Irineo Torres-Pacheco

A Review of Methods for Sensing the Nitrogen Status in Plants: Advantages, Disadvantages and Recent Advances

Nitrogen (N) plays a key role in the plant life cycle. It is the main plant mineral nutrient needed for chlorophyll production and other plant cell components (proteins, nucleic acids, amino acids). Crop yield is affected by plant N status. Thus, the optimization of nitrogen fertilization has become the object of intense research due to its environmental and economic impact. This article focuses on reviewing current methods and techniques used to determine plant N status. Kjeldahl digestion and Dumas combustion have been used as reference methods for N determination in plants, but they are destructive and time consuming. By using spectroradiometers, reflectometers, imagery from satellite sensors and digital cameras, optical properties have been measured to estimate N in plants, such as crop canopy reflectance, leaf transmittance, chlorophyll and polyphenol fluorescence. High correlation has been found between optical parameters and plant N status, and those techniques are not destructive. However, some drawbacks include chlorophyll saturation, atmospheric and soil interference, and the high cost of instruments. Electrical properties of plant tissue have been used to estimate quality in fruits, and water content in plants, as well as nutrient deficiency, which suggests that they have potential for use in plant N determination.

Interactions Between Geminiviruses in a Naturally Occurring Mixture: Pepper huasteco virus and Pepper golden mosaic virus

ABSTRACT Pepper huasteco virus (PHV) and Pepper golden mosaic virus (PepGMV) are found in mixtures in many horticultural crops in Mexico. This combination constitutes an interesting, naturally occurring model system to study several aspects of virus-virus interactions. Possible interactions between PHV and PepGMV were studied at four levels: symptom expression, gene expression, replication, and movement. In terms of symptom expression, the interaction was shown to be host-dependent because antagonism was observed in pepper, whereas synergism was detected in tobacco and Nicotiana benthamiana. PHV and PepGMV did not generate viable pseudorecombinant viruses; however, their replication is increased during mixed infections. An asymmetric complementation in movement was observed because PHV was able to support the systemic movement of PepGMV A whereas PepGMV did not support the systemic distribution of PHV A. Heterologous transactivation of both coat protein promoters also was detected. Several conclusions can be drawn from these experiments. First, viruses coinfecting the same plant can interact at several levels (replication, movement) and in different manners (synergism, antagonism); some interactions might be host dependent; and natural mixed infections could be a potential source of geminivirus variability by generating viable tripartite combinations that could facilitate recombination events.

Oxidative and Molecular Responses in Capsicum annuum L. after Hydrogen Peroxide, Salicylic Acid and Chitosan Foliar Applications

Hydrogen peroxide (H2O2) is an important ROS molecule (Reactive oxygen species) that serves as a signal of oxidative stress and activation of signaling cascades as a result of the early response of the plant to biotic stress. This response can also be generated with the application of elicitors, stable molecules that induce the activation of transduction cascades and hormonal pathways, which trigger induced resistance to environmental stress. In this work, we evaluated the endogenous H2O2 production caused by salicylic acid (SA), chitosan (QN), and H2O2 elicitors in Capsicum annuum L. Hydrogen peroxide production after elicitation, catalase (CAT) and phenylalanine ammonia lyase (PAL) activities, as well as gene expression analysis of cat1, pal, and pathogenesis-related protein 1 (pr1) were determined. Our results displayed that 6.7 and 10 mM SA concentrations, and, 14 and 18 mM H2O2 concentrations, induced an endogenous H2O2 and gene expression. QN treatments induced the same responses in lesser proportion than the other two elicitors. Endogenous H2O2 production monitored during several days, showed results that could be an indicator for determining application opportunity uses in agriculture for maintaining plant alert systems against a stress.

Nitrogen determination on tomato (Lycopersicon esculentum Mill.) seedlings by color image analysis (RGB)

In order to investigate the effectiveness of a new method based on color image analysis and the Minolta SPAD-502 chlorophyll meter for the diagnosis of nitrogen deficiencies of tomato seedlings, a field experiment was conducted. In this study, five levels of nitrogen fertilization were established so as to induce nitrogen deficiencies in tomato seedlings. Thirty-five days after sowing, total nitrogen was evaluated by laboratory analysis. The chlorophyll index was determined using a SPAD-502 chlorophyll meter. Also, color images were taken with a digital camera; the color images were processed in MATLAB in order to determine the averages of the red color, green color and the blue color. The relationships between variables were analyzed by linear regressions and a one way analysis of variance (p < 0.01). Results showed that color image analysis correlated better with the status of plant nitrogen than the SPAD. From the color image analysis, the red and blue colors were more accurate predictors of nitrogen status on plants with R2 above 0.89. Color image analysis provides an accurate and quick way for nitrogen estimation and can contribute for early detection of nitrogen deficiency in tomato seedlings. The SPAD method is not a reliable way to estimate the nitrogen status on tomato seedlings. Keywords: Color image analysis (RGB), chlorophyll meter, nitrogen deficiency African Journal of Biotechnology Vol. 9(33), pp. 5326-5332, 16 August, 2010

Instrumentation in developing chlorophyll fluorescence biosensing: a review.

Chlorophyll fluorescence can be defined as the red and far-red light emitted by photosynthetic tissue when it is excited by a light source. This is an important phenomenon which permits investigators to obtain important information about the state of health of a photosynthetic sample. This article reviews the current state of the art knowledge regarding the design of new chlorophyll fluorescence sensing systems, providing appropriate information about processes, instrumentation and electronic devices. These types of systems and applications can be created to determine both comfort conditions and current problems within a given subject. The procedure to measure chlorophyll fluorescence is commonly split into two main parts; the first involves chlorophyll excitation, for which there are passive or active methods. The second part of the procedure is to closely measure the chlorophyll fluorescence response with specialized instrumentation systems. Such systems utilize several methods, each with different characteristics regarding to cost, resolution, ease of processing or portability. These methods for the most part include cameras, photodiodes and satellite images.

Agriculture and Bioactives: Achieving Both Crop Yield and Phytochemicals

Plants are fundamental elements of the human diet, either as direct sources of nutrients or indirectly as feed for animals. During the past few years, the main goal of agriculture has been to increase yield in order to provide the food that is needed by a growing world population. As important as yield, but commonly forgotten in conventional agriculture, is to keep and, if it is possible, to increase the phytochemical content due to their health implications. Nowadays, it is necessary to go beyond this, reconciling yield and phytochemicals that, at first glance, might seem in conflict. This can be accomplished through reviewing food requirements, plant consumption with health implications, and farming methods. The aim of this work is to show how both yield and phytochemicals converge into a new vision of agricultural management in a framework of integrated agricultural practices.

Machine vision algorithm for whiteflies (Bemisia tabaci Genn.) scouting under greenhouse environment

One of the main problems in greenhouse crop production is the presence of pests. Detection and classification of insects are priorities in integrated pest management (IPM). This document describes a machine vision system able to detect whiteflies (Bemisia tabaci Genn.) in a greenhouse by sensing their presence using hunting traps. The extracted features corresponding to the eccentricity and area of the whiteflies projections allow to establish differences among pests and other insects on both the trap surfaces and dust generated artefacts. Because of whiteflies geometrical characteristics, it was possible to design an efficient (related to manual counting) machine vision algorithm to scout and count units of this pest within a greenhouse environment. These algorithm results show high correlation indexes for both, sticky screens (R2 = 0.97) and plant leaf situations (R2 = 1.0). The machine vision algorithm reduces the scouting time and the associated human error for IPM‐related activities.

Analysis of the infectivity of monomeric clones of pepper huasteco virus.

The infectivity of several monomeric clones of pepper huasteco virus was investigated. All clones were infectious when inoculated excised from the plasmid DNA. However, only certain clones were infectious when inoculated in the non-excised form. Constructs in which the cloning site lies inside regions or genes involved in replication (e.g. Rep-binding site, rep and AC2-AC3 genes) were not infectious, whereas constructs in which the site was located inside the CP or BC1 genes were infectious. A clone that interrupts the BV1 gene was not infectious suggesting an early of BV1 during the establishment of the infection. Linear viral clones containing different DNA fragments at both extremes were also infectious although with a lower efficiency. Analysis of the progeny suggested a precise excision mechanism since in most cases only wild type virus was recovered. The results suggest that excision could be linked to replication through a very specific recombination process.

Current approaches for enhanced expression of secondary metabolites as bioactive compounds in plants for agronomic and human health purposes - a review.

The study of secondary metabolism in plants is an important source for the discovery of bioactive compounds with a wide range of applications. Today these bioactive compounds derived from plants are important drugs such as antibiotics, and agrochemicals substitutes, they also have been economically important as flavors and fragrances, dyes and pigments, and food preservatives. Many of the drugs sold today are synthetic modifications of naturally obtained substances. There is no rigid scheme for classifying secondary metabolites, but they can be divided into different groups based on their chemical components, function and biosynthesis: terpenoids and steroids, fatty acid-derived substances and polyketides, alkaloids, phenolic compounds, non-ribosomal polypeptides and enzyme cofactors. The increasing commercial importance of these chemical compounds has resulted in a great interest in secondary metabolism, particularly the possibility of altering the production of bioactive plant metabolites by means of tissue culture technology and metabolomics. In today’s world the use of bioactive compounds derived from plants plays an important role in pharmaceutical applications. This review presents information about these metabolites and their applications as well as their importance in agronomy and bioactive effects on human health as nutraceuticals. This review includes also the new tendencies to produce these bioactive compounds under different stresses conditions such as biotic and abiotic stress that could be included in production systems.

A Germin-Like Protein Gene (CchGLP) of Capsicum chinense Jacq. Is Induced during Incompatible Interactions and Displays Mn-Superoxide Dismutase Activity

A germin-like gene (CchGLP) cloned from geminivirus-resistant pepper (Capsicum chinense Jacq. Line BG-3821) was characterized and the enzymatic activity of the expressed protein analyzed. The predicted protein consists of 203 amino acids, similar to other germin-like proteins. A highly conserved cupin domain and typical germin boxes, one of them containing three histidines and one glutamate, are also present in CchGLP. A signal peptide was predicted in the first 18 N-terminal amino acids, as well as one putative N-glycosylation site from residues 44–47. CchGLP was expressed in E. coli and the recombinant protein displayed manganese superoxide dismutase (Mn-SOD) activity. Molecular analysis showed that CchGLP is present in one copy in the C. chinense Jacq. genome and was induced in plants by ethylene (Et) and salicylic acid (SA) but not jasmonic acid (JA) applications in the absence of pathogens. Meanwhile, incompatible interactions with either Pepper golden mosaic virus (PepGMV) or Pepper huasteco yellow vein virus (PHYVV) caused local and systemic CchGLP induction in these geminivirus-resistant plants, but not in a susceptible accession. Compatible interactions with PHYVV, PepGMV and oomycete Phytophthora capsici did not induce CchGLP expression. Thus, these results indicate that CchGLP encodes a Mn-SOD, which is induced in the C. chinense geminivirus-resistant line BG-3821, likely using SA and Et signaling pathways during incompatible interactions with geminiviruses PepGMV and PHYVV.