Ontogenetic changes in stomatal size and conductance of sunflowers

The ontogenetic changes in stomatal size, frequency and conductance (g_s) on abaxial and adaxial leaf surfaces of sunflower plants (Helianthus annuus L. Russian Mammoth) were examined under controlled environmental conditions. The stomatal frequency on the adaxial and abaxial leaf surfaces decreased with leaf ontogeny and insertion level. The ratio of adaxial to abaxial stomatal frequency did not change with leaf ontogeny and insertion level, and 42–44% of total stomata was apportioned to the adaxial surface. Ontogenetic changes in stomatal pore length were detected and increased with ontogenesis. The stomatal length of both leaf surfaces had linear relationships with leaf area. Ontogenetic changes in g_s were similar between the two surfaces. However the adaxial g_s was lower than abaxial g_s in leaves of higher insertion levels. Conductance had a linear relationship with width x frequency but not with pore area.     

Abaxial and Adaxial Stomatal Density, Stomatal Conductances and Water Status of Bean Primary Leaves as Affected by Paclobutrazol

The plant growth retardant, paclobutrazol at 8.5 or 17.0 μM concentrations effectively inhibited the stem elongation and primary leaf expansion of bean seedlings. Although the retardant reduced the relative water content in well-watered plants, the water and pressure potentials remained high in the primary leaves. K⁺, Na⁺, Mg²⁺ and Ca²⁺ contents in the primary leaves of the paclobutrazol-treated plants were not significantly different from those in the control. The stomatal density increased on both surfaces but the length of guard cells was not reduced significantly on the adaxial epidermes of the paclobutrazol-treated primary leaves. The inhibitory effect of paclobutrazol on the abaxial stomatal conductances became more pronounced with time during the light period but the adaxial surfaces displayed similar or slightly higher conductances than those of the control. The transpiration rate on a unit area basis did not change significantly or increased in the treated leaves thus the reduced water loss of paclobutrazol-treated plants was due to the reduced leaf area. Stomatal conductances of the adaxial surfaces responded more intensively to exogenous abscisic acid and the total leaf conductance decreased faster with increasing ABA concentration in the control than in the paclobutrazol-treated leaves. Paclobutrazol, an effective inhibitor of phytosterol biosynthesis, not only amplified the stomatal differentiation but increased the differences between the adaxial and abaxial stomatal conductances of the primary leaves.     

Effects of low level O3 exposure on leaf diffusive conductance and water-use efficiency in hybrid poplar

Abstract Young, amphistomatous hybrid poplar (Populus deltoides x trichocarpa) plants were exposed daily to either background (0.025 cm³ m^-3) or elevated (0.125 cm³ m^-3) concentrations of O₃. Levels of abaxial and adaxial leaf conductance were affected interactively by pollutant treatment, leaf age, and photon fluence rate. Consequently, conductance in O₃-treated leaves was sometimes higher and sometimes lower than in comparable control leaves, depending on leaf age or level of photon fluence rate. For example, at low photon fluence rate or in the dark, conductance was greater in O₃-treated than in control plants, while at high photon fluence rate that relationship was reversed. Exposure to O₃ also reduced the water-use efficiency and range of leaf conductance of individual leaves, and altered the relationship between the conductances of the two leaf surfaces (the ratio of abaxial to adaxial leaf conductance was increased). Furthermore, O₃ treatment resulted in diminished stomatal control of water loss; excised O₃-treated leaves had higher conductances and wilted sooner than excised control leaves of identical ages. Overall, the data indicate that exposure to O₃ resulted in impaired stomatal function.     

Development of water stress in kale leaves of different insertion levels

The mutual relationship between the water potential (γ _w ), its components, namely the osmotic potential (γ _s ) and the pressure potential (γ _p ), and the water saturation deficit (ΔW _sat ) were determined in the leaves of different insertion levels. During the water stress development in kale plants induced by decreasing soil moisture theγ _w decreased, parallely in all the leaves but the same decrease ofγ _q was accompanied by the highest decrease of theγ _p , probably due to the accumulation of osmotically active solutes, and the lowest decrease ofγ _p in the upper leaves and with the lowest decrease ofγ _s and the highest decrease ofγ _p in the lower leaves. Also the corresponding values of the ΔW _sat were always lower in the upper than in the middle and lower leaves. Thus the upper leaves wilted at more negative values ofγ _w than the other leaves. On the contrary, during the wilting of the cut off leaves the relationship betweenγ _w and ΔW _sat in the upper, middle and lower leaves was practically the same. The very slightly higher decrease ofγ _s in the upper leaves in comparison with the other leaves was compensated by a lower deerease of theirγ _p . These changes in the ratios ofγ _w ,γ _s ,γ _p and ΔW _sat with the leaf insertion levels enabled the preference of the upper leaves in retaining the necessary water supply during the wilting of plantsin situ.     

Water stress development in kale leavesin situ and in water supplied cut leaves

The development of temporary water stress during the day-light hours, characterized by a decrease of the values of the water potential (?_w) and increase of the values of water saturation deficit (ΔW _sat) was found not only in the leaves of intact kale plants but also in cut leaves with their petioles immersed in water. These results indicate that the leaf resistance to water transport could not be supposed as negligible. The same decrease of ? _w was accompanied with the higher increase of ΔW _sat in cut leaves than in leavesin situ.     

Kinetic characterization of reduced pyridine nucleotide dehydrogenases (duroquinone-dependent) in cucurbita microsomes

Stomatal conductances of normally oriented and inverted leaves were measured as light levels (photosynthetic photon flux densities) were increased to determine whether abaxial stomata of Vicia faba leaves were more sensitive to light than adaxial stomata. Light levels were increased over uniform populations of leaves of plants grown in an environmental chamber. Adaxial stomata of inverted leaves reached maximum water vapor conductances at a light level of 60 micromoles per square meter per second, the same light level at which abaxial stomata of normally oriented leaves reached maximum conductances. Abaxial stomata of inverted leaves reached maximum conductances at a light level of 500 micromoles per square meter per second, the same light level at which adaxial stomata of normally oriented leaves reached maximum conductances. Maximum conductances in both normally oriented and inverted leaves were about 200 millimoles per square meter per second for adaxial stomata and 330 millimoles per square meter per second for abaxial stomata. Regardless of whether leaves were normally oriented or inverted, when light levels were increased to values high enough that upper leaf surfaces reached maximum conductances (about 500 micromoles per square meter per second), light levels incident on lower, shaded leaf surfaces were just sufficient (about 60 micromoles per square meter per second) for stomata of those surfaces to reach maximum conductances. This `coordinated' stomatal opening on the separate epidermes resulted in total leaf conductances for normally oriented and inverted leaves that were the same at any given light level. We conclude that stomata in abaxial epidermes of intact Vicia leaves are not more sensitive to light than those in adaxial epidermes, and that stomata in leaves of this plant do not respond to light alone. Additional factors in bulk leaf tissue probably produce coordinated stomatal opening on upper and lower leaf epidermes to optimally meet photosynthetic requirements of the whole leaf for CO₂.     

Water potential,water saturation deficit and their relationship in leaves of different insertion levels

The water potential (Ψ _w ) and the water saturation deficit (δW _sat) in leaves of different insertion levels of potted kale plants were simultaneously measured. In non-wilting plantsδW _sat gradually decreased andΨ _w slightly increased from the upper to the lower leaves. During the wilting of the plants induced by decreasing of soil moistureΨw practically decreased paralelly in all the leaves but the same decrease ofΨ _w was connected with the lowest increase ofδW _sat in upper leaves and the highest increase ofδW _sat in lower leaves. Not only the values ofΨ _w andδW _sat but also their relationship varied considerably with the leaf insertion levels.     

Water potential — water saturation deficit relationship during dehydration and resaturation of leaves

The relationship between the water potential (Ψ_w) and the water saturation deficit (Δ W _sat) in kale and maize leaf tissue was measured during dehydration and resaturation either of leavesin situ or of cut leaves. The curves relating Ψ_w toΔW _sat were similar in all variants, but at the same values ofΔ W _sat corresponding values of Ψ_w were always lower in leavesin situ than in cut leaves and during dehydration than during resaturation.     

Photosynthetic costs and benefits of abaxial versus adaxial anthocyanins in Colocasia esculenta ‘Mojito’

Main conclusion

Anthocyanins in upper (adaxial) leaf tissues provide greater photoprotection than in lower (abaxial) tissues, but also predispose tissues to increased shade acclimation and, consequently, reduced photosynthetic capacity. Abaxial anthocyanins may be a compromise between these costs/benefits. Plants adapted to shaded understory environments often exhibit red/purple anthocyanin pigmentation in lower (abaxial) leaf surfaces, but rarely in upper (adaxial) surfaces. The functional significance of this color pattern in leaves is poorly understood. Here, we test the hypothesis that abaxial anthocyanins protect leaves of understory plants from photo-oxidative stress via light attenuation during periodic exposure to high incident sunlight in the forest understory, without interfering with sunlight capture and photosynthesis during shade conditions. We utilize a cultivar of Colocasia esculenta exhibiting adaxial and abaxial anthocyanin variegation within individual leaves to compare tissues with the following color patterns: green adaxial, green abaxial (GG), green adaxial, red abaxial (GR), red adaxial, green abaxial (RG), and red adaxial, red abaxial (RR). Consistent with a photoprotective function of anthocyanins, tissues exhibited symptoms of increasing photoinhibition in the order (from least to greatest): RR, RG, GR, GG. Anthocyanic tissues also showed symptoms of shade acclimation (higher total chl, lower chl a/b) in the same relative order. Inconsistent with our hypothesis, we did not observe any differences in photosynthetic CO₂ uptake under shade conditions between the tissue types. However, GG and GR had significantly (39 %) higher photosynthesis at saturating irradiance (A _sat) than RG and RR. Because tissue types did not differ in nitrogen content, these patterns likely reflect differences in resource allocation at the tissue level, with greater nitrogen allocated toward energy processing in GG and GR, and energy capture in RG and RR (consistent with relative sun/shade acclimation). We conclude that abaxial anthocyanins are likely advantageous in understory environments because they provide some photoprotection during high-light exposure, but without the cost of decreased A _sat associated with adaxial anthocyanin-induced shade syndrome.     

Photosynthetic CO2 uptake byZea mays leaves as influenced by unilateral irradiation of adaxial and abaxial leaf surfaces

A study was made on the effect of increasing photon fluence rate (I) at a unilateral irradiation of adaxial (normal leaf position) and abaxial (inverse leaf position) blade surface of maize leaves of various insertion levels on net photosynthetic CO₂ uptake (P _n ) by the leaves, as well as the contribution of individual surfaces toP _n of the leaves, and the significance of, or relationship between the stomatal (g _s ) and intracellular (gm) conductances at the CO₂ transport.P _n of leaves of various age according to their insertion level was unaffected by the direction of incident irradiation. Upon irradiation of the leaves in normal and inverse position the contribution of the adaxial and abaxial surfaces toP _n ,g _s and g_m was different. On irradiating the leaves in normal position, the contribution of the irradiated adaxial surface to the characteristics mentioned made on the average 55% of total values, the contribution of the abaxial surface irradiated in inverse position made on the average 70% inP _n andg _m , and 80% ing _s . At lowerI’s g _m was higher thang _s both in irradiated and non-irradiated surfaces. The ratio ofg _s to g_m gradually got square with increasingI. In the irradiated adaxial surface the equilibrium (g _s /g _m = 1.0) took place at the highestI’s, in the irradiated abaxial surface between 500 to 1000 μmol m⁻² s⁻¹. The significance of the ratiog _m in the CO₂ transport through the individual surfaces is discussed.     

Purification of the Trehalase GMTRE1 from Soybean Nodules and Cloning of Its cDNA. GMTRE1 Is Expressed at a Low Level in Multiple Tissues

The effects of ultraviolet-B (UV-B) radiation on stomatal conductance (g_s) in pea (Pisum sativum L.), commelina (Commelina communis L.), and oilseed rape (Brassica napus L.) plants were investigated. Plants were grown in a greenhouse either with three different high ratios of UV-B to photosynthetically active radiation or with no UV-B radiation. Pea plants grown in the highest UV-B radiation (0.63 W m⁻²) exhibited a substantial decrease of adaxial and abaxial g_s (approximately 80% and 40%, respectively). With growth in 0.30 W m⁻² of UV-B adaxial g_s was decreased by 23%, with no effect on abaxial g_s, and lower UV-B irradiance of 0.21 W m⁻² had no effect on either surface. Although abaxial g_s increased when leaves were turned over in control plants, it did not in plants grown with the highest UV-B. Adaxial g_s in commelina and oilseed rape also decreased on exposure to high UV-B (0.63 W m⁻²). For previously unexposed pea plants the time course of the effect of UV-B on g_s was slow, with a lag of approximately 4 h, and a time constant of approximately 3 h. We conclude that there is a direct effect of UV-B on stomata in addition to that caused by changes in mesophyll photosynthesis.     

Studies on octylphenoxy surfactants: IX. Effect of oxyethylene chain length on GA3 absorption by sour cherry leaves

The effect of a homologous series of octylphenoxy surfactants, α-[4-(1,1,3,3-tetramethylbutyl)phenyl]-ω-hydroxypoly-(oxy-1,2-ethanediyl), condensed with 5, 7–8, 9–10, 16, and 30 oxyethylene (EO) units on enhancement of gibberellic acid (GA₃) absorption by leaves ofPrunus cerasus cv. Montmorency was studied. Increasing EO chain length (5–30 EO) increased surface tension (27.5–35.3 mN m^?1) and contact angles on adaxial (21–36°) and abaxial (28–49°) leaf surfaces. With increasing EO content, the form of GA₃ deposits from droplets on the leaf surface changed from an annulus shape (5 and 7–8 EO) to globular forms covering increasingly smaller interface areas (9–10 to 30 EO). The surfactants increased GA₃ uptake, the magnitude decreased with an increase in oxyethylene chain length. Similar trends were found for both the adaxial and abaxial surfaces. Penetration through the abaxial surface was linearly related to the logarithm of the oxyethylene content of the surfactant molecule (r ²=0.934^**) and to the hydrophilic: lipophilic balance (r ²=0.926^**). Absorption by the abaxial surface was approximately one order of magnitude greater than by the adaxial surface.     

Diffusive conductance of rice (Oryza sativa) leaves during gradually induced soil water stress

The diffusive conductance (C_s) of rice (Oryza sativa cvs Jaya and Bala) leaves was measured during a soil drying cycle from flooding to decreasing soil water potential (φ_s) in a controlled-environment chamber. Plants were grown continuously under 5 cm submergence up to 69 days after transplanting and thereafter were subjected to gradual soil drying for a period of 17 days in the vegetative growth stage. In both the cultivars, the values of C_s were generally more on adaxial than abaxial leaf surfaces. This response of stomata during the period of soil drying was independent of leaf rolling. Further, the slopes of the curves (C_s, vs φ_s) also did not differ significantly (P= 0·05). The total C_s, of both cultivars during flooding was almost equal (0·60 cm s^-1) but at the end of the soil drying cycle, the values of total C_s, were 0·11 cm s^-l at ψ_s of -1·3 MPa and 0·08 cm s^-1 at ψ_s, of -0·8 MPa in cvs Jaya and Bala, respectively. For total C_s, slopes differed significantly (P = 0·05). A close relationship between total C_s, and ψ_s, in both cultivars (C_s, = 0·58-0·40 ψ_s, for cv. Jaya and C_s= 0·46-0·56 ψ_s, for cv. Bala) indicated that stomata were sensitive to increasing soil water deficit.     

An apparent anomaly in peanut leaf conductance

Conductance to gaseous transfer is normally considered to be greater from the abaxial than from the adaxial side of a leaf. Measurements of the conductance to water vapor of peanut leaves (Arachis hypogaea L.) under well watered and stress conditions in a controlled environment, however, indicated a 2-fold higher conductance from the adaxial side of the leaf than from the abaxial. Studies of conductance as light level was varied showed an increase in conductance from either surface with increasing light level, but conductance was always greater from the adaxial surface at any given light level. In contrast, measurements of soybean (Glycine max [L.] Merr.) and snapbean (Phaseolus vulgaris L.) leaf conductance showed an approximate 2-fold greater conductance from the abaxial surface than from the adaxial. Approximately the same number of stomata were present on both peanut leaf surfaces and stomatal size was similar. Electron microscopic examination of peanut leaves did not reveal any major structural differences between stomata on the two surfaces that would account for the differences in conductance. Light microscope studies of leaf sections revealed an extensive network of bundle sheaths with achloraplastic bundle sheath extensions; the lower epidermis was lined with a single layer of large achloraplastic parenchyma cells. Measurements of net photosynthesis made on upper and lower leaf surfaces collectively and individually indicated that two-thirds of the peanut leaf's total net photosynthesis can be attributed to diffusion of CO₂ through the adaxial leaf surface. Possibly the high photosynthetic efficiency of peanut cultivars as compared with certain other C₃ species is associated with the greater conductance of CO₂ through their upper leaf surfaces.     

The citrus leaf cuticle in relation to measurement of leaf water potential using thermocouple psychrometers*

Abstract. Cuticular resistance to water vapour diffusion is an important aspect of thermocouple psychrometry and may introduce significant error in the measurement of leaf water potential (Ψ). The effect of the citrus (Citrus mitis Blanco) leaf cuticle on water vapour movement was studied using the times required for vapour pressure equilibration during thermocouple psychrometric measurement of Ψ. Cuticular abrasion with various carborundum powders was used to reduce the diffusive resistance of both the adaxial and abaxial leaf surfaces, and the extent of the disruption to the leaf was investigated with light and electron microscopy. Cuticular abrasion resulted in reduced equilibration times due to decreased cuticular resistance and greater water vapour movement between the leaf and the psychrometer chamber. Equilibration times were reduced from over 5 h in the unabraded control leaves to 1 h with cuticle abrasion. This was associated with the decrease in diffusive resistance with cuticular abrasion from over 55 s cm^?1 to less than 8 s cm^?1 for both the adaxial and abaxial leaf surfaces. Scanning electron micrographs of the abraded leaf tissue revealed considerable disruption of the stomatal ledge and of the guard cells, surface smoothing and displacement of waxes into the stomatal aperture, and damage to veins. Observations with the transmission electron microscope revealed frequent disruption of epidermal cell walls, and damage to both the cytoplasmic and vacuolar membranes.     

Effect of hydration level in primary bean leaves on the activity of photosystems 1 and 2 in isolated chloroplasts

Water stress in the leaves was induced by gradual decreasing of substrate moisture in five-day cycles.The hydration level of the leaves was characterized by their water potential (ψ_w), osmotic potential (ψ_s), pressure potential ψ_p and water saturation deficit(ΔW _sat ).The activities of Photosystems 1 and 2 were determined polarographically with Pt/Ag(AgOH) electrode as changes in oxygen concentration in chloroplast suspensions. The shape of light curves of Hill reaction was not influenced by leaf (ψ_w), hence both quantum efficiency and dark phase of this process were affected in a similar manner by water deficit. The activities of both photosystems measured at saturating photon flux density declined with the lowering of leaf (ψ_w) (in the range from -5 to -14 x 10⁵ Pa) and the decrease in activity of Photosystem 2 was more rapid than that of Photosystem 1. The ratio of activities of Photosystems 1 and 2 was mildly enhanced by a lowering of (ψ_w), but it decreased with increasing age. The lowering of ψ_winduced lowering in the chlorophyll a/b ratio thus concealing the usual ontogenetic course of this ratio.     

Gas exchange of root hemi-parasite Striga hermonthica and its host Sorghum bicolor under short-term soil water stress

The gas exchange of the upper fully expanded leaf of the root parasite Striga hermonthica and of its host Sorghum bicolor was measured under wet and dry conditions to identify the mechanisms of the devastating effects of the parasite on its hosts under drought. The short-term water stress severely reduced photosynthetic rate in infected sorghum, but less in S. hermonthica. Soil water stress did not affect leaf respiration rate in either S. hermonthica or infected sorghum. This suggests that under dry conditions both infected sorghum and S. hermonthica decreased autotrophic carbon gain. The transpiration rate of S. hermonthica, a major driving force for assimilate uptake from the host, was higher and less affected by water stress than that of infected sorghum. Stomatal density on the abaxial surfaces of the leaves was higher in S. hermonthica than in sorghum. Both S. hermonthica infection and water stress decreased stomatal conductance of the sorghum leaves. S. hermonthica, irrespective of soil water status, had greater stomatal aperture on the adaxial and abaxial surfaces of its leaves than infected sorghum. These results indicate that the higher transpiration rate of S. hermonthica even under water stress, achieved through higher stomatal density on the abaxial surfaces of the leaves and greater stomatal aperture on both surfaces of the leaves, may induce the maintenance of water and solute transfers from the host to the parasite leading to severe damage to the host under drought.     

The boundary layer and the apparent responses of stomatal conductance to wind speed and to the mole fractions of CO2 and water vapour in the air

The experiments and simulations reported in this paper show that, for stomata sensitive to both CO₂ and water vapour concentrations, responses of stomatal conductance (g^w_s) to boundary layer thickness have two components, one resulting from changes in intercellular CO₂ concentration (χ^c_i) and another from changes in leaf surface water vapour saturation deficit (D^w_s). The experiments and simulations also show that the boundary layer conductance (g^w_b) can significantly alter the apparent response of g^w_s to ambient air CO₂ mole fraction (χ^c_a) and water vapour mole fraction (χ^w_a). Because of the feedback loop involved the responses of g^w_s for χ^c_a and χ^w_a each include responses to both χ^c_i and D^w_s. The boundary layer alters the state of the variables sensed by the guard cells—i.e. χ^c_i and D^w_s—and so it is a source of feedback. Thus, when scaling up from responses of stomata to the response of g^w_s for a whole leaf, the effect of the boundary layer must be considered. The results indicate that, for given responses of g^w_s to χ^c_i and D^w_s, the apparent responses of g^w_s to D^w_a and χ^c_a depend on the size of the leaf and wind speed, showing that this effect of the boundary layer should be considered when comparing data measured under different conditions, or with different methods.     

CO2 and water vapour exchange through adaxial and abaxial surfaces of tobacco leaves of different insertion level

CO₂ uptake (P _N ) and water vapour efflux (E) through adaxial and abaxial surfaces were measured separately and the corresponding diffusive resistances for water vapour (r ₁) were calculated in leaves of different insertion levels during vegetative growth of tobacco plants. Relatively higher values of the abaxialP _N/E ratio in comparison with the adaxial one were found in agreement with relatively higherE _ad/E _ab coefficients and the distribution of the gas exchange in plants in all measurements carried out. Because of the more rapid decrease of theP _N rates as compared with theE rates theP _N/E ratios of both surfaces decreased gradually from young to old leaves. The decreasing values ofE _ad/E _ab andP _N,ab/P _N,ab coefficients showed thatr _1,ab increased with the age of the leaves more quickly thanr _1,ab.     

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.