Hanno Richter

The Water Status in the Plant Experimental Evidence

In Part 1:B and 1:C of this volume Oertli gives a detailed theoretical treatment of water in the plant body and in the soil-plant-atmosphere continuum. This leaves the task of providing quantitative data for at least some of the parameters discussed. The choice of these parameters and of the papers dealing with them has to be rather subjective, since even the most recent literature is far too voluminous to be covered completely.

Graphical evaluation and partitioning of turgor responses to drought in leaves of durum wheat

The relationship between relative water content (R) and turgor potential (Ψp) may be derived from pressure-volume (PV) curves and analyzed in various ways. Fifty PV curves were measured with the pressure chamber on leaves of durum wheat (Triticum durum L.). The plots of Ψp versus R were highly variable and could not be adequately described by a single mathematical function. The area below the curve was therefore determined by means of an area meter. This procedure gave the integral of turgor from full saturation to the turgor-loss point. Responses to drought treatment could thus be quantified and partitioned into effects of osmotic adjustment and elastic adjustment. These two adjustment responses, which are probably of different metabolic origin, together improve turgor maintenance in durum wheat considerably.

Die Reaktion hochpermeabler Pflanzenzellen auf drei Gefrierschutzstoffe (Glyzerin, äthylenglykol, Dimethylsulfoxid)

Zusammenfassunga)Die Arbeit behandelt die Resistenz pflanzlicher Dauergewebszellen, zumal der Epidermen einiger Glockenblumenarten, gegen höhere Konzentrationen dreier Chemikalien, die als Schutzstoffe gegen den Gefriertod tierischer Zellen empfohlen werden.b)Der besondere Bau der pflanzlichen Zellen erfordert Vorsicht bei der Anwendung osmotisch wirksamer Substanzen. Eine Methode zur überführung der hochpermeablen Epidermiszellen vonCampanula in konzentrierte Lösungen von Glyzerin wird beschrieben.c)Campanula- Zellen sind gegen Glyzerin überaus unempfindlich. Nach eintägigem Aufenthalt in fünfzigprozentigen Lösungen konnten Schnitte mit guter Ausbeute an lebenden Zellen wieder in Leitungswasser zurückgeführt werden. Die Plasmaströmung setzte wieder ein. Selbst in 100% Glyzerin (p. A., Merck) zeigten die Zellen noch Plasmolyserückgang, Neutralrotspeicherung und erneute Plasmolyse in Glyzerin-Zucker-Gemischen.d)Hingegen sind sowohlCampanula- als auchAllium- Zellen recht empfindlich gegen äthylenglykol und Dimethylsulfoxid. Die mikroskopischen Beobachtungen deuten auf eine Beeinträchtigung der Membransysteme, was sich aus der Lipoidlöslichkeit dieser beiden Stoffe verständlich machen läßt.Summarya)This paper is concerned with the resistance of cells of permanent plant tissues, especially the epidermis of some bellflower species, against high concentrations of three substances recommended as cryoprotective for animal cells.b)Because of the peculiar structure of plant cells any osmotically active substance should be applied with caution. A method is described for transferring the highly permeable epidermis cells ofCampanula into concentrated solutions of glycerol.c)Bellflower cells are extremely indifferent to glycerol. Having remained in a 50% solution for a day, sections could be brought back to tap water with a good yield of living cells. Protoplasmic streaming started again. 6ven in pure glycerol (G. R. Merck) cells showed deplasmolysis, neutral red staining and renewed plasmolysis in mixtures of glycerol and sugar.d)On the other hand,Campanula as well asAllium cells are rather sensitive against ethylene glycol and dimethyl sulfoxide. Microscopic observations suggest injuries to cytoplasmic membranes. This may be explained as a consequence of the lipid solubility of both of these substances.

Developmental Effects on Leaf Water Relations of two Evergreen Shrubs (Prunus laurocerasus L. and Ilex aquifolium L.)

Summary Leaf water characteristics of two evergreen shrubs, Prunus laurocerasus L. and Ilex aquifolium L., were followed for one year by means of the pressure-volume curve technique. Osmotic potentials of newly emerged leaves were about 1 MPa higher (less negative) than those of mature, over-wintered leaves. This difference disappeared during the first months of leaf development, when the vacuolar solution in newly emerged leaves gradually became more concentrated. Daycourses of total water potential show the most negative values for fully mature leaves. Pressurevolume curves were used to convert these field data into corresponding values for the turgor potential, which were byfar higher for old than for young leaves. Recently emerged leaves in spring may therefore come under severe stress during periods of only moderately lowered total water potentials.

A Comparison of Methods for the Determination of Water Status in Quercus ilex L.

Summary Water saturation deficit (WSD), osmotic potential of the cell sap ( Ψ o ) and total water potential ( Ψ t ) were determined in drying shoots and saplings of the Mediterranean evergreen oak, Quercus ilex L. Reliability as well as time and material requirements were assessed. Thermocouple psychrometry and the pressure chamber technique offer great advantages over refractometry of exchange solutions for the determination of Ψ t . The relationship between WSD, Ψ o and Ψ t was evaluated by means of the «pressure-volume curve« technique in the modification of Talbot et al. (1975). While the direct comparison of the cryoscopically determined osmotic potential and the psychrometrically determined total water potential suggests the occurrence of negative turgor, this evidence appears doubtful after a scrutiny of the pressure-volume curves. Some advantages of this evaluation technique are emphasized: osmotic relations may be analyzed in organs where the cryoscopic technique cannot be applied, e.g. in stem disks; linear regressions may be calculated for data from cryoscopy and vapour pressure osmometry as well as from different Ψ t -techniques; and curves may be extrapolated to high WSDs, whereas direct determinations are not feasible with most of methods due to technical limitations.

Water Stress Resistance of Photosynthesis: Some Aspects of Osmotic Relations

The generally accepted tolerance-avoidance classification of resistance mechanisms is rather problematic in the case of water stress. This is mostly due to the multiple effects of water stress which inhibits several fundamental processes at different levels of tissue water potential. A less ambiguous evaluation is possible for mechanisms involved in the resistance of single processes, as for instance photosynthesis. In this paper, attention is concentrated on the components of total water potential which permit plants to resist the negative effects of water stress on photosynthesis. For several shrub species a close connection between turgor loss and increased stomatal resistance has been demonstrated; osmotic potentials in mature leaves of these species remain constant under water stress. Wheat and other cereals make use of different strategies: turgor loss and stomatal closure occur at different relative water contents, and osmotic adjustment leads to rapid responses under the impact of water stress. A method for inducing osmotic adjustment in detached leaves is described and the value of osmotic adjustment as an avoidance strategy for the relief of photosynthesis is discussed.

Erhöhte Saugspannungswerte und morphologische Veränderungen durch transversale Einschnitte in einem Taxus-Stamm

Summary Total suction tension (or, according to the ψ -nomenclature, total water potential) at a certain point in the plant body is the sum of three components: S = S H + S B + S R , with S H =hydrostatic tension, S B = static soil tension and S R = frictional tension due to water movement in soil and plant. Experimental increase of the total tension is usually achieved by reducing the soil water content. This approach has a readily measurable effect on S B , but it must also influence the soil component of S R to an extent not easily assessed. Since both S B and the soil component of S R act from outside the plant body, variations in the irrigation pattern do not provide a means to influence selectively the tensions in a certain region of the plant body while leaving other parts unchanged. In a large tree, however, total tensions at various heights above ground are widely different. This is due far more to an increase with height I of conduit resistances (i. e., S R ) than to the simple height effect of S H . The influence of S R on tota potentials in the crown of a large tree may be simulated experimentally by means of a double sawcut in the stem of a small tree, which increases transport resistances of the conduit. In the early spring of 1972, such an experiment was set up with a large bush of yew ( Taxus baccata , L.), and suction tensions were followed with a pressure bomb. Diurnal courses of suction tensions are presented for typical days. Some general trends become evident: 1. Tensions are always higher in the experimental part than in the control, but the extent of the difference depends on the climatic conditions. 2. Values in the control reach a minimum in the late evening, while those in the experimental twigs continue to decline during the night. An eventual coincidence of the two curves is prevented by the onset of transpiration in the morning. 3. Tensions in the control follow changes in the vapour pressure deficit rather closely, while the experimental part shows a tendency to hold a plateau value at about 21 atm under different atmospheric conditions. Thus, maximum tension differences occur whenever there is a sudden fall in Δ p-values. Such a situation leads to a rapid tension drop in the control twigs, while the experimental parts remain at their previous high level, sometimes for a prolonged period. It is supposed that differences in the tension pattern similar to those described may play an important role in the establishment of physiological and morphological differences between lower and upper crown of a high tree. Shoot and needle lengths and needle distances were compared for experimental and control parts in 1972 and 1973. Results agree with previous work on artificial drought and its morphological consequences in conifers. Since in most earlier experiments drought was induced in young plants by means of infrequent irrigation, the similarity of results obtained in an old tree by the sawcut technique seems to be of some significance.

Mistletoes and mutant albino shoots on woody plants as mineral nutrient traps

Background and Aims Potassium, sulphur and zinc contents of mistletoe leaves are generally higher than in their hosts. This is attributed to the fact that chemical elements which are cycled between xylem and phloem in the process of phloem loading of sugars are trapped in the mistletoe, because these parasites do not feed their hosts. Here it is hypothesized that mutant albino shoots on otherwise green plants should behave similarly, because they lack photosynthesis and thus cannot recycle elements involved in sugar loading. Methods The mineral nutrition of the mistletoe Scurrula elata was compared with that of albino shoots on Citrus sinensis and Nerium oleander. The potential for selective nutrient uptake by the mistletoe was studied by comparing element contents of host leaves on infected and uninfected branches and by manipulation of the haustorium–shoot ratio in mistletoes. Phloem anatomy of albino leaves was compared with that of green leaves. Key Results Both mistletoes and albino leaves had higher contents of potassium, sulphur and zinc than hosts or green leaves, respectively. Hypothetical discrimination of nutrient elements during the uptake by the haustorium is not supported by our data. Anatomical studies of albino leaves showed characteristics of release phloem. Conclusions Both albino shoots and mistletoes are traps for elements normally recycled between xylem and phloem, because retranslocation of phloem mobile elements into the mother plant or the host is low or absent. It can be assumed that the lack of photosynthetic activity in albino shoots and thus of sugars needed in phloem loading is responsible for the accumulation of elements. The absence of phloem loading is reflected in phloem anatomy of these abnormal shoots. In mistletoes the evolution of a parasitic lifestyle has obviously eliminated substantial feeding of the host with photosynthates produced by the mistletoe.

Die Gefrierresistenz glyzerinbehandelterCampanula-Zellen

Zusammenfassung1.Epidermisschnitte verschiedener Arten der GattungCampanula lassen sich langsam in Lösungen mit sehr hohem Glyzeringehalt überführen, ohne daß die Zellen dadurch geschädigt würden. Das erlaubt Versuche zur Gefrierkonservierung glyzerinbehandelter Zellen.2.Von Versuchen an tierischem Material ist bekannt, daß bei einer Temperatursenkung von −1° C pro Minute, gemessen im Kühlbad, zahlreiche Zellsorten auf Temperaturen zwischen − 70 und − 80° C überführt und längere Zeit ohne Schädigung gelagert werden können. Alle Versuche, ungehärteteCampanula- Zellen in Lösungen mit einem Glyzeringehalt bis zu 60% (v/v) mit der erwähnten Gefriergeschwindigkeit lebend auf Temperaturen unter − 70° C abzukühlen, schlugen jedoch fehl.3.Eine Änderung der Abkühlweise (Temperatursenkung von 5° C pro Stunde) verbesserte die Ergebnisse bis zu einer maximalen Ausbeute an lebenden Zellen von 30%, wenn die Objekte bald nach dem Einfrieren wieder aufgetaut wurden. Längere Lagerung bei der Temperatur des Trockeneis-Alkohol-Bades erwies sich jedoch als tödlich. Für diese Lagerungsschäden sind Kristallisations- und Rekristallisationsvorgänge in den nicht völlig entwässerten Zellen und ihrer Umgebung verantwortlich zu machen.4.Steigert man die Glyzerinkonzentration bis über 70% (v/v) Merck-Glyzerin, dann erstarren die Lösungen bei jeder Abkühlgeschwindigkeit glasig, ohne Eis abzuscheiden. Derart „vitrifizierte“ Zellen erweisen sich nach dem Erwärmen als ungeschädigt.5.Vitrifikation der Lösung gelingt auch, wenn man Glyzerinlösungen von 50 und 60% Gehalt mit hohen Dosen von Polyäthylenglykol