Differential expression of salt-responsive genes to salinity stress in salt-tolerant and salt-sensitive rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) at seedling stage

The understanding of physio-biochemical and molecular attributes along with morphological traits contributing to the salinity tolerance is important for developing salt-tolerant rice (Oryza sativa L.) varieties. To explore these facts, rice genotypes CSR10 and MI48 with contrasting salt tolerance were characterized under salt stress (control, 75 and 150 mM NaCl) conditions. CSR10 expressed higher rate of physio-biochemical parameters, maintained lower Na/K ratio in shoots, and restricted Na translocation from roots to shoots than MI48. The higher expression of genes related to the osmotic module (DREB2A and LEA3) and ionic module (HKT2;1 and SOS1) in roots of CSR10 suppresses the stress, enhances electrolyte leakage, promotes the higher compatible solute accumulation, and maintains cellular ionic homeostasis leading to better salt stress tolerance than MI48. This study further adds on the importance of these genes in salt tolerance by comparing their behaviour in contrasting rice genotypes and utilizing specific marker to identify salinity-tolerant accessions/donors among germplasm; overexpression of these genes which accelerate the selection procedure precisely has been shown.     

Potassium uptake efficiency and dynamics in the rhizosphere of maize (Zea mays L.), wheat (Triticum aestivum L.), and sugar beet (Beta vulgaris L.) evaluated with a mechanistic model

Plant species differ in nutrient uptake efficiency. With a pot experiment, we evaluated potassium (K) uptake efficiency of maize (Zea mays L.), wheat (Triticum aestivum L.), and sugar beet (Beta vulgaris L.) grown on a low-K soil. Sugar beet and wheat maintained higher shoot K concentrations, indicating higher K uptake efficiency. Wheat acquired more K because of a greater root length to shoot dry weight ratio. Sugar beet accumulated more shoot K as a result of a 3- to 4-fold higher K influx as compared to wheat and maize, respectively. Nutrient uptake model NST 3.0 closely predicted K influx when 250 mg K kg^?1 were added to the soil, but under-predicted K influx under low K supply. Sensitivity analysis showed that increasing soil solution K concentration (C_Li) by a factor of 1.6–3.5 or buffer power (b) 10- to 50-fold resulted in 100% prediction of K influx. When both maximum influx (I_max) and b were increased by a factor of 2.5 in maize and wheat and 25 in sugar beet, the model could predict measured K influx 100%. In general, the parameter changes affected mostly calculated K influx of root hairs, demonstrating their possible important role in plant K efficiency.     

Phosphorus efficiency of wheat and sugar beet seedlings grown in soils with mainly calcium,or iron and aluminium phosphate

Phosphorus is often limiting crop growth in soils low in P supplying capacity. The objective of this study was to investigate whether there are differences in P efficiency between sugar beet and wheat and to search for the plant properties responsible for different P efficiencies encountered and furthermore to see whether the kind of P binding in soil affects the P efficiency of crops. For this a pot experiment with an Oxisol with P mainly bound to Fe and Al (Fe/Al-P) and a Luvisol with P mainly bound to Ca (Ca-P) was run with increasing P fertilizer levels from 0 to 400 mg kg^–1 in a climate chamber. Shoot dry weights of wheat and sugar beet increased strongly with P application in both soils. Both crops, despite their large differences in plant properties, had the same P efficiency in both soils. Therefore none of the species was especially able to use either Fe/Al-P or Ca-P. Wheat relied on a somewhat lower internal requirement, a large root system (high root/shoot ratio) and a low shoot growth rate with a low influx while sugar beet with a small root system and a large shoot growth rate relied on a 5 to 10 times higher influx. A mechanistic mathematical model for calculation of uptake and transport of nutrients in the rhizosphere was used to assess the influence of morphological and physiological root properties on P influx. A comparison of calculated and measured P influx showed that prediction by the model is reasonably accurate for Luvisol. For Oxisol, the predicted P influx was much less than the observed one, even when P influx by root hairs was considered. A sensitivity analysis showed that physiological uptake parameters like I _max, K _m, and C_{L min} had no major influence on predicted influx. The greatest influence on influx had the P soil solution concentration C _{L i}. It is assumed that both species had used mechanisms to increase P availability in the rhizosphere similar to an increase of C _{L i}. Such mechanisms could be the exudation of organic acids, which are known as a sorption competitor to phosphate bound to Fe/Al-oxides or humic-Fe-(Al) complexes or to build soluble complexes with Fe and P. The close agreement between calculated and measured P influx in the Luvisol even at P deficiency indicates that root exudates were not able to mobilize Ca-bound P, whereas Fe/Al-P could be mobilized easily.     

Phosphorus uptake kinetics,size of root system and growth of maize and groundnut in solution culture

Phosphorus acquisition efficiency of maize (Zea mays L.) and groundnut (Arachis hypogaea L.) was investigated in a flowing nutrient solution culture at constant P concentrations of 0.2, 1 and 100 μM. To calculate the P influx and study changes in plant growth and P uptake in relation to plant age, four harvests were taken. Phosphorus uptake kinetics of the roots, i.e. maximum influx, I_\max, the Michaelis constant, K_m, and the minimum concentration, C_Lmin (the concentration at which no net uptake occurs) were estimated in a series of short-term experiments, based on the rate of depletion of P from solution over a range of concentrations. At 1 μM P, maize was more P efficient producing up to 90% of its maximum yield as compared to groundnut with only 20% of maximum yield. A 3 times faster P uptake rate was the reason for the maize P efficiency. In contrast for groundnut at 1 μM P, a net efflux was observed at some development stages of this crop indicating a much higher P requirement at the root surface for maximum growth. Maize had a 6 times higher I_\max value and a 2 times higher K_m value as compared to groundnut. The higher influx of maize was mainly because of the higher I_\max. Maize previously grown at low P concentrations had a C_Lmin of 0.1 μM, while groundnut had values of 0.2 and 0.6 μM. Furthermore groundnut previously grown at 100 μM, was not able to absorb P even at 40 μM. Acclimation to low P concentrations in solution by increasing I_\max or decreasing K_m was not evident in this study. Differences in P acquisition efficiency between maize and groundnut in solution culture were mainly because of differences in P-uptake kinetics, and to a lesser extent to the size of the root system.     

Growth, nitrogen fixation, yield and kernel quality of peanut in response to lime, organic and inorganic fertilizer levels

The aim of this investigation was to study the effect of different levels of chemical fertilizers alone and in combination with farmyard manure and lime on growth, nitrogen fixation, yield and kernel quality of peanut in an acid lateritic soil. Five fertilization levels viz., no chemical fertilizer (CF) (F0), CF @ 20:40:30 (F1), CF @ 40:80:60 (F2) kg ha(-1) NPK, F1 +2.5 t ha(-1) FYM (F3) and F2 +5 t ha(-1) FYM (F4) with and without liming (2 t ha(-1)) were tested. Results revealed that integrated application of FYM+CF at F3 level significantly (P0.05) improved the nitrogen content of nodules (12.4%), kernel yield (19.3%), mineral composition, oil content (4.8%), protein content (28.2%) and hydration coefficient (11.6%) of kernels over sole CF at F1 level. Maximum level of CF or FYM+CF though improved the population of symbiotic nitrogen fixing bacteria in the peanut rhizosphere, however, could not improve nitrogen fixation, yield and kernel quality.     

Dynamic trajectories of volatile and non‐volatile specialised metabolites in ‘overnight’ fragrant flowers of Murraya paniculata

• Ephemeral flowers, especially nocturnal ones, usually emit characteristic scent profiles within their post‐anthesis lifespans of a few hours. Whether these flowers exhibit temporal variability in the composition and profile of volatile and non‐volatile specialised metabolites has received little attention.
• Flowers of Murraya paniculata bloom in the evenings during the summer and monsoon, and their sweet, intense fragrance enhances the plant's value as an ornamental. We aimed to investigate profiles of both volatile and non‐volatile endogenous specialised metabolites (ESM) in nocturnal ephemeral flowers of M. paniculata to examine whether any biochemically diverse groups of ESM follow distinct patterns of accumulation while maintaining synchrony with defensive physiological functions.
• Targeted ESM contents of M. paniculata flowers were profiled at ten time points at 2‐h intervals, starting from late bud stage (afternoon) up to the start of petal senescence (mid‐morning). Emitted volatiles were monitored continuously within the whole 20‐h period using headspace sampling. The ESM contents were mapped by time point to obtain a highly dynamic and biochemically diverse profile. Relative temporal patterns of ESM accumulation indicated that the active fragrance‐emitting period might be divided into ‘early bloom’, ‘mid‐bloom’ and ‘late bloom’ phases. Early and late bloom phases were characterised by high free radical generation, with immediate enhancement of antioxidant enzymes and phenolic compounds. The mid‐bloom phase was relatively stable and dedicated to maximum fragrance emission, with provision for strong terpenoid‐mediated defence against herbivores. The late bloom phase merged into senescence with the start of daylight; however, even the senescent petals continued to emit fragrance to attract diurnal pollinators.
• Our study suggests that dynamic relations between the different ESM groups regulate the short‐term requirements of floral advertisement and phytochemical defence in this ephemeral flower. This study also provided fundamental information on the temporal occurrence of emitted volatiles and internal pools of specialised metabolites in M. paniculata flowers, which could serve as an important model for pollination biology of Rutaceae, which includes many important fruit crops.