Anoxic stress leads to hydrogen peroxide formation in plant cells.

Hydrogen peroxide (H2O2) was detected cytochemically in plant tissues during anoxia and re-oxygenation by transmission electron microscopy using its reaction with cerium chloride to produce electron dense precipitates of cerium perhydroxides. Anoxia-tolerant yellow flag iris (Iris pseudacorus) and rice (Oryza sativa), and anoxia-intolerant wheat (Triticum aestivum) and garden iris (Iris germanica) were used in the experiments. In all plants tested, anoxia and re-oxygenation increased H2O2 in plasma membranes and the apoplast. In the anoxia-tolerant species the response was delayed in time, and in highly tolerant I. pseudacorus plasma membrane associated H2O2 was detected only after 45 d of oxygen deprivation. Quantification of cerium precipitates showed a statistically significant increase in the amount of H2O2 caused by anoxia in wheat root meristematic tissue, but not in the anoxia-tolerant I. pseudacorus rhizome parenchyma. Formation of H2O2 under anoxia is considered mainly an enzymatic process (confirmed by an enzyme inhibition analysis) and is due to the trace amount of dissolved oxygen (below 10(-5) M) present in the experimental system. The data suggest oxidative stress is an integral part of oxygen deprivation stress, and emphasize the importance of the apoplast and plasma membrane in the development of the anoxic stress response.     

Comparison of carbohydrate utilization and energy charge in the yellow flag iris (Iris pseudacorus) and garden iris (Iris germanica) under anoxia

Carbohydrate and energy metabolism of the flooding- and anoxia-tolerant Iris pseudacorus and the intolerant Iris germanica rhizomes were investigated under experimental anoxic conditions. Rhizomes of I. pseudacorus and I. Germanica were incubated in the absence of oxygen from 0 to 60 and 16 days, respectively. Amounts of glucose, total reducing sugars and non-reducing sugars (starch, fructan and oligosaccharides) in the rhizomes were measured. Ethanol concentration and adenylate energy charge were determined enzymatically. Glucose content of I. pseudacorus rhizomes decreased gradually during the first 30 days under anoxia and then increased at the same time as adenylate energy charge values started to decline. In I. germanica rhizomes the changes were more dramatic and the time scale was much shorter than in I. pseudacorus but the changes were similar. Non-reducing sugar content of I. pseudacorus rhizomes decreased rapidly during the first 15 days under oxygen deprivation and then increased again, to near starting levels at 35 days. In I. germanica the amount of non-reducing sugars decreased gradually during the anoxic incubation. Under aerobic control conditions, adenylate energy charge (AEC) of I. pseudacorus and I. germanica rhizome tissue was 0.87±0.01 and 0.81±0.01, respectively. In I. pseudacorus AEC remained high until 30 days under anoxia. In contrast, the energy charge of I. germanica rhizome tissue remained above 0.6 for 4 days only. Large amounts of ethanol were found in anoxic rhizome tissues of I. pseudacorus (up to 0.21 M ) and I. germanica (0.06 M ) after 45 days and 8 days, respectively. The results are discussed in relation to flooding tolerance of these species.     

The Effects of Increased Illumination and Shading on the Low-Light-Induced Decline in Photosynthesis in Cotton Leaves

An experiment was carried out to study whether low-light-induced damage to the photosynthetic system in leaves of cotton (Gossypium hirsutum cv. Deltapine) which are below the compensation point in the canopy can be arrested and reversed by increased illumination. In addition it was intended to find out whether the photosynthetic system in leaves of shade plants show a greater resistance to low-light-induced damage than leaves of plants from more exposed habitats. The plants were grown at high density, and increased illumination to the shade leaves in the canopy was achieved by thinning the stand. Thinning was carried out at two stages and its effects on the decline in the photosynthetic capacity of the 4th leaf were followed. An early thinning was carried out shortly after the 4th leaf dropped below the compensation point and a late thinning 2 weeks later. Comparison was also made between the low-light-induced damage to the photosynthetic capacity of the 4th leaf in plants grown under two light regimes during the progressive increase in self-shading of the 4th leaf within the canopy. It was observed that both types of thinning arrested the low-light-induced damage to the photosynthetic system in shade leaves. The decline in photosynthetic capacity of the 4th leaf was stopped after both early and late thinning. The dry weight of the shoot system in the early and late thinned plants was not significantly different. It was double that of the control plants. The plants thinned early did not have higher shoot weight than the late thinned plants since there was a rapid shedding of flowers and fruits after early thinning. The 4th leaf in the early thinned plants showed a 30% increase in chlorophyll content and dry weight per unit leaf area. It is suggested that shedding of flowers and fruits, and increases in chlorophyll and dry weight per unit leaf area in the early thinned plants were caused by a change in the hormonal balance of the plants. The photosynthetic system in leaves of shade plants showed a greater resistance to damage by low light intensity than the photosynthetic system in leaves of plants grown at higher light intensities.     

Relationships between lipid peroxidation and anoxia tolerance in a range of species during post-anoxic reaeration

Peroxidation was studied in anoxically treated plant tissues and quantified as conjugated dienes/trienes in the total lipid fraction and as the production of thiobarbituric acid reactive substances (TBARS). Oxidative stress caused by re-exposure of plants to oxygen led to an increase of conjugated diene/triene formation in rhizomes of Iris germanica and roots of wheat ( Triticum aestivum L.) and oats ( Avena sativa L.), and after a long anoxic exposure (45 days) in the rhizomes of the very anoxia tolerant Iris pseudacorus . Second derivative (SD) spectrophotometry of the UV spectrum of lipid extracts confirmed the formation of dienes. However, determination of TBARS in Iris spp. showed no lipid peroxidation in the anoxia tolerant I. pseudacorus . In the rhizomes of the anoxia intolerant I. germanica , elevated levels of TBARS correlated positively with conjugated diene/triene formation. The results suggest that anoxic stress may induce qualitative changes in membrane lipids, as indicated by lipid peroxidation after restoration of aerobic conditions. The rate of lipid peroxidation correlated negatively with anoxic stress tolerance.     

A leaf gas exchange model that accounts for intra-canopy variability by considering leaf nitrogen content and local acclimation to radiation in grapevine (Vitis vinifera L.)

Understanding the distribution of gas exchange within a plant is a prerequisite for scaling up from leaves to canopies. We evaluated whether leaf traits were reliable predictors of the effects of leaf ageing and leaf irradiance on leaf photosynthetic capacity (V(cmax) , J(max) ) in field-grown vines (Vitis vinifera L). Simultaneously, we measured gas exchange, leaf mass per area (LMA) and nitrogen content (N(m) ) of leaves at different positions within the canopy and at different phenological stages. Daily mean leaf irradiance cumulated over 10 d (PPFD(10) ) was obtained by 3D modelling of the canopy structure. N(m) decreased over the season in parallel to leaf ageing while LMA was mainly affected by leaf position. PPFD(10) explained 66, 28 and 73% of the variation of LMA, N(m) and nitrogen content per area (N(a) ), respectively. Nitrogen content per unit area (N(a) = LMA × N(m) ) was the best predictor of the intra-canopy variability of leaf photosynthetic capacity. Finally, we developed a classical photosynthesis-stomatal conductance submodel and by introducing N(a) as an input, the model accurately simulated the daily pattern of gas exchange for leaves at different positions in the canopy and at different phenological stages during the season.     

Contrasting effects of N and P deprivation on the regulation of photosynthesis in tomato plants in relation to feedback limitation

The effects were studied of both nitrogen and phosphorus limitation and irradiance on the performance and operation of photosynthesis in tomato leaves (Lycopersicon esculentum Mill.). Plants were grown at low N, high N, low P or high P supply and at two irradiances. Using mature leaves, measurements were made of the irradiance dependencies of the relative quantum efficiencies of photosystems I and II, and of the rate of carbon dioxide fixation. Measurements were also made of foliar starch and chlorophyll concentrations. The results showed that photosynthetic light-harvesting and electron-transport activity acclimate to nutrient stress and growth irradiance such that the internal relationships between electron transport by photosystems I and II do not change; the linear relationship between PhiPSII, and PhiPSI was not affected. It was also evident that under N stress photosynthesis was reduced by a decreased light absorption and by the decreased utilization of assimilates, while P stress mainly affected the carboxylation capacity. Under N stress foliar starch levels increased and the oxygen sensitivity of CO2 fixation decreased, whereas P stress resulted in decreased starch levels and increased oxygen sensitivity of CO2 fixation. The relationship between starch accumulation and oxygen sensitivity (increased starch correlated with decreased oxygen sensitivity) was always the same across the nutrient treatments. These results are consistent with N deprivation producing an increasing limitation of photosynthesis, possibly by feedback from the leaf carbohydrate pool, whereas, although P deprivation produces a decreased rate of CO2 fixation, this is accompanied by a increase in oxygen sensitivity, suggesting that feedback limitation is decreased under P stress.     

Tolerance of crop plants to oxygen deficiency stress: fermentative activity and photosynthetic capacity of entire seedlings under hypoxia and anoxia

The study investigates the reactions of rice, wheat and maize to anoxia (plants without access to oxygen) and hypoxia (roots with very limited access to oxygen). We studied the adaptations of these intact crop plants because they are known to differ widely in their tolerance to oxygen deficiency. In hypoxia, there was an accumulation of sugars, especially in wheat and maize, although both flood-sensitive species significantly increased the activities of fermentative and glycolytic enzymes, clearly more than in rice. In rice, avoiding an oxygen limitation due to the effective aeration system (30% of root cross-sectional area) may have accounted for only a minor metabolic reaction to hypoxia. In anoxia, maize and wheat quickly lost viability and nearly all photosynthetic capacity, while most rice leaves stayed turgid and green, losing only 50% of the photosynthetic capacity. A strong metabolic arrest under anoxia was obvious for the sucrolytic, glycolytic and fermentative enzymes in all tested species, but was most pronounced in rice. Of the 14 enzymes studied, rice showed the lowest activity increase in hypoxia for 11 enzymes, and the strongest activity decrease in anoxia for 8 enzymes. However, rice was able even under anoxia to keep a 1/4 of the ATP level of the aerated control, while it was at the detection limit in maize and wheat. It appears that in anoxic rice, the switch to metabolic dormancy and maintenance of basic shoot meristems diminishes the needs for energy and substrate. Additionally, rice already has lower sugar demand under hypoxia, and sugar supply appears to be sustained under anoxia by a functioning anaerobic amylase and by the photosynthetically active shoot.     

Decline of photosynthetic capacity with leaf age in relation to leaf longevities for five tropical canopy tree species

The effect of leaf aging on photosynthetic capacities was examined for upper canopy leaves of five tropical tree species in a seasonally dry forest in Panama. These species varied in mean leaf longevity between 174 and 315 d, and in maximum leaf life span between 304 and 679 d. The light-saturated CO2 exchange rates of leaves produced during the primary annual leaf flush measured at 7-8 mo of age were 33-65% of the rates measured at 1-2 mo of age for species with leaf life span of < 1 yr. The negative regression slopes of photosynthetic capacity against leaf age were steeper for species with shorter maximum leaf longevity. In all species, regression slopes were less steep than the slopes predicted by assuming a linear decline toward the maximum leaf age (20-80% of the predicted decline rate). Maximum oxygen evolution rates and leaf nitrogen content declined faster with age for species with shorter leaf life spans. Statistical significance of regression slopes of oxygen evolution rates against leaf age was strongest on a leaf mass basis (r = 0.49-0.87), followed by leaf nitrogen basis (r = 0.48-0.77), and weakest on a leaf area basis (r = 0.35-0.70).     

High sensitivity of Lobelia dortmanna to sediment oxygen depletion following organic enrichment

? Lobelia dortmanna thrives in oligotrophic, softwater lakes thanks to O(2) and CO(2) exchange across roots and uptake of sediment nutrients. We hypothesize that low gas permeability of leaves constrains Lobelia to pristine habitats because plants go anoxic in the dark if O(2) vanishes from sediments. ? We added organic matter to sediments and followed O(2) dynamics in plants and sediments using microelectrodes. To investigate plant stress, nutrient content and photosynthetic capacity of leaves were measured. ? Small additions of organic matter triggered O(2) depletion and accumulation of NH(4)(+), Fe(2+) and CO(2) in sediments. O(2) in leaf lacunae fluctuated from above air saturation in the light to anoxia late in the dark in natural sediments, but organic enrichment prolonged anoxia because of higher O(2) consumption and restricted uptake from the water. Leaf N and P dropped below minimum thresholds for cell function in enriched sediments and was accompanied by critically low chlorophyll and photosynthesis. ? We propose that anoxic stress restricts ATP formation and constrains transfer of nutrients to leaves. Brief anoxia in sediments and leaf lacunae late at night is a recurring summer phenomenon in Lobelia populations, but increased input of organic matter prolongs anoxia and reduces survival.     

Growth and photosynthetic responses of wheat plants grown in space.

Growth and photosynthesis of wheat (Triticum aestivum L. cv Super Dwarf) plants grown onboard the space shuttle Discovery for 10 d were examined. Compared to ground control plants, the shoot fresh weight of space-grown seedlings decreased by 25%. Postflight measurements of the O2 evolution/photosynthetic photon flux density response curves of leaf samples revealed that the CO2-saturated photosynthetic rate at saturating light intensities in space-grown plants declined 25% relative to the rate in ground control plants. The relative quantum yield of CO2-saturated photosynthetic O2 evolution measured at limiting light intensities was not significantly affected. In space-grown plants, the light compensation point of the leaves increased by 33%, which likely was due to an increase (27%) in leaf dark-respiration rates. Related experiments with thylakoids isolated from space-grown plants showed that the light-saturated photosynthetic electron transport rate from H2O through photosystems II and I was reduced by 28%. These results demonstrate that photosynthetic functions are affected by the microgravity environment.     

Net Photosynthesis, Electron Transport Capacity, and Ultrastructure of Pisum sativum L. Exposed to Ultraviolet-B Radiation

Pisum sativum L. was exposed to ultraviolet-B (UV-B) radiation (280-315 nm) in greenhouse and controlled environment chambers to examine the effect of this radiation on photosynthetic processes. Net photosynthetic rates of intact leaves were reduced by UV-B irradiation. Stable leaf diffusion resistances indicated that the impairment of photosynthesis did not involve the simple limitation of CO₂ diffusion into the leaf. Dark respiration rates were increased by previous exposure to this radiation. Electron transport capacity as indicated by methylviologen reduction was also sensitive to UV-B irradiation. The ability of ascorbate-reduced 2,6-dichlorophenolindophenol to restore much of the electron transport capacity of the UV-B-irradiated plant material suggested that inhibition by this radiation was more closely associated with photosystem II than with photosystem I. Electron micrographs indicated structural damage to chloroplasts as well as other organelles. Plant tissue irradiated for only 15 minutes exhibited dilation of thylakoid membranes of the chloroplast in some cells. Some reduction in Hill reaction activity was also evidenced in these plant materials which had been irradiated for periods as short as 15 minutes.     

林下与全光下地枫皮叶片形态和光合特性的比较

测量了林下与全光下地枫皮的叶片形态和光合-光响应曲线,探讨光强对地枫皮的形态和生理特性的影响。结果表明：林下与全光下地枫皮叶片净光合速率（Pn）、气孔导度（Gs）、蒸腾速率（Tr）和水分利用效率（WUE）对光强的响应趋势均基本一致,但全光下的Pn、Gs和Tr值较高,林下WUE值较高。全光下地枫皮的最大净光合速率、光饱和点和光补偿点均极显著高于林下,但弱光下的量子效率无显著差异;林下地枫皮的叶长、叶宽、干物质重、叶面积和比叶面积等叶片形态参数均极显著大于全光。推断地枫皮为耐阴性较弱的阳生植物,其光合能力和光饱和点较低,是对干旱环境的适应性反应;全光下地枫皮叶片狭小降低了吸光面积,有利于避免过高光强对叶光合器官的损伤。     

Functional mitochondrial complex I is required by tobacco leaves for optimal photosynthetic performance in photorespiratory conditions and during transients

The importance of the mitochondrial electron transport chain in photosynthesis was studied using the tobacco (Nicotiana sylvestris) mutant CMSII, which lacks functional complex I. Rubisco activities and oxygen evolution at saturating CO(2) showed that photosynthetic capacity in the mutant was at least as high as in wild-type (WT) leaves. Despite this, steady-state photosynthesis in the mutant was reduced by 20% to 30% at atmospheric CO(2) levels. The inhibition of photosynthesis was alleviated by high CO(2) or low O(2). The mutant showed a prolonged induction of photosynthesis, which was exacerbated in conditions favoring photorespiration and which was accompanied by increased extractable NADP-malate dehydrogenase activity. Feeding experiments with leaf discs demonstrated that CMSII had a lower capacity than the WT for glycine (Gly) oxidation in the dark. Analysis of the postillumination burst in CO(2) evolution showed that this was not because of insufficient Gly decarboxylase capacity. Despite the lower rate of Gly metabolism in CMSII leaves in the dark, the Gly to Ser ratio in the light displayed a similar dependence on photosynthesis to the WT. It is concluded that: (a) Mitochondrial complex I is required for optimal photosynthetic performance, despite the operation of alternative dehydrogenases in CMSII; and (b) complex I is necessary to avoid redox disruption of photosynthesis in conditions where leaf mitochondria must oxidize both respiratory and photorespiratory substrates simultaneously.     

The relationship between anatomy and photosynthetic performance of heterobaric leaves

Heterobaric leaves show heterogeneous pigmentation due to the occurrence of a network of transparent areas that are created from the bundle sheaths extensions (BSEs). Image analysis showed that the percentage of photosynthetically active leaf area (Ap) of the heterobaric leaves of 31 plant species was species dependent, ranging from 91% in Malva sylvestris to only 48% in Gynerium sp. Although a significant portion of the leaf surface does not correspond to photosynthetic tissue, the photosynthetic capacity of these leaves, expressed per unit of projected area (Pmax), was not considerably affected by the size of their transparent leaf area (At). This means that the photosynthetic capacity expressed per Ap (P*max) should increase with At. Moreover, the expression of P*max could be allowing the interpretation of the photosynthetic performance in relation to some critical anatomical traits. The P*max, irrespective of plant species, correlated with the specific leaf transparent volume (lambda(t)), as well as with the transparent leaf area complexity factor ((CF)A(t)), parameters indicating the volume per unit leaf area and length/density of the transparent tissues, respectively. Moreover, both parameters increased exponentially with leaf thickness, suggesting an essential functional role of BSEs mainly in thick leaves. The results of the present study suggest that although the Ap of an heterobaric leaf is reduced, the photosynthetic performance of each areole is increased, possibly due to the light transferring capacity of BSEs. This mechanism may allow a significant increase in leaf thickness and a consequent increase of the photosynthetic capacity per unit (projected) area, offering adaptive advantages in xerothermic environments.     

Stomatal limitation of photosynthesis and reduced growth of the halophyte, Plantago maritima L., at high salinity

Abstract. Plantago maritima L. was grown at three levels of salinity, 50, 200, 350 mol m⁻³ NaCl, and the effects on growth, ion content and photosynthetic capacity were studied. Shoot and root dry weight, leaf production and leaf length were all substantially reduced in plants grown at high salinity. Total leaf area of plants grown at 350 mol m⁻³ NaCl was only 20% of that in plants at low salinity. Both the Na⁺ and K⁺ content of leaves and roots increased with external salinity. There was no change in the Na⁺/K⁺ ratio of leaves or roots at different salinity levels. Despite the large reductions in growth and high accumulation of Na⁺ ions, leaf photosynthetic rate was only slightly reduced by salinity stress. The reduction in photosynthesis was not caused by reduced biochemical capacity as judged by photosynthetic response to intercellular CO₂ and by ribulose-1,5-bisphosphate carboxylase activity, but was due to reduced leaf conductance and low intercellular CO₂ concentration. The increased stomatal limitation of photosynthesis resulted in higher water-use efficiency of plants grown at high salinity.     

Changes in the Biochemical Composition, Structure, and Function of Pea Leaf Chloroplasts in Iron Deficiency and Root Anoxia

A combined effect of iron deficiency and root anoxia on the biochemical composition, function, and structure of pea leaf chloroplasts was studied. It was found that the chlorosis of apical leaves in response to iron deficiency was determined by the reduction of light-harvesting complexes I and II. Under root anoxia, complexes of the reaction centers of photosystems I and II degraded first. Weak activity was preserved even in yellow and white leaves under the effect of both factors. The ultrastructure of leaf chloroplasts gradually degraded. Initially, intergranal thylakoid sites were reduced, and the longitudinal orientation of grana was disturbed. However, yellow and white leaves still retained small thylakoids and grana. It is concluded that the degrading effects of iron deficiency and root anoxia on the complex composition and leaf chloroplast structure and function are additive because of their autonomous mechanisms.     

Antioxidant status of anoxia-tolerant and -intolerant plant species under anoxia and reaeration

The redox potential of the cell, as well as the antioxidant status of the tissue, are considered to be important regulatory constituents in an adaptive response in plants. Here the involvement of active antioxidants ascorbic acid (AA), reduced glutathione (GSH) and α - and β -tocopherols in reactive oxygen species scavenging, and the effect of anoxic stress on their reduction state were studied in 4 anoxia-tolerant and -intolerant plant species: Iris germanica L., Iris pseudacorus L., wheat ( Triticum aestivum L. cv. Leningradka) and rice ( Oryza sativa L. cv. VNIIR). The initial antioxidant content (both AA and GSH) was higher in the rhizomes of the more anoxia-tolerant Iris spp., as compared with that of the roots of the cereals. The predominant form of ascorbate was dehydroascorbic acid (DHA) in the cereals and AA in the Iris spp. Imposition of anoxia with subsequent reoxygenation resulted in an overall depletion of the reduced forms of antioxidants. No concurrent increase in oxidised forms (DHA and conjugated glutathione) was observed in anoxic samples. α -tocopherol content in Iris spp. was in the range 1–2 μg g⁻¹ fresh weight, while β -tocopherol content was higher in the anoxia-intolerant I. germanica (7.2 μg g⁻¹ fresh weight) as compared with the tolerant I. pseudacorus (1.5 μg g⁻¹ fresh weight). In I. pseudacorus , a significant decrease in α - and β -tocopherol levels was observed only after long-term (45 days) anoxia. The results suggested exclusion of AA and GSH from the redox cycling under prolonged anoxia, and a concomitant decrease in the redox state, as well as an anoxia-induced depletion of α - and β -tocopherols.     

Changes in the biochemical composition, structure, and function of pea leaf chloroplasts in iron deficiency and root anoxia

A combined effect of iron deficiency and root anoxia on the biochemical composition, function, and structure of pea leaf chloroplasts was studied. It was found that the chlorosis of apical leaves in response to iron deficiency was determined by the reduction of light-harvesting complexes I and II. Under root anoxia, complexes of the reaction centers of photosystems I and II degraded first. Weak activity was preserved even in yellow and white leaves under the effect of both factors. The ultrastructure of leaf chloroplasts gradually degraded. Initially, intergranal thylakoid sites were reduced, and the longitudinal orientation of grana was disturbed. However, yellow and white leaves still retained small thylakoids and grana. It is concluded that the degrading effects of iron deficiency and root anoxia on the complex composition and leaf chloroplast structure and function are additive because of their autonomous mechanisms.     

再力花地下部水浸提液对几种水生植物幼苗的化感作用

采用砂培法研究了不同浓度再力花地下部水浸提液对荇菜、苦草、水田芥、芦苇和黄菖蒲幼苗的生长、光合速率、根系活力、叶绿素含量以及抗氧化保护酶活性的影响,并采用气相色谱-质谱(GC-MS)联用技术对再力花地下部水浸提液的化学成分进行了分析。结果表明:再力花地下部水浸提液对荇菜、苦草、水田芥、芦苇和黄菖蒲5种水生植物幼苗生长有明显的影响,其中使用50mg干重/mL再力花水浸提液处理5种水生植物幼苗,对其生长指标有着极显著的抑制作用(P<0.01),苦草、水田芥和黄菖蒲的净光合速率分别降低69.0%、63.7%和73.5%,荇菜、苦草、水田芥和黄菖蒲幼苗根系活力分别降低67.3%、65.4%、52.2%和46.7%,5种水生植物幼苗叶绿素含量分别下降59.7%、71.2%、35.2%、50.0%和76.5%。当处理浓度为5mg/mL时,对5种水生植物幼苗体内过氧化物酶(POD)、超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性有显著的促进作用;当浓度为50mg/mL时,对5种水生植物幼苗体内POD、SOD和CAT有显著的抑制作用,丙二醛(MDA)含量增加。分析显示,再力花地下部水浸提液中主要含有愈创木酚(78.93%)、邻苯二甲酸二丁基酯(7.13%)、邻苯二甲酸二乙氧基乙酯(1.48%)、香豆满(1.09%)、邻苯二甲酸二乙酯(0.98%)、松油醇(0.70%)、吲哚(0.65%)、二丁基羟基甲苯(0.64%),合计占到总量的91%以上。     

RESPONSE OF LEAF ANATOMY AND PHOTOSYNTHETIC CAPACITY IN ALOCASIA MACRORRHIZA (ARACEAE) TO A TRANSFER FROM LOW TO HIGH LIGHT

Alocasia macrorrhiza plants were grown in 1% and 20% full sunlight, and their leaf anatomical and physiological parameters were measured. Total leaf thickness was 41% greater and mesophyll thickness was 52% greater in high-light leaves than in low-light leaves. This increase in thickness resulted from both increased cell size and number. Maximum leaf photosynthetic capacity was also 66% greater in high- than in low-light leaves. When low-light plants were transferred to high light, the thickness of mature leaves did not increase but the thickness of the first leaf to expand after the transfer was significantly greater than that of the low-light leaves. Thus, only leaves that were still expanding at the time of transfer developed leaf thickness greater than plants remaining in low light. Fully mature leaves showed no change in photosynthetic capacity in response to transfer. Leaves that had just completed expansion at the time of low- to high-light transfer were able to develop slightly higher maximum photosynthetic capacities than older leaves. However, full photosynthetic acclimation to the new light environment did not occur until the second new leaf expanded after transfer. These results are discussed in relation to the timing and mechanisms of whole plant acclimation to increased light.