Changes In Chlorophyll Content Research Articles

Influence of short-term exposure to high light on photosynthesis and proteins involved in photo-protective processes in tomato leaves

Plants in natural environments have to cope with fluctuations in light conditions on different timescales, ranging from seconds to days. Toward this, plants employ both adaptive and protective mechanisms. Here, we studied the response of low-light-grown tomato plants to short-term high light (HL) exposure followed by a recovery period using large-scale proteomic profiling, photosynthetic- and biochemical measurements. We found that following a 6-h HL treatment, plants exhibited photosystem II photoinhibition, a tendency toward a reduced electron transport and induction of non-photochemical quenching (NPQ). The proteomic data showed that key enzymes of the Mg-branch of the tetrapyrrole pathway, leading to chlorophyll biosynthesis, were significantly down-regulated by HL. Nonetheless, no changes in chlorophyll content or in the levels of most photosynthetic proteins, including all identified photosystem and light-harvesting antenna proteins, were detected. Notably, we observed that following a recovery period (24 h), plants were characterized by higher electron transport and an increased NPQ capacity, indicative of an acclimation that resulted in better photosynthetic performance. Our proteomic analysis also revealed prominent up-regulation of several enzymes of the flavonoid pathway, as well as of enzymatic components of other plant antioxidant systems. In accord with these, we found significant increases in the content of flavonoids and ascorbate, and in the activity of ascorbate peroxidase following the HL and recovery. Together, the results highlight the key alterations involved in photo-protection and detoxification of reactive oxygen species which take part in the short-term response to HL.

Copper and mercury induced oxidative stresses and antioxidant responses of Spirodela polyrhiza (L.) Schleid

Duckweed is recognized as a phytoremediation aquatic plant due to the production of large biomass and a high level of tolerance in stressed conditions. A laboratory experiment was conducted to investigate antioxidant response and mechanism of copper and mercury tolerance of S. polyrhiza (L.) Schleid. To understand the changes in chlorophyll content, MDA, proline, and activities of ROS-scavenging enzymes (SOD, CAT, GPOD) during the accumulation of Cu+2 and Hg+2, S. polyrhiza were exposed to various concentrations of Cu+2 (0.0–40 μM) and Hg+2 (0.0–0.4 μM). antioxidant activity initially indicated enhancing trend with application of 10 μM Cu+2; 0.2 μM Hg+2 (SOD), of 20 μM Cu+2; 0.2 μM Hg+2 (CAT) and of 10 μM Cu+2;0.2 μM Hg+2 (GPOD) and then decreased consistently up to 40 μM Cu+2 and 0.4 μM Hg+2. In the experiment chlorophyll and frond multiplication initially showed increasing tendency and decreased gradually with the application of increased metal concentration. Application of heavy metal has constantly enhanced proline and MDA content while the maximum increase was observed with the application of 40 μM Cu; 0.4 μM Hg for proline and MDA respectively. The upregulation of antioxidant enzymes and proline reveals that S. polyrhiza has strong biochemical strategies to deal with the heavy metal toxicity induced by the accumulation of Cu+2 and Hg+2.

Growth Stages Classification of Potato Crop Based on Analysis of Spectral Response and Variables Optimization.

Potato is the world’s fourth-largest food crop, following rice, wheat, and maize. Unlike other crops, it is a typical root crop with a special growth cycle pattern and underground tubers, which makes it harder to track the progress of potatoes and to provide automated crop management. The classification of growth stages has great significance for right time management in the potato field. This paper aims to study how to classify the growth stage of potato crops accurately on the basis of spectroscopy technology. To develop a classification model that monitors the growth stage of potato crops, the field experiments were conducted at the tillering stage (S1), tuber formation stage (S2), tuber bulking stage (S3), and tuber maturation stage (S4), respectively. After spectral data pre-processing, the dynamic changes in chlorophyll content and spectral response during growth were analyzed. A classification model was then established using the support vector machine (SVM) algorithm based on spectral bands and the wavelet coefficients obtained from the continuous wavelet transform (CWT) of reflectance spectra. The spectral variables, which include sensitive spectral bands and feature wavelet coefficients, were optimized using three selection algorithms to improve the classification performance of the model. The selection algorithms include correlation analysis (CA), the successive projection algorithm (SPA), and the random frog (RF) algorithm. The model results were used to compare the performance of various methods. The CWT-SPA-SVM model exhibited excellent performance. The classification accuracies on the training set (Atrain) and the test set (Atest) were respectively 100% and 97.37%, demonstrating the good classification capability of the model. The difference between the Atrain and accuracy of cross-validation (Acv) was 1%, which showed that the model has good stability. Therefore, the CWT-SPA-SVM model can be used to classify the growth stages of potato crops accurately. This study provides an important support method for the classification of growth stages in the potato field.

Detection of chlorophyll content in growth potato based on spectral variable analysis

Monitoring the chlorophyll content in tuber formation and tuber bulking stage has great significance for the nutritional status diagnosis in the potato field. In this paper, the 314 canopy spectra of potato crops were collected at four stages, respectively. The leaves were collected simultaneously to measure the chlorophyll content. After spectra pre-processing, the dynamic changes in chlorophyll content and spectral response during growth were analyzed. Two variable selection algorithms (successive projection algorithm, and random frog algorithm) were employed to select chlorophyll characteristic wavelengths. The partial least square algorithm was used for modeling analysis. The performance of sensitive wavelengths selected by two algorithms was compared, respectively, from the perspective of correlation with chlorophyll, reflecting leaf information, and model result. The sensitive wavelengths selected by random frog was optimal. The determination coefficient of calibration and validation set of the detection model established based on above sensitive wavelengths was respectively 0.827 and 0.798. The results showed the chlorophyll content of potato could be detected accurately based on the spectroscopy method.

Impact of foliar application of some metal nanoparticles on antioxidant system in oakleaf lettuce seedlings

BackgroundNanoparticles (NPs) serve various industrial and household purposes, and their increasing use creates an environmental hazard because of their uncontrolled release into ecosystems. An important aspect of the risk assessment of NPs is to understand their interactions with plants. The aim of this study was to examine the effect of Au (10 and 20 ppm), Ag, and Pt (20 and 40 ppm) NPs on oakleaf lettuce, with particular emphasis on plant antioxidative mechanisms. Nanoparticles were applied once on the leaves of 2-week-old lettuce seedlings, after next week laboratory analyses were performed.ResultsThe antioxidant potential of oakleaf lettuce seedlings sprayed with metal NPs at different concentrations was investigated. Chlorophylls, fresh and dry weight were also determined. Foliar exposure of the seedlings to metal NPs did not affect ascorbate peroxidase activity, total peroxidase activity increased after Au-NPs treatment, but decreased after applying Ag-NPs and Pt-NPs. Both concentrations of Au-NPs and Pt-NPs tested caused an increase in glutathione (GSH) content, while no NPs affected L-ascorbic acid content in the plants. Ag-NPs and Pt-NPs applied as 40 ppm solution increased total phenolics content by 17 and 15%, respectively, compared to the control. Carotenoids content increased when Ag-NPs and Au-NPs (20 and 40 ppm) and Pt-NPs (20 ppm) were applied. Plants treated with 40 ppm of Ag-NPs and Pt-NPs showed significantly higher total antioxidant capacity and higher concentration of chlorophyll a (only for Ag-NPs) than control. Pt-NPs applied as 40 ppm increased fresh weight and total dry weight of lettuce shoot.ConclusionsResults showed that the concentrations of NPs applied and various types of metal NPs had varying impact on the antioxidant status of oakleaf lettuce. Alteration of POX activity and in biosynthesis of glutathione, total phenolics, and carotenoids due to metal NPs showed that tested nanoparticles can act as stress stimuli. However, judging by the slight changes in chlorophyll concentrations and in the fresh and dry weight of the plants, and even based on the some increases in these traits after M-NPs treatment, the stress intensity was relatively low, and the plants were able to cope with its negative effects.

Differing photosynthetic responses to excess irradiance in the two coexisting seagrasses, Halophila ovalis and Halophila decipiens: Chloroplast avoidance movement, chlorophyll fluorescence, and leaf optical properties

Seagrasses cope with excess irradiance using a suit of photoprotective mechanisms, however, Halophila species are the only seagrasses known to exhibit chloroplast avoidance movement. Here we examined this phenomenon together with concurrent change in photosynthetic and leaf optical properties in H. ovalis and H. decipiens. Although co-existing, these two seagrasses displayed different light use characteristics derived from rapid light curves; H. ovalis and H. decipiens showed features of sun- and shade-adapted plants, respectively. Experimentally the seagrass leaves were exposed to low, medium, and high irradiance (80, 200 and 800 μmol photons m−2 s−1, respectively) for 60 min, followed by 60 min in darkness. Chloroplast movement occurred in H. ovalis exposed to medium or high irradiance and in H. decipiens exposed to low or medium irradiance. Chloroplast gathering was observed after 20 min of exposure and chloroplast dispersal was observed after 20 min in darkness, dependent on treatment and species. Increasing irradiance lowered the effective quantum yield and increased the non-photochemical quenching (NPQ). Despite stronger up-regulation in NPQ, photoinhibition was detected in H. decipiens. The absorption factor and the Soil-Plant Analysis Development value were modulated by chloroplast movement rather than a change in chlorophyll content, except for H. decipiens exposed to high irradiance where photodamage of chlorophylls may have occurred. Chloroplast movement in both seagrasses was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, indicating regulation by photosynthesis. Our results suggest that H. ovalis has a higher tolerance to excess irradiance than H. decipiens and that this is assisted partly by chloroplast avoidance movement.

Strontium Uptake and Effects in Hydroponically Cultivated Celery

The artificial radionuclide 90Sr is the main radionuclide in radioactive environmental pollution. In this study, celery was cultured in a laboratory hydroponics system for 21 days with strontium (Sr) levels of 0 (control), 0.5, 1, 2.5, 5, and 10 mM. The changes in the Sr contents in celery leaves and roots as well as the translocation factor (TF) values (ratio of the Sr concentration in aerial plant parts to that in roots) under different Sr concentrations were studied. Additionally, the effects of Sr stress on the absorption of six nutrients, the chlorophyll content, and the biomass of the celery were investigated. The results showed that the Sr contents in celery leaves and roots increased with the increasing Sr concentration in the hydroponic solution, but the increase of the Sr concentration in roots slowed under the 10 mM Sr treatment. The mean TF values ranged from 0.40 ± 0.01 to 1.12 ± 0.17. With the increase in Sr concentration in the hydroponic medium, the contents of calcium, iron, and potassium in the celery leaves were significantly reduced, and the absorption of calcium, iron, and magnesium by roots was significantly inhibited. Compared with the control, sulfur concentration in celery roots increased significantly under the Sr treatments increasing except the 10 mM Sr treatment. The changes in chlorophyll content were consistent with those of celery biomass, and the values of both these parameters were high under the 5 mM Sr treatment.

Effect of Heat Stress on Sargassum fusiforme Leaf Metabolome

Temperature is a major environmental factor affecting the growth, development, and productivity of Sargassum fusiforme. We aimed to assess the metabolic processes and regulatory mechanisms in S. fusiforme during a 7-day high-temperature (27 °C and 32 °C) experiment. Changes in chlorophyll content and electrolyte leakage after high-temperature treatment were investigated. Metabolic changes in the leaves of S. fusiforme were analysed using gas chromatography–mass spectrometry. High temperatures suppressed chlorophyll content and increased electrolyte leakage. Further, a strong modulation of various metabolisms was observed: organic acids, amino acids, sugars or sugar alcohols, esters, and amines. These metabolisms were significantly enriched in ten pathways under the 27 °C treatment: aminoacyl-tRNA biosynthesis; glycine, serine, and threonine metabolism; alanine, aspartate, and glutamate metabolism; valine, leucine, and isoleucine biosynthesis; cyanoamino acid metabolism; cysteine and methionine metabolism; arginine and proline metabolism; tyrosine metabolism; citrate cycle (TCA cycle); and glucosinolate biosynthesis. The various metabolisms significantly enriched seven pathways under the 32 °C treatment, namely, alanine, aspartate, and glutamate metabolism; aminoacyl-tRNA biosynthesis; phenylalanine metabolism; tyrosine metabolism; arginine and proline metabolism; nitrogen metabolism; and isoquinoline alkaloid biosynthesis. These changes in metabolic pathways may contribute to the tolerance and adaptability of S. fusiforme to high-temperature stress.

Non-Destructive Detection of Tea Leaf Chlorophyll Content Using Hyperspectral Reflectance and Machine Learning Algorithms.

Tea trees are kept in shaded locations to increase their chlorophyll content, which influences green tea quality. Therefore, monitoring change in chlorophyll content under low light conditions is important for managing tea trees and producing high-quality green tea. Hyperspectral remote sensing is one of the most frequently used methods for estimating chlorophyll content. Numerous studies based on data collected under relatively low-stress conditions and many hyperspectral indices and radiative transfer models show that shade-grown tea performs poorly. The performance of four machine learning algorithms—random forest, support vector machine, deep belief nets, and kernel-based extreme learning machine (KELM)—in evaluating data collected from tea leaves cultivated under different shade treatments was tested. KELM performed best with a root-mean-square error of 8.94 ± 3.05 μg cm−2 and performance to deviation values from 1.70 to 8.04 for the test data. These results suggest that a combination of hyperspectral reflectance and KELM has the potential to trace changes in the chlorophyll content of shaded tea leaves.

AtPPRT1 negatively regulates salt stress response in Arabidopsis seedlings

ABSTRACTSalt stress is one of the environmental factors that negatively affect plant growth and development. We have previously reported a putative C3HC4 zinc-finger ubiquitin E3 ligase (AtPPRT1) negatively regulates Abscisic acid (ABA) and drought stress response. According to previous studies, the accumulation of ABA in plants can further regulate the salt stress response. Therefore, in this study, we further analyzed whether AtPPRT1 negatively regulates the salt stress response. The results showed that AtPPRT1 expression was induced by salt stress. Furthermore, under salt stress, the β-glucuronidase (GUS) gene driven by the AtPPRT1 promoter has shown increased activity in the hypocotyl and petioles of Arabidopsis seedlings. Additionally, seedlings of the T-DNA insertion mutant atpprt1 showed significant growth advantage under salt stress, whereas overexpressing AtPPRT1 (OE lines) in Arabidopsis seedlings displayed hypersensitive under salt stress. Etiolated atpprt1 seedlings also demonstrated significantly elongated hypocotyl lengths in salt stress. The elevated or reduced salt tolerance of atpprt1 and AtPPRT1 overexpressing lines was confirmed by the changes in chlorophyll content and 3,3ʹ-Diaminobenzidine (DAB) staining. The above data suggest that AtPPRT1 has a negative effect on salt tolerance in Arabidopsis seedlings.

Physiological Responses of Wetland Species Rumex Hydrolapathum to Increased Concentration of Biogenous Heavy Metals Zn and Mn in Substrate

Abstract The aim of the present study was to determine if individuals of Rumex hydrolapathum Huds native to saline wetlands are able to tolerate high concentration of biogenous heavy metals Zn and Mn in substrate and to accumulate high concentration of these metals in aboveground parts. Plant physiological status was monitored by using non-destructive analysis of chlorophyll and chlorophyll a fluorescence. R. hydrolapathum plants accumulated up to 1840 mg·kg−1 Zn and 6400 mg·kg−1 Mn in older leaves. The usefulness of monitoring changes in chlorophyll concentration and chlorophyll a fluorescence parameters to predict physiological response of R. hydrolapathum plants to excess Zn and Mn was not supported, as the lack of significant changes indicated that the model species showed adaptation to increased amount of metals in actively photosynthesizing tissues. It appears that Zn and Mn tolerance of R. hydrolapathum is based primarily at the physiological level where metal accumulation in younger leaves and roots is restricted, and development of new leaves is promoted together with induction of senescence in older leaves that have accumulated the majority of Zn and Mn. R. hydrolapathum can be characterised as a very promising model species for further studies for practical phytoremediation needs.

Interaction Between Induced and Natural Variation at oil yellow1 Delays Reproductive Maturity in Maize

We previously demonstrated that maize (Zea mays) locus very oil yellow1 (vey1) encodes a putative cis-regulatory expression polymorphism at the magnesium chelatase subunit I gene (aka oil yellow1) that strongly modifies the chlorophyll content of the semi-dominant Oy1-N1989 mutants. The vey1 allele of Mo17 inbred line reduces chlorophyll content in the mutants leading to reduced photosynthetic output. Oy1-N1989 mutants in B73 reached reproductive maturity four days later than wild-type siblings. Enhancement of Oy1-N1989 by the Mo17 allele at the vey1 QTL delayed maturity further, resulting in detection of a flowering time QTL in two bi-parental mapping populations crossed to Oy1-N1989. The near isogenic lines of B73 harboring the vey1 allele from Mo17 delayed flowering of Oy1-N1989 mutants by twelve days. Just as previously observed for chlorophyll content, vey1 had no effect on reproductive maturity in the absence of the Oy1-N1989 allele. Loss of chlorophyll biosynthesis in Oy1-N1989 mutants and enhancement by vey1 reduced CO2 assimilation. We attempted to separate the effects of photosynthesis on the induction of flowering from a possible impact of chlorophyll metabolites and retrograde signaling by manually reducing leaf area. Removal of leaves, independent of the Oy1-N1989 mutant, delayed flowering but surprisingly reduced chlorophyll contents of emerging leaves. Thus, defoliation did not completely separate the identity of the signal(s) that regulates flowering time from changes in chlorophyll content in the foliage. These findings illustrate the necessity to explore the linkage between metabolism and the mechanisms that connect it to flowering time regulation.

Study on the Effect of Exogenous Salicylic Acid on Algae Growth in the Environment

With the development of industry, synthetic drugs and their secondary metabolites bring some hidden dangers to environmental safety. As an excellent drug, salicylic acid is widely used in cardiovascular drugs, industrial dyes, skin care and acne products, etc. Therefore, it is possible to detect salicylic acid molecules, its derivatives or secondary metabolites in the natural environment. It should be noted that salicylic acid, as an endogenous signal molecule, can greatly affect plant growth. In this study, the common algal Spirogyra in fresh water was taken as the research object. The effects of exogenous salicylic acid on the growth of Spirogyra were analyzed through the changes of chlorophyll content and plant cross section during the growth of Spirogyra. It is found that the concentration of salicylic acid in the natural environment generally promotes the development of algae and improves their resistance to environmental stress. Therefore, as a possible correlation index of algal blooms, it deserves our attention.

Changes in chlorophyll concentration and phenology in the North Sea in relation to de‐eutrophication and sea surface warming

AbstractAt least two major drivers of phytoplankton production have changed in recent decades in the North Sea: sea surface temperature (SST) has increased by ~ 1.6°C between 1988 and 2014, and the nitrogen and phosphorus loads from surrounding rivers have decreased from the mid‐1980s onward, following reduction policies. Long time series spanning four decades (1975–2015) of nutrients, chlorophyll (Chl), and pH measurements in the Southern and Central North Sea were analyzed to assess the impact of both the warming and the de‐eutrophication trends on Chl. The de‐eutrophication process, detectable in the reduction of nutrient river loads to the sea, caused a decrease of nutrient concentrations in coastal waters under riverine influence. A decline in annual mean Chl was observed at 11 out of 18 sampling sites (coastal and offshore) in the period 1988–2016. Also, a shift in Chl phenology was observed around 2000, with spring bloom formation occurring earlier in the year. A long time series of pH in the Southern North Sea showed an increase until the mid‐1980s followed by a rapid decrease, suggesting changes in phytoplankton production that would support the observed changes in Chl. Linear correlations, however, did not reveal significant relationships between Chl variability and winter nutrients or SST at the sampling sites. We propose that the observed changes in Chl (annual or seasonal) around 2000 are a response of phytoplankton dynamics to multiple stressors, directly or indirectly influenced by de‐eutrophication and climate warming.

Pokkah boeng resistance in popular rabi sorghum cultivars and effects of the disease on leaf chlorophyll

Field experiments were conducted with nineteen sorghum (Sorghum bicolor L. Moench) cultivars that included fifteen rabi varieties, two kharif varieties and two rabi parental lines for evaluation of pokkah boeng (c.o. Fusarium subglutinans) resistance. Stem injection method of artificial inoculation was used to develop the disease under field conditions during two successive rabi seasons of 2015 and 2016. Leaf chlorophyll was measured by SPAD-502 chlorophyll meter to compare changes in chlorophyll content in inoculated plants over the control. Disease severity index ranged from 9.5–27.0% in 2015 and 10.4–32.5% in 2016. The cultivars widely varied in pokkah boeng resistance. CSV 19SS was identified as the most resistant among the test cultivars CSV 18R, DSV4, E 36-1 and CSV 8R as moderately resistant and SLR 30, RS 585 and M35-1 as susceptible cultivars. The disease had adverse effects on leaf chlorophyll content at vegetative stage particularly in susceptible cultivar (~ 21% reduction). This is the first information on the status of pokkah boeng resistance in popular rabi sorghum cultivars, which will help selection of varieties for cultivation.

Evaluation of Biological Response of Lettuce (Lactuca sativa L.) and Weeds to Safranal Allelochemical of Saffron (Crocus sativus) by Using Static Exposure Method.

Safranal, the main volatile chemical of Saffron (Crocus sativus) was studied to estimate its allelopathic effects on the photosynthetic pigment chlorophyll, leaf electrolyte leakage, fresh weight, catalase (CAT), and peroxidase (POX) activity of the test plant Lettuce (Lactuca sativa). In this study, the effective concentration (EC50) of safranal on CAT was estimated to be 6.12 µg/cm3. CAT activity was inhibited in a dose-dependent manner by the increase in the safranal concentration while POX activity was increased. Moreover, Safranal caused significant physiological changes in chlorophyll content, leaf electrolyte leakage, and fresh weight of several weed species with Lolium multiflorum being the most sensitive. Furthermore, 5 µM Safranal showed significant inhibitory activity against dicotyledonous in comparison to the monocotyledons under greenhouse conditions. The inhibition of the CAT by safranal was similar to those of uncompetitive inhibitors, and therefore the decline in carbon fixation by plants might be the mechanism behind the inhibitory activity of safranal.

Effects of drought stress on morphological, physiological, and biochemical characteristics of stock plant (Matthiola incana L.)

The allocation of new water resources to grow ornamental plants, especially in arid and semi-arid areas has usually faced numerous problems. Therefore, it is essential to study and select tolerant ornamental plants for use in these areas. This study was carried out in a completely randomized block design with five irrigation levels; 60, 70, 80, 90 and 100% of field capacity, using a surface irrigation system for two cultivars of stock flower (Matthiola incana L.), i.e., PanAmerican and Cinderella. The results showed that, although the number of flowers in Cinderella cultivar and relative water content in PanAmerican did not change significantly with increasing drought stress, plant height, shoot fresh weight, shoot dry weight, root fresh weight, and root dry weight significantly decreased in both cultivars (P < 0.01). Results also revealed that the changes in chlorophyll content and some biochemical properties of both cultivars including catalase enzyme activity, anthocyanin content, phenolic compounds, and proline content were statistically significant (P < 0.01) due to moderate and severe drought stress. In general, the results of this study indicate that drought stress has undesirable effects on morphological, physiological and biochemical characteristics of stock plants and therefore, their irrigation should be carefully controlled.

Effects of Exogenous Melatonin on the Physiological Characteristics of Kiwifruit Hayward under Salt Stress

To explore the effect of exogenous melatonin (MT) on the physiological characteristics in kiwi under the salt stress, Hayward seedlings primed with 0.1μmol•L−1 MT solution were used as the experimental material and treated with 100 mmol• L−1 NaCl in hydroponic culture condition. The results showed that the effect of exogenous MT on chlorophyll content changes, cell membrane permeability increase and damage mitigation of plasma membrane of hydroponic seedlings was not obvious, but the ability to alleviate the damage was shown in the early stage of the study.

Collaborative inversion heavy metal stress in rice by using two-dimensional spectral feature space based on HJ-1 A HSI and radarsat-2 SAR remote sensing data

Accurate and extensive monitoring of heavy metal pollution levels in rice fields is crucial to agricultural production and food safety.Most previous studies used optical remote sensing data to monitor heavy metal stress in rice in which way the remote sensing features are not diversified and the monitoring accuracy is relatively low. Compared with that optical remote sensing can monitor features like color and cell internal structure, microwave remote sensing can monitor the morphology and geometrical features. The complementary characteristics of multi-source remote sensing data are reflected in two aspects. On the one hand, the high spectral resolution characteristics of hj-1a HIS and the high spatial resolution characteristics of radarsat-2 SAR satellite are used for feature fusion to obtain the image data of high altitude spectral resolution; on the other hand, the two remote sensing data can depict the vegetation characteristics from different angles. In order to fully extract the characteristics of crop stress, the model was constructed by utilizing the complementary characteristics of multi-source remote sensing data. This paper synergized optical and microwave remote sensing to construct the crop heavy metal stress monitoring model. To this end, certain rice-growing areas polluted by heavy metal in Suzhou city were selected as the experimental areas, where ASD spectrum data, biochemical parameters and heavy metal content data of rice were collected during critical growth periods on one hand, HJ-1 A HIS and Radarsat-2 SAR satellite data were obtained almost simultaneously on the other hand. Based on heavy metal stress-responsive mechanism of rice, NVI (R598, R508) and SVI(HV,VH,HH,VV), spectral indexes sensitive to heavy metal stress, were extracted from the optical and radar data respectively to construct a two-dimensional feature space, based on which an optical-and-radar-remote-sensing-combined model for monitoring heavy metal stress in rice was constructed. In this paper, the study and main conclusions are as follows:(1) It used spectral characteristics analysis combined with statistic methods or random forest algorithm to build the canopy chlorophyll index NVI, which is sensitive to chlorophyll content changes of rice under heavy metal stress, and a heavy metal stress level inversion model was built based on hyperspectral HSI data accordingly. Also, it used statistic method to build the microwave index SVI, which is sensitive to biomass changes of rice under heavy metal stress, and a heavy metal stress level inversion model was built based on microwave SAR images as a result. (2) A combination of biochemical and morphological parameters, both responding to heavy metal stress, was synergized with NVI and SVI, sensitive to chlorophyll and biomass changes respectively, to build a two-dimensional feature space. Heavy metal stress levels were classified in this space. Thus, a synergetic model to retrieve heavy metal stress based on multi-source remote sensing data was developed. In this paper, the innovation lies in a model constructed by synergizing optical and radar remote sensing data to monitor heavy metal stress in rice based on a multi-dimensional spectral feature space and this model can be applied to monitoring multiple environmental stresses in crops.

Phenological Changes in the Chlorophyll Content and Its Fluorescence in Field-Grown Sugarcane Clones Under Over-Wintering Conditions

As a step toward breeding cultivars with tolerance to chilling stress, phenological changes in chlorophyll content (SPAD index) and its fluorescence (Fv/Fm) were investigated under over-wintering conditions using different sugarcane clones. A leading commercial cultivar in Japan, NiF8, and two interspecific lines, KY11-6114 and KY08-1200, were tested in this study. Daily minimum temperature decreased gradually with the advance of winter, and the lowest temperature of 1.2 °C was recorded in January. Although the temperature increased toward spring season, it remained below 10 °C until the end of experiment. Stem elongations in KY11-6114 and KY08-1200 during winter were significantly greater than in NiF8. The decrease in SPAD index was calculated from the difference between the beginning of winter and each measuring time. KY08-1200 and KY11-6114, with longer stem elongation, had a smaller decrease in SPAD index than NiF8 under over-wintering conditions. The Fv/Fm of all three clones decreased in January when the lowest temperature was recorded and recovered toward spring. Among three clones, KY08-1200 was less affected by chilling stress and presented a higher value of Fv/Fm up to the end of experiment. Considering these results, we concluded that the decreased chlorophyll content measured by the SPAD index was a simple indicator for screening chilling-tolerant clones.