Lishu Wu

Seed Priming Alters the Production and Detoxification of Reactive Oxygen Intermediates in Rice Seedlings Grown under Sub-optimal Temperature and Nutrient Supply

The production and detoxification of reactive oxygen intermediates (ROIs) play an important role in the plant response to nutrient and environmental stresses. The present study demonstrated the behavior of growth, ROIs-production and their detoxification in primed and non-primed rice seedlings under chilling stress (18°C) and nitrogen-(N), phosphorus-(P), or potassium-(K) deprivation. The results revealed that chilling stress as well as deprivation of any mineral nutrient severely hampered the seedling growth of rice, however, seed priming treatments (particularly selenium- or salicylic acid-priming), were effective in enhancing the rice growth under stress conditions. The N-deprivation caused the maximum reduction in shoot growth, while the root growth was only decreased by P- or K-deprivation. Although, N-deprivation enhanced the root length of rice, the root fresh weight was unaffected. Rate of lipid peroxidation as well as the production of ROIs, was generally increased under stress conditions; the K-deprived seedlings recorded significantly lower production of ROIs than N- or P-deprived seedlings. The responses of enzymatic and non-enzymatic antioxidants in rice seedlings to chilling stress were variable with nutrient management regime. All the seed priming were found to trigger or at least maintain the antioxidant defense system of rice seedlings. Notably, the levels of ROIs were significantly reduced by seed priming treatments, which were concomitant with the activities of ROIs-producing enzymes (monoamine oxidase and xanthine oxidase), under all studied conditions. Based on these findings, we put forward the hypothesis that along with role of ROIs-scavenging enzymes, the greater tolerance of primed rice seedlings can also be due to the reduced activity of ROIs-producing enzymes.

Cell Wall Pectin and its Methyl-esterification in Transition Zone Determine Al Resistance in Cultivars of Pea (Pisum sativum)

The initial response of plants to aluminum (Al) is the inhibition of root elongation, while the transition zone is the most Al sensitive zone in the root apex, which may sense the presence of Al and regulate the responses of root to Al toxicity. In the present study, the effect of Al treatment (30 μM, 24 h) on root growth, Al accumulation, and properties of cell wall of two pea (Pisum sativum L.) cultivars, cv Onward (Al-resistant) and cv Sima (Al-sensitive), were studied to disclose whether the response of root transition zone to Al toxicity determines Al resistance in pea cultivars. The lower relative root elongation (RRE) and higher Al content were founded in cv Sima compared with cv Onward, which were related to Al-induced the increase of pectin in root segments of both cultivars. The increase of pectin is more prominent in Al-sensitive cultivar than in Al-resistant cultivar. Aluminum toxicity also induced the increase of pectin methylesterases (PME), which is 2.2 times in root transition zone in Al-sensitive cv Sima to that of Al resistant cv Onward, thus led to higher demethylesterified pectin content in root transition zone of Al-sensitive cv Sima. The higher demethylesterified pectin content in root transition zone resulted in more Al accumulation in the cell wall and cytosol in Al-sensitive cv Sima. Our results provide evidence that the increase of pectin content and PME activity under Al toxicity cooperates to determine Al sensitivity in root transition zone that confers Al resistance in cultivars of pea (Pisum sativum).

Metabolic profiling reveals altered pattern of central metabolism in navel orange plants as a result of boron deficiency.

We focused on the changes of metabolite profiles in navel orange plants under long-term boron (B) deficiency using a gas chromatography-mass spectrometry (GC-MS) approach. Curling of the leaves and leaf chlorosis were observed only in the upper leaves (present before start of the treatment) of B-deficient plants, while the lower leaves (grown during treatment) did not show any visible symptoms. The metabolites with up-accumulation in B-deficient leaves were mainly proline, l-ornithine, lysine, glucoheptonic acid, fucose, fumarate, oxalate, quinate, myo-inositol and allo-inositol, while the metabolites with down-accumulation in B-deficient leaves were mainly serine, asparagine, saccharic acid, citrate, succinate, shikimate and phytol. The levels of glucose and fructose were increased only in the upper leaves by B deficiency, while starch content was increased in all the leaves and in roots. The increased levels of malate, ribitol, gluconic acid and glyceric acid occurred only in the lower leaves of B-deficient plants. The increased levels of phenols only in the upper leaves indicated that the effects of B on phenol metabolism in citrus plants may be a consequence of disruptions in leaf structure. Metabolites with opposite reactions in upper and lower leaves were mainly glutamine, glycine and pyrrole-2-carboxylic acid. To our knowledge, the phenomena of allo-inositol even higher than myo-inositol occurred characterized for the first time in this species. These results suggested that the altered pattern of central metabolism may be either specific or adaptive responses of navel orange plants to B deficiency.

Boron Uptake and Retranslocation in Cultivars of Brassica napus Differing in Boron Efficiency

Oil rapeseed is one of the most important oil crops worldwide. In China, the planting area of oil rapeseed surpassed 6.67 million hectare providing 60% of food oil for Chinese. Brassica napus is found on 80% of the total oil rapeseed area.It is mainly distributed in East China, Middle and Down Stream of Yangtze River, Southwest in China, and now it is spreading in South and North China.

Different metabolite profile and metabolic pathway with leaves and roots in response to boron deficiency at the initial stage of citrus rootstock growth

Boron (B) is a microelement required for higher plants, and B deficiency has serious negative effect on metabolic processes. We concentrated on the changes in metabolite profiles of trifoliate orange leaves and roots as a consequence of B deficiency at the initial stage of growth by gas chromatography-mass spectrometry (GC-MS)-based metabolomics. Enlargement and browning of root tips were observed in B-deficient plants, while any obvious symptom was not recorded in the leaves after 30 days of B deprivation. The distinct patterns of alterations in metabolites observed in leaves and roots due to B deficiency suggest the presence of specific organ responses to B starvation. The accumulation of soluble sugars was occurred in leaves, which may be attributed to down-regulated pentose phosphate pathway (PPP) and amino acid biosynthesis under B deficiency, while the amount of most amino acids in roots was increased, indicating that the effects of B deficiency on amino acids metabolism in trifoliate orange may be a consequence of disruptions in root tissues and decreased protein biosynthesis. Several important products of shikimate pathway were also significantly affected by B deficiency, which may be related to abnormal growth of roots induced by B deficiency. Conclusively, our results revealed a global perspective of the discriminative metabolism responses appearing between B-deprived leaves and roots and provided new insight into the relationship between B deficiency symptom in roots and the altered amino acids profiling and shikimate pathway induced by B deficiency during seedling establishment.

Differential Changes in Cell-Wall Content and Boron and Calcium Concentration in Newhall Navel Orange Grafted on Two Rootstocks Differing in Boron-Deficiency Responses

The study aimed to determine if the variability of the effect of boron (B) deficiency on Newhall navel orange grafted on trifoliate orange (deficient-B-sensitive) and on citrange (deficient-B-tolerant) can be explained on the basis of changes in cell-wall content and in cell-wall B and calcium (Ca) concentrations. The plants were cultured in the nutrient solution (with or without B) for 65 days. Boron deficiency increased the cell-wall content in old leaves (leaves from last season) of trifoliate orange but had no impact on citrange. Boron deficiency did not reduce B concentration in cell walls of old leaves of citrange-grafted plants but increased their Ca concentration. For trifoliate-orange-grafted plants, however, B deficiency decreased the B concentration in cell walls of old leaves and did not increase their Ca concentration. The changes of B and Ca concentrations between with and without B supply in pectin were in good agreement with the changes of those in cell walls. The relatively greater ability of citrange-grafted plants to maintain B and Ca in the cell wall may contribute to their tolerance to low external B.

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed-Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L−1 nitric acid (HNO3) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L−1 ammonium acetate (NH4OAc) and 1.0 mol L−1 HNO3 extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.

Two typical K-efficiency cotton genotypes differ in potassium absorption kinetic parameters and patterns

As a macroelement to plant, potassium (K) absorption mechanism has been widely studied. However, as for cotton genotypes with different K efficiency, how they related to the absorption patterns under K starvation is not fully understood. In this hydroponic experiment, plants were grown at different K levels: low (K1, 2 mg/L) and adequate K level (K2, 20 mg/L) for 2 weeks. K+ absorption kinetic parameters were got by Michaelis–Menten equation. By applying K channel-blocking agent, tetraethylammonium and protein modifying reagent N-ethylmaleimide, we evaluated the differences in K absorption mechanisms for two typical cotton genotypes (K-efficient genotype 103 and K-inefficient genotype 122). Results showed that higher affinity to K+ and better root formation of genotype 103 resulting in better adaptation in low-K+ condition, whether grown in low or adequate K+ environment. Further study with K+ absorption inhibitors suggested the two genotypes grown in low-K+ environment absorbed K+ mainly by high-affinity K+ absorption systems, and for seedlings grown in adequate K condition, genotype 103 absorbed K+ with both K channels and high-affinity proton and mainly by high-affinity K channels, while genotype 122 absorbed K+ by K channels. These results indicated that the low-K condition could induce higher affinity to absorb K+, and the two cottons with different K efficiency mainly due to different low-K adaptation and absorb K+ with different patterns. This could provide a possible theory for the selection of K-efficient varieties.

Phosphorus Efficacy in Four Chinese Long‐Term Experiments with Different Soil Properties and Climate Characteristics

Four long‐term experiments in China were used to study the efficacy of phosphorus (P) fertilizers in soils. The results showed that the increased yield by P fertilization varied with different crops: early rice > late rice. We suggest applying the P fertilizer heavily on winter wheat and early rice. The P agronomic efficiency was about 27 kg rice grain kg−1 and 30.8–55.7 kg wheat grain kg−1. The P recovery efficiency by plants was >80% in three of four sites, and the fertilizer‐use efficiency was 34% on average. The current applications of about 40 kg P ha−1 year−1 for rice–rice rotation could maintain yields of 8–11 t ha−1 year−1, and 65.5 kg P ha−1 year−1 applied for wheat–maize rotation could maintain yields of 5.3–6.2 t ha−1 for wheat and 4.2–6.0 t ha−1 for maize, although no P was added to maize. However, sustaining higher yields will require soil P‐supplying capacity and farm‐specific management targets and strategies.

Changes in chemical composition and structure of root cell wall of citrus rootstock seedlings in response to boron deficiency by FTIR spectroscopy

ABSTRACT Boron (B) is an essential microelement for higher plants, and plays a role in cell wall formation. Citrange seedlings with different amounts of B were studied through Fourier-transform infrared spectroscopy (FTIR) analyses. The results showed that the growth and development of new roots were evidently inhibited by B deficiency. Boron-deficiency significantly increased cell wall biomass (CWB) as a percentage of root fresh weight and the ratio of B concentration in cell wall to the total B in roots. The findings from CWB FTIR spectra showed the band at 3429 cm−1 under control condition was shifted to 3442 cm−1 after being B deprived, suggesting that the mode of hydrogen bonding was changed by B deficiency. Boron deficiency clearly decreased the peak height of carboxylic ester band around 1741 cm−1, but increased that of COO− stretching band around 1400 cm−1, suggesting that the relative amount and degree of esterification of carboxylic groups was decreased and pectin content and structure was altered. These results demonstrate that changes in amount, structure, and assembly of root cell wall polymers may be either specific or adaptive responses of citrange seedlings to B deficiency and FTIR can be an appropriate method to study changes in cell wall under B deficiency.