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Black Sigatoka is a disease that occurs in banana plantations worldwide. This disease is caused by the hemibiotrophic fungus Pseudocercospora fijiensis, whose infection results in a significant reduction in both product quality and yield. Therefore, detection and identification in the early stages of this pathogen in plants could help minimize losses, as well as prevent the spread of the disease to neighboring cultures. To achieve this, a highly sensitive SPR immunosensor was developed to detect P. fijiensis in real samples of leaf extracts in early stages of the disease. A polyclonal antibody (anti-HF1), produced against HF1 (cell wall protein of P. fijiensis) was covalently immobilized on a gold-coated chip via a mixed self-assembled monolayer (SAM) of alkanethiols using the EDC/NHS method. The analytical parameters of the biosensor were established, obtaining a limit of detection of 11.7 µg mL−1, a sensitivity of 0.0021 units of reflectance per ng mL−1 and a linear response range for the antigen from 39.1 to 122 µg mL−1. No matrix effects were observed during the measurements of real leaf banana extracts by the immunosensor. To the best of our knowledge, this is the first research into the development of an SPR biosensor for the detection of P. fijiensis, which demonstrates its potential as an alternative analytical tool for in-field monitoring of black Sigatoka disease.

Catharanthus roseus cell cultures were exposed to different conditions in order to induce alkaloid metabolism. The exposure to jasmonate and fungal elicitors resulted in the transcriptional activation of tryptophan decarboxylase and in the accumulation of the monoterpenoid indole alkaloids ajmalicine and catharanthine, but not of vindoline. The inability of the cell cultures to produce vindoline was related to a lack of expression of the desacetoxyvindoline 4-hydroxylase (D4h) gene. Southern blot analysis revealed that D4h gene was not lost in the cell cultures.

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Amino acids, a major fraction of the low-molecular-weight organic nitrogen in soil, act as signaling molecules that indicate the presence of nutrient-rich patches to the roots. To characterize the effects of amino acids on root growth, we used seedlings of habanero pepper (Capsicum chinense), one of the most widely cultivated annual spice crops in the world. We tested the effect of L-glutamate, L-aspartate, and glycine on the primary root of seedlings grown aseptically under different conditions of pH and light. L-glutamate and L-aspartate did not inhibit the root growth of habanero pepper. In contrast, glycine inhibited the growth of roots, stimulated root hair growth, and induced a significant accumulation of starch grains in the root apex. The use of aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis, and the evaluation of 1-aminocyclopropane-1-carboxylic acid oxidase expression provided evidence of a role for ethylene in the root responses to glycine. We suggest that these changes in the root apex in response to exogenous glycine could be an important adaptive response that allows plants to efficiently access the fluctuating availability of nutrients in the soil.

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