Mathias Neumann Andersen

Soluble Invertase Expression Is an Early Target of Drought Stress during the Critical, Abortion-Sensitive Phase of Young Ovary Development in Maize

To distinguish their roles in early kernel development and stress, expression of soluble (Ivr2) and insoluble (Incw2) acid invertases was analyzed in young ovaries of maize (Zea mays) from 6 d before (−6 d) to 7 d after pollination (+7 d) and in response to perturbation by drought stress treatments. The Ivr2 soluble invertase mRNA was more abundant than the Incw2 mRNA throughout pre- and early post-pollination development (peaking at +3 d). In contrast,Incw2 mRNAs increased only after pollination. Drought repression of the Ivr2 soluble invertase also preceded changes in Incw2, with soluble activity responding before pollination (−4 d). Distinct profiles of Ivr2and Incw2 mRNAs correlated with respective enzyme activities and indicated separate roles for these invertases during ovary development and stress. In addition, the drought-induced decrease and developmental changes of ovary hexose to sucrose ratio correlated with activity of soluble but not insoluble invertase. Ovary abscisic acid levels were increased by severe drought only at −6 d and did not appear to directly affect Ivr2 expression. In situ analysis showed localized activity and Ivr2 mRNA for soluble invertase at sites of phloem-unloading and expanding maternal tissues (greatest in terminal vascular zones and nearby cells of pericarp, pedicel, and basal nucellus). This early pattern of maternal invertase localization is clearly distinct from the well-characterized association of insoluble invertase with the basal endosperm later in development. This localization, the shifts in endogenous hexose to sucrose environment, and the distinct timing of soluble and insoluble invertase expression during development and stress collectively indicate a key role and critical sensitivity of the Ivr2soluble invertase gene during the early, abortion-susceptible phase of development.

Drought stress effect on carbohydrate concentration in soybean leaves and pods during early reproductive development: its implication in altering pod set

Abstract To advance our understanding of the physiological mechanisms by which pod abortion is regulated in soybean ( Glycine max L. Merr.), leaf photosynthetic rates, carbohydrate concentrations and soluble invertase activities in leaves, flowers and pods were determined in plants subjected to drought stress during early reproductive development. Soybeans were grown in pots in an environmentally controlled glasshouse. Drought stress was imposed from −11 to 10 days after anthesis (DAA). Drought decreased photosynthetic rates and water potentials in leaves, flowers and pods. Drought decreased leaf sucrose and starch concentrations but increased hexose (glucose+fructose) concentrations. Drought did not affect the activity of soluble invertase in leaves. In flowers and pods, sucrose concentrations were higher under drought as compared with well-watered controls. Hexose and starch concentrations of flowers and pods were also higher under drought until 7 and 3 DAA, respectively; thereafter they were significantly lower than those of the well-watered controls. Soluble invertase activity was decreased by drought in pods 5–10 DAA. Although the concentrations of non-structural carbohydrate (sucrose+hexose+starch) were higher in droughted flowers and pods, the total amount of non-structural carbohydrate accumulated in pods during the sampling periods was substantially reduced by drought. Pod growth was decreased by drought 3–5 DAA, which coincided with a decrease in hexose to sucrose ratio, when a significant reduction of pod set was occurred. Collectively, the results indicate that both source and sink restrictions are involved in regulating pod set in drought-stressed soybeans. It is suggested that a low availability of current and reverse photosynthate in leaves coupled with an impaired ability to utilize the incoming sucrose by pods resulted in a decreased carbohydrate flux from leaves to pods, together with a decreased hexose to sucrose ratio in pods are potential factors contributing to pod abortion in drought-stressed soybeans.

Loss of pod set caused by drought stress is associated with water status and ABA content of reproductive structures in soybean

Drought stress occurring during flowering and early pod expansion decreases pod set in soybean (Glycine max L. Merr.). The failure of pod set may be associated with changes in water status and ABA content in soybean reproductive structures under drought stress. To test this, pot experiments in an environmentally-controlled greenhouse were conducted, in which soybeans were exposed to drought stress around anthesis. In a preliminary experiment (Expt. I), irrigation was withheld at -6 (D1), -4 (D2) and -2 (D3) to 11 days after anthesis (DAA), then the droughted plants were re-watered to control levels until physiological maturity. Pod set percentage, seed yield and yield components were recorded. In the main experiment (Expt. II), irrigation was withheld from -11 to 10DAA. During the drying cycle, parts of the droughted plants were re-watered at 0, 3, 5, 7 and 10 DAA and kept well-watered until physiological maturity. In Expt. II, water status, ABA contents in xylem sap, leaves, flowers and pods were measured at 0, 3, 5, 7 and 10 DAA. The water potential in the flowers and pods was always lower than the leaf water potential. Turgor was decreased in leaves by drought 3 DAA, but remained at control levels in flowers and pods. Compared with well-watered plants, in severely droughted plants (10 DAA), xylem [ABA] increased about 60-fold; leaf [ABA] increased 9-fold; pod [ABA] increased 6-fold. During soil drying, flower and pod [ABA] was linearly correlated with xylem [ABA] and leaf [ABA], indicating that root-originated ABA and/or leaf ABA were the likely sources of ABA accumulated in the flowers and pods. In Expt. I, pod set and seed number per pod was unaffected by drought stress, while seed yield and individual seed weight was significantly decreased by drought. In Expt. II, significant reductions in pod set and seed yield were observed when re-watering the droughted plants at 3-5 DAA, re-watering the droughted plants later than this stage resulted in a similar pod set. Collectively, these results suggest that drought-induced decrease in water potential and increase in ABA content in flowers and pods at critical developmental stage (3-5 DAA) contribute to pod abortion in soybean.

A Comparison of Soil Microbial Community Structure, Protozoa and Nematodes in Field Plots of Conventional and Genetically Modified Maize Expressing the Bacillus thuringiens is CryIAb Toxin

Field trials were established at three European sites (Denmark, Eastern France, South-West France) of genetically modified maize (Zea mays L.) expressing the CryIAb Bacillus thuringiensis toxin (Bt), the near-isogenic non-Bt cultivar, another conventional maize cultivar and grass. Soil from Denmark was sampled at sowing (May) and harvest (October) over two years (2002, 2003); from E France at harvest 2002, sowing and harvest 2003; and from SW France at sowing and harvest 2003. Samples were analysed for microbial community structure (2003 samples only) by community-level physiological-profiling (CLPP) and phospholipid fatty acid analysis (PLFA), and protozoa and nematodes in all samples. Individual differences within a site resulted from: greater nematode numbers under grass than maize on three occasions; different nematode populations under the conventional maize cultivars once; and two occasions when there was a reduced protozoan population under Bt maize compared to non-Bt maize. Microbial community structure within the sites only varied with grass compared to maize, with one occurrence of CLPP varying between maize cultivars (Bt versus a conventional cultivar). An overall comparison of Bt versus non-Bt maize across all three sites only revealed differences for nematodes, with a smaller population under the Bt maize. Nematode community structure was different at each site and the Bt effect was not confined to specific nematode taxa. The effect of the Bt maize was small and within the normal variation expected in these agricultural systems.

Leaf gas exchange and water relation characteristics of field quinoa (Chenopodium quinoa Willd.) during soil drying

Abstract The effects of soil drying on leaf water relations and gas exchange were studied in quinoa grown in pots with sandy soil and in lysimeter plots with sandy loam in the field. Midday values of leaf water potential ( ψ l ), leaf osmotic potential ( ψ π ), relative water content (RWC), leaf conductance ( g l ), light saturated net photosynthesis ( A sat ), and specific leaf area (SLA) were determined in fully watered and droughted plants. At branching, flowering and grain filling g l in leaves of fully watered plants varied from 0.3 to 1.0, 0.3 to 0.6 and 0.2 to 0.7 mol m 2 s −1 and A sat varied from 18 to 34, 14 to 24 and 8 to 26 μmol m 2 s −1 . In droughted plants stomatal closure began when leaf water potential ( ψ l ) decreased below −1.2 to −1.6 MPa and A sat was reduced to 5–10 μmol m 2 s −1 as a result of stomatal closure, when ψ l decreased to −1.5 to −2.0 MPa. The osmotic potential at full turgor ( ψ π 100 ) decreased by age from −1.0 to −1.4 MPa. During severe water stress quinoa maintained positive turgor down to a zero turgor leaf water potential value ( ψ l 0 ) of −1.8 MPa. Quinoa had a limited osmotic adjustment ψ π 100 between fully watered and droughted plants being 0.3–0.4 MPa at the most. During branching the turgid weight/dry weight (TW/DW) ratio decreased from 9 to 5. At flowering and grain filling the TW/DW ratio was low (4–6). The bulk elastic modulus ( e max ) determined at the beginning of the grain filling period was medium to high (18–22 MPa). SLA was high (23–21 m 2 kg −1 ) during branching and decreased during the later growth stages. Conclusively, both high net photosynthesis rates and SLA values during early vegetative growth probably result in early vigour of quinoa supporting early water uptake and thus tolerance to a following drought. The stomatal response of quinoa was insensitive to drought induced decrease of leaf water status. The leaf water relations were characterised by low osmotic potentials and low TW/DW ratios during later growth stages sustaining a potential gradient for water uptake and turgor maintenance during soil drying.

Development and evaluation of a CERES-type model for winter oilseed rape

Abstract Because of its large N fertiliser requirements and long growth cycle, winter oilseed rape (Brassica napus L.) is considered to expose its environment to substantial risks of N losses. Soil–crop models provide unique tools to analyse such impacts, with an accuracy that primarily relies on the simulation of crop C and N budgets. Here, we describe a model simulating the growth and development of oilseed rape that was adapted from CERES-N Maize and a previously existing rape model. In addition to its soil components, the model, called CERES-Rape, has modules for crop phenology, net photosynthesis, leaf area development and grain filling, as influenced by crop N status. A new feature compared to previous rape models is the ability to predict the crops C and N budgets throughout its growth cycle, including losses from leaves by senescence. It also contains a mechanistic description of N translocation from vegetative parts to pods and grains after the onset of flowering. The model has been calibrated on a one-year experiment with three fertiliser N levels conducted in France, and subsequently tested on a similar experiment from Denmark for which no parameters were adjusted. In the vegetative phase, the time course of biomass and N accumulations in the various plant compartments was well simulated, with predicted values falling within one or two standard deviations from the mean in the measurements, except for the low-N treatments for which the high rates of leaf senescence could not be mimicked. After the onset of flowering, some bias appeared in the simulation of crop N uptake which impaired the predictions of final grain N yields. Simulated grain dry matter yields matched observations within ±15% for the calibration data set, but were over-estimated by a factor of 2 for the other data set. Despite the above shortcomings, the simulation of fertiliser effects on the dynamics of crop N uptake and dry matter was judged sufficiently satisfactory to allow an investigation of N losses from rapeseed–cropped soils with the CERES-Rape model.

Seed glucosinolate, oil and protein contents of field-grown rape (Brassica napus L.) affected by soil drying and evaporative demand

The effect of soil drying on seed yield, oil, protein, and glucosinolate contents was studied in rape (Brassica napus. L) grown in sandy and loamy soils in lysimeters in the field. By controlling irrigation, the plants were exposed to early drought (ED) during the vegetative and the flowering stage or late drought (LD) during the pod filling stage. Under low evaporative demands (2–4 mm day−1) in 1991, seed and oil yields were not significantly influenced by soil drying. Under high evaporative demands (4–5 mm day−1) in 1992, the ED and LD treatments on sand decreased the seed yield by 8% and 17% of the fully irrigated (FI) treatment, respectively; oil yield was significantly decreased (17% in both ED and LD treatments) on sand, only; protein yield was not significantly reduced by drought. In the fully irrigated treatment, the glucosinolate content was 9.7 μmol/g dry matter (d.m.) in 1991 and 13.7 in 1992. Both ED and LD treatments increased glucosinolate content to between 11.7 and 24 μmol/g d.m. in the two years. The results reveal that glucosinolate synthesis was increased when leaf or pod midday water potential was less than − 1.4 MPa for extended periods. Below this potential, the tissue turgor pressure of leaves and pods was low or zero. When turgor was low and the number of stress days (SD) exceeded 6.4, the glucosinolate content increased linearly with the number of stress days by 1.49 μmol (glucosinolate) g−1 (d.m.) SD−1. Water stress occurring during vegetative growth also increased seed glucosinolate content. It is proposed that glucosinolates are produced as secondary metabolites in droughted tissue at low turgor and that under these conditions glucosinolate precursors are produced for later use. In 1992 under severe stress, the glucosinolate content also correlated with seed size.

A review of drought adaptation in crop plants: changes in vegetative and reproductive physiology induced by ABA-based chemical signals

This review discusses the role of abscisic acid (ABA)-based drought stress chemical signalling in regulating crop vegetative and reproductive development and its contributions to crop drought adaptation. Increased concentrations of ABA in the root induced by soil drying may maintain root growth and increase root hydraulic conductivity; both lead to an increase in water uptake and thereby postpone the development of water deficit in the shoot. Root ABA is also transported in the xylem to the shoot and is perceived at the acting sites, where it causes stomatal closure and reduced leaf expansion, thereby preventing dehydration of leaf tissues and enhancing the chance for survival under prolonged drought. ABA-based chemical signalling can be amplified by several factors, particularly increased pH in the xylem/apoplast, which retains anionic ABA. Such an increase in xylem pH detected in field-grown maize might have been brought about by reduced nitrate uptake by plants during soil drying. In contrast, xylem sap alkalinisation was not found in soybeans, which depend on fixing nitrogen through their association with Rhizobium japonicum. Evidence has also shown that the xylem-borne ABA can be transported to plant reproductive structures and influence their development, presumably by regulating gene expression that controls cell division and carbohydrate metabolic enzyme activity under drought conditions. The possible involvement of ABA in the up- and down-regulation of acid invertase in crop source (adult leaves) v. sink (young ovaries) organs indicates a crucial role of the hormone in balancing source and sink relationship in plants according to the availability of water in the soil. A novel irrigation technique named partial root-zone drying (PRD), has been developed to allow exploitation of ABA-based drought stress signalling to improve water-use efficiency (WUE) based on its roles in regulating stomatal aperture and leaf expansion. However, little is known about how crop reproductive development is regulated when irrigated under PRD. We suggest that more attention should be paid to the latter aspect as it directly relates to crop yield and quality.

Hydraulic and chemical signals in the control of leaf expansion and stomatal conductance in soybean exposed to drought stress

Both hydraulic and chemical signals are probably important in regulating leaf growth and stomatal conductance of soybean (Glycine max L. Merr.) under drought stress. However, until now they have not been investigated concomitantly in this species. To explore this, a pot experiment in a temperature-regulated greenhouse was conducted, in which plants were subjected to progressive drought during early reproductive stages. Biophysical parameters, viz. relative leaf expansion rate, stomatal conductance, leaf turgor, leaf [ABA], xylem pH and xylem [ABA] were followed in control and stressed plants. Drought stress decreased relative leaf expansion rate, stomatal conductance and leaf turgor, whereas it increased leaf [ABA], xylem pH and xylem [ABA]. As soil dried, significant differences between water treatments for relative leaf expansion rate, stomatal conductance, leaf turgor, leaf [ABA], xylem pH and xylem [ABA] were observed at 14, 9, 14, 14, 14 and 9 d after imposition of stress, respectively. The relationships of relative values for relative leaf expansion rate, stomatal conductance, leaf turgor, leaf [ABA] and xylem pH to the fraction of transpirable soil water (FTSW) were well described by linear-plateau functions that allowed calculation of the soil-water thresholds at which processes in stressed plants began to diverge from well-watered controls. The soil-water threshold for stomatal conductance (0.64) was significantly higher than that for relative leaf expansion rate (0.29), xylem pH (0.28), leaf [ABA] (0.27) and leaf turgor (0.25). Relative xylem [ABA] increased, first linearly (when FTSW > 0.5) and then exponentially (when FTSW < 0.5) with decreasing FTSW. Relative stomatal conductance decreased exponentially with increasing relative xylem [ABA] (r2=0.98). Decreased stomatal conductance coincided with an increase in xylem [ABA] and occurred before any significant change of leaf turgor could be detected, indicating that chemical signals (seemingly root-originated ABA) control stomatal behaviour at moderate soil water deficits. Relative relative leaf expansion rate was linearly correlated with relative leaf turgor (r2=0.93), relative xylem pH (r2=0.97) and relative leaf [ABA] (r2=0.98), implying that both hydraulic and chemical signals were probably involved in regulation of leaf expansion at severe soil water deficits.

The Interaction Effects of Potassium and Drought in Field-Grown Barley. I. Yield, Water-Use Efficiency and Growth

Abstract In order to study the interaction of K application and drought a field experiment with spring barley (Hordewn distichum L. cv. Gunnar) was conducted in 1985, 1986 and 1987 on coarse-textured sandy soil low in natural K content and water-holding capacity. The drought occurred naturally or was imposed by shelters during the grain-filling period. K was applied as KCl at rates of 50, 125 and 200 kg K/ha top-dressed at emergence. High K applications (125 and 200 kg K/ha) significantly increased rate of growth of the vegetative parts of the crop. With high K application the leaf area increased up to 26% at anthesis, and top dry matter accumulation increased up to 15% between anthesis and milk-ripe stages of growth, resulting in about 10% higher straw yield at final harvest. Also, the number of ears increased with high K application. Final grain yield was unaffected by level of K application in fully irrigated plots. Drought during the grain-filling period decreased grain yield by decreasing grain weigh...