Improving Water Relations and Gas Exchange with Brassinosteroids in Rice under Drought Stress

Drought stress is the most pervasive threat to sustainable rice production and mainly disrupts membrane structure and cell-water relations. Exogenously applied brassinosteroids (BRs) may produce profound changes that may improve drought tolerance in rice. In this study, we monitored some physiological basis of the exogenously applied BRs in improving drought tolerance in fine grain aromatic rice ( Oryza sativa L.). Two BRs i.e. 28-homobrassinolide (HBL) and 24-epibrassinolide (EBL) were used both as seed priming and foliar spray. To prime, the seeds were soaked in 0.01 μ m aerated solution each of HBL and EBL for 48 h and dried back to original weight. Treated and untreated seeds were sown in plastic pots with normal irrigation in a phytotron. At four-leaf stage (3 weeks after sowing), plants were subjected to drought stress at 50 % field capacity by cutting down the water supply. For foliar spray, 0.01 μ m of HBL and EBL solutions were sprayed at five-leaf stage. Drought stress severely reduced fresh and dry weights, whilst exogenously applied BRs improved net CO₂ assimilation, water use efficiency, leaf water status, membrane properties, production of free proline, anthocyanins, soluble phenolics, but declined the malondialdehyde and H₂O₂ production. In conclusion, BRs application improved the leaf water economy and CO₂ assimilation, and enabled rice to withstand drought. Moreover, foliar spray had better effect under drought than seed treatments and of the two BRs, EBL proved more effective.     

The Influence of Plant Water Stress on Net Photosynthesis and Yield of Sunflower (Helianthus annuus L.)

The effect of plant water stress on net photosynthesis, leaf growth, yield and yield-related components were investigated in a single experiment in order to determine in which way water deficits affect sunflower yields.
Sunflower plants, grown under controlled temperature regimes, were stressed during budding, anthesis and seed filling by withholding water until the leaf water potential reached -1600 and -2000 kPa. Leaf area of unstressed plants significantly exceeded that of plants under severe stress during all growth stages investigated. The CO₂ uptake rate per unit leaf area as well as the total uptake rate per plant, significantly diminished with stress, while this effect drastically increased during the reproductive phase of the plant. Although this resulted in significantly smaller heads and kernels, it did not affect the number of seeds borne in the inflorescence. Severe stress during anthesis and seed filling resulted in more empty kernels. Moderate and severe stress during budding significantly lowered both grain and oil yields while plants that experienced moderate stress during anthesis and seed filling significantly outyielded those under severe stress.     

Stoffbildung, CO2-Gaswechsel, Kohlenhydrat- und Stickstoffgehalt von Winterweizen bei erhöhter CO2-Konzentration und Trocken-streß

Dry Matter Production, CO₂ Exchange, Carbohydrate and Nitrogen Content of Winter Wheat at Elevated CO₂ Concentration and Drought Stress
Methods of mathematical modelling and simulation are being used to an increasing degree in estimating the effects of rising atmospheric CO₂ concentration and changing climatic conditions on agricultural ecosystems. In this context, detailed knowledge is required about the possible effects on crop growth and physiological processes. To this aim, the influence of an elevated CO₂ concentration and of drought stress on dry matter production, CO₂ exchange, and on carbohydrate and nitrogen content was studied in two winter wheat varieties from shooting to milk ripeness. Elevated CO₂ concentration leads to a compensation of drought stress and at optimal water supply to an increase of vegetative dry matter and of yield to the fourfold value. This effects were caused by enhanced growth of secondary tillers which were reduced in plants cultivated at atmospheric CO₂ concentration. Analogous effects in the development of ear organs were influenced additionally by competitive interactions between the developing organs. The content and the mass of ethanol soluble carbohydrates in leaves and stems were increased after the CO₂ treatment and exhausted more completely during the grain filling period after drought stress. Plants cultivated from shooting to milk ripeness at elevated CO₂ concentration showed a reduced response of net photosynthesis rate to increasing CO₂ concentration by comparison with untreated plants. The rate of dark respiration was increased in this plants.     

The Influence of Plant Water Stress on Net Photosynthesis and Leaf Area of Two Maize (Zea mays L.) Cultivars

The effect of plant water stress on net photosynthesis and leaf growth were investigated in order to determine to what extent leaf water potential during vegetative growth and silking affects maize development.
Two commercial maize hybrids grown in pots in a glasshouse were subjected to leaf water potentials of -1300 and -1700 kPa during the eighth leaf stage and during silking to -1700 and -2300 kPa to previously unstressed, moderately and severely stressed plants. The effect of stress on inhibiting CO₂ uptake rates and leaf areas, as well as the recovery after alleviating stress, were compared to that of unstressed plants.
No substantial differences in CO₂ uptake rates were found between medium and long seasoned cultivars. The CO₂ uptake rates per unit leaf area decreased to negative values under both moderate and severe stress conditions during both growth stages. During silking, the recovery of CO₂ uptake rate was much lower than during the eight leaf stage. Leaf area decreased proportionally with increased stress but did not recover after alleviating stress on plants stressed during both the eighth leaf and silking stages.     

Cumulative Effects of Pre-sowing Seed Treatment and Foliar Application of Salts in Improving Biomass and Grain Yield of Soybean in Moderate Saline/alkaline Soil

Field trial studies were carried out to find out whether performance of soybean could be improved as a result of pre-sowing soaking treatment of seeds. Comparatively pre-sowing seed treatment with KNO₃, NaNO₃, NaCl, thiourea and di-Ammonium phosphate (DAP) resulted in better development of the root and shoot system than the control. As a result of pre sowing seed treatment, there was an increase in dry matter production by 44, 27 and 32 % over the control in KNO₃, NaNO₃ and DAP treatments respectively. Similarly increase in seed yield was noticed in NaNO₃ (45 %), KNO₃ (40 %) and DAP (50 %) pretreated plants. The number of existing nodules was reduced both in the control and treated plants due to pH (8.4) of the soil.
To investigate the cumulative effects of foliar spray on plants raised from pre-sowing seed treatment, salt solutions (NaCl, KNO₃, NaNO₃, thiourea, DAP) at optimal level were sprayed separately three times at three different stages of development. As a result of foliar spray moderate increase in growth in KNO₃ (20 %), thiourea (29 %) and DAP (25 %) treatment was observed over the control. Seed yield increased significantly (56–70 %) in all treatments except NaCl spray, due to increase in the number of pods (41–63 %) per plant. Foliar spray of nutrients increased protein yield without affecting the oil content. It is suggested that a considerable fertilizer economy may be effected by coupling pre-sowing seed treatment with foliar fertilization.     

Response of Mustard (Brassica juncea L.) to Applied Nitrogen with or without Ethrel Spray under Non-irrigated Conditions

Field studies were conducted during the winter seasons of 1995–96 and 1996–97 at the Agricultural Farm of Aligarh Muslim University, Aligarh, India on mustard ( Brassica juncea L. Czern & Coss., var. Alankar) under non-irrigated conditions, to evaluate the effect of foliar spray of 200 p.p.m. ethrel (2-chloroethyl phosphonic acid) at flowering growth stage along with basal 0, 40, 80 or 120 kg N ha⁻¹ on net photosynthetic rate (P_N), stomatal conductance (C_S), stomatal resistance (R_S), leaf K content, relative water content (RWC), leaf area index (LAI) and total dry matter (TDM) production monitored at 20 days after spray application, and plant N content, seed N content, nitrogen harvest index (NHI), nitrogen yield merit (NYM), pods plant⁻¹, 1000 seed weight, seed yield, biological yield, harvest index (HI), seed yield merit (SYM) and merit of genotype (MOG) at harvest. Results indicated that, at 0 or 40 kg N ha⁻¹, ethrel did not produce any significance effect, but at basal 80 kg N ha⁻¹, ethrel affected the parameters favourably with the exception of 1000 seed weight, HI, seed N and NHI. Ethrel-sprayed plants utilized N from the soil more effectively and showed increased NYM. Yield attributes, seed yield and merit of genotype (in terms of NYM and SYM) were also enhanced. Ethrel spray enhanced seed yield under water stress conditions mainly by increasing K uptake and retaining higher RWC, thereby decreasing R_S and increasing LAI, P_N and TDM production.     

Effect of Whole Season CO2 Enrichment on the Cultivation of a Medicinal Plant, Digitalis lanata

A versatile method was developed for the application of 1000 ppm CO₂ during the whole growth period of plants. Temperature controlled water cooling and ventilation of the greenhouse resulted in a monthly CO₂ enrichment time of 60 to 90 % of the total light period. Digitalis lanata , grown in greenhouses with CO₂ enrichment during the whole growth phase from April to November, produced twice as much biomass as field cultivated plants.
The relative yield of the glycoside digoxin per gram Digitalis drug dry weight was 0.4% in field grown and 0.7% in greenhouse cultivated plants. The production of digoxin per hectare in the greenhouse at 1000 ppm CO₂ was almost 3.5-fold that by field cultivation. Drug yield and secondary metabolite production in D. lanata were remarkably influenced by increased temperature and elevated CO₂ partial pressure in the greenhouse.     

Physiological Basis of Irrigation Scheduling for Seed Production in Egyptian Clover Syn. Berseem (Trifolium alexandrinum L.) Crop

A field experiment was conducted to find out the critical physiological stages of irrigation schedules inducing better growth, physiological efficiency and seed yield potential of berseem ( Trifolium alexandrinum L., Var. S-99-1). For this purpose eight irrigation treatments were made comprised of four treatments of three irrigation (W₁, W₂, W₃ and W₄), three treatments of four irrigation (W₅, W₇ and W₈) and one treatment of five irrigation (W₆) at various physiological stages i. e. regeneration, flower initiation, full bloom, seed initiation and advance seed development stage.
Thus based on the experimental results the physiological role of watering in berseem seed production could be discussed as:
With-holding of irrigation either at regeneration or at full bloom stage developed potential water stress in plants as indicated by high proline content of irrigation treatments — W₄, W₁ and W₇; and further brought out disturbance on the formation of carotene, synthesis of water soluble sugar and translocation of sugar towards reproductive organs during grain development stage. These stresses adversely affected the plant growth and flowering behaviour. The irrigation at seed initiation stage increased the seed yield. Continuous irrigation did not appear to be useful. Thus it can be concluded that irrigation at three critical physiological stages i. e. regeneration, full bloom and seed initiation was found to be essential for obtaining potential seed yield of berseem.     

Effect of Elevated CO2 on the Photosynthesis, Growth and Water Relation of Brassica Species Under Moisture Stress

An attempt has been made to study the interactive effect of elevated CO₂ and moisture stress on photosynthesis, growth and water relations of Brassica species using open top chambers. It was observed that plants responded to elevated CO₂ significantly under moisture stress condition mitigating the adverse effects on photosynthesis and growth of Brassica species. Relatively drought susceptible species, viz. B. campestris and B. nigra , responded to elevated CC₂ markedly as compared to less sensitive B. carinata and B. juncea plants. The water status of plants significantly improved under elevated CO₂ concentration possibly by increasing stomatal resistance and/or by increased root growth.     

Seed Composition, Seedling Emergence and Early Seedling Vigour of Red Kidney Bean Seed Produced at Elevated Temperature and Carbon Dioxide

Understanding the influence of growth temperature and carbon dioxide (CO₂) on seed quality in terms of seed composition, subsequent seedling emergence and early seedling vigour is important under present and future climates. The objective of this study was to determine the combined effects of elevated temperature and CO₂ during seed-filling of parent plants on seed composition, subsequent seedling emergence and seedling vigour of red kidney bean ( Phaseolus vulgaris ). Plants of cultivar 'Montcalm', were grown at daytime maximum/nighttime minimum sinusoidal temperature regimes of 28/18 and 34/24 °C at ambient CO₂ (350 μmol mol⁻¹) and at elevated CO₂ (700 μmol mol⁻¹) from emergence to maturity. Seed size and seed composition at maturity and subsequent per cent emergence, early seedling vigour (rate of development) and seedling dry matter production were measured. Elevated CO₂ did not influence seed composition, emergence, or seedling vigour of seeds produced either at 28/18 or 34/24 °C. Seed produced at 34/24 °C had smaller seed size, decreased glucose concentration, but significantly increased concentrations of sucrose and raffinose compared to 28/18 °C. Elevated growth temperatures during seed production decreased the subsequent per cent emergence and seedling vigour of the seeds and seedling dry matter production of seed produced either at ambient or elevated CO₂.     

Response of Mustard to Ethrel Spray and Basal and Foliar Application of Nitrogen

In a field trial conducted during 1992–93 and 1993–94, the effect of basal (B) nitrogen (N) (45 and 60 kg N ha⁻¹) and foliar application (F) of water (W) or 10 kg N ha⁻¹ and 400 or 600 ppm ethrel (E) (2-Chloro ethyl phosphonic acid) at 70 days after sowing was studied on leaf area index and dry mass at 90 days and pod number per plant, seeds per pod, 1000 seed weight, seed yield, oil content and oil vield at harvest of mustard ( Brassica juncea L. Czern & Coss.) cv. T-59. Recommended basal (B) application of 90 kg N ha (BN₉₀) was used as control. On the basis of 2 year data it was found that basal application of 60 kg N and foliar spray of 10 kg N ha ⁻¹ and 600 ppm ethrel gave higher values for growth and yield characteristics and enhanced seed yield and oil yield by 12.5 and 14.8%, respectively over control BN_90.     

Seasonal Changes in the Photosynthetic Capacity of Winter Rape Plants under Different Nitrogen Regimes Measured in the Field

Winter rape (cv.'Falcon') grown under different nitrogen regimes (N₀, N₁₂₀; 0 and 120 kg.ha⁻¹, respectively) in northern Germany was investigated over the 1996 spring–summer season. Using a CO₂, H₂O diffusion porometer, diurnal courses or net photosynthesis and respiration were measured in situ and were related to microclimatic conditions and leaf water relations. Photosynthesis was modelled and daily CO₂ gain was calculated. In contrast to the N₁₂₀ plants, plants of the low nitrogen plot (N₀) grew less densely and their leaves behaved more like sun leaves. Increased nitrogen supply had little influence on photosynthetic capacity but it increased productivity through higher leaf area index and an extended period of photosynthetic activity. N₁₂₀ plants also appeared to be better acclimated to hot, summer conditions. Higher nitrogen supply substantially increased seed production with the yield of the N₁₂₀ plants being 16% of the N₀ plants.     

Plant Growth Regulators Influence 14CO2 Assimilation and Translocation of Assimilates in Indian Mustard

Effect of plant growth regulators Naphthalene acetic acid (NAA), Gibberellic acid (GA₃) and Kinetin on ¹⁴CO₂ assimilation, partitioning of ¹⁴C into major biochemical fractions and translocation of assimilates was studied in different parts of Indian Mustard ( Brassica juncea ) at late ripening stage. Leaves, stem and pod walls are photosynthetically active and are important sources for seed filling. NAA and kinetin increased the ¹⁴CO₂ assimilation rate in all the three photosynthetically active parts. All the three growth regulators increased the export of ¹⁴assimilates out of source organs and increased the movement of assimilates into the reproductive parts (pods). The increased movement of photoassimilates into the developing pods may be due to the stimulation of sink activity by the growth regulators which resulted in the higher demand for photoassimilates. It was suggested that growth regulators may increase yield by altering distribution of assimilates in the mustard plants.     

Effect of Elevated CO2 and Nitrogen Nutrition on Photosynthesis, Growth and Carbon-Nitrogen Balance in Brassica juncea

The response of Brassica juncea var. Bio-183-92 to elevated CO₂ under increased nitrogen treatment was studied. There was an interactive effect of CO₂ and nitrogen nutrition, indicating that, on the addition of more nitrogen, the plants sustained the positive effect of CO₂ enrichment by utilizing additional carbohydrates for the development of new sinks. Excess carbohydrate enables plants to be flexible and responsive to additional nitrogen application to sustain the CO₂ enrichment effect.     

Assimilation, Dissimilation and Accumulation of 14C in Two Maize (Zea mays L.) Hybrids of Different Drought Tolerance

The effects of exposure in the vegetative phase of growth to 5- or 10-day spells of soil drought (30% field water capacity) on assimilation, dissimilation and accumulation of ¹⁴C and on dry matter growth were studied in two maize hybrids, nos. 8344 and 8388 (Garst Seed Co.) of high and low drought tolerance. Under control water regime in soil there was no difference in ¹⁴CO₂ uptake and dry matter growth between hybrids. After five days of drought ¹⁴CO₂ assimilation dropped by about 75% referred to unit weight of dry matter in hybrid 8344 and by 56% in hybrid 8388. After 10 days of drought ¹⁴CO₂ assimilation rate was reduced by 75% in both hybrids. Soil drought increased the ¹⁴C dissimilation. There were no significant differences between hybrids in all treatments, with the exception of 5 days drought; after this treatment the dissimilation rate of hybrid 8344 was higher than that of 8388. Changes of translocation of ¹⁴C and its accumulation in particular organs occurred in drought treated plants; the amount of ¹⁴C accumulated in roots of plants of hybrid 8344 increased, while that of hybrid 8388 decreased. Changes of ¹⁴C accumulation in roots were positively correlated to changes of dry matter of those organs. One day after 10 days of drought assimilation and dissimilation rates in both hybrids were about 60% of controls.     

Exogenously Applied Nitric Oxide Enhances the Drought Tolerance in Fine Grain Aromatic Rice (Oryza sativa L.)

Drought stress is a severe threat to the sustainable rice production, which causes oxidative damage and disturbs plant water relations, while exogenously applied nitric oxide (NO) may have the potential to alleviate these effects in rice plants. In this study, the role of NO to improve drought tolerance in fine grain aromatic rice ( Oryza sativa L. cv. Basmati 2000) was evaluated. Sodium nitroprusside, a NO donor, was used at 50, 100 and 150  μ mol l⁻¹ both as seed priming and foliar spray. To prime, the seeds were soaked in aerated NO solution of respective solution for 48 h and dried back to original weight. Primed and non-primed seeds were sown in plastic pots with normal irrigation in a greenhouse. At four leaf stage, plants were subjected to drought stress except the controls, which were kept at full field capacity. Drought was maintained at 50 % of field capacity by watering when needed. Two controls were maintained; both receiving no NO treatments as foliar application or seed treatment, one under drought conditions and the other under well-watered conditions. Drought stress seriously reduced the rice growth, but both methods of NO application alleviated the stress effects. Drought tolerance in rice was strongly related to the maintenance of tissue water potential and enhanced capacity of antioxidants, improved stability of cellular membranes and enhanced photosynthetic capacity, plausibly by signalling action of NO. Foliar treatments proved more effective than the seed treatments. Among NO treatment, 100  μ mol l⁻¹ foliar spray was more effective.     

Exogenous Application of Glycinebetaine Modulates Activities of Antioxidants in Maize Plants Subjected to Salt Stress

The influence of exogenously applied glycinebetaine (0, 50 and 100 m m ) as a foliar spray at different growth stages, i.e. vegetative, reproductive or both at the vegetative and reproductive stages on gas exchange characteristics, glycinebetaine (GB) and the activities of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) was examined in plants of two maize cultivars, Golden and C-20 grown under saline conditions. Salt stress caused a marked decrease in photosynthetic capacity, chlorophyll contents and SOD activity in both maize cultivars. However, activities of CAT and POD remained almost unchanged in both maize cultivars under salt stress. Accumulation of GB increased with an increase in exogenous level of GB, i.e. 100 m m GB spray caused a greater accumulation of GB in the leaves of maize plants than did 0 or 50 m m . Although exogenously applied GB enhanced photosynthetic capacity of salt-stressed plants of both cultivars, it enhanced the activities of antioxidant enzymes, SOD, CAT and POD, in salt-stressed plants of cv. C-20 only. Overall, the adverse effects of salt stress on maize plants were alleviated by the exogenous application of GB at different growth stages, which up-regulated photosynthetic capacity and the activities of some antioxidant enzymes.     

Influence of Soil Drought on Plant Growth, Assimilation and Dissimilation of CO2 and Accumulation of Photosynthates in Field Bean (Vicia faba L. minor) During Pod Formation and Rapid Pod Growth

Field bean planes cultivar Nadwiślański were submitted to soil drought (30 % of field soil water capacity) for 5 days at the stage of pod formation (A) and of rapid pod growth (B) and then exposed for 20 minutes to ¹⁴CO₂. Radioactivity of leaves, stems, roots, and pods or pod shells and seeds was measured 1, 5, 24 and 48 hours after exposition.
In both stages soil drought reduced by about five times total CO₂ assimilation, mainly owing to lower activity of the photosynthetic apparatus and also, though less so, to reduced leaf growth. Photosynthetic activity referred to the dry weight of the leaves dropped to 22-35% of controls. Accumulation of photosynthetates in generative organs was much less depressed than ¹⁴CO₂ assimilation. 48 hours after exposition to ¹⁴CO₂ of drought treated plants, the contents of ¹⁴C of pods in phase A, and seeds in phase B, amounted to respectively 24% and 36% of assimilated ¹⁴C and equalled 91.5% and 74% of the corresponding values for controls.
The progressive decline of radioactivity in leaves and stems after ¹⁴CO₂ exposition was distinctly correlated to the rise of radioactivity of generative organs both in soil drought treated plants and in controls. Slightly lower values of correlation coefficients in drought treated plants may indicate impairment under drought conditions of synchronization in processes of unloading and accumulation of assimilates.
In plants drought treated in phase A the ability to dissimilate ¹⁴C was reduced to about 59% of that in controls, but when drought was applied in phase B, dissimilation rate was about three times as high.     

水分亏缺下化肥减量配施有机肥对棉花光合特性与产量的影响

Fixed position experiments were conducted in 2017 and 2018, and split plot arrangement with the main treatment for full irrigation (W₁) with irrigation amount was 4800 cubic meters per hectare and deficit irrigation (W₂) was 2400 cubic meters per hectare, and the secondary treatment including treatments without fertilization (CK), single application of chemical fertilizer (CF), 75% chemical fertilizer with 25% organic fertilizer (M₁), 50% chemical fertilizer with 50% organic fertilizer (M₂), and 25% chemical fertilizer with 75% organic fertilizer (M₃). The effects of chemical fertilizer reduction and organic fertilizer application on photosynthetic characteristics and yield of cotton were studied to provide theoretical basis for rational utilization of organic fertilizer and reduction of chemical fertilizer input under water deficit. Under deficit irrigation, leaf area index (LAI), net photosynthetic rate (P_n), stomatal conductance (G_s), above-ground dry matter accumulation and seed yield of cotton were all lower than that under full irrigation, while irrigation water productivity (IWP) and intercellular CO₂ concentration (C_i) were higher. The chemical fertilizer reduction combined with application of organic fertilizer could effectively improve the LAI after the full squaring stage, improve P_n and G_s of cotton in all stage, promote the accumulation of vegetative and reproductive organs dry matter, improve its transfer to the reproductive organs, improve the IWP and seed yield, and also increase the moisture content of soil surface in the period of full boll stage and boll opening stage. The effects among different organic fertilizer treatments on LAI, P_n and seed yield were all presented as M₁ > M₂ > M₃, and under the treatment of M₁, the average seed cotton yield of two years increased compared with CF and CK by 6.9% and 62.1% respectively. Whereas, the effects under deficit irrigation were presented as M₂ > M₁ > M₃, and the two years’ average seed yield increased by 19.9% and 79.3% respectively compared with CF and CK under M₂. Chemical fertilizer reduction and organic fertilizer application were beneficial to increase the yield of seed cotton under water deficit, and alleviate the influence of water deficit on cotton growth and development, M₂ (50% fertilizer +50% organic fertilizer) was the best treatment.     

Relationships between seed oil content and fatty acid composition in high stearic acid sunflower

The high stearic acid sunflower mutant CAS-3 is characterized by a low seed oil content, which might represent a constraint for the commercial production of high stearic acid sunflower oil. The objective of the present research was to investigate the relationships between fatty acid profile and seed oil content in CAS-3. Plants of CAS-3 were reciprocally crossed with plants of breeding line ADV-37, with high oil content and standard fatty acid profile. Oil content and fatty acid composition were measured in individual F₂ seeds and F₂ plants (F₃ seeds averaged). Both F₂ seeds and F₂ plants from the cross ADV-37 × CAS-3 had a significantly higher oil content than those from the reciprocal cross, which indicated the existence of cytoplasmic effects in the genetic control of the trait. A consistent negative correlation between oil content and palmitic acid and a positive correlation between oil content and oleic acid were detected both in F₂ seeds and F₂ plants. Conversely, no consistent correlation between oil content and stearic acid was observed, which suggested the feasibility of simultaneous selection for both traits.