Short-Term Flooding Effects on Gas Exchange and Quantum Yield of Rabbiteye Blueberry (Vaccinium ashei Reade)

Roots of 1.5-year-old `Woodard' rabbiteye blueberry plants (Vaccinium ashei Reade) were flooded in containers or maintained at container capacity over a 5-day period. Carbon assimilation, and stomatal and residual conductances were monitored on one fully expanded shoot/plant using an open flow gas analysis system. Quantum yield was calculated from light response curves. Carbon assimilation and quantum yield of flooded plants decreased to 64 and 41% of control values, respectively, after 1 day of flooding and continued decreasing to 38 and 27% after 4 days. Stomatal and residual conductances to CO₂ also decreased after 1 day of flooding compared with those of unflooded plants with residual conductance severely limiting carbon assimilation after 4 days of flooding. Stomatal opening occurred in 75 to 90 minutes and rate of opening was unaffected by flooding.     

Leaf growth, stomatal diffusion resistances and photosynthesis during droughting of Lolium perenne populations selected for contrasting stomatal length and frequency

Lolium perenne selection lines with high calculated stomatal resistances to diffusion (r_s) as a result of either few or short stomata, maintained leaf extension rates and photosynthetic rates longer than selection lines with low resistances when deprived of water. There were no significant differences between high and low r_s plants in light saturated CO₂ uptake of turgid attached leaves. When grown in soil drying to 21% moisture, plants with low calculated r_s exhibited lower minimum leaf resistances (r_l) than those with high, measured with a diffusion porometer, on all except the last day. The daily maximum r_l (1.5 h after the start of the light period) became greater among low than high r_s plants as the difference in rate of leaf extension between the two groups of plants increased with drying soil. Rate of leaf extension was negatively correlated with daily maximum r_l and started to decline when relative leaf water content (RLWC), at 5 h after the start of the light period, fell below about 88%. Transpiration rate of plants grown in different soil moisture regimes was correlated (r=+ 0.83, P < 0.01) with mean maximum adaxial leaf conductance (reciprocal of resistance). There was a highly significant correlation (r=+ 0.62, P < 0.01) between calculated adaxial r_s and mean minimum measured r_l among plants growing at high or intermediate soil moisture, but not at low. Therefore, some random variation in minimum r_l, even with adequate moisture, seemed to be unaccounted for by variation in stomatal numbers or size. Selection for increased numbers of adaxial stomata also resulted in more on the abaxial surface, but mean adaxial/abaxial ratio in the ‘frequent’ stomata plants was still only about 9:1.     

Light-flecks cause non-uniform stomatal opening – studies with special emphasis on Fagus sylvatica L.

The appearance of stomatal patchiness in response to rapid (seconds) changes in light has been studied in European beech, Fagus sylvatica L., and, by comparison, in a further 17 different woody species from the understorey of a European beech forest, using a simple water infiltration method. Water infiltrated areoles indicate open stomata. Since infiltration changes optical characteristics of a leaf section it can be analysed by photography, computer-aided image analysis and by weighing. For F. sylvatica clear differences were found between infiltration of cotyledons (no patchy pattern) and any other leaf type. Despite identical cultivation, leaves of the same type and age from different individual plants responded differently to application of 30 s of light after darkness. In contrast, the patchiness patterns were very similar for leaves of the same type originating from the same plant. Infiltration patterns after a light-fleck, observed on different leaves as a series of momentary clusters, probably indicate waves of opening stomata moving across the leaf blade. During and after a 30 s light-fleck infiltration increased and it continued to increase in the dark up to 10 min, indicating increasing stomatal opening over that period. In general, shade leaves became more infiltrated (by weight) than half-shade or sun leaves, due to larger intercellular air spaces. All species, without exception, showed patchy infiltration and, thus, non-uniform stomatal opening. Measuring leaf gas exchange (as ”quasi-steady states” using a fast responding system) during photosynthetic induction resulted in very similar CO₂ responses of net photosynthesis (A/c _i) as in the true steady state, proving that, in shade and half-shade leaves, the presence of stomatal patchiness does not necessarily affect the calculation of intercellular CO₂ concentrations. Causes and consequences of stomatal patchiness are discussed. Received: 18 November 1998 / Accepted: 1 July 1999     

Temperature-dependent stomatal movement in tulip petals controls water transpiration during flower opening and closing

Temperature‐dependent tulip petal opening and closing movement was previously suggested to be regulated by reversible phosphorylation of a plasma membrane aquaporin ( Azad et al., 2004a ). Stomatal apertures of petals were investigated during petal opening at 20°C and closing at 5°C. In completely open petals, the proportion of open stomata in outer and inner surfaces of the same petal was 27 ± 6% and 65 ± 3%, respectively. During the course of petal closing, stomatal apertures in both surfaces reversed, and in completely closed petals, the proportion of open stomata in outer and inner surfaces of the same petal was 74 ± 3% and 29 ± 6%, respectively, indicating an inverse relationship between stomatal aperture in outer and inner surfaces of the petal during petal opening and closing. Both petal opening and stomatal closure in the outer surface of the petal was inhibited by a Ca²⁺ channel blocker and a Ca²⁺ chelator, whereas the inner surface stomata remained unaffected. On the other hand, sodium nitroprusside, a nitric oxide donor, had no effect on stomatal aperture of the outer surface but influenced the inner surface stomatal aperture during petal opening and closing, suggesting different signalling pathways for regulation of temperature‐dependent stomatal changes in the two surfaces of tulip petals. Stomata were found to be differentially distributed in the bottom, middle and upper parts of tulip petals. During petal closing, water transpiration was observed by measuring the loss of ³H₂O. Transpiration of ³H₂O by petals was fivefold greater in the first 10 min than that found after 30 min, and the transpiration rate was shown to be associated with stomatal distribution and aperture. Thus, the stomata of outer and inner surfaces of the petal are involved in the accumulation and transpiration of water during petal opening.     

Physiological,morphological, and growth responses ofPlatanus occidentalis seedlings to flooding

Summary Flooding ofPlatanus occidentalis L. seedlings for up to 40 days induced several changes including early stomatal closure, greatly accelerated ethylene production by stems, formation of hypertrophied lenticels and adventitious roots on submerged portions of stems, and marked growth inhibition. Poor adaptation ofPlatanus occidentalis seedlings to soil inundation was shown in stomatal closure during the entire flooding period, inhibition of root elongation and branching, and death of roots. Some adaptation to flooding was indicated by (1) production of hypertrophied lenticels which may assist in exchange of dissolved gases in flood water and in release of toxic compounds, and (2) production of adventitious roots on stems which may increase absorption of water. These adaptations appeared to be associated with greatly stimulated ethylene production in stems of flooded plants. The greater reduction of root growth over shoot growth in flooded seedlings will result in decreased drought tolerance after the flood waters recede. The generally low tolerance to flooding of seedlings of species that are widely rated as highly flood tolerant is emphasized.     

Growth Responses and Adaptations of Fraxinus pennsylvanica Seedlings to Flooding

Flooding induced several physiological and morphological changes in Fraxinus pennsylvanica seedlings, with stomatal closure among the earliest responses. Subsequent changes included: reduction in dry weight increment of roots, stems, and leaves; formation of hypertrophied lenticels and production of adventitious roots on submerged portions of the stem above the soil line; leaf necrosis; and leaf abscission. After 15 days of stomatal closure as a result of flooding, stomata began to reopen progressively until stomatal aperture was similar in flooded and unflooded plants. Adventitious roots began to form at about the time stomatal reopening began. As more adventitious roots formed, elongated, and branched, the stomata opened further. The formation of adventitious roots was an important adaptation for flooding tolerance as shown by the high efficiency of adventitious roots in absorption of water and in high correlation between the production of adventitious roots and stomatal reopening.     

Stomatal movement and potassium transport in epidermal strips of Zea mays: The effect of CO2

Summary The correlation between stomatal action and potassium movement in the epidermis of Zea mays was examined in isolated epidermal strips floated on distilled water. Stomatal opening in the isolated epidermis is reversible in response to alternate periods of light or darkness, and is always correlated with a shift in the potassium content of the guard cells. K accumulates in guard cells during stomatal opening, and moves from the guard cells into the subsidiary cells during rapid stomatal closure. When epidermal strips are illuminated in normal air, as against CO₂-free air, the stomata do not open and there is a virtually complete depletion of K from the stomatal apparatus. In darkness CO₂-containing air inhibits stomatal opening and K accumulation in guard cells, but does not lead to a depletion of K from the stomata as observed in the light.     

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.     

Changes in stomatal frequency, stomatal conductance and cuticle thickness during leaf expansion in the broad-leaved evergreen species, Eucalyptus regnans

Aspects of leaf anatomical and physiological development were investigated in the broad-leaved evergreen species, Eucalyptus regnans F.Muell. Newly emergent leaves were tagged in the field and measured for stomatal conductance while a subset was collected every 14 days for the measurement of stomata and cuticle over a 113-day period. Cuticle thickness increased during leaf expansion, the increase following a sigmoid curve. Stomatal frequency (no. mm⁻²) decreased from 56 to 113 days after leaf emergence. The frequency of both immature and intermediate developmental stages of stomata also decreased over this time, but the total number of stomata per leaf remained relatively constant. Stomatal conductance (g _s) of young expanding leaves increased during expansion, and was significantly linearly correlated with stomatal frequency (excluding immature stomata), and with cuticle thickness. The progressive increase in g _s in young developing leaves was contrary to the observed changes in structural characteristics (increased cuticle thickness and decreased stomatal frequency). This increase in g _s with development may be related to the progressive increase in number of mature stomata with larger apertures and, therefore, a higher total pore area in fully expanded leaves.     

Overexpression of the Arabidopsis ��-expansin gene AtEXPA1 accelerates stomatal opening by decreasing the volumetric elastic modulus

Guard cell walls of stomata are highly specialized in plants. Previous research focused on the structure and anatomy of guard cell walls, but little is known about guard cell regulation during stomata movement. In this work, we investigate the possible biological role of the Arabidopsis expansin gene AtEXPA1 in stomatal opening. The AtEXPA1 promoter drove the expression of the GUS reporter gene specifically in guard cells. Light-induced stomatal opening was accelerated in 35S::AtEXPA1 lines, whereas the anti-AtEXPA1 antibody decelerated light-induced stomatal opening. The inhibition of the anti-AtEXPA1 antibody on stomatal opening was largely dependent on the environmental pH. The volumetric elastic modulus (ε) was measured as an indicator of changes in the cell wall. The ε value of guard cells in 35S::AtEXPA1 lines was smaller than in the wild types. The putative role of AtEXPA1 as controller of stomatal opening rate and its regulation are discussed.     

Effects of soil flooding and changes in light intensity on photosynthesis of <Emphasis Type="Italic">Eugenia uniflora</Emphasis> L. seedlings

The increased frequency of heavy rains as a result of global climate change can lead to flooding and changes in light availability caused by the presence of thick clouds. To test the hypothesis that reduction in light availability can alleviate the harmful effects of soil flooding on photosynthesis, the authors studied the effects of soil flooding and acclimation from high to low light on the photosynthetic performance of Eugenia uniflora. Seedlings acclimated to full sunlight (about 35 mol m⁻² d⁻¹) for 5 months were transferred to partial sunlight (about 10 mol m⁻² d⁻¹) and were either subjected to soil flooding or not flooded. Chlorophyll fluorescence was measured throughout the flooding period and leaf gas exchange was measured 16 days after flooding was initiated. Minimal fluorescence yield (Fo) was significantly higher and the quantum efficiency of open PSII centres (Fv/Fm) was significantly lower in flooded than in non-flooded plants in full sunlight. Sixteen days after flooding was initiated, stomatal conductance (gs_sat) and net photosyntheses expressed on a leaf area (A_sat-area), weight (A_sat-wt) and chlorophyll (A_sat-Chl) basis decreased in response to soil flooding. Flooding decreased stomatal conductance by similar amounts in full and partial sunlight, but A_sat-area in partial and full sunlight was 3.4 and 16.8 times lower, respectively, in flooded than in non-flooded plants. These results indicate that changes from full to partial sunlight during soil flooding can alleviate the effects of flooding stress on photosynthesis in E. uniflora seedlings acclimated to full sunlight. The responses of photosynthesis in trees to flooding stress may be dependent on changes in light environment during heavy rains.     

Direct Observation of Reversible and Irreversible Stomatal Responses of Attached Sunflower Leaves to SO(2)

The effects of SO₂ on stomatal aperture of attached sunflower leaves were observed with a remote-control light microscope system that permitted continuous observation of stomatal responses over periods of several hours. The relationship between actual stomatal aperture and stomatal conductance, measured with a porometer, also was examined on leaves before and after exposure to SO₂.

A distinction between uninjured and injured regions was clearly visible on leaves after exposure to 1.5 microliters per liter SO₂ for less than an hour. During the exposure, the mean value of apertures for many stomata, which indicates stomatal conductance and transpiration rate, tended to decrease simultaneously in the uninjured and injured regions. However, the rate of decrease in the injured region was slower than that in the uninjured region because of a transient opening induced by water-soaking in the injured region. The transient opening was less common in stomata near veins and veinlets.

There was a good correlation between pore width and stomatal conductance measured with a porometer before exposure to SO₂. This correlation continued in leaves exposed to SO₂ until visible, irreversible injury occurred, but then it disappeared.

The results of these experiments indicate the necessity of continuous observation of individual stomata under the microscope to understand the effects of air pollutants such as SO₂ on stomatal behavior.

     

Stomatal Opening Mechanism of CAM Plants

Stomata usually open when leaves are transferred from darkness to light. However, reverse-phase stomatal opening in succulent plants has been known. CAM plants such as cacti and Opuntia ficus–indica achieve their high water use efficiency by opening their stomata during the cool, desert nights and closing them during the hot, dry days. Signal transduction pathway for stomatal opening by blue light photoreceptors including phototropins and the carotenoid pigment zeaxanthin has been suggested. Blue light regulated signal transduction pathway on stomatal opening could not be applied to CAM plants, but the most possible theory for a nocturnal response of stomata in CAM plants is photoperiodic circadian rhythm.     

Responses of Melaleuca quinquenervia seedlings to flooding

Abstract Studies were conducted on effects of flooding for 15, 30, 60, and 90 days on morphological changes, stomatal aperture, water potential, and growth of seedlings of Melaleuca quinquenervia, a species often planted for reclamation of swamps. Flooding rapidly induced formation of many hair-like adventitious roots as well as a few thick adventitious roots that originated on the original root system. Some adventitious roots also formed on submerged portions of the stem. Melaleuca seedlings were very tolerant of flooding as shown by only slight reduction in dry weight increment of shoots after 30 days of flooding in stagnant water. Although flooding for 60 or 90 days significantly reduced dry weight increment of leaves, dry weight increment of roots was not inhibited by any flooding treatment, reflecting both degeneration of some of the original roots and compensatory growth of adventitious roots. On certain days flooding induced stomatal closure on both adaxial and abaxial leaf surfaces. Extensive production of adventitious roots and some stomatal reopening after a critical period of flooding appeared to be important factors in the flooding tolerance of Melaleuca and are consistent with its aggressiveness and vigorous growth on wet sites.     

Role of H2O2 dynamics in brassinosteroid‐induced stomatal closure and opening in Solanum lycopersicum

Brassinosteroids (BRs) are essential for plant growth and development; however, their roles in the regulation of stomatal opening or closure remain obscure. Here, the mechanism underlying BR‐induced stomatal movements is studied. The effects of 24‐epibrassinolide (EBR) on the stomatal apertures of tomato (Solanum lycopersicum) were measured by light microscopy using epidermal strips of wild type (WT), the abscisic acid (ABA)‐deficient notabilis (not) mutant, and plants silenced for SlBRI1, SlRBOH1 and SlGSH1. EBR induced stomatal opening within an appropriate range of concentrations, whereas high concentrations of EBR induced stomatal closure. EBR‐induced stomatal movements were closely related to dynamic changes in H₂O₂ and redox status in guard cells. The stomata of SlRBOH1‐silenced plants showed a significant loss of sensitivity to EBR. However, ABA deficiency abolished EBR‐induced stomatal closure but did not affect EBR‐induced stomatal opening. Silencing of SlGSH1, the critical gene involved in glutathione biosynthesis, disrupted glutathione redox homeostasis and abolished EBR‐induced stomatal opening. The results suggest that transient H₂O₂ production is essential for poising the cellular redox status of glutathione, which plays an important role in BR‐induced stomatal opening. However, a prolonged increase in H₂O₂ facilitated ABA signalling and stomatal closure.     

Inhibition of stomatal opening in sunflower leaves by carbon monoxide,and reversal of inhibition by light

When leaves of Helianthus annuus, whose stomates had been opened in the dark in the absence of CO₂, were exposed to 25% carbon monoxide (CO), stomatal conductivity for water vapor decreased from about 0.4 to 0.2 cm·s^-1. The CO effect on stomatal aperture required a CO/O₂ ratio of about 25. As this ratio was decreased the stomata opened, indicating that inhibitio of cytochrome-c oxidase by CO is competitive in respect to O₂. Photosynthetically active red light was unable to reverse CO-induced stomatal closure even at high irradiances, when CO₂ was absent. When it was present, stomatal opening was occasionally, but not consistently observed. Carbon monoxide did not inhibit photosynthetic carbon reduction in leaves of Helianthus.In contrast to red light, very weak blue light (405 nm) increased the stomatal aperture in the presence of CO. It also increased leaf ATP/ADP ratios which had been decreased in the presence of CO. The blue-light effect was not related to photosynthesis. Neither could it be explained by photodissociation of the cytochrome a ₃-CO complex which has an absorption maximum at 430 nm. The data indicate that ATP derived from mitochondrial oxidative phosphorylation provides energy for stomatal opening in sunflower leaves in the dark as well as in the light. Indirect transfer of ATP from chloroplasts to the cytosol via the triose phosphate/phosphoglycerate exchange which is mediated by the phosphate translocator of the chloroplast envelope can support stomatal opening only if metabolite concentrations are high enough for efficient shuttle transfer of ATP. Blue light causes stomatal opening in the presence of CO by stimulating ATP synthesis.     

Physiological changes and growth of micropropagated chile ancho pepper plantlets during acclimatization and post-acclimatization

Little is known about physiological changes that occur with micropropagated chile ancho pepper (Capsicum annuum L. cv. San Luis) plantlets during acclimatization. Plantlets were transferred to ex vitro conditions to study selected physiological changes and growth performance during acclimatization and post-acclimatization. The physiology of the plantlets was characterized by measuring leaf gas exchange and water status. Plant growth was determined by assessing plant height, leaf number, total leaf area, relative growth rate (RGR), and leaf, root, and stem dry matter (DM). Chile pepper plantlets became acclimatized within 6 days after transplantation. During this period, physiological adjustments occurred, which were critical for plantlet survival. After initial ex vitro transplanting, plantlets experienced water deficit [leaf wilting and reduced relative water content (RWC)], which corresponded with reduced stomatal conductance (g _s) and transpiration (E), and an increase in stomatal resistance (r _s). Thus, leaf stomata that developed in vitro were functional ex vitro. Because of this stomatal control, plantlets minimized transplant shock, recovered and survived. Prior to transplanting, plantlets were photomixotrophic, as indicated by low photosynthetic rates (A). During acclimatization, RWC, g _s, E, and A were significantly lower two days after transplanting. However, within 6 days after transplanting, plantlets recovered and became photoautotrophic – attaining high A, g _s, and E. Water use efficiency was initially low during the first days after transplanting, but increased dramatically at the end of the acclimatization period in part due to increased A. The stabilization and improvement of plantlet water status and gas exchange during acclimatization and post-acclimatization closely correlated with increased plantlet growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

Stomatal diffusion resistances and leaf growth during droughting of Lolium perenne plants selected for contrasting epidermal ridging

Groups of Lolium perenne plants selected for either deep or shallow adaxial epidermal ridging were grown in a 16 h day of 70 W m^-2 at 25°C, and either watered daily to 33% or allowed to dry to and then watered daily to 21% or to 16% soil moisture. During a 9 day experimental period, adaxial leaf resistances (r₁) were measured with a diffusion porometer four times daily, transpiration was estimated gravimetrically, and daily rates of leaf extension were recorded. Measurements were also made of minimum abaxial resistances, stomatal frequencies and lengths, and relative leaf water content (RLWC). At 33%, 21% or 16% soil moisture, leaf extension rates of deep ridged leaves were, respectively, slower, the same, and more rapid than those with shallow ridges. At 21% or 16% soil moisture, the adaxial r_l of deep-ridged was much lower than that of shallow-ridged leaves at all four sampling times. This difference was most marked on leaves below the youngest fully expanded, and was observed among older leaves even when plants were well watered. At low RLWC (< 85%), leaf resistance was greatest in leaves with shallow ridges. There was no significant difference between the leaf types in the calculated contributions of stomatal frequency or of morphology at any one pore opening, to r_l but deep-ridged leaves had more stomataonthe abaxial surface. Daily rate of plant water loss was directly correlated (r=+ 0.86, P < 0.01) with mean daily maximum stomatal conductance (1/r_l), and rate of leaf extension negatively with maximum r_l. It is suggested that stomata operating in the concavity formed by deep ridges open wider and are less responsive to internal changes in, for example, leaf water status, than those on shallow-ridged leaves because of a more humid microenvironment at the epidermal surface. The results are discussed in relation to the concept of ‘water-savers’ and ‘water-spenders’ and its application to breeding for dry conditions.     

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.

     

Isotachophoretic Analysis of Ions in Guard Cells of Vicia faba

Isotachophoretic analysis of ions was performed on guard cells of Vicia faba cv. Ryosai Issun with either open or closed stomata. In guard cells of open stomata, K⁺ and malic acid concentrations were 5–7 and 5–10 times higher, respectively, than in guard cells of closed stomata. The content of citric acid (plus isocitric acid) also increased during stomatal opening, but the increment was smaller than that of malic acid. Sodium ions, phosphoric and glyceric acids were present in low concentrations but did not increase during the opening. Other cations and anions could not be measured because of low concentrations. Malic acid provided 68–79% of the counter anions for the potassium taken up by guard cells during stomatal opening.