Phenolic metabolism in root slices of selected carrot cultivars

Carrot root slices, stored for 4 days at 20 °C reacted with a strong accumulation of total phenols, especially chlorogenic acid. A significant accumulation of isocoumarin content within the peel was observed in stored slices. Synthesis of phenols was accompanied by an increase in phenylalanine ammonia lyase activity, wound induced respiration and ethylene production. The great variability among the studied four cultivars was found concerning isocoumarin synthesis, PAL activity, respiration rate and ethylene evolution, but less distinct in the case of chlorogenic acid accumulation. The carrot slices obtained from freshly harvested roots were more sensitive to mechanical damage and short-term storage than those prepared from roots previously stored.     

The mechanism of changes in respiratory activity during callus formation in carrot root slices cultured in vitro

The rates of both O₂ uptake in air and CO₂ output in N₂ perprotein nitrogen and per cell increased markedly during thelag phase of callus formation, and decreased rapidly then graduallyduring the exponential and subsequent phases in carrot-rootphloem slices cultured in vitro. Rates of ¹⁴CO₂ output fromlabeled citrate and succinate supplied to the slices changedsimilarly. Respiration of the cultured slices became more sensitiveto fluoride and cyanide during the lag phase and less sensitiveduring the exponential phase. These results suggest that activitiesof both the glycolytic pathway and the TCA cycle rise duringthe lag phase and decline during the exponential one. The activities per protein nitrogen of the glycolytic enzymes,hexokinase, phosphoglucose isomerase, phosphofructokinase, aldolaseand pyruvate kinase remarkably increased during the lag phaseafter a little decline in the first day of culture, and decreasedas the callus developed. A similar pattern of change was observedin the number and the respiratory activity of mitochondria percell. It was concluded, therefore, that changes in respiratoryactivity during callus formation may depend mainly on changesin capacity of the respiratory machinery, although the increasein respiratory activity at the beginning of culture may be dueto some other mechanism, such as an increase in the turnoverrate of ATP. (Received May 11, 1972; )     

Effects of ethylene biosynthesis in carrot root slices on 6-methoxymellein accumulation and resistance to Botrytis cinerea

The role of ethylene biosynthesis in the resistance response of carrot ( Daucus carota L., cv. Chantenay red-cored) slices to infection by Botrytis cinerea Pers. ex Pers. was investigated using aminoethoxyvinylglycine (AVG) and inhibitor of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (EC 4.4.1.-), and norbornadiene, an inhibitor of ethylene binding. Carrot slices became susceptible to a normally non-invasive level (10⁵ ml^-1) of spores of B. cinerea after treatment with AVG. ACC partially reversed the susceptibility induced by AVG. The ability of a crude pectic enzyme preparation from B. cinerea to induce resistance to a normally invasive level of B. cinerea spores (10⁶ ml^-1) was prevented by AVG. Accumulation of the carrot phyto-alexin 6-methoxymellein (6-MM) was prevented by norbornadiene, but it had no effect on the resistance response. An event associated with ethylene biosynthesis other than 6-MM accumulation appears to be responsible for the resistance of carrot slices to infection by B. cinerea.     

Control of barley root respiration

Evidence from barley [ Hordeum distichum (L.) Lam. cv. Maris Mink], and from many other species, suggests that respiration is controlled by either supply of carbohydrate or demand for ATP. The relationship between root respiration rate (measured as O₂ consumption or CO₂ production) and ethanol-soluble carbohydrate content altered with time following selective pruning, and the change could not be accounted for by buffering of the cytoplasmic carbohydrate concentration by sugars in the vacuole. Exogenous sucrose supplied to the roots prevented any decline of the respiration rate in shoot-pruned plants, and if supplied for 24 h stimulated the respiration rate after any treatment. Root extension responded to sucrose in a similar manner. We suggest that respiration is under fine control by adenylates, but the capacity of the respiratory system is fixed by the supply of sucrose, possibly via coarse control of the respiratory machinery, or of the processes requiring metabolic energy.     

Biosynthesis of phytoalexin in carrot root requires ethylene action

The role of ethylene in phytoalexin production by carrot ( Daucus carota L.) roots was investigated using the ethylene action inhibitor 1-methylcyclopropene (MCP). Exposure of carrot roots to ethylene, UV-B irradiation, inoculation with fungal pathogens, treatment with 2,4-D or methyl jasmonate induced accumulation of the phytoalexin 6-methoxymellin (6-ME). Exposure to MCP for 4–12 h prior to the treatments completely inhibited 6-ME accumulation, indicating that 6-ME synthesis by carrot roots requires ethylene action.     

Secretion kinetics of hydroxyproline-containing macromolecules in carrot root discs

Short-term pulse-chase studies using radioactive L-proline on carrot tissue support the classical endomembrane route for secretory proteins. Labelled hydroxyproline residues were first detectable in fractions containing the endoplasmic reticulum (ER) after a 5 min pulse. Upon chase-out this fraction looses and, initially, the Golgi apparatus (GA) fraction gains radioactivity. Unlike ER and GA fractions which show chase-out characteristics a plasma membrane (PM) containing-fraction reveals retention of some of the radioactivity.     

Differential control of ethylene-induced gene expression and respiration in carrot roots

Ethylene treatment of carrot roots elicits a developmental program encompassing an increase in respiration rate and changes in gene expression. Both phenomena are potentiated when ethylene is administered in O₂. Our previous studies showed that both respiration and a number of ethylene specific mRNAs increase together in response to ethylene through some 21 hours, whereas thereafter respiration continues to rise, while the level of induced mRNAs drops. Herein we ask whether an experimentally effected drop in the respiration rate within the first 21 hours caused by the withdrawal of ethylene, or substitution of air for O₂ in the continued presence of ethylene, is linked to a drop in the level of ethylene-induced mRNA. Quantitative estimation of two ethylene evoked mRNAs by dot blot hybridization with appropriate cDNA clones has shown that under the specified treatment the induced mRNA levels remain constant while the respiration rate drops, suggesting that gene expression, as reflected in induced mRNA levels, and respiration rate are separately regulated facets of the ethylene response.     

Cytosine-rich messenger RNA from carrot root discs

The total poly A⁺ RNA from aerated carrot root discs was further fractionated into a cytosine-rich mRNA fraction by oligo (dG) cellulose chromatography. C-rich mRNA was purified at least 10-fold by this procedure and, when translated in wheat germ lysates, codes for 57 and 53 Kdalton peptides. Translation in double label amino acid mixtures indicates that C-rich mRNA codes for proline-rich peptides which may be precursors to the hydroxyproline-rich glycoprotein synthesized $\text{in}\text{vivo}$ by this tissue.