Leaf Diffusive Resistance Research Articles

Insight into chilling stress response of key citrus grafting combinations grown in Egypt

One way to help plants deal with unfavorable temperatures is to graft elite cultivars onto adaptable rootstocks. Citrus macrophylla is a newly introduced rootstock in Egypt. Still, it needs to be evaluated in terms of its response to chilling stress compared to the most widely used rootstock (Citrus volkameriana). Thus, the present work assessed the physiological, biochemical, and anatomical responses of C. volkameriana (Volkamer) and C. macrophylla (Alemow) rootstocks and the cultivars ‘Olinda Valencia orange’ and ‘Murcott Tangerine’ grafted onto them to chilling stress. Plants were subjected to low-night temperatures for 48 h at 20/4 °C ± 1 (day/night), followed by three days of recovery at 30/25 °C ± 1 (day/night). Under low-night temperatures, all plants recorded a significant increment in malondialdehyde (MDA), peroxidase (POX), superoxide dismutase (SOD), proline, and leaf diffusion resistance (LDR). At the same time, a significant reduction was found in the photosynthetic apparatus (stomatal conductance (GS), transpiration (TR), and chlorophyll), polyphenol oxidase (PPO), and catalase (CAT). Moreover, anatomical damage was observed in total leaf thickness, palisade tissue thickness, spongy tissue thickness, midvein vascular bundle thickness, upper epidermis thickness, lower epidermis thickness, and spongy ratio (SR). Our results also indicated that the Volkamer, Olinda Valencia orange/Volkamer, and Murcott Tangerine/Volkamer were slightly damaged and showed a relatively high level of antioxidant activity (SOD and POX), LDR, and a more significant decrease in TR. However, they were less affected anatomically than Alemow rootstock and the scions grafted on it. These results demonstrated that grafting on Volkamer could improve the physiological, biochemical, and anatomical structural responses of the scions grafted on it to low-night temperature stress compared with grafting on Alemow.

Alterações no aparelho fotossintético, sistemas antioxidantes e estrutura anatômica das folhas de alguns genótipos cítricos enxertados no recém-introduzido porta-enxerto ‘Macrophylla’ em resposta ao estresse por resfriamento

Abstract One-year-old transplants of ‘Olinda Valencia orange’, ‘Murcott Tangerine’, and ‘Limoneira 8A Lisbon’ genotypes were grafted on ‘Macrophylla’ rootstock and subjected, along with ‘Macrophylla’ rootstock, to 24 h of the night chilling (nocturnal) at 20/4 °C±1 (day/night) for three days, (8 h per day), followed by three days of recovery at 30/25 °C±1 (day/night). The results showed that leaf diffusion resistance (LDR), proline, malondialdehyde (MDA), peroxidase (POX), and superoxide dismutase (SOD) increased significantly in all genotypes, while there was a significant decrease in photosynthetic apparatus, polyphenol oxidase (PPO), and catalase (CAT) under nocturnal chilling stress. Under the chilling, Macrophylla rootstock had the highest concentrations of proline and SOD, whereas it had the lowest MDA and total chlorophyll concentrations. Noticeably, the enzymatic antioxidant profiles were enhanced after being recovered. Moreover, ‘Murcott’ had the highest LDR, MDA concentration, thickness of lamina, midvein, palisade tissue, spongy tissue, and dimension of midvein vascular bundle. Meanwhile, it had the lowest stomatal conductance (GS) and transpiration rate (E). Similar results were obtained with ‘Valencia’ genotype. In contrast, the ‘Limoneira 8A’ genotype under the chilling had the lowest levels of LDR, antioxidant enzymes (POX, CAT, and PPO), thickness of lamina, midvein, palisade tissue, spongy tissue, and dimension of midvein vascular bundle.

Comprehensive Selection Criteria for Some Barley Genotypes under Different Water Stress Treatments

Nowadays, water scarcity is a great danger to agriculture development, in semiarid and arid regions beside climate change risks. Egypt is suffering from scarce water resources for agriculture; it is of high priority to rationalize irrigation water use. During two seasons, 2019/2020 and 2020/2021 the experimental were carried out to investigate the effect of three different irrigation water treatments (I1 at 45, I2 at 60 and I3 at 75% depletion of available soil moisture) on some photosynthetic, agronomical, grain quality parameters, water productivity for eight barley genotypes. Also, classify them on the SSR molecular level. The results showed that there were high genetic variations found among the eight genotypes with significant responses to irrigation water treatments. Rationalize irrigation water from I1 to I3 had a negative effect on all studied phenotypic traits, whereas had an appositive effect on leaf diffusive resistance and cured protein content and inducement all genotypes to flower early by average increasing (27.7, 12.7 and 7.08%) respectively. Giza 138, Giza 131, and Line 4 gave high mean performance values of the measured characters besides, attaining high WP values were 1.14, 1.08, and 0.89 kg grain/m3 applied water I1, I2, and I3 irrigation treatments, respectively. While, WUE values increased with increasing water availability. Water use efficiency values were 1.92, 1.71, and 1.34 kg grain/m3 consumed water for I1, I2, and I3 irrigation treatments, respectively. Twenty-six alleles were generated using ten SSR primers with a mean value of 2.6 alleles per locus. The Polymorphism Information Content (PIC) value of each SSRs marker ranged from 0.33 (Bmag 0387) to 0.47 (Bmac 0167) with an average value of 0.34. Cluster analysis clustered the eight barley genotypes into two major clusters divided according to their response to water stress tolerance. The genetic information about eight barley genotypes for water stress tolerance was established, for use them in breeding programs in Egypt.

Effect of straw mulching and irrigation on physiological activities, yield of maize (Zea mays L.) and soil physical properties under available soil moisture depletion conditions in Mollisols

A field experiment was conducted during winter season of 2016-17 and 2017-18 to evaluate the effect of residue mulch and irrigation on the physiological response and yield of maize and soil physical properties at G. B. Pant University of Agriculture and Technology, Pantnagar. The experiment was laid-out in split-plot design which includes three irrigation scheduling in main plots and four residue mulch practices in sub plots. Soil temperature at 15 cm enhanced by 0.6-9.8 0C under mulch and by 0.7-1.2 0C with irrigation at 20% DASM over other irrigation levels. Mulch significantly decreased bulk density by 1.43-3.59% while increased saturated hydraulic conductivity by 3.8-41.0% and mean weight diameter by 6.0-20.0%. Irrigation at less depletion of available soil moisture favoured soil physical properties. Mulch and increase in irrigation frequency tended to increase in relative water content and transpiration rate while decreased leaf diffusive resistance. No noticeable differences in leaf temperature were observed under mulch and irrigation. Green gram straw mulch and irrigation given at 20% DASM produced 2.6-14.2 % and 1.3-9.2% higher grain yield, respectively. Combined application of green gram straw mulch @ 5 t ha-1 along with irrigation at 20% DASM was found most beneficial for maintaining favourable soil environment and can be recommended for obtaining higher maize yield in Mollisols.

Effect of straw mulching and irrigation on physiological activities, yield of maize (Zea mays L.) and soil physical properties under available soil moisture depletion conditions in Mollisols

A field experiment was conducted during winter season of 2016-17 and 2017-18 to evaluate the effect of residue mulch and irrigation on the physiological response and yield of maize and soil physical properties at G. B. Pant University of Agriculture and Technology, Pantnagar. The experiment was laid-out in split-plot design which includes three irrigation scheduling in main plots and four residue mulch practices in sub plots. Soil temperature at 15 cm enhanced by 0.6-9.8 0C under mulch and by 0.7-1.2 0C with irrigation at 20% DASM over other irrigation levels. Mulch significantly decreased bulk density by 1.43-3.59% while increased saturated hydraulic conductivity by 3.8-41.0% and mean weight diameter by 6.0-20.0%. Irrigation at less depletion of available soil moisture favoured soil physical properties. Mulch and increase in irrigation frequency tended to increase in relative water content and transpiration rate while decreased leaf diffusive resistance. No noticeable differences in leaf temperature were observed under mulch and irrigation. Green gram straw mulch and irrigation given at 20% DASM produced 2.6-14.2 % and 1.3-9.2% higher grain yield, respectively. Combined application of green gram straw mulch @ 5 t ha-1 along with irrigation at 20% DASM was found most beneficial for maintaining favourable soil environment and can be recommended for obtaining higher maize yield in Mollisols

Molecular markers and GGE biplot analysis for selecting higher‐yield and drought‐tolerant maize hybrids

AbstractImproving maize (Zea mays L.) genotypes for higher productivity and tolerance to drought stress depends mainly on physiological and molecular markers. Therefore, this study aims at breeding maize for drought tolerance and high potentiality by selection based on molecular markers, photosynthetic parameters; and easy graphic methods that help in selecting elite genotypes across diverse environments. An 8 × 8 half diallel analysis was used at two locations involving drought and normal irrigation treatments to study parental genetic diversity (GD) and combining ability (general combing ability [GCA] and specific combining ability [SCA]) in F1 of maize. Fingerprinting of parents was made using simple sequence repeat (SSR) markers. Fifty‐eight alleles were ranged from two to five alleles per locus with an average of 0.63 alleles per locus. The average of polymorphic information content (PIC) was 0.63. Cuvette temperature (oc) was lowest by the cross L14 × L36. The cross L8 × L34 expresses the highest value for Quantum sensor (μmol m–2 s–1), net CO2 assimilation rate and chlorophyll content. As for leaf diffusive resistance (LDR) four crosses exhibited significant desirable LDR values. Concerning rate of leaf transpiration (LTR) (μg cm−2 S−1) the cross (L5 × L104) gave the lowest value. Most hybrids exhibited desirable values for drought susceptibility index. For grain yield plant–1, five F1 crosses, that is, L5 × L34, L8 × L14, L8 × L14, L30 × L104, and L36 × L104 expressed the most desirable SCA effects. These crosses are promising in maize breeding programs. Based on GGE biplot analysis, genotype nos. 8 and 10 exhibited the highest grain yield plant−1 and ranked the first across all environments.

Atmospheric CO2 enrichment effect on water use efficiency in chickpea (Cicer arietinum L.)

AbstractEffect of atmospheric CO2 enrichment on crop water relations was evaluated in an open‐top chamber experiment on kabuli chickpea (Cicer arietinum L.; Pusa 1,105). Increase in atmospheric CO2 concentration (e[CO2], 580 ± 20 μmol/mol) resulted in 21%–46% increase in leaf water potential, and 7%–11% in relative leaf water content, indicating higher water content in leaves, compared to the ambient level (a[CO2], 384 ± 12 μmol/mol). Higher leaf water status was connoted through spectral indices over the growing period. A rise in CO2, however, brought increase in leaf diffusive resistance and canopy temperature by 15%–35% and 3%–11%, respectively, potentially indicating partial closure of stomata. Increase in leaf area index (13%–73%), and higher spectral vegetation index suggested improved growth of chickpea under e[CO2]. An increase in leaf area compensated the decrease in diffusive resistance, and therefore seasonal total water use was similar between enriched and ambient conditions. Although water use efficiency (WUE) increased by 30% (p < .05) due to an increase in crop biomass under e[CO2], the canopy conductance remained unaffected. Results suggest a possibility of improved plant water status, enhanced biomass production and increased WUE for chickpea, with similar crop water use under future e[CO2] levels.

Soybean irrigation requirements and canopy-atmosphere coupling in Southern Brazil

The lack of base information on crop water requirements under tropical conditions is one of the causes for inefficient water use and inadequate irrigation management. The crop coefficient (Kc) approach is universally adopted for scheduling and quantifying the water management and, recently, its relation with the evaporative atmosphere demand has been included in this approach to improve the decision-making on irrigation management. In this paper, we measured crop evapotranspiration (ETc) in two experiments as evaporative heat flux from a centre pivot-irrigated soybean plantations in tropical Brazil to quantify the crop water needs. Irrigation requirements were determined by comparing ETc with reference evapotranspiration (ETo), derived from FAO-56 (Allen et al., 1998). In this study, the average Kc value obtained was 0.92, which is nearly 20% lower than those recommended by the FAO-56 (Allen et al., 1998) and varied inversely as a function of ETo. Based on aerodynamic and leaf diffusive resistance (rs) data, Ω was computed and presented values relatively high compared to other crops, which means a relatively poor coupling of soybean canopies to the atmosphere. Throughout both experiments, the Kc value decreased by up to 44.8% when the ETo increased from 2 to 4 mm d−1, depending on the phenological phase, indicating the need for taking into account the ETo values when selection the Kc values for improving the irrigation management in tropical soybean.

Genotypically Identifying Wheat Mesophyll Conductance Regulation under Progressive Drought Stress.

Photosynthesis limitation by CO2 flow constraints from sub-stomatal cavities to carboxylation sites in chloroplasts under drought stress conditions is, at least in some plant species or crops not fully understood, yet. Leaf mesophyll conductance for CO2 (gm) may considerably affect both photosynthesis and water use efficiency (WUE) in plants under drought conditions. The aim of our study was to detect the responses of gm in leaves of four winter wheat (Triticum aestivum L.) genotypes from different origins under long-term progressive drought. Based on the measurement of gas-exchange parameters the variability of genotypic responses was analyzed at stomatal (stomata closure) and non-stomatal (diffusional and biochemical) limits of net CO2 assimilation rate (AN). In general, progressive drought caused an increasing leaf diffusion resistance against CO2 flow leading to the decrease of AN, gm and stomatal conductance (gs), respectively. Reduction of gm also led to inhibition of carboxylation efficiency (Vcmax). On the basis of achieved results a strong positive relationship between gm and gs was found out indicating a co-regulation and mutual independence of the relationship under the drought conditions. In severely stressed plants, the stomatal limitation of the CO2 assimilation rate was progressively increased, but to a less extent in comparison to gm, while a non-stomatal limitation became more dominant due to the prolonged drought. Mesophyll conductance (gm) seems to be a suitable mechanism and parameter for selection of improved diffusional properties and photosynthetic carbon assimilation in C3 plants, thus explaining their better photosynthetic performance at a whole plant level during periods of drought.

Effects of water stress on physiological processes and yield attributes of different mungbean (L.) varieties

In order to investigate the effect of water stress on Mungbean varieties and its physiological responses to yield, a field experiment was carried out according to split plot design with twenty treatments combination and three replications during 2010 and 2011 at Crop Research Centre of Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut (Uttar Pradesh). The results indicated that drought tolerant varieties maintained highest xylem water potential (XWP), transpiration resistance (TR) and lowest leaf diffusive resistance (LDR) and canopy temperature minus air temperature (Tc – Ta) while drought susceptible varieties maintained lowest XWP,TR and highest LDR and Tc – Ta during the 1300 -1330 h. The rate of net photosynthesis decreased in all the varieties in treatment samples at various stages with the decrease in external CO2 concentrations. Increase in free proline was observed from vegetative to active pod filling stages in all the varieties. The resistant varieties accumulated higher level of proline under water stress. SML-668 recorded the highest free proline content than all the other varieties. Variety SML-668 produced significantly higher grain yield. Key words: Mungbean, water stress, yield and yield components.

Nutrient Management on Soil Health, Nutrient Uptake and Yield of Maize under Temporary Submerged Condition in Mollisol

A field experiment was conducted during Kharif 2010 with a view to find out the effect of different integrated nutrient management practices on soil quality parameters, growth, yields and yield attributes and nutrient uptake by maize (PEHM-5) under managed temporary excess soil moisture stress at knee high stage in mollisol. Results showed an improvement in soil quality parameters in plots supplied with organic sources either individually or combination of all with 100% NPK fertilizers to that grown with inorganics alone or no fertilizers. Bulk density was lowest under combined application of vermicompost, zinc, PSB and Azospirillum with 100% NPK but applied ZnSO4 increased bulk density to a maximum of 1.38 Mg m-3 . Inoculation of biofertilizers along with vermicompost enhanced organic carbon by 0.02 - 0.14 per cent over other treatments. Availability of N, P, K and Zn was significantly influenced by applied organic sources with chemical fertilizers. Treatments received 100% NPK along with zinc, Azospirillum, PSB and vermicompost significantly recorded higher values of 187.32, 31.96, 178.35 and 2.71 kg ha -1 available N, P, K and Zn, respectively, but individual application of Azospirillum, PSB and zinc responded to least availability of zinc, N and P, respectively. Higher total uptake of N, P, K and Zn was recorded with combined application of organic and inorganic inputs with 100% NPK followed by 100% NPK+ vermicompost. Nutrient management practices had significant effect on growth, yields and yield attributing parameters; however nodes with brace roots and ASI were not significantly affected. Different organic and inorganic combinations produced 144-917 kg ha -1 more grain yield over 100% NPK whereas reduced by 1237-2154 kg ha -1 to the treatment subjected to no submergence. Inclusion of Azospirillum and PSB with 100% NPK gave statistically on par grain yields. Maize plants grown with vermicompost, 125% NPK and combination of all inputs showed in general, lower net photosynthetic rate, transpiration rate and leaf temperature, respectively, while higher leaf diffusive resistance to that of normal condition. Integrated use of biofertilizers and vermicompost with 100% NPK was found to be the best for maize production under excess soil moisture stress.

Effect of Water Deficit Stress on the Physiology, Growth and Leaf Cell Ultrastructure of Sorghum (<i>Sorghum bicolor</i>r (L.) Moench)

An experiment was conducted in growth chambers to study the response of sorghum cultivars to water deficit stress. Seven sorghum cultivars were evaluated under three water deficit levels [control (-0.05 MPa), mild stress (-0.27 MPa), and severe stress (-0.96 MPa)] in a hydroponic culture in a completely randomised block design replicated three times. The three water deficit levels were created by adding 0, 10 and 20% (w/v) polyethylene glycol 6000 (PEG 6000) to the nutrient solution. The results indicated that water deficit, especially severe water deficit (-0.96 MPa), severely affected the growth and physiology of sorghum. Water deficit stress reduced plant height, leaf area, dry matter accumulation, water use efficiency, root length, and stomatal density. Water deficit stress increased stomatal closure and thus leaf diffusive resistance. Stressed plants deposited larger amounts of epicuticular wax on leaf surfaces and stomatal openings. Water stress significantly reduced the amount of starch grains in the chloroplasts. Sorghum cultivars displayed distinctive response to water deficit stress for many of the parameters. Jigurti, Gambella 1107 and Meko grew better than P9403 and SA1486 under water deficit conditions. Jigurti showed no significant reduction in any of the growth parameters even under severe water deficit (-0.96 MPa) conditions. Keywords: Epicuticular wax; Leaf diffusive resistance; Leaf relative water content; Starch; Stomata; Water use efficiency.Ethiopian Journal of Biological Sciences Vol. 5 (2) 2006: pp. 161-176

Plant water relations and proline accumulation on two cowpea (Vigna unguiculata (L.) Walp.) cultivars as a response to water stress

Cowpeas produced under rainfed conditions of arid and semiarid areas of Sub-Saharan Africa often experience periods of water stress. It is therefore important to identify drought tolerant cultivars of cowpeas and the mechanisms involved in their ability to withstand these conditions. The aim of this study was to evaluate the responses of physiological parameters such as leaf water potential, leaf diffusive resistance, relative water content, leaf proline content and cell membrane stability to water stress and to identify the parameters, which can be used to distinguish between drought tolerant and drought susceptible cowpea cultivars. Water stress was applied from 16 to 30 days after emergence (DAE) to two cowpea cultivar namely Akkerbone Bechuana Wit (AB Wit) and Akkerbone CH 14 (ACH 14) by withholding water to the stressed plants. Well-watered plants were watered regularly to keep the soil moisture content close to or at field water capacity. Water stress increased leaf diffusive resistance (LDR) and proline accumulation and decreased relative water content (RWC) in both cultivars and water potential only in AB Wit. Increases in proline content seemed to correlate more closely to changes in relative water content than changes in water potential. Water potential, relative water content and proline accumulation, therefore, seemed to be useful parameters to distinguish between drought tolerant and drought susceptible cowpea cultivars.

Diurnal changes in photosynthetic characteristics of sweet potato (Ipomoea batatas L.)

Diurnal changes in single leaf photosynthetic rate, leaf diffusive resistance, and stomatal conductance were observed in three sweet potato cultivars, S-108, Kanhangad, and Sree Badhra (S-1010), grown under field conditions. The highest photosynthetic rate and stomatal conductance were observed between 10.00 and 11.00 hr. The two parameters declined between 11.00 and 14.00 hr and increased between 14.00 and 15.00 hr. Stomatal resistance was low between 10.00 and 11.00 hr, increased between 11.00 and 14.00 hr and then declined between 14.00 and 17.00 hr. The diurnal variations in single leaf photosynthetic rate, stomatal conductance and diffusive resistance are attributed to changes in solar radiation, relative humidity and air temperature. There was no significant difference among the three cultivars in diurnal photosynthesis and storage root yield.

Root-derived trans-zeatin riboside and abscisic acid in drought-stressed and rewatered sunflower plants: interaction in the control of leaf diffusive resistance?

Four-week-old potted sunflower plants (Helianthus annuus L.) were exposed to drought for up to two days by withholding irrigation. During the stress treatment and after rewatering, xylem sap was collected from decapitated hypocotyls by pressurising the root system. The water potential (Ψw) of the hypocotyl, the diffusive resistance of the second leaf pair, total transpiration and the concentration and flux rates of ABA and trans-zeatin riboside (ZR), identified by combined gas chromatography-mass spectrometry (GC-MS) as the dominant cytokinin in xylem sap, were determined. ABA contents were also analysed in root and leaf tissue. When Ψw of the hypocotyl decreased, the concentration and flux rate of ZR decreased drastically after a transient rise. A significant rise in ABA concentration and flux rate in xylem sap as well as a parallel rise in leaf diffusive resistance occurred as soon as Ψw reached values of -0.4 MPa and lower. Root ABA concentration began to rise at the same water potential parallel to the rise in xylem sap, whereas the ABA concentration in leaves began to rise only at Ψw values lower than -0.6MPa. Treatment of the root system with norflurazon prior to drought stress suppressed the increase in the ABA concentration in xylem sap and caused higher transpiration rates. Watering the drought-stressed plants led to a rapid decrease in ABA content of the xylem sap within three hours, whereas the decrease in leaf diffusive resistance was somewhat slower. The ZR concentration in the xylem sap rose continuously after rewatering, reaching a 60-fold increase after five hours, and declined again afterwards. Studies in which ZR and ABA were applied to cut shoots in concentrations similar to those in xylem sap of well-watered plants (ZR) and drought-stressed plants (ABA) showed that ZR, even in very low concentrations, antagonised the effect of ABA on transpiration. The results are discussed with regard to a possible antagonistic interaction of ZR and ABA as non-hydraulic root-to-shoot signals, and with regard to their interplay with hydraulic signalling.

Calcium distribution in cut roses as related to transpiration

SummaryIn contrast to many other horticultural crops, cut roses show higher concentrations of Ca in the leaves at the top of the flower stem than in those at the bottom. This study aimed to investigate the distribution of Ca along the stem of roses, to assess whether Ca accumulation in roses might be governed by factors other than transpiration. Ca concentrations in the leaves decreased from bottom to top of the stem. The effects of air vapour pressure deficit (VPD), removal of leaves and/or bent down stems on Ca concentrations in the leaves and petals were studied in greenhouse experiments. A lowerVPD resulted in an 11% increase in the number of flowering stems, which was offset by a lower average stem weight. Although transpiration was on average 25% lower in the low-VPD treatment over the whole experimental period, it was not (winter period) or only slightly (summer) related to lower Ca concentrations in the petals, stems or leaves. This limits the possibility for Ca enhancement by influencing transpiration. Removal of part of the leaves and/ or bent-down stems increased Caconcentrations in the remaining leaves and petals, primarily through decreased dryweight accumulation. Leaf diffusion resistance decreased along the stem from bottom to top leaves. In postharvest transpiration studies, stomatal densities and transpiration rates per unit leaf area were both higher in top than in bottom leaves. The findings indicate that local Ca concentrations in the rose organs can be related to their respective transpiration rates.

Influence of drought on some physiological parameters symptomatic for oxidative stress in leaves of chives ( Allium schoenoprasum)

Drought, created by withholding water, led to significant reductions in the absolute (−3.6%) and relative (−24.8%) water content of chives ( Allium schoenoprasum) leaves, a significant rise in the osmolarity of the leaf sap (+18.9%) and a loss of leaf transpiration (leaf diffusion resistance >20 s cm −1). Nevertheless, the leaves did not show signs of oxidative damage, as the concentration of chlorophylls and soluble proteins and the extent of lipid peroxidation did not change compared with well-watered plants. The concentration of carotenoids and UV radiation absorbing substances remained stable indicating no loss of antioxidant capacity. While it did not affect specific guaiacol peroxidase activity, drought increased the specific activity of ascorbate peroxidase significantly by almost 29% and reduced the specific lipoxygenase activity significantly by 60%. Both changes can be considered as beneficial under drought conditions as they potentially reduce the formation of reactive oxygen species. Chives proved to be tolerant to the imposed drought stress, the plants totally recovered within one week after rewatering.

Resistência estomática, tensão de água no xilema e teor de clorofila em genótipos de gravioleira

As variáveis ecofisiológicas exercem grande influência, não somente no comportamento vegetativo das plantas cultivadas, mas sobretudo no seu desempenho em relação às características produtivas. Este trabalho verificou a resistência à difusão de vapor, as relações hídricas e o teor de clorofila em dois genótipos de gravioleira (Morada e Comum), sob condições naturais de cultivo. O estudo foi realizado num pomar comercial do município de Paudalho, PE, em duas épocas (setembro e dezembro de 1998). O delineamento estatístico foi o inteiramente casualizado com seis repetições para cada genótipo. De cada repetição foram selecionadas duas folhas sadias, completamente expandidas, localizadas no terço médio das copas e diretamente expostas à radiação solar. No horário de maior demanda evaporativa (entre 12 e 14 horas) mediram-se, durante três dias consecutivos para cada época, a transpiração (E), a resistência à difusão de vapor (Rs), a temperatura foliar (Tf), a tensão de água no xilema (psiw) e os teores de clorofila a e b. Verificaram-se mudanças no comportamento sazonal em relação às trocas gasosas, Yw e Tf entre os dois materiais genéticos estudados. Registraram-se correlações entre psiw e E e entre psiw e Tf. A umidade relativa do ar apresentou correlação com a Tf e com a Rs. A gravioleira Comum é mais eficiente fotossinteticamente por minimizar a degradação da clorofila b pela incidência da luz. Os genótipos de gravioleira Morada e Comum apresentaram comportamentos distintos em todos os parâmetros ecofisiológicos avaliados. O psiw constitui um bom parâmetro para aferição de diferenças genotípicas em gravioleira. Já a Rs deve ser utilizada como parâmetro para aferição de adaptação ambiental entre genótipos de gravioleira, em épocas de maior demanda evaporativa.

Effect of Water Stress on Physiological Attributes and their Relationship with Growth and Yield of Wheat Cultivars at Different Stages

The effects of water stress on physiological attributes of drought‐sensitive (Kalyansona) and drought‐tolerant (C‐306) wheat cultivars were studied in a pot experiment. Water stress was imposed by withholding irrigation at boot and anthesis stages. Leaf water potential, leaf osmotic potential and leaf turgor potential (measured with pressure chamber and osmometer), as well as leaf diffusive resistance, leaf transpiration rate and leaf‐to‐air transpiration gradient (measured with a steady‐state porometer) were measured diurnally. Growth and yield parameters were recorded after harvesting of the crop. Triplicate data were analysed using a completely randomized design and correlations amongst these parameters were computed.Water stress was found to reduce diurnal leaf water potential and leaf osmotic potential in both the genotypes but leaf osmotic potential was significantly higher in the drought‐tolerant cultivar C‐306 than in the drought‐sensitive cultivar Kalyansona. Positive turgor was recorded in both the genotypes under water stress and non‐stress conditions. Water‐stressed plants showed significantly lower turgor potential than control plants. In diurnal observations, water‐stressed plants exhibited significantly higher leaf diffusive resistance in both genotypes at both stages. The diffusive resistance of C‐306 was predominantly higher than that of Kalyansona. Water stress decreased leaf transpiration rate at both stages but the reduction was higher at the anthesis stage. The leaf‐to‐air temperature gradient was much higher in C‐306 than in Kalyansona at the boot stage but at the anthesis stage genotypic variation was non‐significant. The capacity to maintain cooler foliage was lower at the anthesis stage than at the boot stage in both the cultivars.Shoot dry weight, number of grains, test weight, grain yield, biological yield and harvest index decreased to a greater extent when water stress was imposed at the anthesis stage, while imposition of water stress at the boot stage caused a greater reduction in plant height and number of tillers. Similarly, water stress caused a smaller reduction in growth, yield and yield attributes in C‐306 than in Kalyansona.In general, the correlation coefficient of grain and biological yield with water potential and its components was positive and highly significant. Similarly, turgor potential was also correlated positively and significantly with grain yield at both the stages, but with biological yield it was significant only at the anthesis stage. A negative and significant correlation was obtained for diffusive resistance and leaf‐to‐air temperature gradient with grain yield at the boot and anthesis stages. The rate of transpiration was also positively and significantly correlated to grain and biological yields at both the stages. Amongst the yield attributes, number of leaves and number of tillers were positively correlated at the anthesis stage, whereas leaf area and shoot dry weight were significantly correlated with grain and biological yields at both the stages.

Modifications in vapor diffusion resistence of leaves and water relations in barbados cherry plants under water stress

Young sexually and assexually propagated Barbados cherry plants were submitted to water deficit (20 days without irrigation). During this period the accumulation of proline, water potential of branches, osmotic potential, the relative water content of leaves, the leaf diffusive resistance, the transpiration rate and leaf temperature in the cuvette were determined. In addition, photosynthetically active radiation (PAR) and vapor pressure deficit (VPD) were measured in the porometer cuvette. The concentration of proline for both types of plants began to increase on the fifth day without watering, and reached 38.1 times the concentration in the control plants grown from seeds and 26.4 times the concentration in grafted plants on the tenth day without watering. The lowest levels of leaf water potential in the plants suffering from severe water stress varied from -4.5 to -5.7 MPa, the lowest values being observed in the sexually propagated plants. These plants also showed the highest values for transpiration (0.9 mmol.m-2.s-1) and proline concentration (20.42 mg.g-1 DM), the lowest for relative water content of the leaves (38.4%) and diffusive resistance (940 s.m-1) at the end of the experiment. The Barbados cherry plants developed strategies for surviving drought, with differences between various characteristics, resulting from prolonged stress, which significantly influenced the parameters evaluated, with the exception of leaf temperature.