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Segments of the 4th and 5th internodes of light-grown pea seedlings were used for the study of control of stem elongation. With 5th internodes, at low turgor as well as at water saturation auxin primarily appeared to cause a change in cell wail properties of the epidermis but it showed little effect on expansion of the inner tissues This was confirmed by comparison of expansion between peeled and unpeeled segments, split tests and by measurements of stress-relaxation properties of the epidermal cell wall. Segments with the central part removed elongated well in response to auxin, but the isolated epidermis showed neither auxin-induced elongation nor cell wall loosening. A fungal β-1,3-glucanase appeared, at least partly, to have a similar effect as that of auxin on elongation, by changing cell wall properties of the epidermal cell wall. Peeled segments of 4th internodes expanded very little and auxin had little effect on their epidermal cell wall properties. [ABSTRACT FROM AUTHOR]

The average rate of rotation of circumnutating tendrils of Pisum sativum L. cv. Alaska, was 1.57 ± 0.29 mm/min. 53 % of the tendrils rotated clockwise and 47% counterclockwise. Circumnutation is apparently dependent on the maintenance of sufficient turgor as it stopped when either the roots or all the shoot appendages except the terminal were excised, but resumed when the aerial wounds were covered with petroleum jelly. Both circumnutation and contact coiling were similarly retarded when the plant was cut in the middle of the top internode, or by the use of either juvenile or senescent organs. As the tendril circumnutated rapidly during the sweeping portion of its circuit, it was capable of coiling at only about 57 % of the rate of which it could coil if stimulated during the relatively slow moving turn. Conversely, when the tendril was mechanically stimulated to coil, its rate of circumnutation decreased markedly and remained retarded as long as the tendril continued to coil. On the basis of these observations, it is concluded that contact coiling does not seem to be simply a modified form of circumnutation, but the two modes of movement might be related through a negative feedback system. [ABSTRACT FROM AUTHOR]

When a water deficit was induced in a mature fully turgid leaf of Ricinus communis L. the tissues could completely regain full turgidity by absorption of water at around 1° c. This was true of large water deficits (40%) which greatly exceeded the cell wall volume (12%). This uptake therefore included movement into the protoplasts and was not restricted to the cell walls alone as had been previously supposed (Weatherley, 1963). However, resaturation of leaf tissues taken from plants which had suffered from drought for more prolonged periods, could be separated into two fractions. An uptake at 1°C was attributable as before to recovery of turgor; an extra uptake at 25° C seemed to be a growth phenomenon inhibited at the lower temperature. This represented a rapid cell expansion following a period of growth arrestment due to water stress. The implications of these findings for the measurement of relative water content are discussed. [ABSTRACT FROM AUTHOR]

The mango is an example of a tree in which all the leaves on a shoot develop simultaneously instead of sequentially. The growth in area of all the leaves in a flush was followed at daily intervals. The dry weight, ash weight, water content, relative turgidity and rigidity of the leaves were measured at weekly intervals for the first 6 weeks of their life. They grew by cell division for the first 7 days after the fall of the bud scales and by cell enlargement over the next 7 days, Between day 7 and day 14 the dry Weight per mall leaf area fell. The water content per unit leaf area increased, and the leaf became less rigid, finally hanging limply. After this date these trends were reversed. It is shown that the limpness of the young mature leaves is not due to lack of turgor, but may he correlated with a minimal value of the dry weight per unit leaf area. [ABSTRACT FROM AUTHOR]

The relations between longitudinal growth, Young's modulus, turgor, water potential, and tissue tensions have been studied on growing internodes of etiolated pea seedlings in an attempt to apply some physical concepts to the growth of a well-known plant material. The modulus has been determined by the resonance frequency method and expressed as Etissue. It increases nearly proportional to the turgor pressure and is at water saturation more than 50 times higher than at plasmolysis. Etissue is higher in the epidermis than in the ground parenchyma. Indoleacetic acid causes a decrease in Etissue. Other properties have been studied on intact and split segments of internodes in solutions of graded mannitol additions. — The following tentative picture of the normal course of the growth has been obtained. Auxin induces growth both in the periphery (epidermis) and in the central core (parenchyma) under a decrease in Etissue. This is followed by an increase of Etissue which is independent of auxin but depending upon the turgor pressure. It is assumed to involve internal structural changes of the cell walls of the type of creep. The rapid growth takes place in a dynamic system with a low water potential despite favourable water conditions. Epidermis and parenchyma grow equally rapid without tissue tensions. — Such can be produced artificially by splitting of segments and water uptake. The parenchyma thereby loses its sensitivity to auxin. This is the background of the split stem test for auxin. — Etissue increases when growth is slowing down, probably owing to both synthesis of wall substance and structural changes within the wall. The cells attain a more static condition with Etissue higher in epidermis than in parenchyma. This leads to the normal tissue tensions. — The result agrees with growth according to the multi-net-principle. The cause of the low water potential and low turgor is discussed with reference to the dynamic nature of both growth and water transport and a probably low matric potential of the streaming water. The decrease in Etissue following auxin addition is small but is the net difference between an auxin-induced decrease and an increase through the assumed creep. [ABSTRACT FROM AUTHOR]

Red cabbage sections treated with 0.5 M sucrose showed a slight increase in tolerance on exposure to drought. This was so small that it may simply represent a removal of injury due to excess turgor in distilled water. Drought tolerance was markedly increased by mercaptoethanol (ME), but not by glutathione. Sulfhydryl reagents (PCMB and NEM) were unable to enhance drought tolerance unless replaced by ME during rehydration. [ABSTRACT FROM AUTHOR]

The water deficit of the leaves, the osmotic values of the stomatal cells and epidermal cells at incipient plasmolysis, as well as the width of the stomatal apparatus and pore opening, were measured every hour from 6-17 o'clock under natural environmental conditions. During the noon hours, the intensity of light in clear weather ranged from 40,000-55,000 lux in the open position, and from 15,000-20,000 lux in the shade. The temperature was usually 15-20°C. The experimental object was Vicia Faba growing in a field, both plants freely rooted and plants in pots buried in the soil. The experiments resulted in the following observations and conclusions: 1. When leaves are exposed to strong light, the osmotic value at incipient plasmolysis changes not only in the guard cells, but also in the epidermal cells. If the epidermal cells' osmotic value rises, water is sucked from the guard cells and their uptake of water by suction is decreased, which promotes closure and counteracts opening, respectively. If the value falls, the effect is the reverse. The guard cells react passively to these epidermal changes. The passive stomatal movement elicited in this way has therefore been denoted as "osmopassive", in contrast to the long known passive movement caused by a change in turgor of the epidermal cells, and which has therefore been denoted as "turgorpassive". The osmopassive component of stomatal closure has an earlier and more rapid onset than the hydroactive closing reaction, which consists of a decrease in the guard cells' osmotic value. Stomatal closure often starts with the osmopassive rapid process, and is completed and stabilized by the hydroactive process. It has not been possible to determine whether the osmopassive closing reaction is identical with the rapid reaction previously described, and interpreted as of adenoid nature, and thus belonging to the active group. 2. The osmotic potential of the guard cells — i.e., the difference between the osmotic value of guard cells and epidermal cells at incipient plasmolysis — is, therefore, formed not only by a change in the osmotic value of the former cells, but also by a change in that of the latter. 3. Although the pore width runs largely parallel to the osmotic value of the guard cells, there is greater agreement between pore width and osmotic potential. When the water deficit of the leaf exceeds a certain threshold value, potential and stomatal width start to decrease. Closure is completed when the fall in potential approaches the zero value. If the water deficit subsequently continues to increase, the potential becomes negative and the stomata remain closed. 4. the stomatal movements are regulated by physiological processes which form two kinds of equilibrium between increase and decrease of the osmotic potential of the guard cells, i.e. the osmopassive increase — osmopassive decrease and the photoactive increase — hydroactive decrease. These equilibria complement each other in rate and stability. the osmopassive processes start rapidly and as soon as the deficit changes; hydroactive closure and sometimes also photoactive opening,' are, on the contrary, time-consuming. When the water deficit is suboptimal, turgorpassive opening and closing are superadded, but only in those cases in which the osmotic potential of the guard cells is positive. [ABSTRACT FROM AUTHOR]

The normal movements of the stomata in the course of a day — denoted here us the current movements — contain endogenous and induced elements. The size of the current and the endogenous movements can be determined by direct measurements. The difference between these two values is taken here as a measure of the induced part of the movement. The endogenous, diurnal-periodic movements of the stomata were measured in intact plants (Vicia Faba and Ranunculus repens) in darkness. The objects used for recording the current movements were intact plants growing in their natural environment, and subject to the water deficit occurring in such plants, as well as objects (pieces of leaves floating on water) whose water status is not disturbed by a deficit. The experiments demonstrate the following: 1. The proportion of the endogenous to the induced part of stomatal opening is not the same for the pore width and the width of the guard cells. The endogenous part of the pore is slight, and sometimes inappreciable. Expressed as a percentage of the current diurnal value (mean of measurements during the day) in the light exposed object, the endogenous part is found in three experiments to be 19, 3 and 2 per cent, respectively (the induced part thus being 81, 97 and 98 per cent). The endogenous part of the increase in width of the stomatal apparatus (guard cells + pore) is found to be greater, i.e., 47, 21 and 24 per cent (the induced part therefore being 53, 79 and 76 per cent). 2. The endogenous opening wave occurs during the later part of the night and the first few hours of the morning. During this time, the guard cells undergo a large part of the tension phase, which produces an increase in turgor and cell width. After this preparation, the pore opening can be rapidly formed when day breaks, and initiates the motor phase, i.e., the actual opening. [ABSTRACT FROM AUTHOR]

1. Application of the Onsager theory to a very simple case shows to be unfounded the claim of Levitt (1947) to have established a thermodynamic criterion of the possibility of actively-maintained turgor pressure. 2. Beyond stating that the energy expenditure is greater than zero, thermodynamic alone impose no limitations on its magnitude. 3. The notion of permeability appears to be only loosely defined: its magnitude can vary either through change of structure, or through change of milieu. [ABSTRACT FROM AUTHOR]

An attempt has been made to evaluate the physical meaning of the turgor pressure of a living cell. If by turgor pressure is meant the pressure acting from within the cell on the cell wall, it has the nature of a diffusion pressure and can be computed as T = O--E, where T denotes the turgor pressure, O the D.P.D. of the cell sap with no regard paid to the wall pressure, and E the D.P.D. of the external solution in contact with the cell. T depends upon the difference in diffusion pressures of the solution outside and within the cell, and can only he regarded relative to defined external conditions. This evaluation can be applied to all circumstances, regardless whether the cell is at equilibrium with the external medium or not. The turgor pressure equals the wall pressure only at equilibrium, but is of different physical nature, and can attain any values independently of the wall pressure if the cell is not at equilibrium. The turgor pressure must decrease when a cell absorbs water and the wall pressure increases. Turgor pressure and wall pressure are the only actual pressures existing in the cell. The osmotic diagrams of Höfler and Tamiya are extended to be valid also for cells not at equilibrium. [ABSTRACT FROM AUTHOR]