Direct and indirect effects of light on stomata II. In Commelina communis L.

Abstract. Two experiments are described which test the normal correlations that arise between stomatal conductance, net CO₂ assimilation rate, and intercellular CO₂ concentration (C_i), using whole shoots of Commelina communis L. In the first, conductance increased with decreasing C_i, at four different quantum flux densities, such that there was no unique relationship between conductance and quantum flux density or C_i, In the second, conductance increased hyperbolically with increasing quantum flux density while C_i was held constant at 466, 302, and 46 μmiolmol⁻¹, and the response differed at each C_i. In neither experiment was conductance consistently related to net CO₂ assimilation rate in the mesophyll. In both experiments high C_i suppressed the response of conductance to light, while there was a large response of conductance to light at low C_i, indicating an interaction between the effects of light and CO₂ on stomata. The results show that the parallel responses of assimilation and conductance to light result in constant intercellular CO₂ concentrations, and not that stomata maintain a 'constant C_i'.     

陆生植物气孔参数与大气CO2浓度变化

陆生植物的起源与演化与全球气候和环境的变化密不可分,利用植物气孔参数(气孔密度和气孔指数)来指示或重建古大气CO₂浓度变化是近年来全球变化研究的热点之一。就陆生植物气孔参数的研究进行了概述,对研究中存在的问题及其前景作了简要探讨,并对植物生物学方法在定量研究古气候和古环境变化的趋势进行了分析。     

陆生植物气孔参数与大气CO_2浓度变化

陆生植物的起源与演化与全球气候和环境的变化密不可分,利用植物气孔参数(气孔密度和气孔指数)来指示或重建古大气CO2浓度变化是近年来全球变化研究的热点之一。就陆生植物气孔参数的研究进行了概述,对研究中存在的问题及其前景作了简要探讨,并对植物生物学方法在定量研究古气候和古环境变化的趋势进行了分析。     

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.     

Effects of radiation quality on the opening of stomata in intact Phaseolus vulgaris L. leaves

In intact French bean (Phaseolus vulgaris L.) leaves blue radiation enhanced opening of stomata both when it was used individually and when it was used as preirradiation before "white light" irradiation. Effects of red radiation were just the contrary. This revised version was published online in June 2006 with corrections to the Cover Date.     

Separation and measurement of direct and indirect effects of light on stomata

Conductance for water vapor, assimilation of CO₂, and intercellular CO₂ concentration of leaves of five species were determined at various irradiances and ambient CO₂ concentrations. Conductance and assimilation were then plotted as functions of irradiance and intercellular CO₂ concentration. The slopes of these curves allowed us to estimate infinitesimal changes in conductance (and assimilation) that occurred when irradiance changed and intercellular CO₂ concentration was constant, and when CO₂ concentration changed and irradiance was constant. On leaves of Xanthium strumarium L., Gossypium hirsutum L., Phaseolus vulgaris L., and Perilla frutescens (L.), Britt., the stomatal response to light was determined to be mainly a direct response to light and to a small extent only a response to changes in intercellular CO₂ concentration. This was also true for stomata of Zea mays L., except at irradiances < 150 watts per square meter, when stomata responded primarily to the depletion of the intercellular spaces of CO₂ which in turn was caused by changes in the assimilation of CO₂.     

Physiological acclimation dampens initial effects of elevated temperature and atmospheric CO2 concentration in mature boreal Norway spruce

Physiological processes of terrestrial plants regulate the land–atmosphere exchange of carbon, water, and energy, yet few studies have explored the acclimation responses of mature boreal conifer trees to climate change. Here we explored the acclimation responses of photosynthesis, respiration, and stomatal conductance to elevated temperature and/or CO₂ concentration ([CO₂]) in a 3‐year field experiment with mature boreal Norway spruce. We found that elevated [CO₂] decreased photosynthetic carboxylation capacity (?23% at 25 °C) and increased shoot respiration (+64% at 15 °C), while warming had no significant effects. Shoot respiration, but not photosynthetic capacity, exhibited seasonal acclimation. Stomatal conductance at light saturation and a vapour pressure deficit of 1 kPa was unaffected by elevated [CO₂] but significantly decreased (?27%) by warming, and the ratio of intercellular to ambient [CO₂] was enhanced (+17%) by elevated [CO₂] and decreased (?12%) by warming. Many of these responses differ from those typically observed in temperate tree species. Our results show that long‐term physiological acclimation dampens the initial stimulation of plant net carbon assimilation to elevated [CO₂], and of plant water use to warming. Models that do not account for these responses may thus overestimate the impacts of climate change on future boreal vegetation–atmosphere interactions.     

Direct and indirect effects of light pollution on the performance of an herbivorous insect

Light pollution is a global disturbance with resounding impacts on a wide variety of organisms, but our understanding of these impacts is restricted to relatively few higher vertebrate species. We tested the direct effects of light pollution on herbivore performance as well as indirect effects mediated by host plant quality. We found that artificial light from streetlights alters plant toughness. Additionally, we found evidence of both direct and indirect effects of light pollution on the performance of an herbivorous insect, which indicates that streetlights can have cascading impacts on multiple trophic levels. Our novel findings suggest that light pollution can alter plant-insect interactions and thus may have important community-wide consequences.     

CO2 gas exchange and phosphoenolpyruvate carboxylase activity in leaves of Zea mays L.

Important gas exchange characteristics of C4 plants depend on the properties of phophoenolpyruvate carboxylase (PEPC), the enzyme catalysing the primary fixation of CO2 during C4 photosynthesis. In this study, the relationship between intracellular resistance for CO2 fixation (r_i) at high photosynthetically active photon flux densities (PPFD) and maximum PEPC activity in vitro (V_pm) was examined in leaves of Zea mays L. The analysis allowed the estimation of the Michaelis constant K_p of the enzyme for CO2 (or the equivalent number for bicarbonate) in vivo. At low PPFD (below 100 mol m-2 s-1) the initial slopes of the curves describing net CO2 uptake rate A as a function of intercellular CO2 concentration c_i increased with increasing PPFD. The increase (i. e. a decrease in r_i) was interpreted as due to a reversible activation of PEPC by light. Including this assumption into a model of C4 photosynthesis enabled us to reproduce A(c_i) response curves measured at low levels of PPFD. Fitting the model to experimental data resulted in values for K_I, the PPFD at which PEPC reaches half of its full activation, of about 200 mol m-2 s-1. Similar results were derived from the dependence of r_i on PPFD. The analysis of the relationships between r_i and V_pm and between r_i and PPFD, as well as fitting of the model to gas exchange data all gave rise to estimates for the resistance for CO2 transfer within mesophyll cells that are comparable with those known from C3 plants.     

Direct and indirect climate change effects on photosynthesis and transpiration

Climate change affects plants in many different ways. Increasing CO(2) concentration can increase photosynthetic rates. This is especially pronounced for C(3) plants, at high temperatures and under water-limited conditions. Increasing temperature also affects photosynthesis, but plants have a considerable ability to adapt to their growth conditions and can function even at extremely high temperatures, provided adequate water is available. Temperature optima differ between species and growth conditions, and are higher in elevated atmospheric CO(2). With increasing temperature, vapour pressure deficits of the air may increase, with a concomitant increase in the transpiration rate from plant canopies. However, if stomata close in response to increasing CO(2) concentration, or if there is a reduction in the diurnal temperature range, then transpiration rates may even decrease. Soil organic matter decomposition rates are likely to be stimulated by higher temperatures, so that nutrients can be more readily mineralised and made available to plants. This is likely to increase photosynthetic carbon gain in nutrient-limited systems. All the factors listed above interact strongly so that, for different combinations of increases in temperature and CO(2) concentration, and for systems in different climatic regions and primarily affected by water or nutrient limitations, photosynthesis must be expected to respond differently to the same climatic changes.     

光质及种子大小对普洱地区14种植物种子萌发的影响

以普洱地区14种常见植物种子为材料,在实验室条件下研究了其在白光、黑暗、红光和蓝光条件下的萌发特性,并分析了种子大小与萌发率、萌发速率、萌发开始时间的关系。结果表明:光质对四方蒿、沙针、尖子木、藿香蓟种子萌发率和萌发速率均有显著影响(P0.05)。光质对大叶斑鸠菊、云南山枇花、臭灵丹、车桑子、光萼猪屎豆、葫芦茶、云南地桃花、西南宿苞豆、岗柃、中国宿苞豆10个物种的种子萌发率和萌发速率均没有显著影响(P0.05),以上物种中除中国宿苞豆外,其他物种种子萌发率均在20%以下,处于休眠状态。四方蒿种子在白光(89.9%)和红光(84.7%)下萌发率最高,红光下种子萌发最快(4.93),蓝光下种子萌发开始时间最晚(11.3 d);沙针种子在白光下萌发率最高(80.4%)、萌发速率最快(2.71),在黑暗和蓝光下萌发率较低(43.9%和38%)、萌发速率最慢(0.73和0.85),白光、红光下萌发开始最早(11 d),黑暗条件下萌发开始最晚(21.7 d);尖子木种子萌发率在白光、黑暗、蓝光下均在86%以上,而红光下仅32%且萌发速率最慢(1.29),在蓝光下萌发开始时间最晚(13 d);藿香蓟种子萌发率和萌发速率在红光下最高(分别为71.3%和6.46),黑暗条件下最低(分别为42.5%和2.62);大叶斑鸠菊萌发开始时间在黑暗条件下最早(6 d),其次是白光下(7 d),蓝光和红光下较晚,分别为8 d和7.7 d。14个物种种子的萌发率与种子大小间均有显著负相关关系;种子萌发速率、萌发开始时间与种子大小间也有负相关关系,但不显著;种子大小与萌发率、萌发速率和萌发开始时间的关系不会随着光质的变化而发生变化。     

The effects of SAN 9789 and light on phytochrome and the germination of lettuce seeds

Photoblastic seeds (akenes) of lettuce (Lactuca sativa (L.) cv. Grand Rapids) were treated with SAN 9789 [4-chloro-5-(methylamine)-2-a, a, a,-trifluoro-m-tolyl-3-(2H)-pyridasinone]. The seeds weere placed in Petri dishes on filter paper soaked with water or SAN solution. The treatment increased the germination in darkness from 17% for water to 78% for SAN treated seeds. An irradiation with 5 min red light gave a germination of 98% both in water and in SAN. In water the effect of red irradiation could be reversed with a short irradiation (8 min) of far red light (17% germination), while in SAN solution the far red reversibility was poor (92% germination). If the far red light was given repeatedly (5 min per h) it had a slightly larger effect. If given continuously for 24 hours, the germination in water was decreased to 0.3% and in SAN solution to 9%. Possible mechanisms for the SAN effect are discussed.     

Effects of far-red light on the growth,mycorrhizas and mineral nutrition of Scots pine seedlings

The effects of supplementary far-red sidelight on the formation of mycorrhizas and on the accumulation and allocation of dry weight and mineral nutrients were studied in Scots pine (Pinus sylvestris L.) seedlings. Starting one week after germination the seedlings were subjected to two different light quality regimes: control and simulated sparse-canopy conditions (FR+). In the FR+ regime, light reflected by neighbouring plants was simulated by means of supplementary far-red light sources, which reduced the horizontal red/far-red photon ratio (R:FR) without affecting PAR. Seedlings were harvested after three months of treatment. FR+ increased stem height and decreased the total dry weight of seedlings. Dry weight allocation to needles was not affected, whereas dry weight allocation to roots was reduced and that to stems was increased in FR+ treated seedlings. The total number of short root tips and developing mycorrhizas per seedling were lower in FR+ than in control plants. Most short roots were developing mycorrhizas, while non-mycorrhizal short roots and mycorrhizas with mantle or external mycelium were very scarce. Changes in the allocation of nutrients in general followed the changes in dry weight allocation, and changes in nutrient content followed those in total dry weight. However, mismatches among these changes resulted in significant changes in nutrient concentrations in some organs: the concentrations of nitrogen and potassium in needles and the concentration of nitrogen in stems were higher in FR+ than in control seedlings. Changes in biomass and nutrient allocation under low R:FR may promote rapid height growth during early development in stands of Scots pine seedlings, but concomitant reductions in growth of the root system and mycorrhizas may negatively affect tree performance over the long term.     

Abaxial and adaxial stomata from Pima cotton (Gossypium barbadense L.) differ in their pigment content and sensitivity to light quality

Sensitivity to light quality and pigment composition were analysed and compared in abaxial and adaxial stomata of Gossypium barbadense L. (Pima cotton). In most plants, abaxial (lower) stomatal conductances are higher than adaxial (upper) ones, and stomatal opening is more sensitive to blue light than to red. In greenhouse-grown Pima cotton, abaxial stomatal conductances were two to three times higher than adaxial ones. In contrast, adaxial stomatal conductances were 1·5 to two times higher than abaxial ones in leaves from growth chamber-grown plants. To establish whether light quality was a factor in the regulation of the relationship between abaxial and adaxial stomatal conductances, growth-chamber-grown plants were exposed to solar radiation outdoors and to increased red light in the growth chamber. In both cases, the ratios of adaxial to abaxial stomatal conductance reverted to those typical of greenhouse plants. We investigated the hypothesis that adaxial stomata are more sensitive to blue light and abaxial stomata are more sensitive to red light. Measurements of stomatal apertures in mechanically isolated epidermal peels from growth chamber and greenhouse plants showed that adaxial stomata opened more under blue light than under red light, while abaxial stomata had the opposite response. Using HPLC, we quantified the chlorophylls and carotenoids extracted from isolated adaxial and abaxial guard cells. All pigments analysed were more abundant in the adaxial than in the abaxial guard cells. Antheraxanthin and β-carotene contents were 2·3 times higher in adaxial than in abaxial guard cells, comparing with ad/ab ratios of 1·5–1·9 for the other pigments. We conclude that adaxial and abaxial stomata from Pima cotton have a differential sensitivity to light quality and their distinct responses are correlated with different pigment content.     

Blue light effects on rose photosynthesis and photomorphogenesis

Through its impact on photosynthesis and morphogenesis, light is the environmental factor that most affects plant architecture. Using light rather than chemicals to manage plant architecture could reduce the impact on the environment. However, the understanding of how light modulates plant architecture is still poor and further research is needed. To address this question, we examined the development of two rose cultivars, Rosa hybrida‘Radrazz’ and Rosa chinensis‘Old Blush’, cultivated under two light qualities. Plants were grown from one‐node cuttings for 6 weeks under white or blue light at equal photosynthetic efficiencies. While plant development was totally inhibited in darkness, blue light could sustain full development from bud burst until flowering. Blue light reduced the net CO₂ assimilation rate of fully expanded leaves in both cultivars, despite increasing stomatal conductance and intercellular CO₂ concentrations. In ‘Radrazz’, the reduction in CO₂ assimilation under blue light was related to a decrease in photosynthetic pigment content, while in both cultivars, the chl a/b ratio increased. Surprisingly, blue light could induce the same organogenetic activity of the shoot apical meristem, growth of the metamers and flower development as white light. The normal development of rose plants under blue light reveals the strong adaptive properties of rose plants to their light environment. It also indicates that photomorphogenetic processes can all be triggered by blue wavelengths and that despite a lower assimilation rate, blue light can provide sufficient energy via photosynthesis to sustain normal growth and development in roses.     

Direct and indirect effects of elevated atmospheric CO2 on net ecosystem production in a Chesapeake Bay tidal wetland

The rapid increase in atmospheric CO₂ concentrations (C_a) has resulted in extensive research efforts to understand its impact on terrestrial ecosystems, especially carbon balance. Despite these efforts, there are relatively few data comparing net ecosystem exchange of CO₂ between the atmosphere and the biosphere (NEE), under both ambient and elevated C_a. Here we report data on annual sums of CO₂ (NEE_net) for 19 years on a Chesapeake Bay tidal wetland for Scirpus olneyi (C₃ photosynthetic pathway)‐ and Spartina patens (C₄ photosynthetic pathway)‐dominated high marsh communities exposed to ambient and elevated C_a (ambient + 340 ppm). Our objectives were to (i) quantify effects of elevated C_a on seasonally integrated CO₂ assimilation (NEE_net = NEE_day + NEE_night, kg C m^?2 y^?1) for the two communities; and (ii) quantify effects of altered canopy N content on ecosystem photosynthesis and respiration. Across all years, NEE_net averaged 1.9 kg m^?2 y^?1 in ambient C_a and 2.5 kg m^?2 y^?1 in elevated C_a, for the C₃‐dominated community. Similarly, elevated C_a significantly (P < 0.01) increased carbon uptake in the C₄‐dominated community, as NEE_net averaged 1.5 kg m^?2 y^?1 in ambient C_a and 1.7 kg m^?2 y^?1 in elevated C_a. This resulted in an average CO₂ stimulation of 32% and 13% of seasonally integrated NEE_net for the C₃‐ and C₄‐dominated communities, respectively. Increased NEE_day was correlated with increased efficiencies of light and nitrogen use for net carbon assimilation under elevated C_a, while decreased NEE_night was associated with lower canopy nitrogen content. These results suggest that rising C_a may increase carbon assimilation in both C₃‐ and C₄‐dominated wetland communities. The challenge remains to identify the fate of the assimilated carbon.     

The effects of blue and red light on Acetabularia mediterranea after long exposure to darkness

After Acetabularia mediterranea cells were kept in darkness for 2–8 weeks, all the cellular processes were arrested and the algae did not grow. In particular, the transcellular electrical potential (V_AB) decreased to almost zero and cytoplasmic streaming was arrested. Upon illumination with continous blue light (BL), the first events were (as with white light (WL)), immediate increase in V_AB and movements of water, followed, after a lag period of 1–3 min, by transient recovery of cytoplasmic streaming which lasted about 16 min. After 10 min (earlier than in WL), the frequency of the spontaneous action potentials increased much more than in WL. Then, after 1.5–4 hr during which V_AB often decreased to zero while the cytoplasmic movements stopped, both activities resumed with diurnal oscillations. BL stimulated (as WL) rRNA synthesis, migration of rRNA from nucleus towards apex and cell growth. Upon illumination with red light (RL), V_AB also increased, but water movements were much less pronounced than in BL. The transient streaming phase was shorter. The spontaneous action potentials increased in frequency much later (several hr) and much less than in BL or WL. V_AB did not decreased at any time and was maintained at particularly high values. Cytoplasmic streaming resumed, but showed very attenuated or no rhythm. rRNA synthesis and migration remained low. Cell growth did not resume during the experiments. By comparing our results with those of other studies relating to growth, morphogenesis and photosynthesis, we suggest that BL and RL could affect all these processes by differentially modifying the cytoplasmic concentrations of ions which may influence the functions of the cytoskeleton.     

Coaction of blue/ultraviolet-A light and light absorbed by phytochrome in controlling the appearance of ferredoxin-dependent glutamate synthase in the Scots pine (Pinus sylvestris L.) seedling

The appearance of NADH- and ferredoxin (Fd)-dependent glutamate synthases (GOGATs) was investigated in the major organs (roots, hypocotyl and cotyledonary whorl) of the Scots pine seedling. It was found that cytosolic NADH-GOGAT (EC 1.4.1.14) dropped to a low level during the experimental period (from 4 to 12 d after sowing) and was not significantly affected by light. On the other hand, plastidic Fd-GOGAT (EC 1.4.7.1) increased strongly in response to light. Whereas similar amounts of NADH-GOGAT were found in the different organs, Fd-GOGAT was mainly found in the cotyledons even in the presence of nitrate. Protein chromatography revealed only a single Fd-GOGAT peak. No isoforms were detected. Experiments to investigate regulation of the appearance of Fd-GOGAT in the cotyledonary whorl yielded the following results: (i) In darkness, neither nitrate (15 mM KNO₃) nor ammonium (15 mM NH₄Cl) had an effect on the appearance of Fd-GOGAT. In the light, nitrate stimulated Fd-GOGAT activity by 30% whereas ammonium had no effect. The major controlling factor is light. (ii) The action of long-term white light (100 W · m^–2) could be replaced quantitatively by blue light (B, 10 W · m^–2). Since the action of long-term far-red light was very weak, operation of the High Irradiance Reaction of phytochrome is excluded. On the other hand, light-pulse experiments with dark-grown seedlings showed the involvement of phytochrome. (iii) Red light, operating via phytochrome, could fully replace B, but only up to 10 d after sowing. Thereafter, there was an absolute requirement for B for a further increase in the enzyme level. It appears that the operation of phytochrome was replaced by the operation of cryptochrome (B/UV-A photoreceptor). (iv) However, dichromatic experiments (simultaneous treatment of the seedlings with two light beams to vary the level of the far-red-absorbing form of phytochrome (Pfr) in blue light) showed that B does not affect enzyme appearance if the Pfr level is low. It is concluded that B is required to maintain responsiveness of Fd-GOGAT synthesis to phytochrome (Pfr) beyond 10 d after sowing.Abbreviations and Symbols B blue light - c continuous - D darkness - Fd-GOGAT ferredoxin-dependent glutamate synthase (EC 1.4.7.1) - FR far-red light - HIR high-irradiance reaction of phytochrome - NADH-GOGAT nicotinamide-dinucleotide-dependent glutamate synthase (EC 1.4.1.14) - R red light - RG9 long-wavelength far-red light defined by the properties of the Schott glass filter (_RG9<0.01) - Pfr/Ptot far-red-absorbing form of phytochrome/total phytochrome, wavelength-dependent photoequilibrium of the phytochrome system Research supported by Deutsche Forschungsgemeinschaft (SFB 46 und Schwerpunkt Physiologie der Bäume). We thank E. Fernbach for his help with the dichromatic experiments.     

In the light of stomatal opening: new insights into 'the Watergate'

Stomata can be regarded as hydraulically driven valves in the leaf surface, which open to allow CO2 uptake and close to prevent excessive loss of water. Movement of these 'Watergates' is regulated by environmental conditions, such as light, CO2 and humidity. Guard cells can sense environmental conditions and function as motor cells within the stomatal complex. Stomatal movement results from the transport of K+ salts across the guard cell membranes. In this review, we discuss the biophysical principles and mechanisms of stomatal movement and relate these to ion transport at the plasma membrane and vacuolar membrane. Studies with isolated guard cells, combined with recordings on single guard cells in intact plants, revealed that light stimulates stomatal opening via blue light-specific and photosynthetic-active radiation-dependent pathways. In addition, guard cells sense changes in air humidity and the water status of distant tissues via the stress hormone abscisic acid (ABA). Guard cells thus provide an excellent system to study cross-talk, as multiple signaling pathways induce both short- and long-term responses in these sensory cells.