dry days, indicating that calcium wasthen supplied by transpirational water flow. Humid nights, drydays and weak nutrient solutions minimize the risk of leaf tipburnin strawberry. Fragaria ananassa Duch., strawberry, tipburn, calcium transport, relative humidity, nutrient supply, guttation     

Cell water balance of white button mushrooms (Agaricus bisporus) during its post-harvest lifetime studied by quantitative magnetic resonance imaging

A combination of quantitative water density and T2 MRI and changes therein observed after infiltration with 'invisible' Gd-DTPA solution was used to study cell water balances, cell water potentials and cell integrity. This method was applied to reveal the evolution and mechanism of redistribution of water in harvested mushrooms. Even when mushrooms did not lose water during the storage period, a redistribution of water was observed from stipe to cap and gills. When the storage condition resulted in a net loss of water, the stipe lost more water than the cap. The water density in the gill increased, probably due to development of spores. Deterioration effects (i.e. leakage of cells, decrease in osmotic water potential) were found in the outer stipe. They were not found in the cap, even at prolonged storage at 293 K and R.H.=70%. The changes in osmotic potential were partly accounted for by changes in the mannitol concentration. Changes in membrane permeability were also indicated. Cells in the cap had a constant low membrane (water) permeability. They developed a decreasing osmotic potential (more negative), whereas the osmotic potential in the outer stipe increased, together with the permeability of cells.     

The uptake of mannitol by higher plants

Experiments with youngHordeum sativum andHelianthus annus plants showed that in the excretion of mannitol in the guttation liquid observed byGroenewegen andMills (1960) after uptake by the root system of plants, the osmotic concentration of mannitol in the nutrient medium and the temperature are significant. The beginning of mannitol excretion during guttation is accelerated considerably by the increase of the osmotic concentration of mannitol in the nutrient medium and the rising temperature. The osmotic concentration of mannitol is also important for the duration of mannitol excretion in the guttation liquid after transfer of the plants into a nutrient medium without mannitol. In the presence of mannitol in the nutrient medium water uptake by the root system and growth are inhibited and the tissues of the organs above ground and of the root system are dehydrated. The inhibitory effect of mannitol on the water uptake by the root system is immediate.