Analytical study of ipomeamarone & chlorogenic acid alterations in sweet potato roots infected by Ceratocystis fimbriata

Metabolomic and Transcriptomic Analyses of Quality Deterioration in Fusarium solani-Infected Sweet Potato (Ipomoea batatas (L.) Lam cv Xinxiang) Storage Roots

Fusarium solani-induced quality deterioration in stored sweet potato is poorly characterized and understood. This study examined the effects of F. solani infection in Xinxiang sweet potato roots during storage. The results showed that while there were no external symptoms following F. solani infection, upon cutting the roots, the cut surface of the infected root rapidly turned black, whereas the untreated control roots remained unaffected. The metabolites and transcriptive differences between F. solani-infected and control sweet potato roots were investigated with high-performance liquid chromatography, metabolomic analysis, and an Illumina Novaseq platform. The results showed that levels of the toxic ipomeamarone accumulated as high as 2.36 mg/kg DW in tissue after F. solani inoculation and 6 days storage at 28 °C, where the control tissue sample did not accumulate any ipomeamarone. Metabolomic analysis showed that isochlorogenic acid and l-tyrosine significantly increased in the infected tissue and associated with the darkening cut surface of the infected sweet potato. In transcriptomic analysis, a total of 13, 14, and 6 key genes in ipomeamarone, isochlorogenic acid, and l-tyrosine biosynthesis pathways, respectively, were identified. A conceptual model elucidating the physiological and molecular mechanism of F. solani-induced quality deterioration in sweet potato is proposed.

Ceratocystis fimbriata Employs a Unique Infection Strategy Targeting Peltate Glandular Trichomes of Sweetpotato (Ipomoea batatas) Plants

The infection processes of Ceratocystis fimbriata BMPZ13 (BMPZ13) was elucidated on vegetative tissues of sweetpotato plants employing light and scanning electron microscopy. Vegetative tissues infected with C. fimbriata BMPZ13 by either wounding or nonwounding inoculation methods developed typical disease symptoms, establishing black rot in stems and necrosis on buds, young leaves, and stems of sprouts, in addition to wilt on leaves and shoot cuttings, typical of vascular associated diseases. The runner hyphae of C. fimbriata BMPZ13 formed from germinated conidia were able to directly penetrate the epidermal cuticle for initial infection and invade sweetpotato peltate glandular trichomes, specialized secretory structures to store and secrete metabolites. A two-step biotrophic phase was observed with nonwounding inoculation on leaves and stems, featuring both intercellular and intracellular invasive hyphae, with the latter found within living cells of the leaf epidermis. Subsequent to the biotrophic phase was a necrotrophic phase displaying cell death in infected leaves and veins. Additionally, this cell death was an iron-associated ferroptosis, supporting the notion that iron is involved in the necrotrophic phase of C. fimbriata BMPZ13 infection. Significantly, we establish that C. fimbriata employs a unique infection strategy: the targeting of peltate glandular trichomes. Collectively, our findings show that C. fimbriata is a plant fungal pathogen with a hemibiotrophic infection style in sweetpotato vegetative tissues.

Effect of coffee alkaloids and phenolics on egg-laying by the coffee leaf miner Leucoptera coffeella

The recognized importance of coffee alkaloids and phenolics mediating insect-plant interactions led to the present investigation aiming to test the hypothesis that the phenolics chlorogenic and caffeic acids and the alkaloid caffeine and some of its derivatives present in coffee leaves affect egg-laying by the coffee leaf miner Leucoptera (=Perileucoptera) coffeella (Guérin-Méneville & Perrottet) (Lepidoptera: Lyonetiidae), one of the main coffee pests in the Neotropical region. These phytochemicals were, therefore, quantified in leaves from 12 coffee genotypes and their effect on the egg-laying preference by the coffee leaf miner was assessed. Canonical variate analysis and partial canonical correlation provided evidence that increased leaf levels of caffeine favour egg-laying by the coffee leaf miner. An egg-laying preference bioassay was, therefore, carried out to specifically test this hypothesis using increasing caffeine concentrations sprayed on leaves of one of the coffee genotypes with the lowest level of this compound (i.e. Hybrid UFV 557-04 generated from a cross between Coffea racemosa Lour. and C. arabica L.). The results obtained allowed the recognition of a significant concentration-response relationship, providing support for the hypothesis that caffeine stimulates egg-laying by the coffee leaf miner in coffee leaves.

Nitrogen recycling during phenylpropanoid metabolism in sweet potato tubers

In the first step of the phenylpropanoid metabolic pathway, L-phenylalanine (L-Phe) is deaminated to form E-cinnamate, in a conversion catalyzed by phenylalanine ammonia-lyase (PAL; EC 4.3.1.5). The metabolic fate of the ammonium ion (NH4+) produced in this reaction was investigated in sweet potato (Ipomoea batatas) tuber discs. [15N]-Labeled substrates including L-Phe, in the presence or absence of specific enzyme inhibitors, were administered to sweet potato discs in light under aseptic conditions. 15N-Nuclear magnetic resonance spectroscopic analyses revealed that the 15NH4+ liberated during the PAL reaction is first incorporated into the amide nitrogen of L-glutamine (L-Gln) and then into L-glutamate (L-Glu). These results extend our previous observations in pine and potato that PAL-generated NH4+ is assimilated by the glutamine synthetase (GS; EC 6.3.1.2)/glutamate synthase (GOGAT; EC 1.4.1.13) pathway, with the NH4+ so formed ultimately being recycled back to L-Phe via L-Glu as aminoreceptor and donor.

Structure and characterization of a cDNA clone for phenylalanine ammonia-lyase from cut-injured roots of sweet potato

A cDNA clone for phenylalanine ammonia-lyase (PAL) induced in wounded sweet potato (Ipomoea batatas Lam.) root was obtained by immunoscreening a cDNA library. The protein produced in Escherichia coli cells containing the plasmid pPAL02 was indistinguishable from sweet potato PAL as judged by Ouchterlony double diffusion assays. The M(r) of its subunit was 77,000. The cells converted [(14)C]-l-phenylalanine into [(14)C]-t-cinnamic acid and PAL activity was detected in the homogenate of the cells. The activity was dependent on the presence of the pPAL02 plasmid DNA. The nucleotide sequence of the cDNA contained a 2121-base pair (bp) open-reading frame capable of coding for a polypeptide with 707 amino acids (M(r) 77, 137), a 22-bp 5'-noncoding region and a 207-bp 3'-noncoding region. The results suggest that the insert DNA fully encoded the amino acid sequence for sweet potato PAL that is induced by wounding. Comparison of the deduced amino acid sequence with that of a PAL cDNA fragment from Phaseolus vulgaris revealed 78.9% homology. The sequence from amino acid residues 258 to 494 was highly conserved, showing 90.7% homology.

Toxicants in plants and plant products

Toxicants are widely distributed in plants and plant products, including intentionally added, incidentally added, and naturally occurring food toxicants. This review covers the toxicity of some food additives: the distribution, residues, toxicity, and methods of removal of some pesticides and toxic metals; and the presence of naturally occurring toxicants in plants and plant products. Extensive review has been done, particularly on natural toxicants. However, there are still extensive gaps in our knowledge pertaining to effect upon the health of many of the substances known to be present in natural plant food products, as well as even the identity of many natural chemical components of plant foods and their potential toxicological significance. An understanding of their presence, formation, and toxicity is important as far as public health is concerned.

Dehydroipomeamarone as an Intermediate in the Biosynthesis of Ipomeamarone, a Phytoalexin from Sweet Potato Root Infected with Ceratocystis fimbriata

Recently, we isolated dehydroipomeamarone, a new sesquiterpenoid from sweet potato (Ipomoea batatas Lam.) root tissue infected with Ceratocystis fimbriata (Ell. et Halst.). The purpose of this investigation was to determine whether dehydroipomeamarone was a precursor in the biosynthetic pathway of ipomeamarone. The incorporation of acetate-2-(14)C into ipomeamarone was markedly inhibited by the presence of dehydroipomeamarone. Radioactive dehydroipomeamarone was efficiently converted into ipomeamarone, and the compound was biosynthesized earlier than ipomeamarone according to a time course analysis of the production of the terpenoid. These results support the notion that dehydroipomeamarone is an immediate precursor of ipomeamarone. On the other hand, the production of ipomeamarone was slightly lessened in the presence of dehydroipomeamarone. Thus, the marked reduction of acetate-2-(14)C incorporation into ipomeamarone by dehydroipomeamarone may result from both isotopic dilution and an inhibitory effect by exogenous dehydroipomeamarone.

De novo synthesis of peroxidase isozymes in sweet potato slices

The peroxidase content of sweet potato slices (Ipomoea batatas Lam.) increased nearly 100-fold following 84 hours incubation in an air atmosphere containing ethylene, 1 microliter per liter. The object of experiments reported here is to determine if this increase in peroxidase activity results from synthesis de novo of the enzyme or from activation of a preexisting inactive form of the enzyme.The enzymatic activity of each peroxidase isozyme increased during the incubation period, and each peroxidase isozyme appeared to incorporate (14)C-leucine. Polyacrylamide gel electrophoresis of the neutral peroxidase fraction showed that all peroxidase activity and essentially all radioactivity migrated as a single superimposable band. The other peroxidase fractions were less pure. Treatment of fresh slices, or slices collected midway in the time course with the inhibitor of protein synthesis, blasticidin S, (1 microgram per milliliter for one minute) caused an abrupt cessation of peroxidase formation and simultaneously an abrupt cessation of incorporation of (14)C-leucine into peroxidase isozymes. These observations indicate that the rapid increase in peroxidase activity in sweet potato slices results from synthesis de novo of the enzyme.