Wen-Dar Huang

Effect of magnesium deficiency on antioxidant status and cadmium toxicity in rice seedlings

Cadmium (Cd) is one of the most toxic heavy metals and inhibits physiological processes of plants. Magnesium (Mg) is known as one of the essential nutrients for plants. Mg deficiency in plants affects metabolic processes. Plants grown in the field may encounter several abiotic stresses, rather than a single stress. Thus, the relationship between Mg nutrition and Cd toxicity is of ecological importance. In this study, effects of Mg deficiency on antioxidant systems and Cd toxicity in rice seedlings were investigated. Mg deficiency significantly decreased Mg concentrations in shoot and roots of rice seedlings. However, fresh weight and dry weight of rice seedlings were not affected by Mg deficiency. The contents of ascorbate and glutathione (GSH), the ratio of GSH/oxidized glutathione, and the activities of superoxide dismutase, ascorbate peroxidase, glutathione reductase, and catalase in Mg-deficient leaves were higher than respective control leaves. Cd toxicity was judged by the decrease in biomass production, decrease in chlorophyll, and induction of oxidative stress. Based on these criteria, we demonstrated that Mg deficiency protected rice seedlings from Cd stress. Moreover, chlorophyll destruction by paraquat was higher in detached leaves from Mg-sufficient than Mg-deficient seedlings. Cd concentration was higher in Mg-deficient shoot and roots than their respective control shoot and roots, suggesting that the protective effect of Mg deficiency against Cd toxicity is not due to reduction of Cd uptake. Moreover, we observed that Cd-decreased Fe and Zn contents in Mg-deficient seedlings were more pronounced than that in Mg-sufficient seedlings. Of particular interest is the finding that the increase in OsIRT1, OsZIP1, and OsZIP3 transcripts caused by Cd in Mg-deficient roots was greater than that in control roots.

Salicylic acid-mediated hydrogen peroxide accumulation and protection against Cd toxicity in rice leaves

The role of H2O2 in salicylic acid (SA)-induced protection of rice leaves against subsequent Cd toxicity was investigated. SA pretreatment resulted in an increase in the contents of endogenous SA, as judged by the expression of OsWRKY45 (a SA responsive gene), and H2O2 in rice leaves. Diphenyleneiodonium (DPI) and imidazole (IMD), inhibitors of NADPH oxidase, prevented SA-increased H2O2 production, suggesting that NADPH oxidase is a H2O2-generating enzyme in SA-pretreated rice leaves. DPI and IMD also inhibited SA-increased activities of superoxide dismutase (SOD), ascorbate peroixdase (APX), and glutathione reductase (GR) activities, but had no effect on SA-increased catalase (CAT) activity. Moreover, SA-induced protection against subsequent Cd toxicity could also be prevented by DPI and IMD. The inhibitory effect of DPI and IMD on SA-induced protection against subsequent Cd toxicity could be reversed by exogenous H2O2. All these results suggested that SA-induced protection against subsequent Cd toxicity is mediated through H2O2. This conclusion is supported further by the observations that exogenous H2O2 application resulted in an increase in SOD, APX, and GR activities, but not CAT activity and a protection against subsequent Cd toxicity of rice leaves.

Effect of nitrogen deficiency on antioxidant status and Cd toxicity in rice seedlings

Effect of nitrogen (N) deficiency on antioxidant status and Cd toxicity in rice seedlings was investigated. N deficiency resulted in a reduction of shoot growth but not root growth. The contents of N-containing compounds such as nitrate, chlorophyll, and protein decreased in leaves of rice seedlings grown under N deficiency. Accumulation of abscisic acid and H2O2 in leaves was induced by N deficiency. The content of ascorbate and the activities of ascorbate peroxidase, glutathione reductase, and catalase in N-deficient leaves were lower than their respective control leaves. However, glutathione content was not affected and superoxide dismutase activity was increased by N deficiency. Cd toxicity in N-deficient seedlings was more pronounced than that in N-sufficient ones. Pretreatment with ascorbate or L-galactono-1,4-lactone, a biosynthetic precursor of ascorbate resulted in a reduction of Cd toxicity enhanced by N deficiency. N deficiency also resulted in an enhancement of Cd uptake in rice seedlings. The possible mechanism of Cd toxicity enhanced by N deficiency is discussed.

Leaf‐derived cecidomyiid galls are sinks in Machilus thunbergii (Lauraceae) leaves

Three relevant hypotheses - nutrition, environment and the enemies hypothesis - often invoked to explore source and sink relationships between galls and their host plants are still under dispute. In this research, chlorophyll fluorescence, gas exchange capacity, stomatal conductance, total carbon and nitrogen, total soluble sugars and starches, and scanning and transmission electron microscopy of two types of galls were used to investigate source-sink relationships. Compared with host leaves, these galls demonstrated slightly lower chlorophyll fluorescence; however, gas exchange capacity and stomatal conductance were not detected at all. Scanning electron micrographs demonstrated that the abaxial epidermis of host leaves contain normal amounts of stomata, whereas no stomata were observed on the exterior and interior surfaces of both types of galls. In addition, gall inner surfaces were covered with many kinds of fungal hyphae. Gall total carbon (C) and nitrogen (N) levels were lower but the C/N ratio was higher in galls than host leaves. Both types of galls accumulated higher total soluble sugars and starches than host leaves. Transmission electron micrographs also revealed that both types of galls contain plastoglobuli and giant starch granules during gall development. Results strongly indicate that leaf-derived cecidomyiid galls are sinks in Machilus thunbergii leaves. However, it is perplexing how larvae cycle and balance CO(2) and O(2) in gall growth chambers without stomata.

Structural, biochemical, and physiological characterization of photosynthesis in leaf-derived cup-shaped galls on Litsea acuminata

BackgroundThe source and sink relationships between insect-induced galls and host plant leaves are interesting. In this research, we collected cup-like galls induced by Bruggmanniella sp. (Diptera: Cecidomyiidae) on host leaves of Litsea acuminata and assessed them to investigate source-sink relationships between galls and host leaves. We characterized several of their photosynthetic characteristics including chlorophyll fluorescence (Fv/Fm), stomatal conductance, and photosynthetic capacity, biochemical components such as total soluble sugar, starches, free amino acids, and soluble proteins. The structural analyses were performed under confocal, light, and scanning electron microscopies.ResultsCompared with host leaves, galls exhibited slightly lower chlorophyll fluorescence; however, stomatal conductance and photosynthetic capacity were not detected at all. Galls accumulated higher total soluble sugars and free amino acids but less soluble proteins than host leaves. No stomata was observed on exterior or interior gall surfaces under light or scanning electron microscopy, but their inner surfaces were covered with fungal hyphae. Confocal imagery showed a gradient of chloroplasts distribution between gall outer and inner surfaces.ConclusionsOur results strongly suggest that leaf-derived cecidomyiid galls are a type of chlorophyll-deficient non-leaf green tissue and consists on a novel sink in L. acuminate.

Photosynthetic responses of Jatropha curcas to spider mite injury

The spider mite Tetranychus urticae Koch is emerging as a major problem in Jatropha curcas cultivation. The goal of this study was to investigate the photosynthetic responses of Jatropha to spider mite infestation. Leaf CO2 assimilation rate, stomatal conductance, transpiration, intracellular CO2 concentration, and instantaneous carboxylation efficiency significantly decreased in mite-infested leaves compared with controls. Lower water content and specific leaf area of the mite-infested leaves were positively related to symptoms of wrinkling and curling. Leaf electrolyte leakage remained unchanged in the mite-infested leaves, revealing no effect on leaf membrane integrity. Leaves exhibited reductions in soluble protein and soluble sugar in association with photosynthetic impairment. Although decreases in photochemical activity and chlorophyll fluorescence parameters suggested damage to the photosynthetic apparatus, although there were no measurable reductions in chlorophyll or carotenoid contents associated with photosynthetic apparatus impairment. The decrease in the leaf CO2 assimilation rate was partially attributed to stomatal and metabolic limitations in the mite-infested leaves.

Eliminating interference by anthocyanins when determining the porphyrin ratio of red plant leaves

Anthocyanins (Ants) are water-soluble secondary metabolites that are responsible for red colour of plant leaves. To determine photosynthetic pigments, 80% acetone was used to extract Ants from Ant-containing leaves of test plants. However, using the 80% acetone extraction method can lead to interference between chlorophylls (Chls) and Ants. Porphyrins, such as protoporphyrin IX (PPIX), Mg-protoporphyrin IX (MgPP), and protochlorophyllide (Pchlide), are Chl biosynthetic intermediates and demonstrate photospectrometric characteristics similar to those of Chl. Although the ether/water extraction method was able to remove Ants interference when detecting porphyrins, the porphyrins extraction efficiency was lower than that of the 80% acetone extraction method. Low Ants levels interfered with individual porphyrin ratios, and the extent of the effect was correlated with Ants concentrations. We developed the three equations could eliminate interference by Ants when determining the porphyrin molecular percentage (%) and were comprehensively applied to all tested species of Ants-containing leaves.

Grey relational analysis between agronomic characters and maturity of sugarcane

This study applied grey system theory to analyze the relationship between eight agronomic characters including plant height, leaf fresh weight, leaf dry weight, leaf water content, internodes number of dead-leaf stalk, internodes number of green-leaf stalk, juice brix of dead-leaf stalk and juice brix of green-leaf stalk, and the maturity of sugarcane. The contribution degrees of agronomic characters, indicated by grey order, to maturity of sugarcane were: juice brix of green-leaf stalk＞leaf dry weight＞juice brix of dead-leaf stalk＞plant height＞internodes number of green-leaf stalk＞leaf fresh weight＞leaf water content＞internodes number of dead-leaf stalk. Therefore, the juice brix of green-leaf stalk and dead-leaf stalk, leaf dry weight and plant height were the most critical characters to the maturity of sugarcane. The result based on grey relational analysis might be used as a valuable reference on the field management of sugarcane.

Effect of Nutrient on Growth of Dwarf ＂Kandelia Candel＂ (L.) Druce Evaluated by Grey Relational Analysis

Grey relational analysis was employed to study the effect of nitrogen (N) and/or phosphorus (P or NP) nutrients on the growth of dwarf ＂Kandelia candel＂ (L.) Druce in the Chuwei Mangrove Nature Preserve. A field fertilization experiment was designed using ammonium sulfate and superphosphate as the main sources of N and P. Shoots with at least 8 pairs of leaves, of which the two oldest pairs were yellowing, were collected at one year after fertilization. Chlorophyll content of eight proposed stages, including pigment synthesis and degradation, was determined. The primitive sequence data were constructed, and the grey initial normalization and mean normalization were calculated. For chlorophyll content and a/b ratio, the grey relational grade and order, based on both initial and mean normalization, is Γ_P＞Γ_(NP)＞Γ_N, indicating the similarity with non-fertilizer plants is P ＞ NP ＞N. In other words, P treatment affected chlorophyll accumulation and the a/b ratio patterns were less than NP and N treatment. Thus, the order of the factor importance, which is the reverse sequence of the grey relational grade, is N＞NP＞P. The grey relational analysis strongly indicated that N is the most important factor affecting the synthesis and degradation of chlorophyll in dwarf ＂K. candel＂ (L.) Druce; P is not so important as N; however, the combination of N and P had the same effect as N.

Effects of Climate Factors on Normalized Difference Vegetation Index Taking from Satellite Remote Sensing at the Mt. Huangzui Area of Taiwan

Eight sets of SPOT satellite images, covering nine years from 1994 to 2002 and equivalent to eight months, were used to monitor seasonal changes in the normalized difference vegetation index (NDVI) over the Mt. Huangzui area in the Yangminshan National Park of northern Taiwan. The grey system theory was applied to analyze the degree of contribution of the five climate factors on NDVI of four major vegetation types Axonopus affinis, Miscanthus foridulus, Eurya crenatifolia and broad leaf vegetation. Results from grey relational analysis showed that the contribution of climate factors to satellite NDVI can be ranked in order of monthly mean temperature＞daily cumulative irradiance＞daily insolation percentage＞monthly mean relative humidity＞monthly cumulative precipitation. It suggests that light and temperature-related climate factors play more important roles in determining the satellite NDVI than water-related climate factors in the Mt. Huangzui area.