Experimental Studies of the Factors Controlling Transpiration: III. THE INTERRELATIONS BETWEEN TRANSPIRATION RATE, STOMATAL MOVEMENT, AND LEAF-WATER CONTENT

Transpiration rates of single leaves of Pelargonium and wheatwere measured under constant conditions of light, temperature,and air flow. Concurrently, stomatal movement was followed withthe resistance porometer during cycles of changing water contentof the leaf and changes induced by light and darkness. Stomatalmovement was found to exert a large controlling influence onthe transpiration rate, whereas water content had an extremelysmall or negligible effect. An approximately inverse linearrelation between transpiration rate and logarithm of resistanceto viscous flow through the leaf is believed to be the resultantof an inverse curvilinear relationship between the diffusiveconductance of the stomata and log. leaf resistance and thedecreasing difference of vapour pressure arising from the highertranspiration rates with increasing stomatal conductances. Nevertheless,the relation demonstrates that the transpiration rate is influencedby the degree of stomatal opening throughout its entire range. There was some evidence of lower transpiration rates duringand after recovery from wilting than before wilting. This isattributed to a decrease in a cell-wall conductance, the evaporatingsurface being located within the cell wall. During wilting partiallyirreversible contraction of the cell wall occurs. There wasalso evidence of slow changes in cell volume at full turgidityattributable to plastic flow. These occurred when the leaf wastransferred from environments of a high to low potential forevaporation. Extensive movement of the stomata followed changes in leaf water,passive opening resulting from decrease and closure from increaseof leaf water. It is suggested that the direction and extentof stomatal changes induced by water deficits is a consequenceof the rate of change of leaf water content and not of the absolutevalues. The stomata also showed an enhanced tendency to closein dry moving air following a period of wilting even after theleaf had regained turgidity.     

Marginal and laminar hydathode-like structures in the leaves of the desiccation-tolerant angiosperm Myrothamnus flabellifolius Welw.

The fan-shaped leaves of the resurrection plant Myrothamnus flabellifolius Welw. fold during episodes of drought and consequent desiccation of the tissue. The leaf teeth of M. flabellifolius have several features characteristic of hydathodes. Tracheary elements from the three vein endings that converge in each leaf tooth subtend and extend into a cluster of cells significantly smaller than those of the adjacent mesophyll. The stomata overlying this putative epithem are larger than the other stomata on the leaf surface. Crystal violet is absorbed via these stomata in non-transpiring leaves, suggesting that they are water pores. Two to four such water pores occur per hydathode and are readily distinguished in desiccated leaves. Laminar hydathodes apparently also occur in the leaves of M. flabellifolius. Branched vein endings that terminate in short, wide tracheary elements subtend the outer edges of the abaxial leaf ridge, which otherwise lack stomata, and coincide with regions of crystal violet uptake. Guttation could not be induced in M. flabellifolius. However, desiccated leaves readily absorb liquid water through the leaf surface. The use of Calcafluor White to trace the pathway of apoplastic water movement suggests a role for both types of hydathode in foliar water uptake during rehydration while the accumulation of Sulphorhodamine G (indicating solute retrieval from the apoplast) in the epithem of transpiring plants suggests the hydathodes may be a pathway of water loss in the desiccating leaf.     

Stomatal crypts may facilitate diffusion of CO2 to adaxial mesophyll cells in thick sclerophylls

In some plants, stomata are exclusively located in epidermal depressions called crypts. It has been argued that crypts function to reduce transpiration; however, the occurrence of crypts in species from both arid and wet environments suggests that crypts may play another role. The genus Banksia was chosen to examine quantitative relationships between crypt morphology and leaf structural and physiological traits to gain insight into the functional significance of crypts. Crypt resistance to water vapour and CO₂ diffusion was calculated by treating crypts as an additional boundary layer partially covering one leaf surface. Gas exchange measurements of polypropylene meshes confirmed the validity of this approach. Stomatal resistance was calculated as leaf resistance minus calculated crypt resistance. Stomata contributed significantly more than crypts to leaf resistance. Crypt depth increased and accounted for an increasing proportion of leaf resistance in species with greater leaf thickness and leaf dry mass per area. All Banksia species examined with leaves thicker than 0.6 mm had their stomata in deep crypts. We propose that crypts function to facilitate CO₂ diffusion from the abaxial surface to adaxial palisade cells in thick leaves. This and other possible functions of stomatal crypts, including a role in water use, are discussed.     

A fast method to detect the occurrence of nonhomogeneous distribution of stomatal aperture in heterobaric plant leaves

Summary Pressure infiltration of water into a leaf via the stomatal pores can be used to quickly determine whether all stomata are open, or as recently described for several mesophytic and xerophytic species, whether there is a non-homogeneous distribution of stomatal opening (stomatal patchiness) on the leaf surface. Information about this phenomenon is important since the commonly used algorithms for calculation of leaf conductance from water vapor exchange measurements imply homogeneously open stomata, which in the occurrence of stomatal patchiness will lead to erroneous results. Infiltration experiments in a growth chamber with leaves of the Mediterranean evergreen shrub Arbutus unedo, carried out under simulated Mediterranean summer day conditions, where the species typically exhibits a strong midday stomatal closure, revealed a temporary occurrence of stomatal patchiness during the phase of stomatal closure in the late morning and during the stomatal reopening in the afternoon. Leaves were, however, found to be fully (i.e. homogeneously) infiltratable in the morning and in the evening. At midday during maximum stomatal closure, leaves were almost non-infiltratable. During the day, the infiltrated amount of water was found to be linearly correlated with porometer measurements of leaf conductance of the same leaves, carried out with the attached leaves immediately before infiltration.     

MOVEMENT OF EELWORMS

Tracks were plotted of about 300 individual eelworms comprising six species among water droplets on a glass surface. Measurements of the tracks indicated that the product of length and activity of an eelworm divided by its speed was a constant. This supports the hypothesis that the speed of an eelworm among water droplets is a function of its length and activity. This principle can only be applied to movement in soil where the length of the eelworm is less than about three times the particle diameter. Under such conditions the eelworms move in thin films or water droplets over particles. Among smaller-sized particles the speed of the eelworms is influenced by particle size. With increasing eelworm length there is an increase in soil particle size for maximum mobility.     

新疆2种盐生补血草营养器官的解剖学研究

采用叶片离析法和石蜡切片法,对生长在新疆盐渍环境中的大叶补血草[Limonium gmelinii(Willd.) Kuntze]和耳叶补血草[Limoniumotolepis(Schrenk) Kuntze]的营养器官解剖学特征进行了观察研究.结果显示,2种补血草属典型泌盐植物,茎和叶片表皮上分布有多细胞组成的盐腺;叶表皮细胞排列紧密,其外切向壁增厚,表皮外还被有厚的角质层;上下表皮都有气孔,气孔与表皮细胞平齐,为不等型气孔;其中大叶补血草为异面叶,而耳叶补血草为等面叶.2种补血草茎中都散生有多轮维管束;大叶补血草根中还有大量通气组织等.研究结果表明,2种补血草的解剖结构表现出与其生境相适应的特征.     

Evidence for the Uptake of Large Anions through Stomatal Pores

Experiments were conducted with leek (Allium porrum L.) leaves to investigate whether aqueous solutions are able to penetrate stomata. Epidermal strips were used for the determination of transport rates. Stomata were opened by fusicoccin or closed by darkness or abscisic acid. A droplet containing the anionic fluorescent dye, uranine, was placed on the physiologically outer side of the epidermis and allowed to dry. With open stomata 30 times more uranine penetrated through the epidermal strips than with closed stomata (comparison of medians). In another experiment droplets of uranine solution were placed on leaf segments and epidermal strips were removed after drying of the droplets. Penetration of uranine through stomata was detectable under the microscope both with epidermal strips from the transport experiments and with strips obtained after application on leaf segments. As maximum uptake rates occurred during the drying process, it is concluded that penetration took place via water films. These results show that the physical restrictions preventing stomatal penetration of static droplets are not decisive for drying droplets and that stomatal uptake of dissolved ionic substances occurs under natural conditions, i.e. without surfactants or applied pressure.     

Some Differences in the Responses of Stomata of the Two Leaf Surfaces in Cotton

Some differences in the responses of the upper and lower stomatain cotton (Gossypium hirsutuni) are presented. These differenceswere observed in the course of some studies in which the transpirationof the two leaf surfaces was measured under controlled environmentconditions and the transpiration data used as an estimate ofstomatal response. In darkness the upper stomata were more or less effectivelyclosed while the lower stomata were partially open. Upon illuminationof the leaf with non-saturation or saturation radiation theupper stomata were slower to open than the lower stomata. Thereductions in stomatal aperture which occurs with the increasein age of leaves commenced earlier in the upper stomata andproceeded at a faster rate than the lower stomata. Sudden exposureto saturation radiation caused the stomata of the two leaf surfacesto oscillate. These oscillations were not observed in youngleaves but in older leaves. During ageing of leaves oscillationsof the upper stomata commenced earlier than oscillations ofthe lower stomata. When the petiole was excised in darknessor light the upper stomata showed a transient increase but notthe lower stomata. Gossypium hirsutum, stomatal responses, transpiration     

MORPHOLOGY,SEASONAL VARIATION,AND FUNCTION OF RESIN GLANDS ON BUDS AND LEAVES OF POPULUS DELTOIDES (SALICACEAE)

When buds form in summer or early fall, modified stipules act as bud scales and their adaxial epidermis secretes a resin that fills the bud. This secretory layer collapses in the dormant bud. Immature leaves, stipules, and leaf primordia occupy the center of the bud; all lack functional resin glands. In spring, stipules of emerging leaves develop an adaxial palisadelike secretory epidermis that becomes more ridged longitudinally in successive stipules. Marginal teeth of the first leaves to emerge are covered with trichomes and lack a secretory epidermis. In successive leaves the teeth become glandular and secrete resin as the lamina unrolls. Later in the season, marginal leaf glands account for much of the resin. Unspecialized hydathodes or extrafloral nectaries occur proximal to each glandular tip. Guttation of water or nectar occurs here through stomata located above a vein ending. On the basis of field observations and a laboratory feeding experiment, the resin seems to function mainly as an insect repellent. It may also reduce water loss from young leaves.     

Ecological physiology of Pereskia guamacho, a cactus with leaves

The specialized physiology of leafless, stem-succulent cacti is relatively well understood. This is not true, however, for Pereskia (Cactaceae), the 17 species of leafy trees and shrubs that represent the earliest diverging lineages of the cacti. Here we report on the water relations and photosynthesis of Pereskia guamacho, a small tree of the semiarid scrubland of Venezuela's Caribbean coast. Sapwood-specific xylem conductivity (Ksp) is low when compared to other vessel-bearing trees of tropical dry systems, but leaf-specific xylem conductivity is relatively high due to the high Huber value afforded by P. guamacho's short shoot architecture. P. guamacho xylem is not particularly vulnerable to drought-induced cavitation, especially considering the high leaf water potentials maintained year round. This is confirmed by the lack of significant variation exhibited in Ksp between wet and dry seasons. In the rainy season, P. guamacho exhibited C3-like patterns of stomatal conductance, but during a prolonged drought we documented nocturnal stomatal opening with a concomitant accumulation of titratable acid in leaves. This suggests that P. guamacho can perform drought-induced crassulacean acid metabolism (CAM photosynthesis), although delta 13C values imply that most carbon is assimilated via the C3 pathway. P. guamacho leaves display very low stomatal densities, and maximum stomatal conductance is low whether stomata open during the day or night. We conclude that leaf performance is not limited by stem hydraulic capacity in this species, and that water use is conservative and tightly regulated at the leaf level.     

Infraspecific variation of leaf anatomy in Origanum vulgare grown wild in Greece

The histological components of the leaf were studied in dried herbarium material of the three Origanum vulgare subspecies (subsp. hirtum , subsp. viridulum and subsp. vulgare ) grown wild in Greece. These three, geographically distinct, taxa showed remarkable differences in their leaves. The leaves of subsp. hirtum grown in the Mediterranean climatic zone of Greece are characterized by thick cutinized outer walls of the epidermal cells and a thick mesophyll with highly developed chlorophyllous tissues. Peltate glandular trichomes and stomata are numerous on bom leaf surfaces. The thickness of the mesophyll decreases in the other two subspecies grown in the northern part of the country, where a Continental type of climate occurs. The number of glandular trichomes and stomata also decreases. Besides these differences, a noticeable reduction in the size of the essential oil-accumulating subcuticular chamber of the glandular trichomes and in the number of the peribasal cells, has also been recorded in die plants of subsp. vulgare and viridulum.     

Effects of low concentrations of O3, leaf age and water stress on leaf diffusive conductance and water use efficiency in soybean

Ozone, leaf age and water stress each affected leaf conductance in soybean [ Glycine max (L.) Merr. Hodgson], but there were no interactions among these factors. Exposure to increased concentrations of O₃ (0.01, 0.05, 0.09. and 0.13 μl l⁻¹) resulted in linear declines in abaxial and adaxial conductances in leaves of all ages. There were no differences in relative response to O₃ between the two leaf surfaces. For well-watered plants, water use efficiency also decreased with exposure to increased O₃ concentrations (water-stressed plants were not tested). Abaxial conductance increased as leaves aged from 4 to 10 days and then declined with further aging. Adaxial conductance decreased with all increases in leaf age beyond 4 days, and the ratio of abaxial/adaxial conductance increased continuously throughout the leaf lifespan. During water-stress cycles (water withheld for 2–3 days) leaves of water-stressed plants had lower conductances than those from well-watered plants, and there was no difference in relative response between abaxial and adaxial stomata.     

Field Studies of the Wheat Stomata Resistance Influenced by Soil Water Content

Concurrent observations of soil water potential and leaf stomata diffusion resistance were made on two, plots of wheat grown at Datun Agro-ecological Experimental Station in Beijing under two different soil water conditions. These data were further complemented by weather and physiological observation. In this paper, we mainly analysed the influence of soil water potential on the status of wheat leaf stomatal resistance. The results indicate that: (1) there is a obvious influence of soil water potential on the status of wheat leaf stomata under normal conditions and (2) there is a different upper and lower epidermis stomata of wheat leaf respond to the soil water potential. The lower epidermis stomata are more sensitive to soil water potential than upper epidermis one. (3) There is a linear relationship between the ratio of lower and upper epidermis stomata resistance and soil water potential in root layer, according to this we can diagnose the degree of wheat water deficit.     

Water Loss via the Glandular Trichomes of Chickpea (Cicer arietinum L.)

During late vegetative growth chickpea leaves and stems canbe covered with aqueous glandular droplets. If these dropletspersist at low humidities there may be substantial water lossvia the glandular trichomes Four solution culture experimentsin growth chambers tested for glandular water loss at differenthumidities. In the daytime, exudate persisted between relativehumidities of 55% and 95%, and the exudate water potential variedbetween - 2.0 M Pa and - 8.0 M Pa. Even by night, chickpea leaves,like wetted alfalfa leaves, were cooler than non-wetted alfalfaleaves or the ambient air. Daytime leaf temperatures were significantlyhigher in a mutant that produced fewer droplets than in itsnormal parent. It was concluded that water loss via the glandulartrichomes can be enough to lower leaf temperature by severaldegrees C within a wide range of atmospheric conditions. The exudate solutes, analysed to confirm the osmotic potentialmeasurements, were primarily malic, hydrochloric and oxalicacid. Without the strong acids a chickpea leaf, wet even ondry days, would be ripe for parasitic attack. Key words: Add exudate, leaf hairs, transpiration, leaf temperature     

抗寒性不同的油橄榄品种和单株叶片扫描电镜观察

抗寒性强的油橄榄——克里302、尼基特371的叶片,扫描电镜下的特征是:(1) 近轴表皮角质膜厚,蜡质结晶致密。(2) 远轴表皮内陷气孔,密被鳞毛。(3) 叶两面栅栏组织发达,为旱生形态阳叶结构。     

PHYSIOLOGICAL STUDIES ON THE VERTICILLIUM WILT DISEASE OF TOMATO

The water loss per unit leaf area of tomato plants was decreased after inoculation with Verticillium albo-atrum. When diseased plants began to wilt water loss temporarily increased, but then rapidly decreased to become less than that of healthy plants grown under conditions of adequate or restricted water supply.
The transpiration of excised leaves from plants grown with a restricted water supply was reduced, but not so severely as that of comparable leaves from infected plants. Water loss from leaves on infected plants was reduced irrespective of any blocking of the petiolar xylem.
The rate of water loss from turgid leaf disks on mannitol solutions, and the rate of water uptake of leaf disks on water was similar for disks cut from wilting or turgid leaves of diseased plants or healthy plants grown with an adequate or restricted water supply.
Disease or poor water supply reduced leaf growth but had no effect on the rate of leaf initiation. Although the density of stomata was higher on leaves of diseased plants the stomatal area was less than on healthy plants.
The resistance to water flow in diseased stems was high and was correlated with vessel blockage. About half the blocked vessels contained hyphae. The severity and localization of symptoms in inoculated plants growing on susceptible or resistant rootstocks was directly related to the extent of invasion by the pathogen and to vessel blockage.
Experiments on the wilting activity of cell-free filtrates from cultures of the pathogen in vitro indicated that it produced a stable substance, not an enzyme, that caused wilting in cut shoots by blocking the end of the stem. It is suggested that an increasing internal water shortage causes major symptoms of disease.     

Concurrent comparisons of stomatal behavior, water status, and evaporation of maize in soil at high or low water potential

Concurrent measurements of evaporation, leaf conductance, irradiance, leaf water potential, and osmotic potential of maize (Zea mays L. cv. Pa602A) in soil at either high or low soil water potential were compared at several hours on two consecutive days in July. Hourly evaporation, measured on two weighing lysimeters, was similar until 1000 hours Eastern Standard Time, but thereafter evaporation from the maize in the dry soil was always less than that in the wet soil; before noon it was 62% and by midafternoon, only 35% of that in the wet soil. The leaf water potential, measured with a pressure chamber, was between −1.2 and −2.5 bars and between −6.8 and −8 bars at sunrise (about 0530 hours Eastern Standard Time) in the plants in the wet and dry soil, respectively, but decreased quickly to between −8 and −13 bars in the plants in the wet soil and to less than −15 bars in the plants in the dry soil by 1100 to 1230 hours Eastern Standard Time. At this time, the leaf conductance of all leaves was less than 0.1 cm sec⁻¹ in the maize in the dry soil, whereas the conductance was 0.3 to 0.4 cm sec⁻¹ in the leaves near the top of the canopy in the wet soil. The osmotic potential, measured with a vapor pressure osmometer, also decreased during the morning but to a smaller degree than leaf water potential, so that by 1100 to 1230 hours Eastern Standard Time the leaf turgor potential was 1 to 2 bars in all plants. Thereafter, leaf turgor potential increased, particularly in the plants in soil at a high water potential, whereas leaf water potential continued to decrease even in the maize leaves with partly closed stomata. Evidently maize can have values of leaf conductance differing 3- to 4- fold at the same leaf turgor potential, which suggests that stomata do not respond primarily to bulk leaf turgor potential. Evidence for some osmotic adjustment in the plants at low soil water potential is presented. Although the degree of stomatal closure in the maize in dry soil did not prevent further development of stress, it did decrease evaporation in proportion to the decrease in canopy conductance.     

STUDIES IN THE RELATIONSHIP OF EELWORMS AND BACTERIA TO CERTAIN PLANT DISEASES

Two types of organism are known to be present in strawberry plants suffering from cauliflower disease, namely, eelworms, Aphelenchoides ritzema-bosi and/or Aphelenchoides fragariae , and a bacterium, Corynebacterium fascians. Neither type, inoculated separately, has consistently reproduced the disease.
An experimental investigation of a possible obligate etiological relationship between the eelworm and the bacterium is described, in which Aphelenchoides ritzema-bosi and several strains of Corynebacterium fascians were inoculated together and separately.
No abnormalities appeared in the absence of the eelworm. Typical cauliflower symptoms were reproduced only by a combination of the eelworm and strains of C. fascians originally isolated from cauliflower strawberries. Small alaminate leaves and enations appeared in all treatments where the eelworm was introduced, including those where no bacteria were co-inoculated. Subsequent isolations, however, demonstrated the presence of contaminant strains of C. fascians in the latter plants. The severity of the enation symptom was related to the presence of a particular strain of C. fascians , but the alaminate leaves showed no such correlation. Evidence on the source of the contaminant strains found in the experimental plants is discussed.
In parallel field investigations it was established that eelworm-infested strawberries showing no cauliflower symptom frequently bore alaminate leaves, with which C. fascians was consistently associated. It is suggested therefore that cauliflower is simply the least frequent of a range of symptoms of a bacterial disease endemic in strawberry plants infested with Aphelenchoides spp.     

Photosynthesis, Transpiration, Leaf Temperature, and Stomatal Activity of Cotton Plants under Varying Water Potentials

Cotton plants, Gossypium hirsutum L. were grown in a growth room under incident radiation levels of 65, 35, and 17 Langleys per hour to determine the effects of vapor pressure deficits (VPD's) of 2, 9, and 17 mm Hg at high soil water potential, and the effects of decreasing soil water potential and reirrigation on transpiration, leaf temperature, stomatal activity, photosynthesis, and respiration at a VPD of 9 mm Hg.

Transpiration was positively correlated with radiation level, air VPD and soil water potential. Reirrigation following stress led to slow recovery, which may be related to root damage occurring during stress. Leaf water potential decreased with, but not as fast as, soil water potential.

Leaf temperature was usually positively correlated with light intensity and negatively correlated with transpiration, air VPD, and soil water. At high soil water, leaf temperatures ranged from a fraction of 1 to a few degrees above ambient, except at medium and low light and a VPD of 19 mm Hg when they were slightly below ambient, probably because of increased transpirational cooling. During low soil water leaf temperatures as high as 3.4° above ambient were recorded. Reirrigation reduced leaf temperature before appreciably increasing transpiration. The upper leaf surface tended to be warmer than the lower at the beginning of the day and when soil water was adequate; otherwise there was little difference or the lower surface was warmer. This pattern seemed to reflect transpiration cooling and leaf position effects.

Although stomata were more numerous in the lower than the upper epidermis, most of the time a greater percentage of the upper were open. With sufficient soil water present, stomata opened with light and closed with darkness. Fewer stomata opened under low than high light intensity and under even moderate, as compared with high soil water. It required several days following reirrigation for stomata to regain original activity levels.

Apparent photosynthesis of cotton leaves occasionally oscillated with variable amplitude and frequency. When soil water was adequate, photosynthesis was nearly proportional to light intensity, with some indication of higher rates at higher VPD's. As soil water decreased, photosynthesis first increased and then markedly decreased. Following reirrigation, photosynthesis rapidly recovered.

Respiration was slowed moderately by decreasing soil water but increased before watering. Respiration slowed with increasing leaf age only on leaves that were previously under high light intensity.

     

水淹导致皇冠草光合机构发生变化并加剧其出水后光抑制

通过气体交换和叶绿素荧光等方法研究了水淹及胁迫解除后皇冠草不同功能叶的光合特性及光抑制的变化.结果表明:与对照相比,气生叶(全淹组淹水前形成的功能叶)在水淹条件下叶片大小和气孔没有明显变化,但沉水叶(全淹组淹水后新生的功能叶)的叶面积增加,气孔变小,上表皮气孔密度增加.水淹导致气生叶碳同化能力、光化学效率和叶绿素含量下降.沉水叶在发育过程中碳同化能力、光化学效率和叶绿素逐渐升高.气生叶和沉水叶出水后其活体叶片在强光下的相对含水量急剧下降,发生明显的光抑制;而弱光下无明显光抑制发生.出水后离体叶片强光照射下6h后两种功能叶均发生严重光抑制,且弱光下不能恢复.因此,可以认为淹水条件下,沉水叶上表皮气孔密度的增加使其蒸腾速率提高;沉水叶较强的碳同化能力和增加的叶面积是确保其植株水下生存的重要因素;强光使气生叶和沉水叶出水后均发生严重光抑制,导度和蒸腾速率提高导致的叶片失水则加剧了这一过程,两者共同作用导致自然条件下两种功能叶的出水死亡.