Stomatal responsiveness to leaf water status in common bean (Phaseolus vulgaris L.) is a function of time of day

Stomatal response to leaf water status was experimentally manipulated by pressurizing the soil and roots of potted common bean plants enclosed in a custom‐built root pressure chamber. Gas exchange was monitored using a whole‐plant cuvette and plant water status using in situ leaf psychrometry. Bean plants re‐opened their stomata upon pressurization, but the extent of re‐opening was strongly dependent on the time of day when the soil was pressurized, with maximum re‐opening in the morning hours and limited re‐opening in the afternoon. Neither leaf nor xylem abscisic acid concentrations could explain the reduced response to pressurization in the afternoon. The significance of this phenomenon is discussed in the context of circadian rhythms and of other recent findings on the ‘apparent feed‐forward response’ of the stomata of some species to vapour pressure deficit.     

Stomatal Opening in Isolated Epidermal Strips of Vicia faba. I. Response to Light and to CO(2)-free Air

This paper reports a consistent and large opening response to light + CO₂-free air in living stomata of isolated epidermal strips of Vicia faba. The response was compared to that of non-isolated stomata in leaf discs floating on water; stomatal apertures, guard cell solute potentials and starch contents were similar in the 2 situations. To obtain such stomatal behavior, it was necessary to float epidermal strips on dilute KCl solutions. This suggests that solute uptake is necessary for stomatal opening.

The demonstration of normal stomatal behavior in isolated epidermal strips provides a very useful system in which to investigate the mechanism of stomatal opening. It was possible to show independent responses in stomatal aperture to light and to CO₂-free air.

     

Response of stomatal resistance and photosynthesis to night temperature in Populus deltoides

Summary Ramets from stem cuttings of three populations of Populus deltoides Bartr. from Wisconsin, Illinois, and Louisiana representing a latitudinal gradient were grown in pots outdoors at Urbana, Illinois and brought indoors for growth chamber studies. Leaf resistance and photosynthetic response to low night temperatures of 4° and 10° C were determined relative to 20° C controls for plants measured over one growing season. Plants from Louisiana, where nights are warm, reacted to cool nights of 4° and 10° C by opening their stomata slower upon illumination the following day than those from farther north where nights are cooler. The optimum night temperature for rate of opening was lower in the Wisconsin population than in populations from farther south. The Wisconsin population showed more ideal homeostasis of photosynthesis at different temperatures than the southern population which exhibited greater plasticity. No seasonal differences in these relationships were apparent other than at the time of leaf senescence.As plants approached senescence, which occurred earliest in the Wisconsin population, leaf resistance increased and photosynthesis declined, but stomata still retained their functional ability to respond to changes in night temperature. The change in leaf resistance, noted in the Wisconsin population, was related more to closure of lower-leaf surface stomata than upper. Only the Louisiana population had significantly more stomata on the lower than upper leaf surface.     

Design of a bacterial speck resistant tomato by CRISPR/Cas9‐mediated editing of SlJAZ2

Due to their different lifestyles, effective defence against biotrophic pathogens normally leads to increased susceptibility to necrotrophs, and vice versa. Solving this trade‐off is a major challenge for obtaining broad‐spectrum resistance in crops and requires uncoupling the antagonism between the jasmonate (JA) and salicylate (SA) defence pathways. Pseudomonas syringae pv. tomato (Pto) DC3000, the causal agent of tomato bacterial speck disease, produces coronatine (COR) that stimulates stomata opening and facilitates bacterial leaf colonization. In Arabidopsis, stomata response to COR requires the COR co‐receptor AtJAZ2, and dominant AtJAZ2Δjas repressors resistant to proteasomal degradation prevent stomatal opening by COR. Here, we report the generation of a tomato variety resistant to the bacterial speck disease caused by PtoDC3000 without compromising resistance to necrotrophs. We identified the functional ortholog of AtJAZ2 in tomato, found that preferentially accumulates in stomata and proved that SlJAZ2 is a major co‐receptor of COR in stomatal guard cells. SlJAZ2 was edited using CRISPR/Cas9 to generate dominant JAZ2 repressors lacking the C‐terminal Jas domain (SlJAZ2Δjas). SlJAZ2Δjas prevented stomatal reopening by COR and provided resistance to PtoDC3000. Water transpiration rate and resistance to the necrotrophic fungal pathogen Botrytis cinerea, causal agent of the tomato gray mold, remained unaltered in Sljaz2Δjas plants. Our results solve the defence trade‐off in a crop, by spatially uncoupling the SA‐JA hormonal antagonism at the stomata, entry gates of specific microbes such as PtoDC3000. Moreover, our results also constitute a novel CRISPR/Cas‐based strategy for crop protection that could be readily implemented in the field.     

The role of epidermal turgor in stomatal interactions following a local perturbation in humidity

Humidity in a small area of a Vicia faba L. leaf was perturbed with a flow of dry air from an 80 µm (inside diameter) needle, while the remainder of the leaf was maintained at high and constant humidity. The influence of the needle flow on the humidity at the leaf surface was quantified by using a spatially explicit dewpoint hygrometer to observe condensation patterns. When the dry air from a needle was applied to the leaf, stomata within the influence of the needle opened within the first few minutes of the perturbation, and local epidermal turgor pressure declined within the same time frame. When the needle flow was removed from the leaf, these responses were reversed, but with more variable kinetics. Stomata and epidermal cells outside the influence of the needle flow, which were exposed to a constant and high humidity, showed similar, but smaller, responses when the needle flow was applied to the leaf. Since the opening of these stomata should have had only a small effect on transpiration (because of the high humidity), it is likely that the reduction in epidermal turgor was the cause (rather than the result) of the stomatal opening. The magnitude of the turgor response was only loosely related to the distance from the needle flow up to distances of almost 400 µm. The data support the idea that neighbouring stomata can interact through the influence of transpiration on epidermal turgor.     

Stomatal Responses of Fraxinus pennsylvanica Seedlings during and after Flooding

Effects of flooding for 10, 20, 30, or 40 days on leaf diffusion resistance (r₁) of fraxinus pennsylvanica seedlings were studied during the period of flooding and continuing for 17 days after flooding. All Flooding treatments induced stomatal closure, as indicated by increased r₁. There was some evidence of stomatal adaptation to flooding, with stomata beginning to reopen after a critical period of flooding. After termination of flooding, stomata opened further within 6 to 10 days to near preflooding levels. The degree of stomatal opening was only slightly higher after 10 days than after 40 days of flooding. Some stomata may have been permanently damaged by flooding. The stomatal adaptation to flooding as well as rapid recovery of stomatal opening, even after prolonged flooding, appeared to be important factors in the flooding tolerance of Fraxinus petmsylvanica and are consistent with its distribution on wet sites.     

中国北方鸢尾属植物叶片解剖结构特征及分类学价值研究

以中国北方生长的鸢尾属9种植物为研究对象,利用光学显微镜对叶表皮细胞形状及大小、气孔大小、气孔分布及气孔密度、气孔指数等叶表皮构造特征进行观察,并探讨了叶表皮特征在鸢尾属内各个亚属、亚组间的分类学价值,结果表明：表皮细胞的形状和大小显示了同亚属或同亚组植物之间较为明显的亲缘关系,在区分鸢尾属下不同亚属或亚组植物上也有一定的分类学价值。气孔密度和气孔指数在鸢尾属内分类学价值不大,但却能很好地反映不同鸢尾属植物与生境之间的密切关系。并从表皮构造特征上证实了野鸢尾与射干有很强的亲缘关系,且近于鸢尾属内的其他植物的结论;此外,通过对鸢尾属植物叶横切解剖结构的观察：从维管束、横切面形状、表皮细胞与角质层、乳突、气孔、气室大小、叶肉细胞的分化这7个较为明显的特征上的相关性和差异性,探讨了由于生境的不同而产生的植物形态结构的差异。     

Drought-induced increase in xylem malate and mannitol concentrations and closure of Fraxinus excelsior L. stomata

Changes in the malate and mannitol composition of ash leaf (Fraxinus excelsior L.) xylem sap were studied in response to water deficit. Xylem sap was collected by the pressure method from the petiole of leaves sampled on irrigated and non-irrigated ash seedlings. As the leaf water potential decreased from -0.3 to -3.0 MPa, there was a significant increase in malate and mannitol xylem concentrations, and a concomitant decrease in maximal stomatal conductance. The functional significance of the increased malate and mannitol concentrations was investigated by using a transpiratory bioassay with mature detached leaves which exhibited, for stomatal conductance, the typical pattern showed by expanded leaves during dark/light transitions. Supplying detached leaves with mannitol in a range of concentrations found in the xylem sap had no effect on stomatal movements, but malate, for concentrations between 0.5 and 3 mM, was effective in preventing stomatal opening. The ability of malate to inhibit stomatal opening appeared to be rather non-specific. Two structural malate analogues, citrate and aspartate or an unrelated anion, shikimate, also inhibited this process. Given the drought-induced increase in xylem malate concentrations, and the fact that the range of malate levels required to close stomata was very similar to that of the concentrations found in the xylem sap, it has been hypothesized that malate is involved in the stomatal closure of ash leaves under drying conditions.Key words: Fraxinus excelsior: L., malate, mannitol, xylem sap, stomata, water deficit.      

Effects of humidity on light-induced stomatal opening: evidence for hydraulic coupling among stomata

A mechanism for co-ordinating behaviour of stomata within an areole during patchy stomatal conductance has recently been proposed. This mechanism depends on hydraulic interactions among stomata that are mediated by transpiration-induced changes in epidermal turgor. One testable prediction that arises from this proposed mechanism is that the strength of hydraulic coupling among stomata should be proportional to evaporative demand and, therefore, inversely proportional to humidity. When a leaf is illuminated following a period of darkness, there is typically a period of time, termed the Spannungsphase, during which guard cell osmotic and turgor pressure are increasing, but the pore remains closed. If hydraulic coupling is proportional to evaporative demand, then variation among stomata in the duration of the Spannungsphase should be lower for leaves at low humidity than for leaves at high humidity. A similar prediction emerged from a computer model based on the proposed hydraulic mechanisms. These predictions were tested by measuring individual stomatal apertures on intact transpiring leaves at low and high humidity and on vacuum-infiltrated leaf pieces (to eliminate transpiration) as PFD was increased to high values from either darkness or a low value. Results showed that the range of Spannungsphasenamong stomata was reduced at low humidity compared to high humidities. Experiments that began at low PFD, rather than at darkness, showed no delay in stomatal opening. These results are discussed in the context of the proposed hydraulic coupling mechanisms.     

Effect of the Mesophyll on Stomatal Opening in Commelina communis

The effect of a number of factors on the opening of stomatain the intact leaf and in the isolated leaf epidermis of Commelinacommunishas been investigated. Stomata in the intact leaf opened widein the light and closed rapidly on transfer to the dark. Theywere also sensitive to CO₂. In contrast, stomata in isolatedepidermis floated on an incubation solution containing 100 molm^–3KCl responded neither to light nor CO₂. They opened as widelyas those in the intact leaf when treated with fusicoccin. Stomata in isolated epidermis opened almost as wide as thosein the intact leaf when they were incubated with isolatedmesophyllcells in the light. The solution in which the mesophyll cellswere incubated was separated by centrifugation. Themedium fromcells previously incubated in the light caused the stomata inisolated epidermis to open but that from cells kept inthe darkhad no effect. A similar effect was observed when isolated chloroplastswere incubated with the isolated epidermis.However, the supernatantfrom the chloroplast suspension had no significant effect onstomatal opening. These results indicate that the mesophyll plays an importantrole in stomatal opening in the light. The mesophyll appearstoproduce in the light, but not in the dark, a soluble compoundwhich moves to the guard cells to bring about stomatal opening.Theexperiments with isolated chloroplasts suggest that this substanceis a product of photosynthesis. Key words: Commelina communis, stomata, light, mesophyll     

Distinct light responses of the adaxial and abaxial stomata in intact leaves of Helianthus annuus L

Using a laboratory-constructed system that can measure the gas exchange rates of two leaf surfaces separately, the light responses of the adaxial and abaxial stomata in intact leaves of sunflower ( Helianthus annuus L.) were investigated, keeping the intercellular CO₂ concentration ( C _i) at 300  µ L L⁻¹. When evenly illuminating both sides of the leaf, the stomatal conductance ( g _s) of the abaxial surface was higher than that of the adaxial surface at any light intensity. When each surface of the leaf was illuminated separately, both the adaxial and abaxial stomata were more sensitive to the light transmitted through the leaf (self-transmitted light) than to direct illumination. Relationships between the whole leaf photosynthetic rate ( A _n) and the g _s for each side highlighted a strong dependence of stomatal opening on mesophyll photosynthesis. Light transmitted through another leaf was more effective than the direct white light for the abaxial stomata, but not for the adaxial stomata. Moreover, green monochromatic light induced an opening of the abaxial stomata, but not of the adaxial stomata. As the proportion of blue light in the transmitted light is less than that in the white light, there may be some uncharacterized light responses, which are responsible for the opening of the abaxial stomata by the transmitted, green light.     

The influence of water stress on the photosynthetic performance and stomatal behaviour of tree seedlings subjected to variation in temperature and irradiance

Summary Seedlings of Betula pendula Roth. and Gmelina arborea L. were subjected to variation in temperature and irradiance. The influence of a mild water-stressing treatment on the photosynthetic performance and stomatal behaviour of these plants was assessed. For both species, the shape of the relationships between irradiance and photosynthesis and temperature and photosynthesis resembled those reported for other species. The effect of water stress was to reduce the rate of photosynthesis, particularly at high temperatures. This was largely a function of a reduction in mesophyll conductance under these conditions. The optimum temperature for stomatal opening was significantly lower than the optimum temperature for photosynthesis, which was in turn lowered by the water stress treatment. The stomata of birch seedlings showed maximum opening at an intermediate temperature while the stomata of Gmelina generally exhibited a closing movement when leaf temperatures increased from 15° C. Mesophyll conductances of both species increased with increasing temperature.The physiological basis for the variation in photosynthetic performance and stomatal behaviour and the ecological significance of this variation are discussed.     

Cropping intensity and rainfall effects on upland rice yields in northern Laos

Two fractions of earthworm humic substances, differing in nominal molecular weight, containing a very low amount of free IAA, and exhibiting auxin-like properties, were prepared and characterised by infrared and ¹H-NMR spectroscopy. In this study we investigate their effects on stomatal opening, as influenced by phospholipase A₂, in leaf of the Argenteum mutant of pea (Pisum sativum L.) Both of the humic fractions caused stomatal opening in the epidermal peels. The response showed a broad biphasic dose dependence and the effective concentrations were similar for the two fractions. The maximal stomatal apertures in response to both humic substances were similar to that caused by IAA and somewhat less than the response to white light or fusicoccin. Two inhibitors of phospholipase A₂ selectively blocked the response of stomata to both IAA and humic substances, without affecting the response to light or fusicoccin. We conclude that stomatal opening in response to auxin and humic substances involves activation of a phospholipase A₂ that is not involved in signalling the response to light or fusicoccin.     

Variations among woody plants in stomatal conductance and photosynthesis during and after drought

Acer saccharum, Fraxinus americana, Juglans nigra, Acer rubrum, Cornus amomum, and Ulmus americana seedlings were subjected to a soil drying cycle and then rewatered. At frequent intervals during the drying cycle and following rewatering, determinations were made of equilibrium photosynthesis rates, leaf conductances and leaf water potentials. As the drying cycle progressed, leaf water potentials decreased, stomata closed, and rates of transpiration and photosynthesis were reduced. Stomata of the two Acer species initially were more sensitive to water stress than were those of the other species. At low leaf water potentials, stomata of Juglans and Cornus were more open than those of the other species. Photosynthesis of Acer saccharum, Fraxinus and Juglans was significantly reduced by plant water stress, while photosynthetic water use efficiency of Cornus and Juglans was most unfavourable. Photosynthesis/leaf conductance ratios in water stressed leaves were higher in Fraxinus than in the other species. Immediately after rewatering, only limited stomatal opening occurred in Acer saccharum and Cornus with recovery of stomatal opening most protracted in Fraxinus and Ulmus. There was extended reduction of photosynthesis of all species as a result of the soil drying treatment. This effect was most significant in Acer saccharum and Juglans. Survival of plants on moist and dry sites is discussed in relation to stomatal control of transpiration and metabolic responses to water stress. Research supported by the College of Agricultural and Life Sciences, University of Wisconsin-Madison and the International Shade Tree Conference. The cooperation of the Wisconsin Department of Natural Resources is acknowledged. Research supported by the College of Agricultural and Life Sciences, University of Wisconsin-Madison and the International Shade Tree Conference. The cooperation of the Wisconsin Department of Natural Resources is acknowledged.     

Penetration of stomata by liquids: dependence on surface tension, wettability, and stomatal morphology

Wettability of the leaf surface, surface tension of the liquid, and stomatal morphology control penetration of stomata by liquids. The critical surface tension of the lower leaf surface of Zebrina purpusii Brückn. was estimated to be 25 to 30 dyne cm⁻¹. Liquids having a surface tension less than 30 dyne cm⁻¹ gave zero contact angle on the leaf surface and infiltrated stomata spontaneously while liquids having a surface tension greater than 30 dyne cm⁻¹ did not wet the leaf surface and failed to infiltrate stomata. Considering stomata as conical capillaries, we were able to show that with liquids giving a finite contact angle, infiltration depended solely on the relationship between the magnitude of the contact angle and the wall angle of the aperture. Generally, spontaneous infiltration of stomata will take place when the contact angle is smaller than the wall angle of the aperture wall. The degree of stomatal opening (4, 6, 8, or 10 μm) was of little importance. Cuticular ledges present at the entrance to the outer vestibule and between the inner vestibule and substomatal chamber resulted in very small if not zero wall angles, and thus played a major role in excluding water from the intercellular space of leaves. We show why the degree of stomatal opening cannot be assessed by observing spontaneous infiltration of stomata by organic liquids of low surface tension.     

CO2-Gaswechsel amphistomatischer Blätter

Summary The time-response of the CO₂-exchange of both leaf surfaces was measured separately. Leaves of Primula palinuri and Zea mays were used for the study. After short dark-periods (3 min) the stomata are not closed. Consequently CO₂-uptake starts quickly after re-illumination and reaches the steady-state value very rapidly. The time-response of stripped leaves of Primula and of normal leaves after short dark-periods is identical. Accordingly, the conclusion seems to be evident that in both cases we are measuring the time-response of photosynthesis, which is not influenced by stomatal reactions. After long dark-periods (60 min) the stomata are closed. After re-illumination the CO₂ released by respiration is immediately reassimilated. There is a distinct lag-phase in time-response which is more or less located in the CO₂-compensation point. This lag-phase is of different length for both leaf surfaces, and is interpreted as being the lag-phase of stomatal opening reactions. The consequence of the observed different time response of photosynthesis and stomatal reactions is discussed: under non-steady-state conditions photosynthesis is limited by slow stomatal opening reactions.     

Guard cells of Commelina communis L. do not respond metabolically to osmotic stress in isolated epidermis: Implications for stomatal responses to drought and humidity

We investigated the hypothesis that stomatal aperture is regulated by epidermal water status. Detached epidermal peels of Commelina communis L. or leaf disks with epidermis attached were incubated in graded solutions of mannitol (0–1.2 M) containing KCl. In isolated epidermis, guard-cell solute content of open stomata did not decrease in response to desiccation. Guard cells of closed stomata accumulated solutes to the same extent in all levels of mannitol tested. There was no evidence of stress-induced hydroactive closure nor of inhibition of hydroactive opening, even when guard cells of closed stomata were initially plasmolyzed. Hydropassive, osmometer-like, changes in stomatal aperture in the isolated epidermis were induced by addition or removal of mannitol, but these did not involve changes in guard-cell solute content. In leaf disks, stomata exhibited clear hydroactive stomatal responses. Steady-state guard-cell solute content of initially open and initially closed stomata decreased substantially with increasing mannitol. Stomata were completely closed above approx. 0.4 M mannitol, near the turgor-loss point for the bulk leaf tissue. Stomata of Commelina did not exhibit direct hydroactive responses to environmental or epidermal water status. Stomatal responses to water deficit and low humidity may be indirect, mediated by abscisic acid or other signal metabolite(s) from the mesophyll.Abbreviations ABA abscisic acid - EGTA ethyleneglycol-bis-(-aminoethyl ether)-N,N,N,N-tetraacetic acid - Mes 2-(N-morpholino)ethanesulfonic acid     

Tropic failure of Phyllactinia corylea contributes to the mildew resistance of mulberry genotypes

Different mulberry genotypes show great variation in their resistance to the powdery mildew Phyllactinia corylea. Conidial germination and hyphal growth of P. corylea on the leaf surface of two susceptible mulberry genotypes, viz., Kanva 2 (K2) and Victory 1 (V1) varieties of Morus indica, and on two resistant species, viz., M. laevigata and M. serrata were studied by scanning electron microscopy. Conidial germination and growth of germ tubes were normal on all the leaves. The hyphae of P. coryleaidentify stomata on host leaves by their topographical features to produce the stomatopodia precisely over them. The holes and/or the grooves of stomata appear to provide the signals for the initiation of stomatopodia and similar structures are erratically developed over many local depressions or grooves on leaf surface. The abaxial surface of K2 leaf is smooth without prominent undulations of epidermal cell surface, and the stomata are flush with the leaf surface. Although successful penetration is also achieved on V1 leaf, its slightly undulated surface occasionally provides inaccurate tropic signals to the hyphae, inducing the development of stomatopodia away from the stomata. The leaf surfaces of M. laevigata and M. serrata are very rough with highly sculptured cuticle and abundant epidermal outgrowths. Stomata mostly remain sunken or hidden amidst the cuticular ornamentations and the hyphae fail to recognise the precise signals from them. As the surface architecture of the leaves provides many immense sources of tropic signals, stomatopodia are often produced over local depressions or grooves. In these cases the fungus fails to penetrate the leaf, does not develop beyond 24 h and penetration is rarely achieved on the leaves of the resistant plants. The study indicates that the stimulatory effect of the leaf surface topography of resistant varieties misleads the pathogen from successful penetration, thus contributing to the plant's resistance.This revised version was published online in October 2005 with corrections to the Cover Date.     

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.