Bioaccumulation of Lanthanum and Its Effect on Growth of Maize Seedlings in a Red Loamy Soil

Through a pot culture lanthanum nitrate was applied to maize seedlings grown in a red loamy soil to investigate the physiological and toxic effects of added La on the growth of crop seedlings and La bioaccumulation to help understand the environmental chemistry behaviors of rare earth element as fertilizers in soils. Compared to the control, La concentrations in shoots and especially in roots of maize seedlings increased with an increase of La in the soil. Also, with added concentrations of La≥0.75 g La kg-1 soil and≥0.05 g La kg-1 soil, the dry weight of shoots and roots of maize seedlings was significantly reduced (P≤0.05), respectively, compared with the control. Additionally, La≥0.5 g kg-1 in the soil significantly inhibited (P≤0.05) primary root elongation. Roots were more sensitive to La stress than shoots and thus could be used as a biomarker to La stress. Overall, in the red loamy soil studied, La had no significant beneficial effects on the growth of maize at the added La levels above 0.1 g kg-1 soil.

Regulation of Foliar Application DCPTA on Growth and Development of Maize Seedling Leaves in Heilongjiang Province

DCPTA （2-diethylaminoethyl-3, 4-dichlorophenylether） is a new plant regulator which can be used to regulate growth and development for crops. Experiments on maize seedlings were conducted in the growth chamber to study the effects of foliar applied DCPTA. The plant pots were placed in a completely randomized design with three replicates. The maize seedlings were treated with 0 mg·L-1 （control）, 20 mg·L-1 and 40 mg·L-1 DCPTA solution. The effects of DCPTA on the photosynthetic characteristics （photosynthesis, stomata conductance, intercellular CO2, and transpiration rate）, related physiological characteristics （contents of soluble sugar and starch）, chlorophyll fluorescence parameters （Fo, Fro, Fv/Fm, Fv/Fo, qP, and qN） and the weight of dry matter in maize seedling were studied. The results showed that DCPTA enhanced photosynthesis of maize seedling. In general, photosynthetic rate in leaves was significantly promoted through spraying DCPTA solution, and 40 rag＂ L~ DCPTA was found to be the best concentration for maize. The relationship between stomata conductance and transpiration rate in maize leaves could be described as linear. With regard to the chlorophyll fluorescence parameters, our fmdings showed that 40 mg·L-1 DCPTA in maize seedling caused an increase in Fm, Fv/Fm, Fm/Fo, qP and a decrease in Fo and qN at some time points checked. It is suggested that DCPTA increased photosynthetic rate by raising both the content of chlorophyll and activities of PSII and the contents of sugar and starch. Compared with the control, the treated maize seedling caused an increase in plant height, root length, shoot dry mass, root dry mass, or the total （root plus shoot） dry mass.

Influence of Low-temperature Stress on Photosynthetic Traits in Maize Seedlings

Three varieties were employed as materials to study changes of photosynthetic traits under low-temperature stress. The results showed that Pn, Gs and Tr decreased under low-temperature treatment. Ci decreased under low-temperature treatment 18℃/ 9℃, and 16℃/7℃, and it decreased in earlier stage after increased under 14℃/5℃. WUE was increased in earlier stage and after stabilized. The order of the three varieties of cold resistance were Jinyu 5〉Xingken 3〉Jidan 198. They could make self-regulation through adjusting Gs, Tr, Ci and WUE.

An Analysis to the Driving Forces for Water and Salt Absorption in Roots of Maize Seedlings Under Salt Stress

When maize seedlings were subjected to salt stress,a decline in root xylem pressure was observed within seconds,followed by a gradual increase in Na＋ deposition in the seedlings.The magnitude of xylem pressure response was positively correlated with,but not proportional to the intensity of the stress.A continuous recording of the xylem pressure profile showed that self-regulation of the xylem pressure existed before and after the imposition of salt stress when the environmental conditions were relatively stable.The salt induced increase in xylem tension dominated the total water potential of the plant when the salt stress was mild,but the osmotic potential became more prominent when the NaCl concentration in the root bathing solution was raised to over 100 mol m-3.The average transpiration rate of the seedlings dropped by 40% when the NaCl concentration in the root ambient was increased to 150 mol m-3.Although salt stress resulted in the decline of both the xylem pressure potential and the osmotic potential in the root xylem,the changes in the total water potential of the root xylem solution were always smaller than the changes in the water （osmotic） potentials of the solution bathing the root.An analysis to the water relations of maize seedlings showed that not only the water potential components,but the radial reflection coefficient of the roots was also dependent on the level of salinity.When the NaCl level in the root bathing solution was raised from 25 to 150 mol m-3,the radial reflection coefficient of the root declined from 0.43 to 0.31.This small change resulted in a remarkable increase in the normalised relative NaCl absorption by 2.4 times,indicating that the radial reflection coefficient of root played a very important role in regulating the absorption of NaCl in maize seedlings under salt stress.

Contribution of an Auxin to the Uptake of Nickel and Cadmium in Maize Seedlings

Maize seedlings were cultured in nickel or cadmium contaminated sand treated with α-naphthylacetic acid (NAA). The effeets of NAA on nickel and cadmium uptake in roots, shoots, and subcellular fractions (cell wall, nuclei and remained parts of seedling cells) were determined. The data showed growth promotion when NAA was applied at low concentrations and inhibition at high concentrations. Uptake of nickel and cadmium content increased concurmntly in roots and shoots. In thesubcellular fraction, nickel and cadmium was greatest in the cell wall. The changes in growth had greatest cormlation Wtih nickel and cadmium content in the subeellular fraction.

Large-scale Proteomic and Phosphoproteomic Analyses of Maize Seedling Leaves During De-etiolation

De-etiolation consists of a series of developmental and physiological changes that a plant undergoes in response to light.During this process light,an important environmental signal,triggers the inhibition of mesocotyl elongation and the production of photosynthetically active chloroplasts,and etiolated leaves transition from the"sink"stage to the"source"stage.De-etiolation has been extensively studied in maize(Zea mays L.).However,little is known about how this transition is regulated.In this study,we described a quantitative proteomic and phosphoproteomic atlas of the de-etiolation process in maize.We identified 16,420 proteins in proteome,among which 14,168 proteins were quantified.In addition,8746 phosphorylation sites within 3110 proteins were identified.From the combined proteomic and phosphoproteomic data,we identified a total of 17,436 proteins.Only 7.0%(998/14,168)of proteins significantly changed in abundance during de-etiolation.In contrast,26.6%of phosphorylated proteins exhibited significant changes in phosphorylation level;these included proteins involved in gene expression and homeostatic pathways and rate-limiting enzymes involved in photosynthetic light and carbon reactions.Based on phosphoproteomic analysis,34.0%(1057/3110)of phosphorylated proteins identified in this study contained more than 2 phosphorylation sites,and 37 proteins contained more than 16 phosphorylation sites,indicating that multi-phosphorylation is ubiquitous during the de-etiolation process.Our results suggest that plants might preferentially regulate the level of posttranslational modifications(PTMs)rather than protein abundance for adapting to changing environments.The study of PTMs could thus better reveal the regulation of de-etiolation.

Transition from a maternal to external nitrogen source in maize seedlings

Maximizing NO3 uptake during seedling development is important as it has a major influence on plant growth and yield. However, little is known about the processes leading to, and involved in, the initiation of root NO3 uptake capacity in developing seedlings. This study examines the physiological processes involved in root NO3 uptake and metabolism, to gain an understanding of how the NO3 uptake system responds to meet demand as maize seedlings transition from seed N use to external N capture. The concentrations of seedderived free amino acids within root and shoot tissues are initially high, but decrease rapidly until stabilizing eight days after imbibition （DAI）. Similarly, shoot N% decreases, but does not stabilize until 12-13 DAI. Following the decrease in free amino acid concentrations, root NO3- uptake capacity increases until shoot N% stabilizes. The increase in root NO3 uptake capacity corresponds with a rapid rise in transcript levels of putative NO3 transporters, ZmNRT2.1 and ZmNRT2.2. The processes underlying the increase in root NO3- uptake capacity to meet N demand provide an insight into the processes controlling N uptake.

Seedling-growing tray made of rice straw for maize seedling transplantation and its shear mechanics test

The plant-made seedling-growing tray cultivation technique is an effective way to improve maize yield and quality in China’s cold northern area.However,the corn seedling nursery carrier and tray cultivation technique has been proved poor in adaptability.After comparing several nursery carriers,a design for a plant-made seedling-growing tray that is suitable for maize transplantation was proposed in which rice straw was used as the primary raw material.The preparation method,processing and structural dimensions of the tray were investigated and designed,five types of plant-made seedling-growing trays with different formulations were proposed.The shear mechanical properties and the shear strength of the plant-made seedling-growing trays were tested to determine the shear force needed for cutting through trays prepared with increasing mass ratios of rice straw and the effect of the shearing rate on the shear strength.The results showed that at a shearing rate of 100 mm/min,the maximum shear force decreased gradually as the mass ratio of straw was increased and that the hardness of the tray decreased as its shear strength decreased.Under three shearing rates(100 mm/min,200 mm/min and 500 mm/min)and a blade displacement of 10 mm,the shear force was the highest at the point at which the tray was cut through;the required shear force to cut through the tray then gradually decreased.Trays with the same straw composition showed no significant influence of shearing rate on the tray’s shear strength at shearing rates of 100 mm/min,200 mm/min or 500 mm/min.This study describes a multi-tray,single-strip nursery carrier for use in plant-made seedling-growing tray cultivation and proposes a theoretical basis for the design of a rotary transplanting device,the key part of a maize plant-made seedling-growing tray transplanter.

Maize(Zea mays L.)seedling detection based on the fusion of a modified deep learning model and a novel Lidar points projecting strategy

Accurate crop detection is the prerequisite for the operation of intelligent agricultural machinery.Image recognition usually lacks accurate orientation information,and Lidar point clouds are not easy to distinguish different objects.Fortunately,the fusion of images and Lidar points can complement each other.This research aimed to detect maize(Zea mays L.)seedlings by fusing Lidar data with images.By applying coordinate transformation and time stamps,the images and Lidar points were realized homogeneous in spatial as well as temporal dimensions.Deep learning was used to develop a maize seedling recognition model,then the model recognized maize seedlings by labeling them with bounding boxes.Meanwhile,Lidar points were mapped to the bounding boxes.Only one-third of points that fell into the right middle of bounding boxes were selected for clustering operation,the calculated center of the cluster provided spatial information for target maize seedlings.This study modified the classical single shot multi-box detector(SSD)by merely linking the last feature map to the final output layer,owing to the higher feature maps having the unique advantages of detecting relatively larger objects.In images,maize seedlings were just the largest objects owing to be shot on purpose.This modification enabled the recognition model to finish recognizing an image by only consuming around 60 ms,which saved about 10 ms/image compared with the classical SSD model.The experiment was conducted in a maize field,and the maize was during the elongation stage.Experimental results demonstrated that the standard deviations for maximum distance error and maximum angle error were 1.4 cm and 1.1°,respectively,which can be tolerated under current technical requirements.Since agricultural fields are subject to staple crop-orientated and changeable ambient environment,the fusion of images and Lidar points can derive more precision information,and make agricultural machinery smarter.This study can act as an upstream technology for other researches on intelligent agricultural machinery.