An Explanation for the Difference in Photosynthetic Capabilities of Healthy and Beet Yellows Virus-infected Sugar Beets (Beta vulgaris L.)

Sugar beets (Beta vulgaris L.) infected with the Beet Yellows Virus exhibit lower rates of net photosynthesis at light saturation than do healthy plants. These Pn reductions were correlated with increases in leaf resistance to water vapor loss. Theoretical analyses demonstrated that, although the leaf resistance to water vapor loss increases could account for a major part of the net photosynthesis decreases, some other aspect of leaf functioning also was debilitated by infection. Both the levels and the activities of ribulose-1, 5-diP carboxylase were less on a leaf area basis in extracts from infected leaves than from healthy ones. Soluble carbohydrates accumulate in Beet Yellows Virus-infected leaves, but inhibiting translocation in several ways provided no evidence in support of the hypothesis that the accumulation of photosynthates in leaves has a direct, short term, feed-back effect upon the photosynthetic rate.     

Isozyme profiles associated with the hypersensitive response of Chenopodium foetidum to plum pox virus infection

Isozyme profiles of esterases (E.C. 3.1.1.1), glutamate oxaloacetate transaminase (E.C. 2.6.1.1) and peroxidases (E.C. 1.11.1.7) have been determined in healthy tissues of Chenopodium foetidum as well as their modifications during leaf development. The effect of plum pox virus infection on the isozyme profiles has also been studied. Virus-induced necrotic lesions displayed a peroxidase (POX) pattern that has not been found in any other tissue of the plant so far analyzed. The pattern was similar to that of old yellow leaves, except that POX-B, which was detected in the necrotic lesions, has not been detected in any developmental stage of healthy leaves. Changes in the peroxidase profile seem to begin early during infection, even before necrosis is visible. We suggest that senescence is established at necrotic lesions extending from there to the rest of the infected leaf affecting the peroxidase isozyme pattern. However, other changes, which induce POX-B, must also take place at necrotic lesions. These do not extend to the rest of the infected leaves. Plum pox virus infection has less effect on the glutamate oxaloacetate transaminase and esterase isozyme patterns, inducing an almost normal senescence pattern.     

The effect of Albugo Candida (white blister rust) on the photosynthetic and carbohydrate metabolism of leaves of Arabidopsis thaliana

Albugo candida (pers.) O. Kuntze (white blister rust) is a biotrophic fungus which infects cruciferous plants including Arabidopsis thaliana (L) Heynh. We report the effect of this pathogen on the photosynthetic and carbohydrate metabolism of A. thaliana. As infection progressed A. Candida caused a reduction in the rate of photosynthesis when measured at either ambient or saturating concentrations of CO₂. These data suggested that both chlorophyll and Rubisco were lost from regions of infected leaves, and measurements of chlorophyll, Rubisco content and activity supported these observations. The reduction in the rate of photosynthesis was not caused by closure of stomata as transpiration was unaffected by the disease. Infected leaves accumulated both soluble carbohydrates and starch. The activities of sucrose-phosphate synthase, sucrose synthase and ADP glucose pyrophosphorylase did not change in response to infection. However, the activities of both the wall-bound and soluble acid invertases were higher in infected leaves than in controls; a new soluble invertase isoform with a pl of 5-1 appeared in infected leaves. The possible origin of the increase in wall-bound and soluble invertase activities and its effect on the carbohydrate and photosynthetic metabolism of the leaf are discussed.     

Inducible malondialdehyde pools in zones of cell proliferation and developing tissues in Arabidopsis

Malondialdehyde (MDA) is a natural and widespread genotoxin. Given its potentially deleterious effects, it is of interest to establish the identities of the cell types containing this aldehyde. We used in situ chemical trapping with 2-thiobarbituric acid and mass spectrometry with a deuterated standard to characterize MDA pools in the vegetative phase in Arabidopsis thaliana. In leaves, MDA occurred predominantly in the intracellular compartment of mesophyll cells and was enriched in chloroplasts where it was derived primarily from triunsaturated fatty acids (TFAs). High levels of MDA (most of which was unbound) were found within dividing cells in the root tip cell proliferation zone. The bulk of this MDA did not originate from TFAs. We confirmed the localization of MDA in transversal root sections. In addition to MDA in proliferating cells near the root tip we found evidence for the presence of MDA in pericyle cells. Remodeling of non-TFA-derived MDA pools occurred when seedlings were infected with the fungus Botrytis cinerea. Treatment of uninfected seedlings with mediators of plant stress responses (jasmonic acid or salicylic acid) increased seedling MDA levels over 20-fold. In summary, major pools of MDA are associated with cell division foci containing stem cells. The aldehyde is pathogen-inducible in these regions and its levels are increased by cellular mediators that impact defense and growth.     

Biochemical changes during the development of witches' broom: the most important disease of cocoa in Brazil caused by Crinipellis perniciosa

Witches' broom disease (WBD) is caused by the hemibiotrophic basidiomycete fungus Crinipellis perniciosa, which is one of the most important diseases of cocoa in the western hemisphere. In this study, the contents of soluble sugars, amino acids, alkaloids, ethylene, phenolics, tannins, flavonoids, pigments, malondialdehyde (MDA), glycerol, and fatty acids were analysed in cocoa (Theobroma cacao) shoots during the infection and development of WBD. Alterations were observed in the content of soluble sugars (sucrose, glucose, and fructose), asparagine and alkaloids (caffeine and theobromine), ethylene, and tannins. Ethylene and tannins increased prior to symptom development and declined with the death of the infected tissues. Furthermore, MDA and glycerol concentrations were higher in infected tissue than in the controls, while fatty acid composition changed in the infected tissues. Chlorophylls a and b were lower throughout the development of the disease while carotenoids and xanthophylls dropped in the infected tissue by the time of symptom development. These results show co-ordinated biochemical alterations in the infected tissues, indicating major stress responses with the production of ethylene. Ethylene levels are hypothesized to play a key role in broom development. Some of the other biochemical alterations are directly associated with ethylene synthesis and may be important for the modification of its effect on the infected tissues.     

Systemic Responses in Arabidopsis thaliana Infected and Challenged with Pseudomonas syringae pv syringae

Attack of plants by necrotizing pathogens leads to acquired resistance to the same or other pathogens in tissues adjacent to or remotely located from the site of initial attack. We have used Arabidopsis thaliana inoculated with the incompatible pathogen Pseudomonas syringae pv syringae on the lower leaves to test the induction of systemic reactions. When plants were challenged with Pseudomonas syringae pv syringae in the upper leaves, bacterial titers remained stable in those preinfected on the lower leaves. However, there was a distinct decrease in symptoms that correlated with a local and systemic increase in salicylic acid (SA) and in chitinase activity. Peroxidase activity only increased at the site of infection. No changes in catalase activity were observed, either at the local or at the systemic level. No inhibition of catalase could be detected in tissue in which the endogenous levels of SA were elevated either naturally (after infection) or artificially (after feeding SA to the roots). The activity of catalase in homogenates of A. thaliana leaves could not be inhibited in vitro by SA. SA accumulation was induced by H2O2 in leaves, suggesting a link between H2O2 from the oxidative burst commonly observed during the hypersensitive reaction and the induction of a putative signaling molecule leading to system acquired resistance.     

THE RESPIRATION OF TOBACCO LEAVES AFTER SYSTEMIC INFECTION WITH TOBACCO MOSAIC VIRUS

The rate of CO, production per g. dry matter of the younger leaves of tobacco plants systemically infected with tobacco mosaic virus was about 10 yo less than that of comparable healthy leaves. Older infected leaves, showing well-developed mosaic symptoms, had the same respiration rate as comparable healthy leaves. These results were independent of seasonal change in light conditions during the growth of the plants. Older leaves, but not younger leaves, of infected plants had a lower initial water content, and both absorbed less water during the experimental period, than leaves from healthy plants. The effects of TMV infection on water content were so great that the rate of CO, production per g. fresh weight was sometimes significantly increased by infection. This reversal of the apparent effect of infection on respiration rate, depending on the basis of reference may partly account for contradictory results reported previously by other workers. Other causes for contradictory results are discussed.     

Carbohydrate Metabolism and Translocation in Healthy and Cocoa Swollen Shoot Virus-Infected Cocoa Plants

Analyses of cocoa swollen shoot virus-infected and healthy cocoa (Theobroma cacao L.) plant tissues were made to determine the effect of virus infection on the metabolism and transport of carbohydrates in affected plants. Starch, sucrose and reducing sugars were found to accumulate in infected tissues. Translocation of photosynthates (mainly as sucrose) to the stem and root system, as estimated by the overnight loss of carbohydrates from the leaves and by ¹⁴CO₂ tracer experiments, was as efficient in the infected plants as in the healthy. Infected plants showed a higher diurnal turnover of carbohydrates in their leaves and, on unit leaf area basis, higher levels of ¹⁴C-labelled assimilates suggesting that they have a greater photosynthetic capacity than the healthy plants. The rate of respiration, as determined by the proportions of organic acids, amino acids and other intermediary metabolites formed from translocated ¹⁴C-labelled sugars, was generally higher in infected than in healthy plants. It is concluded from available data showing the presence in infected tissues of mineral nutrients, protein N and amino acids at the same concentrations as in healthy plants, and from the relatively high rates of photosynthesis and respiration that a high rate of metabolic activity is maintained in the host-virus system. Some factors possibly contributing to the stunted growth of infected plants are discussed in the light of these findings.     

Powdery mildew infection of wheat leaves changes host solute transport and invertase activity

The effect of powdery mildew ( Blumeria graminis ) infection of wheat leaves on solute transport and invertase activity of the host tissue has been examined. Sugars (glucose, sucrose, maltose) and amino acids (glutamine, histidine) were taken up by leaf pieces, and radioactivity was transferred to the fungal mycelium. Infection had a marked effect on sugar uptake, particularly for glucose which was taken up into infected tissue at considerably higher rates than into uninfected tissues. In contrast, amino acid uptake rates into infected tissues were lower when compared with those into uninfected tissue. The increase in glucose uptake could be correlated with a change in sugar transporter gene expression as a wheat homologue of the monosaccharide carrier AtSTP4 was shown to increase in infected tissue. Efflux analysis showed a higher leakage of preloaded glucose from infected leaves in comparison with uninfected tissue and transfer to the mycelium was greater for glucose than for the other solutes measured. All types of invertase, measured enzymatically, showed an increase in infected tissue, with the highest proportional increase observed for cell-wall invertase. A partial-length complementary DNA, TaINV2 , was isolated for a putative cell-wall invertase; expression studies indicated that levels for this or related sequences increased substantially 3 days after infection.     

Peroxidase Activity and Isoperoxidase Pattern in Tobacco Leaves Infected with Tobacco Necrosis Virus and Other Viruses Inducing Necrotic and Non-Necrotic Alterations

The level of peroxidase activity was greatly enhanced in tobacco leaves infected by tobacco necrosis virus (TNV) and other viruses which induce necrotic symptoms (TMV, ToMV and PVY^N). The intensity was related to the age of the leaves infected: absent or neglible in mature leaves and very pronounced in young growing infected leaves. On the contrary, changes in peroxidase activity were negligible when the infection was provoked by viruses which do not produce necrotic reactions (TMV and PVY^O). Analysis of the peroxidase isoenzymes, pattern in tobacco leaves infected by TNV and other necrosis-inducing viruses revealed in all cases, a slight increase in anionic (pl 3.5–3.7) and a considerable increase in moderately anionic isoenzymes particularly the pl 4.6 isoenzyme which in TNV and PVY^N-infected leaves reached levels up to 21 and 72 times the healthy control values. A considerable increase in the cationic (pl9.3–8.8) isoenzymes and the appearance of one moderately cationic isoenzyme (pl 8.2) was also detected. In leaf extracts from-virus-infected tobacco leaves with nonnecrotic response, no, or negligible alterations on the isoenzyme pattern were detected. However, infection by a fungal parasite (Erisyphe cichoracearum), which established a fully compatible, non-necrotic, interaction with tobacco leaves, like the necrosis-inducing viruses, changed the isoperoxidase pattern. The data suggest the necrotic alterations and associated changes in the peroxidase activity and isoperoxidase pattern in virus-infected leaves are not clearly related.     

Tobacco-mosaic-virus-induced increase in abscisic-acid concentration in tobacco leaves:

The concentrations of free and bound abscisic acid (ABA and the presumed ABA glucose ester) increased three- to fourfold in leaves of White Burley tobacco (Nicotiana tabacum L.) systemically infected with tobacco mosaic virus. Infected leaves developed a distinct mosaic of light-green and dark-green areas. The largest increases in both free and bound ABA occurred in dark-green areas. In contrast, virus accumulated to a much higher concentration in light-green tissue. Free ABA in healthy leaves was contained predominantly within the chloroplasts while the majority of bound ABA was present in non-chloroplastic fractions. Chloroplasts from light-green or dark-green tissues were able to increase stromal pH on illumination by an amount similar to chloroplasts from healthy leaf. It is unlikely therefore that any virus-induced diminution of pH gradient is responsible for increased ABA accumulation. Tobacco mosaic virus infection had little effect on free ABA concentration in chloroplasts; the virus-induced increase in free ABA occurred predominantly out-side the chloroplast. The proportional distribution of bound ABA in the cell was not changed by infection. Treatment of healthy plants with ABA or water stress increased chlorophyll concentration by an amount similar to that induced by infection in dark-green areas of leaf. A role for increased ABA concentration in the development of mosaic symptoms is suggested.Abbreviations ABA abscisic acid - TMV tobacco mosaic virus     

旋毛虫病鼠心肌及血清氧自由基变化的实验观察

观察小鼠感染旋毛虫后不同时期的心肌及血清中NOS、CAT、MDA及GSH-PX 4个检测指标的变化,以期从发病学角度分析氧化酶类在旋毛虫病的发生发展中所起的作用。结果显示：小鼠心肌中的NOS、CAT、MDA和GSH-PX 4个检测指标在感染旋毛虫后的不同时期（7-28d)呈现出明显不同的变化。心肌及血液中的MDA在感染过程中一直维持较高水平,而GSH-PX及CAT含量则显著减少。实验结果提示：旋毛虫可诱发氧自由基对心肌产生氧化损伤、氧化代谢产物的堆积及抗氧化能力的改变,这些因素可能是旋毛虫性心肌炎的形成原因。     

Metabolic regulation in diseased leaves. I. The respiratory rise in barley leaves infected with powdery mildew

Photosynthetic and respiratory activities have been measured in leaves of Hordeum vulgare L. var. Manchuria (barley) after infection with Erysiphe graminis var. hordei (powdery mildew). Two isogenic lines, one resistant to infection and the other highly susceptible, were examined.

These isogenic lines showed very different physiological responses following infection. Photosynthesis and the chlorophyll content of resistant leaves was unaffected by infection. Respiration increased slightly and this was accompanied by small increases in activities of enzymes of glycolysis, the pentose-P pathway and the tricarboxylic acid cycle.

The infection of susceptible leaves resulted in a slight increase in photosynthesis 48 hours after inoculation, but subsequently there was a progressive decrease in the photosynthesis of these leaves compared with that of noninfected leaves. The capacity of infected leaves for partial reactions of photosynthesis such as the Hill reaction and the photoreduction of nicotinamide adenine dinucleotide phosphate (NADP¹) decreased during the later stages of infection. The levels of chlorophyll, NADPH-diaphorase and aldolase also declined. There was no detectable difference in the respiration of infected and noninfected leaves until 48 hours after inoculation. After this time, the infected leaves showed a higher respiration, the maximum difference occurring about 144 hours after inoculation. The respiratory increase was not accompanied by significant changes in the levels of enzymes of glycolysis and the tricarboxylic acid cycle with the exception of malate dehydrogenase which was lower in infected leaves. In contrast, the activities of glucose-6-P dehydrogenase and 6-P-gluconate dehydrogenase showed changes similar to that observed for respiration.

The respiration and the activities of glucose-6-P dehydrogenase and 6-P-gluconate dehydrogenase did not increase in infected leaves of etiolated plants, even when excellent growth of the fungus was established by growing the plants in White's basal medium supplemented with sucrose. The respiration of a susceptible mutant barley (the yellow-green virescent mutant of the variety Himalaya) when grown in the light at 11° was not changed by infection although the characteristic respiratory rise occurred in plants grown at 15°. At the lower temperature chloroplasts fail to develop in this mutant, although development is normal at 15°.

It is suggested that the pathogen is not directly responsible for the increase in respiration in green leaves, rather that this is a response in the host cells to a loss of photosynthetic capacity.

     

Modification of the phosphite induced resistance response in leaves of cowpea infected with Phytophthora cryptogea by α-aminooxyacetate

Treatment of detached cowpea leaves with phosphite, the active breakdown product in plant tissues of fosetyl-Al, leads to the cessation of growth of Phytophthora cryptogea within 24 h of inoculation. Pretreatment of leaves with α-aminooxyacetate (AOA), an inhibitor of the phenylpropanoid pathway, increases the size of lesions in phosphite treated leaves and induces a complete susceptibility at 5 mM. By 24 h after inoculation, phenylalanine ammonia-lyase (PAL) activity is higher in phosphite treated leaves than in untreated leaves. The effects of AOA on PAL activity are paralleled with the effects of the increase of the spread of infection. AOA treatment does not affect phosphite uptake by fungal cells and leaf tissues, while it inhibits kievitone and phaseollidin accumulation in infected treated leaves and causes a reduction in extractable PAL activity. These results suggest that cessation of fungal growth in vivo is not as a result of a direct effect of phosphite on the fungus and strongly support a role of the host defence reactions in the mode of action of phosphite.