Browsing by Author "Moola, Naadirah"

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    Open Access
    6-deoxy-6-amino chitosan: A plant defence priming biopolymer that enhances resistance against Botrytis cinerea in tomato and Fusarium verticillioides in maize
    (2024) Moola, Naadirah; Rafudeen, Mohamed; Jardine Mogamat
    Aminochitosan, derived from chitosan, features enhanced water solubility, and improved antifungal efficacy attributed to an additional amine group at the C-6 position, hinting at its superior antifungal potential compared to native chitosan. This PhD thesis aimed to explore the optimal concentration of aminochitosan and its molecular weight fractions for enhanced antifungal and priming properties in the tomato/Botrytis cinerea and maize/ Fusarium verticillioides pathosystems. In the B. cinerea pathosystem, various concentrations of aminochitosan were assessed for their antifungal effectiveness against B. cinerea growth and sporulation. Additionally, in planta studies were conducted to phenotype and quantify temporal stress responses using both qualitative and quantitative chlorophyll fluorescence imaging as well as DAB assays combined with microscopy. Despite batch-to-batch variations, aminochitosan consistently inhibited fungal growth and sporulation in a dose-dependent manner. In planta, aminochitosan pre-treatment induced robust defence responses in tomato leaves, resulting in a resistant phenotype that was mediated through a combination of enhanced photosynthetic efficiency as evidenced by enhanced Fv/Fm and chlorophyll content. The DAB assays suggested that these resistant phenotypes were also ROS-independent (H2O2 specifically) due to the strong positive impact of direct inhibition. The resistant phenotype and optimal efficacy of the aminochitosan MW fractions was observed at 3.5-15 kDa for antifungal efficacy and 15-20 kDa for in planta efficacy. Consequently, leaf senescence, hypersensitive responses and therefore necrosis were mitigated suggesting that aminochitosan primed defence responses in both mock and B. cinerea inoculated leaves. A temporal, label-free quantitative proteomic analysis revealed the differential priming of key molecular mechanisms underpinning aminochitosan primed states both with and without B. cinerea infection at 6 and 9 hpi in the tomato/B. cinerea pathosystem. Aminochitosan treatment (1 mg/mL) differentially regulated proteins as early as 6 hpi with some of the induced responses being sustained up to 9 hpi. Additionally, several proteins were oppositely regulated between aminochitosan pre-treatment and B. cinerea infection, indicating differential regulation patterns between the “primed state” and the “triggered state”. The proteomic data therefore partially validated the ‘priming' capacity of aminochitosan in 5- week-old tomato leaves, specifically diamino 3 when used as a foliar spray at a concentration of 1 mg/mL. The bimodal effects of aminochitosan in a maize/Fusarium verticillioides pathosystem were investigated by assessing the direct antifungal efficacy and elicitation of plant defence properties in planta. Aminochitosan displayed significant antifungal activity on both radial growth and sporulation at a minimum concentration of 1 mg/mL. Aminochitosan was also assessed in planta as preventative or curative treatments in maize seedlings infected with F. verticillioides at two time points. In the preventative treatment, salicylic acid accumulated during the early stages of infection (biotrophic phase) whereas in the curative treatment, jasmonic acid accumulated during the necrotrophic phase. In summary, we demonstrated that water-soluble aminochitosan possesses key properties that enable plant priming in addition to its superior direct antifungal activity compared to native chitosan. We also identified the optimal molecular weights and concentrations necessary for achieving maximum and 50% inhibition activity
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    Open Access
    Investigating the physiological and metabolomic effects of Ecklonia maxima-derived biostimulant foliar application in ameliorating the effects of heat shock in tomato plants
    (2025) Dladla, Unathi; Rafudeen, Mohamed Suhail; Farrant, Jill Margaret; Moola, Naadirah
    Tomato (Solanum Lycopersicum) is a globally popular horticultural commodity with great economic importance and is highly susceptible to heat shock and heat stress. Heat shock has evidenced detrimental effects on plant viability and growth, limiting crop productivity and quality. In addition to physical damage, structural damage to plant cell walls and membranes and the overproduction of reactive oxygen species (ROS) also cause metabolic and cellular disturbances. Concurrently, there has been a growing demand for sustainable and affordable agricultural practices using eco-friendly approaches to increase the heat tolerance of crops. Biostimulants are substances or microorganisms that help improve plant growth, yield, nutrient content and quality and can also enhance plant tolerance to different abiotic stresses either as stress priming agents or mitigating the stress directly. In South Africa, commercial biostimulant manufacture is focused on the brown algae (Phaeophyta), Ecklonia maxima (Osbeck) which grows and is harvested along the southern Atlantic coast of Africa. In this study, the aim was to assess and determine whether the prior foliar application of Ecklonia maxima-derived biostimulant on tomato plants could assist in improving the tolerance of tomato plants to subsequent heat shock stress. The focus was on the physiological, biochemical and metabolic responses of tomato plants treated with or without E. maxima-derived biostimulant and subject to heat shock stress. This was achieved through different plant physiological and biochemical approaches that include electrolyte leakage assay, chlorophyll fluorescence and photosynthetic pigment measurements, FRAP (ferric reducing antioxidant power) and DPPH (2,2-diphenyl1-picrylhydrazyl) measurements and lipid peroxidation and proline assays. In addition, changes in the primary metabolites of the treated tomatoes were measured using gas chromatography mass spectrometry (GC-MS) to further elucidate the metabolic pathways involved in the responses to the different treatments. From the findings, it was shown that a prior foliar application of E. maxima-derived biostimulant resulted in better photosynthetic efficiency and a decrease in the amount of electrolyte leakage from plant cells when subsequently exposed to heat shock stress compared to control plants without prior biostimulant application. This indicates improved cell membrane integrity and enhanced thermotolerance of E. maxima treated plants in response to heat shock stress. There was also a reduction in lipid peroxidation and proline content in heat shocked plants treated prior with E. maxima-derived biostimulant, indicating enhanced ROS scavenging and antioxidant systems in these biostimulant treated plants. The metabolic analysis of the shoots from heat shocked plants that were prior treated with E. maxima-derived biostimulant identified key sugars, organic acids and amino acids. These included phenylalanine, valine, proline, threonine, myo-inositol, citric acid, mannitol, and succinic acid. The identified primary metabolites are linked to the promotion of plant growth by increasing chlorophyll content and mitigate stress by assisting in reducing the levels of ROS in plants and improving the antioxidant defence system. This study showed that the E. maxima-derived biostimulant acts as a priming agent to enhance and protect photosynthesis while improving thermotolerance to heat shock stress by directly and/or indirectly enhancing antioxidant capacity in the plants.
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    Open Access
    Transcriptomic Analysis of a Susceptible African Maize Line to Fusarium verticillioides Infection
    (2020-08-28) Lambarey, Humaira; Moola, Naadirah; Veenstra, Amy; Murray, Shane; Suhail Rafudeen, Mohamed
    Maize (Zea mays L.) is a staple crop providing food security to millions of people in sub Saharan Africa. Fusarium verticillioides, an important fungal pathogen, infects maize causing ‘Fusarium Ear Rot’ disease, which decreases maize kernel yield and the quality of the crop harvested. Currently, no African maize line is completely resistant to infection by F. verticillioides. This study investigated an African maize line, Zea mays CML144, infected with F. verticillioides. Analysis of morphological characteristics showed significant differences between mock-infected and infected plants. RNA-sequencing (RNA-seq) was conducted on plants 14 days post-inoculation to identify differentially expressed genes (DEGs) involved in F. verticillioides infection. Analysis of RNA-seq data revealed DEGs that were both significantly up- and down-regulated in the infected samples compared to the mock-infected control. The maize TPS1 and cytochrome P450 genes were up-regulated, suggesting that kauralexins were involved in the CML144 defense response. This was substantiated by kauralexin analyses, which showed that kauralexins, belonging to class A and B, accumulated in infected maize tissue. Gene ontology terms relating to response to stimulus, chemical stimulus and carbohydrate metabolic processes were enriched, and the genes belonging to these GO-terms were down-regulated. Quantitative real-time PCR was performed on selected DEGs and measurement of phytoalexin accumulation validated the RNA-seq data and GO-analysis results. A comparison of DEGs from this study to DEGs found in F. verticillioides (ITEM 1744) infected susceptible (CO354) and resistant (CO441) maize genotypes in a previous study, matched 18 DEGs with 17 up-regulated and one down-regulated, respectively. This is the first transcriptomic study on the African maize line, CML144, in response to F. verticillioides infection.