Exogenous glycine betaine modulates ascorbate peroxidase and catalase activities and prevent lipid peroxidation in mild water-stressed Carapa guianensis plants

The hypothesis that application of exogenous glycine betaine (GB_EX) may attenuate the effects of mild water deficit in leaf gas exchange and lipid peroxidation in Carapa guianensis was examined. For this reason, 110-d old plants were sprayed with 0, 25, and 50 mM GB_EX and then subjected to two watering regimes. In the first, irrigation was continuously performed to maintain the soil near to field capacity (watered plants). In the second, irrigation was withheld and water deficit resulted from progressive evapotranspiration (water-stressed plants). Treatment comparisons were assessed when predawn leaflet water potential (Ψ_pd) of stressed plants reached ?1.28 ± 0.34 MPa. Regardless of the watering regime, significant (P<0.05) increases in foliar glycine betaine (GB_Leaf) concentration were observed in response to increasing GB_EX; however, such increases were more expressive in stressed plants. The net photosynthetic rate, stomatal conductance to water vapor, and intercellular to ambient CO₂ concentration ratio were significantly lower in water-stressed plants independently of GB_EX concentration sprayed on leaves. The application of 25 and 50 mM GB_EX caused significant (P<0.05) increases in ascorbate peroxidase (APX) activity in stressed plants, while significant (P<0.05) increases in catalase activity was observed just in the stressed plants treated with 50 mM GB_EX. Malondialdehyde concentrations did not differ between watered and stressed plants regardless of GBEX concentration. In conclusion, C. guianensis was able to incorporate GBEX through their leaves and the resulting increases in GB_Leaf attenuated lipid peroxidation in stressed plants through positive modulation of APX and CAT activities.     

Lipid peroxidation, chloroplastic pigments and antioxidant strategies in Carapa guianensis (Aubl.) subjected to water-deficit and short-term rewetting

The effects of drought on membrane lipids and leaf pigments and the ability of andiroba (Carapa guianensis Aubl.) plants to attenuate oxidative damage through antioxidant enzymes or adjusting carotenoids and glycinebetaine (GB) were examined. Assessments were performed when pre-dawn leaf water potential (Ψ_pd) of water-stressed plants reached −1.35 and −3.21 MPa (15 and 27 days after withholding irrigation) and 12 h after resuming watering (short-term rewetting, day 28). Oxidative damages to lipids were evident on day 15, in which drought caused an increase of 47% in malondialdehyde (MDA) content. On day 27, MDA content did not differ between treatments. The activity of superoxide dismutase remained unchanged over experimental period, while significant increases in the ascorbate peroxidase (APX, 110%) and catalase (CAT, 50%) activities were observed only on day 27. GB content was 62% (day 15) and 112% (day 27) higher in water-stressed plants than in control. Regardless of Ψ_pd, both chlorophyll (Chl) a, Chl b and total carotenoids remained unchanged between well-watered and water-stressed plants, indicating that drought did not result in degradation of leaflet pigments. On day 28, Ψ_pd of water-stressed plants increased near to control plants and both activities of APX and CAT did not differ between treatments. Altogether, adjustments in APX and CAT activity and in the GB content were efficient strategies to prevent expressive oxidative damages in water-stressed andiroba plants.     

Characteristics of Crassulacean Acid Metabolism in the Succulent C(4) Dicot, Portulaca oleracea L

Crassulacean acid metabolism (CAM) was investigated in leaves and stems of the succulent C₄ dicot Portulaca oleracea L. Diurnal acid fluctuations, CO₂ gas exchange, and leaf resistance were monitored under various photoperiod and watering regimes. No CAM activity was seen in well watered plants grown under 16-hour days. Under 8-hour days, however, well watered plants showed a CAM-like pattern of acid fluctuation with amplitudes of 102 and 90 microequivalents per gram fresh weight for leaves and stems, respectively. Similar patterns were also observed in detached leaves and defoliated stems. Leaf resistance values indicated that stomata were open during part of the dark period, but night acidification most likely resulted from refixation of respiratory CO₂. In water-stressed plants maximum acid accumulations were reduced under both long and short photoperiods. At night, these plants showed short periods of net CO₂ uptake and stomatal opening which continued all night long during preliminary studies under natural environmental conditions. Greatest acid fluctuations, in P. oleracea, with amplitudes of 128 microequivalents per gram fresh weight, were observed in water-stressed plants which had been rewatered, especially when grown under short days. No net CO₂ uptake took place, but stomata remained open throughout the night under these conditions. These results indicate that under certain conditions, such as water stress or short photoperiods, P. oleracea is capable of developing an acid metabolism with many similarities to CAM.     

Combined Effects of CO2 Enrichment and Drought Stress on Growth and Energetic Properties in the Seedlings of a Potential Bioenergy Crop Jatropha curcas

The rapid growth of worldwide energy demands has led to mounting concerns about energy shortages and has promoted the development of biofuels, which are susceptible to climate change. To evaluate the effects of future environmental changes such as CO₂ enrichment and water stress on the growth and biodiesel production of bioenergy plants, we exposed Jatropha curcas to two levels of CO₂ concentration (ambient and elevated) and three watering regimes (well-watered, moderate drought, and severe drought) to study its biomass accumulation and allocation, energy cost-gain properties, and photosynthetic response. Elevated CO₂ enhanced biomass accumulation of J. curcas by 31.5, 25.9, and 14.4 % under well-watered, moderate drought, and severe drought treatments, respectively, indicating that the stimulating effect was greater under optimum water conditions than in water-deficit conditions. Drought stress significantly increased the biomass allocation to roots, especially the fine roots. CO₂ enrichment also increased the root mass fraction, though not significantly. CO₂ enrichment significantly enhanced the photosynthetic rate measured under growth CO₂ concentration (A _growth) and decreased foliar N content and therefore construction cost irrespective of watering conditions. Under elevated CO₂, J. curcas employed a quicker return energy use strategy indicated by the higher photosynthetic energy use efficiency and lower payback time. There was a pronounced downregulation in the light-saturated photosynthetic rate under the common CO₂ concentration (P _max) under long-term CO₂ exposure, due to a decrease in the initial and total ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities and partially lower foliar N content. The significant interaction of CO₂ enrichment and watering regimes implied that the stimulation of plant growth by CO₂ enrichment may be negated by soil drought in the future. Long-term field experiments manipulating multiple factors simultaneously are needed to explore how the ecophysiological traits measured for J. curcas translate into bioenergy production.     

Effects of Various Levels of CO(2) on the Induction of Crassulacean Acid Metabolism in Portulacaria afra (L.) Jacq

In response to water stress, Portulacaria afra (L.) Jacq. (Portulacaceae) shifts its photosynthetic carbon metabolism from the Calvin-Benson cycle for CO₂ fixation (C₃) photosynthesis or Crassulacean acid metabolism (CAM)-cycling, during which organic acids fluctuate with a C₃-type of gas exchange, to CAM. During the CAM induction, various attributes of CAM appear, such as stomatal closure during the day, increase in diurnal fluctuation of organic acids, and an increase in phosphoenolpyruvate carboxylase activity. It was hypothesized that stomatal closure due to water stress may induce changes in internal CO₂ concentration and that these changes in CO₂ could be a factor in CAM induction. Experiments were conducted to test this hypothesis. Well-watered plants and plants from which water was withheld starting at the beginning of the experiment were subjected to low (40 ppm), normal (ca. 330 ppm), and high (950 ppm) CO₂ during the day with normal concentrations of CO₂ during the night for 16 days. In water-stressed and in well-watered plants, CAM induction as ascertained by fluctuation of total titratable acidity, fluctuation of malic acid, stomatal conductance, CO₂ uptake, and phosphoenolpyruvate carboxylase activity, remained unaffected by low, normal, or high CO₂ treatments. In well-watered plants, however, both low and high ambient concentrations of CO₂ tended to reduce organic acid concentrations, low concentrations of CO₂ reducing the organic acids more than high CO₂. It was concluded that exposing the plants to the CO₂ concentrations mentioned had no effect on inducing or reducing the induction of CAM and that the effect of water stress on CAM induction is probably mediated by its effects on biochemical components of leaf metabolism.     

Shifts in the Carbon Metabolism of Xerosicyos danguyi H. Humb. (Cucurbitaceae) Brought About by Water Stress : I. General Characteristics

Xerosicyos danguyi H. Humb. (Cucurbitaceae) is an unusual leaf succulent endemic to Madagascar. Under well-watered conditions the plant exhibited Crassulacean acid metabolism (CAM), as characterized by large diurnal changes in titratable acidity, predominantly nighttime stomatal opening and CO₂ uptake, and high δ¹³C values. When plants were exposed to water stress for a minimum of a month, they shifted to a mode of carbon metabolism previously labeled CAM-idling. Under this mode of metabolism, the plants exhibited reduced stomatal opening, reduced CO₂ uptake, dampened diurnal fluctuations in titratable acidity, and no apparent changes in the δ¹³C values. Additionally, investigations showed that the stress hormones 1-aminocyclopropane-1-carboxylic acid (an ethylene precursor) and abscisic acid increased as much as 6-fold in the water-stressed plants. The results are discussed in relation to physiological significance and evolution of the CAM-idling mode of metabolism.     

The Response of Leaf Water Potential and Crassulacean Acid Metabolism to Prolonged Drought in Sedum rubrotinctum

Plants of Sedum rubrotinctum R. T. Clausen were studied in a green-house over a 2-year period without watering. Only the apical leaves survived and were turgid at the end of the experiment. The midday leaf water potential of these apical leaves was −1.20 megapascals, while the leaf water potential of comparable leaves on well-watered control plants was −0.20 megapascals. The unwatered plants appear to have maintained turgor by means of an osmotic adjustment. After 2 years without water the plants no longer exhibited a nocturnal accumulation of titratable acidity. However, the daytime levels of titratable acidity of the unwatered plants were more than 2-fold greater than the levels in well-watered control plants. Well-watered plants of S. rubrotinctum exhibited seasonal shifts in biomass stble carbon isotope ratios, indicating a greater proportion of day versus night CO₂ uptake in the winter than in the summer. The imposition of water stress prevented the expression of this seasonal rhythm and restricted the plants to dark CO₂ uptake.     

Characterization and Partial Purification of Aldose-6-phosphate Reductase (Alditol-6-Phosphate:NADP 1-Oxidoreductase) from Apple Leaves

The Pereskia are morphologically primitive, leafed members of the Cactaceae. Gas exchange characteristics using a dual isotope porometer to monitor ¹⁴CO₂ and tritiated water uptake, diurnal malic acid fluctuations, phosphoenolpyruvate carboxylase, and malate dehydrogenase activities were examined in two species of the genus Pereskia, Pereskia grandifolia and Pereskia aculeata. Investigations were done on well watered (control) and water-stressed plants. Nonstressed plants showed a CO₂ uptake pattern indicating C₃ carbon metabolism. However, diurnal fluctuations in titratable acidity were observed similar to Crassulacean acid metabolism. Plants exposed to 10 days of water stress exhibited stomatal opening only during an early morning period. Titratable acidity, phosphoenolpyruvate carboxylase activity, and malate dehydrogenase activity fluctuations were magnified in the stressed plants, but showed the same diurnal pattern as controls. Water stress causes these cacti to shift to an internal CO₂ recycling (“idling”) that has all attributes of Crassulacean acid metabolism except nocturnal stomata opening and CO₂ uptake. The consequences of this shift, which has been observed in other succulents, are unknown, and some possibilities are suggested.     

Leaf gas exchange and multiple enzymatic and non-enzymatic antioxidant strategies related to drought tolerance in two oil palm hybrids

Key message

The drought tolerance in young oil palm plants is related to greater efficiency in preventing oxidative damage by activating enzymatic and non-enzymatic antioxidant strategies simultaneously.

Abstract

Drought is a major environmental constraint limiting growth and yield of oil palm trees. In this study, two oil palm hybrids (BRS Manicoré and BRS C 2501) were grown in large containers and subjected to a water deficit during 57 days. Leaf gas exchange analysis was combined with an in-depth assessment of the antioxidant system over the drought imposition. Under drought, leaf water potential at predawn (Ψ _pd) decreased similarly in both hybrids. In parallel, there were decreases in the net CO₂ assimilation rate (A), chlorophyll concentrations and Rubisco total activity. Overall, these decreases were more pronounced in BRS C 2501 than in BRS Manicoré. BRS C 2501 plants triggered more markedly its enzymatic antioxidant system earlier (Ψ _pd = ?2.1 MPa) than did BRS Manicoré, but these responses were accompanied by higher concentrations of H₂O₂ and malondialdehyde in BRS C 2510 than in BRS Manicoré. With the progress of drought stress (Ψ _pd = ?2.9 MPa and below), BRS Manicoré was better able to cope with oxidative stress through a more robust antioxidant system. In addition, significant decreases in drought-induced NAD⁺-malate dehydrogenase activities were only observed in stressed BRS C 2501 plants. Regardless of watering regimes, the total carotenoid, ascorbate and glutathione concentrations were higher in BRS Manicoré than in BRS C 2501. In conclusion, BRS Manicoré is better able to tolerate drought than BRS C 2501 by triggering multiple antioxidant strategies involved both in reactive oxygen species scavenging and dissipation of excess energy and/or reducing equivalents particularly under severe drought stress.

     

Leaf Wilting Movement Can Protect Water-Stressed Cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.) Plants Against Photoinhibition of Photosynthesis and Maintain Carbon Assimilation in the Field

Under severe water stress, leaf wilting is quite general in higher plants. This passive movement can reduce the energy load on a leaf. This paper reports an experimental test of the hypothesis that leaf wilting movement has a protective function that mitigates against photoinhibition of photosynthesis in the field. The experiments exposed cotton (Gossypium hirsutum L.) to two water regimes: water-stressed and well-watered. Leaf wilting movement occurred in water-stressed plants as the water potential decreased to −4.1 MPa, reducing light interception but maintaining comparable quantum yields of photosystem II (PS II; Yield for short) and the proportion of total PS II centers that were open (qP). Predrawn F _v/F _m (potential quantum yield of PS II) as an indicator of overnight recovery of PS II from photoinhibition was higher than or similar to that in well-watered plants. Compared with water-stressed cotton leaves for which wilting movement was permitted, water-stressed cotton leaves restrained from such movement had significantly increased leaf temperature and instantaneous CO₂ assimilation rates in the short term, but reduced Yield, qP, and F _v/F _m. In the long term, predrawn F _v/F _m and CO₂ assimilation capacity were reduced in water-stressed leaves restrained from wilting movement. These results suggest that, under water stress, leaf wilting movement could reduce the incident light on leaves and their heat load, alleviate damage to the photosynthetic apparatus due to photoinhibition, and maintain considerable carbon assimilation capacity in the long term despite a partial loss of instantaneous carbon assimilation in the short term.     

Crassulacean Acid Metabolism in the Succulent C(4) Dicot, Portulaca oleracea L Under Natural Environmental Conditions

Crassulacean acid metabolism (CAM) was examined under natural environmental conditions in the succulent C₄ dicot Portulaca oleracea L. Two groups of plants were monitored; one was watered daily (well watered), while the other received water once every 3 to 4 weeks to produce a ψ of −8 bars (drought stressed). Gas exchange, transpiration rate, and titratable acidity were measured for 24-hour periods during the growing season. CAM activity was greatest in drought-stressed plants during late August which had 13 hour days and day/night temperatures of 35/15°C. Under these conditions net CO₂ uptake occurred slowly throughout the night. Diurnal fluctuations of titratable acidity took place in both leaves and stems with amplitudes of 17 and 47 microequivalents per gram fresh weight, respectively. Transpiration data indicated greater opening of stomata during the night than the day. CAM was less pronounced in drought-stressed P. oleracea plants in July and September; neither dark CO₂ uptake nor positive carbon balance occurred during the July measurements. In contrast, well-watered plants appeared to rely on C₄ photosynthesis throughout the season, although some acid fluctuations occurred in stems of these plants during September.     

Hydrogen peroxide mediated tolerance to copper stress in the presence of 28-homobrassinolide in Vigna radiata

Hydrogen peroxide (H₂O₂) in minute quantity serves as a signalling molecule. However, the role of H₂O₂ in combination with brassinosteroids (stress regulators) in plants under toxic levels of copper, is poorly understood. With an aim to explore and elaborate their role in plants subjected to abiotic stress, the surface sterilized seeds of mung bean (Vigna radiata) were sown in earthen pots filled with soil and manure enriched with different levels of Cu²⁺ (50 or 100 mg kg^?1 of soil) and allowed to grow under natural environmental conditions. At 15 and 20 days stage, the plants were sprayed with H₂O₂ (2.5 mM) and/or 28-homobrassinolide (HBL, 10^?5 mM), respectively. At 45 days stage, the analysis of the plants revealed that the presence of copper in the soil caused a significant decrease in growth characteristics, activity of carbonic anhydrase and nitrate reductase, relative water content, chlorophyll content and the rate of photosynthesis whereas, the activity of antioxidant enzymes (catalase, peroxidase and superoxide dismutase) and the proline accumulation in leaves increased in Cu stressed plants. However, the exogenously applied HBL and/or H₂O₂, in the absence of Cu-stress strongly favoured the growth, photosynthetic parameters and also improved the activity of antioxidant enzymes and the proline content. Furthermore, the combined application of HBL and H₂O₂ to the foliage of the stressed plants neutralized the toxic impact of all copper regimes. Therefore, we are of the opinion that these chemicals somehow maintained the homeostasis of the metal in the plants that exhibit healthy growth.     

Shifts in the Carbon Metabolism of Xerosicyos danguyi H. Humb. (Cucurbitaceae) Brought About by Water Stress : II. Enzymology

Xerosicyos danguyi Humbert (Cucurbitaceae) is a leaf succulent endemic to Madagascar. Under well-watered conditions, the plant exhibited Crassulacean acid metabolism (CAM) but shifted to a dampened form of CAM, CAM-idling, when subjected to water stress. The purpose of this investigation was to examine the effects of a shift in carbon metabolism on phosphoenolpyruvate carboxylase and on NADP-malic enzyme in X. danguyi. Experiments were conducted to determine the diurnal patterns of enzyme activity and pH optima of both enzymes, as well as the approximate molecular mass, kinetic patterns, malate inhibition, and glucose-6-phosphate stimulation of phosphoenolpyruvate carboxylase. The two enzymes extracted from well-watered and water-stressed plants were similar in most parameters investigated; thus, CAM-idling appeared to be only a dampened form of CAM photosynthesis.     

Effects of Powdery Mildew and Water Stress on CO(2) Exchange in Uninfected Leaves of Barley

Net photosynthesis is stimulated in third seedling leaves of barley plants whose lower two leaves are heavily infected by Erysiphe graminis f.sp. hordei Marchal. Stimulation is greater in water-stressed than in well-watered plants. In stressed, but not in well-watered plants, stimulation is associated with the maintenance of high leaf water potential and high leaf conductance. A small part of the changes in net photosynthesis is attributable to changes in respiratory metabolism in the third leaf, and other possible causes are discussed.     

Effects of CO2 enrichment and water stress on gas exchange of Liquidambar styraciflua and Pinus taeda seedlings grown under different irradiance levels

Summary The effects of CO₂ enrichment and water stress on gas exchange of Liquidambar styraciflua L. (sweetgum) and Pinus taeda L. (loblolly pine) seedlings were examined for individuals grown from seed under high (1000 mol·m^-2·s^-1) and low (250 mol·m^-2·s^-1) photosynthetic photon flux density at 350, 675 and 1000 l·l^-1 CO₂. At 8 weeks of age, half the seedlings in each CO₂-irradiance treatment were subjected to a drying cycle which reduced plant water potential to about -2.5 MPa in the most stressed plants, while control plants remained well-watered (water potentials of -0.3 and -0.7 MPa for sweetgum and loblolly pine, respectively). During this stress cycle, whole seedling net photosynthesis, transpiration and stomatal conductance of plants from each CO₂-irradiance-water treatment were measured under respective growth conditions.For both species, water stress effects on gas exchange were greatest under high irradiance conditions. Waterstressed plants had significantly lower photosynthesis rates than well-watered controls throughout most of the drying cycle, with the most severe inhibition occurring for low CO₂, high irradiance-grown sweetgum seedlings. Carbon dioxide enrichment had little effect on gas exchange rates of either water-stressed or well-watered loblolly pine seedlings. In contrast, water stress effects were delayed for sweetgum seedlings grown at elevated CO₂, particularly in the 1000 l·l^-1 CO₂, high irradiance treatment where net photosynthesis, transpiration and conductance of stressed plants were 60, 36 and 33% of respective control values at the end of the drying cycle. Development of internal plant water deficits was slower for stressed sweetgum seedlings grown at elevated CO₂. As a result, these seedlings maintained higher photosynthetic rates over the drying cycle than stressed sweetgum seedlings grown at 350 l·l^-1 CO₂ and stressed loblolly pine seedlings grown at ambient and enriched CO₂ levels. In addition, water-stressed sweetgum seedlings grown at elevated CO₂ exhibited a substantial increase in water use efficiency.The results suggest that with the future increase in atmospheric CO₂ concentration, sweetgum seedlings should tolerate longer exposure to low soil moisture, resulting in greater first year survival of seedlings on drier sites of abandoned fields in the North Carolina piedmont.     

The effects of water,nutrient availability and their interaction on the growth,morphology and physiology of two poplar species

We exposed cuttings of two poplar species, Populus cathayana Rehder and Populus przewalskii Maximowicz, from Sect. Tacamahaca Spach to two watering regimes (well-watered and water-stressed conditions) and to two nutrient regimes (with or without fertilization) in a greenhouse to determine how fertilization affects the growth, morphology and physiology of poplars under different water conditions. Under stress conditions, changes in early growth and dry matter allocation, and decrease in gas exchange and the related functions are usually observed. Moreover, the measurement of carbon isotope composition (δ¹³C) provides an integrated measurement of water use efficiency. And abscisic acid (ABA) is a phytohormone which plays a prominent role in various physiological and biochemical processes related to environmental stresses. So we determine these characteristics and related parameters, and our results showed the following: (1) Fertilization promoted the growth of poplars under well-watered conditions, while under water-stressed conditions its effect on growth was negative. (2) Fertilization increased δ¹³C, total N concentration, chlorophyll a/b and intrinsic efficiency of photosystem II (Fv/Fm) but decreased relative water content of leaves, stomatal conductance, transpiration rate and C/N ratio under both well-watered and water-stressed conditions. (3) Fertilization appeared to increase net photosynthesis rate and decrease ABA content under well-watered conditions, while it decreased net photosynthesis rate and increased ABA content under water-stressed conditions. Moreover, compared to P. cathayana, collected from a lower altitude region, P. przewalskii, collected from a high-altitude region, has a slower growth rate and stronger adaptability to drought stress, which perhaps resulted from its chronic adaptability to the low water availability of high-altitude region; but to the nutrient stress, there was no difference between the two species.     

Induction of Acid Metabolism in Portulacaria afra

Portulacaria afra, a succulent plant, shifts from a predominantly C₃ mode of gas exchange to a typical Crassulacean acid metabolism type CO₂ uptake in response to water or NaCl stress. Control plants in the absence of water stress assimilated CO₂ during the light (about 7-8 mg CO₂ dm⁻² hr⁻¹), transpiration (about 1.5 g dm⁻² hr⁻¹) was predominantly during the day, stomates were open during the day, and there was little diurnal organic acid fluctuation. Stressed plants showed only dark CO₂ uptake and dark water loss, nocturnal stomatal opening, and an increased diurnal fluctuation of titratable acidity. Within 2 weeks after rewatering, stressed plants returned to the control acid fluctuation levels indicating that the response to stress was reversible.     

Mapping QTLs and meta-QTLs for two inflorescence architecture traits in multiple maize populations under different watering environments

Drought significantly affects the architectural development of maize inflorescence, which leads to massive losses in grain yield. However, the genetic mechanism for traits involved in inflorescence architecture in different watering environments, remains poorly understood in maize. In this study, 19 QTLs for tassel primary branch number (TBN) and ear number per plant (EN) were detected in 2 F_2:3 populations under both well-watered and water-stressed environments by single environment mapping with composite interval mapping (CIM); 11/19 QTLs were detected under water-stressed environments. Moreover, 21 QTLs were identified in the 2 F_2:3 populations by joint analysis of all environments with a mixed linear model based on composite interval mapping (MCIM), 11 QTLs were involved in QTL × environment interactions, seven epistatic interactions were identified with additive by additive/dominance effects. Remarkably, 12 stable QTLs (sQTLs) were simultaneously detected by single environment mapping with CIM and joint analysis through MCIM, which were concentrated in ten bins across the chromosomes: 1.05_1.07, 1.08_1.10, 2.01_2.04, 3.01, 4.06, 4.09, 5.06_5.07, 6.05, 7.00, and 7.04 regions. Twenty meta-QTLs (mQTLs) were detected across 19 populations under 51 watering environments using a meta-analysis, and 34 candidate genes were predicted in corresponding mQTLs regions to be involved in the regulation of inflorescence development and drought resistance. Therefore, these results provide valuable information for finding quantitative trait genes and to reveal the genetic mechanisms responsible for TBN and EN under different watering environments. Furthermore, alleles for TBN and EN provide useful targets for marker-assisted selection to generate high-yielding maize varieties.     

Three Phases of Plant Response to Atmospheric CO(2) Enrichment

Several years of research on seven different plants (five terrestrial and two aquatic species) suggest that the beneficial effects of atmospheric CO₂ enrichment may be divided into three distinct growth response phases. First is a well-watered optimum-growth-rate phase where a 300 parts per million increase in the CO₂ content of the air generally increases plant productivity by approximately 30%. Next comes a nonlethal water-stressed phase where the same increase in atmospheric CO₂ is more than half again as effective in increasing plant productivity. Finally, there is a water-stressed phase normally indicative of impending death, where atmospheric CO₂ enrichment may actually prevent plants from succumbing to the rigors of the environment and enable them to maintain essential life processes, as life ebbs from corresponding ambient-treatment plants.     

Drought-induced acclimatization of a fast-growing plant decreases insect performance in leaf-chewing and sap-sucking guilds

An initial destabilization of functions triggered by drought stress in plants is followed by acclimatization and acquisition of tolerance; however, knowledge remains limited on drought-mediated changes in plant quality for herbivores. We tested whether a water-stressed fast-growing plant negatively affects host-specialist insects in both sap-sucking and leaf-chewing feeding guilds. Collards (Brassica oleracea var. acephala) were grown in well-watered, slightly water-stressed and severely water-stressed conditions. Decreasing soil moisture adversely affected plant development, assessed as a reduction in leaf number and size, stomatal size and relative water content. Severely stressed plants had less fiber and glucosinolates; however, they showed more total nitrogen and lipids. Larval survival, pupal weight, reproductive rate (Ro) and rate of population growth (r) were lower when the leaf-chewing Plutella xylostella was reared with severely stressed collards. In multiple-choice tests, moths laid fewer eggs on leaf discs of collard that were exposed to drought. The fecundity of the sap-sucking Brevicoryne brassicae was higher and the development of alates was lower when insects were fed on plants kept in well-watered regime as compared to slight-stress and severe-stress. Despite higher nitrogen content and fewer glucosinolates, a higher level of leaf surface wax in severely stressed collards possibly decreased food quality for both herbivores. Thus, host-specific herbivores of different guilds showed similar responses to drought-stressed, fast-growing plants. Water-stressed crops could discourage the attack of specialist insects, but the intensity of the stress that is required to achieve this effect will greatly reduce crop production, in terms of plant growth or foliage increment.