Turgor Maintenance Research Articles

INFLUENCE OF WATER AND SALT STRESS ON WATER RELATIONSHIPS AND CARBON DIOXIDE EXCHANGE OF TOP AND ROOTS IN BEANS

SUMMARYWhen low‐salt plants, grown in nutrient solution, were exposed to osmotic potentials in the root medium (πs)* of minus 2.7 and minus 4.7 bar due to the addition of KNO3, osmotic adjustment occurred. The leaf osmotic potential (π1,) decreased, leaf turgor potential (Ψp) and leaf water content (W) were maintained, no wilting took place, stomatal conductance (g) was partially regained and net photosynthesis was only moderately depressed.When low‐salt plants were exposed to πs of minus 2.7 and minus 4.7 bar due to the addition of PEG 1500, no adjustment to water stress was observed. Ψp decreased, the leaves became dehydrated and a high percentage wilted. Stomatal conductance, net photosynthesis, top dark respiration and root respiration were depressed. NO3‐uptake ceased completely at minus 4.7 bar.When low‐salt plants were exposed to πs of minus 4.7 bar, due to both PEG (minus 2 bar) and KNO3 (minus 2 bar), osmotic adjustment took place; π1 decreased, Ψp, W, g, net photosynthesis, top dark respiration and root respiration recovered to some extent, but the proportion of wilted leaves was high.When medium‐ and high‐salt plants, osmotically adjusted to πs of minus 2.7 and minus 4.7 bar due to KNO3 were exposed to water stress due to PEG (minus 2 and minus 4 bar), (Ψp and W were maintained, none or few leaves wilted and g was depressed less than in low‐salt plants. These responses are attributed to influence of pre‐osmotic adjustment on turgor maintenance and hydration of the plant.It is concluded that osmotic adjustment by inorganic solute uptake, before or during exposure to water and salt stress, can reduce the severe effects of low water potentials in the root medium.

Root growth and water relations of oak and birch seedlings.

First year seedlings of English oak (Quercus Cobur) and silver birch (Betula pendula) were subjected to pressure-volume analysis to investigate the water potential components and cell wall properties of single leaves. It was hoped that this rapid-drying technique would differentiate between reductions in plant solute potential resulting from dehydration and the effects of solute accumulation.Comparison of results from these experiments with those of slow drying treatments (over a number of days) with plants growing in tubes of soil, indicated that some solute accumulation may have occurred in drying oak leaves. High leaf turgor and leaf conductance were maintained for a significant period of the drying cycle. Roots of well-watered oak plants extended deep into the soil profile, and possibly as a result of solute regulation and therefore turgor maintenance, root growth of unwatered plants was greater than that of their well-watered counterparts. This was particularly the case deep in the profile. As a result of deep root penetration, water deep in the soil core was used by oak plants to maintain plant turgor, and quite low soil water potentials were recorded in the lower soil segments.Root growth of well-watered birch seedlings was prolific but roots of both well-watered and unwatered plants were restricted to the upper part of the profile. Root growth of unwatered plants was reduced despite the existence of high soil water potentials deep in the profile. Shallow rooting birch seedlings were unable to use this water.Pressure-volume analysis indicated that significant reductions of water potential, which are required for water uptake from drying soil, would occur in oak with only a small reduction in plant water content compared to the situation in birch. This was a result of the low solute potential in oak leaves combined with a high modulus of elasticity of cell walls. Deep rooting of oak seedlings, combined with these characteristics, which will be particularly important when soil deep in the profile begins to dry, mean that this species may be comparatively successful when growing on dry sites.

Changes in Internal Water Relations and Osmotic Properties of Leaves in Maturing Soybean Plants

The changes in the internal water relations of soybean (Glycine max L. Merr.) leaves during vegetative and reproductive growth were studied by following the changes in the pressure-volume curves of soybean leaves. The results demonstrate that soybean leaves undergo a change in their osmotic properties which coincides with the onset of active reproductive growth and is not induced by water stress. The observed osmotic changes resulted in an increase in the leaf relative water content at any given bulk leaf water potential. The volume of leaf water loss needed to reduce turgor potential to zero did not change following this change in osmotic properties. The degree of turgor maintenance after the change in osmotic properties depended on the ability to maintain adequate leaf relative water content. The observed changes in bulk osmotic potential of the soybean leaves would contribute to increased leaf-soil water potential gradients and therefore to improved ability to

Seasonal patterns of leaf water relations in four co-occurring forest tree species: Parameters from pressure-volume curves.

Leaf water relationships were studied in four widespread forest tree species (Ilex opaca Ait., Cornus florida L., Acer rubrum L., and Liriodendron tulipifera L.). The individuals studied all occurred on the same site and were selected to represent a range of growth forms and water relationships in some of the principal tree species of the region. The water relations of the species were analyzed using the concept of the water potential-water content relationship. The pressure-volume method was used to measure this relationship using leaf material sampled from naturally occurring plants in the field. Water potential components (turgor, osmotic, and matric) were obtained by analysis of the pressure-volume curves.Initial osmotic potentials (the value of the osmotic component at full turgidity) were highest (least negative) at the start of the growing season. They decreased (becoming progressively more negative) as the season progressed through a drought period. Following a period of precipitation at the end of the drought period, initial osmotic potentials increased toward the values measured earlier in the season.Seasonal osmotic adjustments were sufficient in all species to allow maintenance of leaf turgor through the season, with one exception: Acer appeared to undergo some midday turgor loss during the height of the July drought period.In addition to environmental influences, tissue stage of development played a role; young Ilex leaves had higher early season initial osmotic potentials than overwintering leaves from the same tree.The seasonal pattern of initial osmotic potential in Liriodendron and the observed pattern of leaf mortality suggested a possible role of osmotic potentials in the resistance of those leaves to drought conditions. The fraction of total leaf water which is available to affect osmotic potentials, called the osmotic water fraction in this study, was greatest in young tissue early in the season and declined as the season progressed.The results of this study showed that the water potential-water content relationship represents a dynamic mechanism by which plant internal water relations may vary in response to a changing external water-availability regime. The measured water relationships confirmed the relative positions of the species along a water-availability gradient, with Cornus at the wettest end and Ilex at the driest end of the gradient. Acer and Liriodendron were intermediate in their water relations. The spread of these species along a water-availability gradient on the same site suggested that coexistence is partially based on differential water use patterns.

Chloride Accumulation as a Homeostatic System: Negative Feedback Signals for Concentration and Turgor Maintenance Differ in a Glycophyte and a Halophyte

Carrot tissue is taken as a representative glycophilic tissue. It accumulates K+, Cl- and total osmotica to a steady level after 10-15 days. This level of Cl- is nearly constant and is independent of external KCl concentration and of turgor. Cl- influx is also independent of turgor. It therefore appears that the Cl- accumulating system in carrot (and possibly in other glycophytes) can, under artificial conditions, act as a homeostat for intracellular C- concentration, and is not the basis of turgor maintenance. It is suggested that turgor might be maintained by controlled accumulation of K+ carboxylates in glycophytes. Beet tissue is taken as a representative halophilic tissue. It accumulates K+, Cl-, and total osmotica to a steady level after about 4 days. At this stage turgor is constant, due to differences in the levels of KCl accumulated. Cl- influx is stimulated by reducing turgor after a lag of 3-5 h. The relationship of Cl- influx to turgor is non-linear. It therefore appears that in beet (and possibly in other halophytes) turgor maintenance is based on the turgor-sensitive accumulation of Cl- salts. Cl- influx in beet is also affected by changes in intracellular Cl- concentration, as in carrot. It is suggested that this feedback relationship may primarily be part of a system for the controlled uptake of nutrients rather than of Cl- in both tissues.

Leaf Conductance and Osmoregulation of Field‐grown Sorghum Genotypes1

The relationship between stomatal activity and leaf water potential components was examined for several sorghum [Sorghum bicolor (L.) Moench] genotypes as a function of growth stage under semi‐arid field conditions. During vegetative development, prior to flowering, genotypic differences were observed in the leaf water potential required to initiate stomatal control of transpirational water loss and the rate of change in conductance per unit change in leaf water potential. No significant genotypic differences existed in conductance when leaf water potential was high. After flowering and attainment of maximum leaf size, conductance remained high even when the leaf water potentials declined to −24 to −26 bars.The relationships between leaf water potential components were examined to help explain the leaf conductance observations. Genotypic differences were observed in the leaf water potential‐leaf turgor potential relationships at each growth stage. Prior to flowering, as leaf water potential declined, leaf turgor declined accordingly with little evidence of osmoregulation, and all genotypes reached calculated 0 turgor at essentially the same leaf water potential (−18 to −20 bars). Genotypic differences were also observed in the leaf turgor‐stomatal conductance relationships.After flowering, during the grain filling stage, significant genotypic differences were observed in the degree of osmotic adjustment. The genetic range in osmotic adjustment represents a potentially important adaptive mechanism to water stress which allows for maintenance of turgor and thus of metabolic functions dependent on turgor. Apparently, water conservation through stomatal control is practiced to some extent in sorghum prior to the onset of reproductive development; however, after flowering photosynthetic productivity is apparently maintained at the expense of water conservation.

Solute regulation and growth by roots and shoots of water-stressed maize plants

Potted maize seedlings were subjected to a single period of water stress. As the severity of water stress increased, measurements were made of leaf and root solute and water potentials, leaf diffusive conductance and leaf and root growth. After day four of the drying cycle, the rate of leaf extension and the development of leaf area were reduced. This reduction correlated well with a reduction in leaf turgor which occurred at this time. A significant accumulation of solutes in the root tips of the unwatered plants resulted in the maintenance of root turgor for the duration of the water stress treatment. Root growth of the unwatered plants was also maintained as the severity of water stress increased. A mild degree of water stress resulted in a net increase in root growth compared to the situation in well-watered plants. The significance of solute regulation and continued root growth for plants growing in drying soil is discussed.

Environmental Effects on Turgor Pressure Response in Range Grasses1

The effect of environment on turgor pressure responses was determined over a range of drought stress for the following grass species: Agropyron caninum (L.) Beauv.; A. desertorum [Fisch. ex Link] Schult.; A. intermedium (Host) Beauv.; A. trachycaulum (Link) Malte ex H. F. Lewis; Elymus cinereus Scribn. & Merr.; E. junceus Fisch. Plants of each species were started from seed and exposed to environments characterized by three nightday temperature combinations of 5/10, 10/15, and 15/25C. Water potential components of detached leaf samples were determined throughout a drying cycle with a psychrometric technique.Turgor pressure responses changed as environmental conditions changed. Generally, plants in the low‐temperature environment maintained turgor over a wider range of leaf water potentials than plants did in the two higher temperature environments. Temperature environments also influenced turgor responses to a larger degree in some species than in others. The effect of environments on the leaf water potential where turgor declined to zero ranged from about 4 bars in E. junceus and A. intermedium to more than 8 bars in E. cinereus. When values of leaf water potential where turgor equals zero were used to rank species for drought resistance, rankings changed in different environments. These resuls suggest that the environments in which plant materials are grown should be carefully considered if maintenance of turgor is used to estimate relative drought resistance.

Seasonal Changes in Water Potential and Turgor Maintenance in Sorghum and Maize under Water Stress

AbstractLeaf water (Ψ) and solute (ψ) potential were measured in field sorghum and maize under well irrigated (I) and dryland (NI) conditions throughout a season. Despite decreases in ψ due to slow soil water depletion and to apparent increases in liquid phase plant resistance, midday leaf turgor (ψp) in the NI sorghum was maintained at similar levels as in the I treatment throughout the season due to concomitant decreases in ψs. Osmotic adjustment was also observed in maize, although ψp was significantly lower in the NI treatment as compared to I during the final stages of grain filling. A seasonal shift in the ψ vs. relative water content relation of NI sorghum leaves was observed, more water being retained by the older leaf at any particular ψ. The major factor for turgor maintenance was a net increase in solutes per unit of tissue. The role played by increases in the proportion of tissue volume occupied by cell wall was also evaluated. No stomatal closure due to water stress was found in NI sorghum even though leaf ψ reached —20 bars late in the season. Under similar conditions, stomata closed at —14 to —16 bars in younger plants where water stress was made to develop much faster.

Solute accumulation in leaves and roots of woody plants subjected to water stress.

Young seedlings of English Oak, Quercus robur L., and Silver Birch, Betula verrucosa Ehrl., were subjected to a number of consecutive periods during which water was withheld. During one 14-day period leaf-and soil-water potentials and leaf- and root-solute potentials of two groups of plants were sampled at noon of each day. One group of plants was watered every day while water was withheld from the other group. Solute accumulation in roots and leaves of oak seedlings subjected to water stress resulted in maintenance of turgor and high leaf conductance as the soil dried. In birch seedlings turgor was only maintained by stomatal closure at high soil water potential.Fourteen consecutive water stress cycles greatly reduced the growth of birch seedlings but had little effect on oak seedlings other than to alter root morphology. Water stress treatment resulted in the production of long thin roots in this plant. Stomatal behaviour in oak and birch seedlings during the 14-week stress period was consistent with observed changes in leaf water and solute potentials. Daily solute accumulation in oak leaves was presumably responsible for the maintenance of plant growth as water potentials fell.

Plant Growth in Polyethylene Glycol Solutions in Relation to the Osmotic Potential of the Root Medium and the Leaf Water Balance

The changes in leaf extension, plant dry weight, leaf area, net assimilation rate (E), relative growth-rate and relative leaf growth-rate (R£), have been studied for four species grown for 2 weeks in solutions of polyethylene glycol 4000 of controlled osmotic potentials. All aspects of growth were decreased by decreasing the osmotic potential (■sol) °f the root medium and the leaf water potential ( p from the values in the control plants decreased growth during the first week but partial recovery was apparent during the second week's growth in solution culture, when leaf extension, E, Ri, and Riiincreased in plants subjected to stress. Examination of the water balance, water potential, osmotic potential, and turgor of the leaf in relation to relative water content suggests that recovery was related to increased turgor and that the ability of the plants to grow at reduced values of the osmotic potential of the root medium and of the leaf water potential depended on the maintenance of turgor.

The osmoregulatory function of the vibratile flames and the contractile vesicle of Asplanchna (Rotifera)

1.The experimental results provide strong evidence that the vibratile flames and contractile vesicle of Asplanchna are components of an osmoregulatory system.2.In fresh water and at constant temperature, the rate of beat of the vibratile flames of Asplanchns and the rate of output of fluid from the contractile vesicle vary from one species to another.3.An increase in the ionic concentration of the external medium results in a decrease in the rat of beat of the vibratile flames, and this effect is reversible.4.An increase in the ionic concentration of the external medium results in a decrease in the rate of output from the contractile vesicle, and this effect is reversible.5.An increase in temperature results in an increase in the rate of beat of the vibratile flames and in the rate of output from the contractile vesicle.6.The increase in rate of beat of the flames in response to increased temperatures above 22°C id greater than that to increased temperatures below 22°C.7.Correlation of flame and vesicle activity suggests that there is an optimum size for the flame bulbs.8.The vibratile flames of Asplanchna show an activity in inverse relationship to the concentration of the medium, and not an “all or none” effect.9.The medium with which the body fluid of Asplanchna is estimated to be isosmotic is 100–160 mOsm sodium chloride/1 for A. priodonta and 130–175 mOsm sodium chloride/1 for A. brightwelli.10.The estimated internal concentration of Asplanchna is comparatively high. It is suggested that this is concentrated with the maintenance of turgor in the animal.11.The turgor pressure of the body fluid of Asplanchna pridonta is suggested as being of the order of 40 mOsm sodium chloride/1.

Antibiotics as a Means of Control of Bacterial Contamination of Storage Tissue Disks

DURING the investigation of metabolism of storage tissues of higher plants, it is common to wash and aerate disks of the tissue for periods of several days or weeks. To this end, a variety of techniques has been reported, but in most cases it was not possible to impose rigorous conditions of sterility, although, in analysing the behaviour of tissues treated in this way, it is evidently necessary to ensure that the presence of micro-organisms is not a significant factor. The experimenter has usually used such criteria as retention of pigment if any, maintenance of turgor, and clarity of the suspending liquid. Recently, Bacon, MacDonald and Knight1 have shown that these criteria may be observed even when substantial contamination of disks by bacteria has occurred, and they found that disks (1 cm diam. and 1 mm thick) of sugar beet showed the presence of about 3 × 107 organisms/disk after washing for 4 days. During a programme of research into enzyme synthesis in storage tissue disks2,3 we have found that artichoke and carrot disks become contaminated with bacteria to a similar degree, ranging from 5 × 105 per disk after 24 h to 4 × 107 after 3 days.

In vitro cultivation of an acanthocephalan, Octospinifer macilentis

Literature relating to in vitro experimentation with acanthocephalans is reviewed. Octospinifer macilentis was studied by axenic cultivation. Experiments were conducted with 192 mature adults, 7 to 18 mm long; 56 cystacanth larvae, 0.7 to 0.9 mm long; and 100 immature adults, 3 to 5 mm long. Worms in the latter group proved most useful. Altogether, 28 media were tested for adequacy by noting, for cultured worms, survival, increase in standard length, and maintenance of normal turgor and body movements. The medium showing greatest potential contained neopeptone, yeast extract, horse serum, glucose, inorganic salts, water soluble vitamins, and essential amino acids. Maximum increase in length was 45% in 43 days. Undoubtedly, O. macilentis reflects causes for stringent host specificity by narrow limits of nutritional and ecological requirements.

Anal and Oral Intake of Water by Crustacea

ABSTRACT In small and transparent Crustacea water can be seen with a microscope to be pumped through the anus into the intestine. The pumping is done by antiperistaltic contractions of rectal muscles, the movements being repeated rhythmically at intervals of one to a few seconds. They may continue almost without interruption or may occur for short periods with intervals of rest. In some genera the entrance of water by successive gulps is quite clear; this is the case, for example, in Triops, Sida, Diaphanosoma, Leptodora, Mysis, Sphaeroma, Ligia, Corophium. In other genera, such as Artemia, Chirocephalus, Limnadia and Bythotrephes, it is not obvious that water enters, although waves of contraction are seen to pass inwards over the rectal musculature. In Daphnia the gulps cannot be seen when the antiperistalsis is slow, but they are clearly visible when it is rapid.