The activity of antioxidative enzymes,contents of H<Subscript>2</Subscript>O<Subscript>2</Subscript> and of ascorbate in tomato leaves of cultivars more or less sensitive to infection with <Emphasis Type="Italic">Botrytis cinerea</Emphasis>

The aim of the present studies was to compare H₂O₂ and ascorbate contents as well as peroxidase (PO) and catalase (CAT) activities in leaves of less susceptible cultivar Perkoz and more susceptible Corindo after B. cinerea infection. Increase in H₂O₂ contents in both Perkoz and Corindo cytosol was observed, however, it appeared earlier in the less susceptible cultivar. The increase in PO activity in the cytosol fraction was observed 48 hours after infection in both cultivars but it was greater in the less susceptible Perkoz. No significant differences between the tested cultivars were observed in ascorbate peroxidase (APX) activity and in reduced and oxidated ascorbate contents. PO activity was thoroughly analyzed in the apoplast fraction. It was measured with syringaldazine (S), tetramethylbenzidine (TMB) and ferulic acid (FA)—substrates characteristic of isoenzymes involved in lignification and stiffening of a cell wall. Increase in PO activity with these substrates was observed earlier in cultivar Perkoz than in cultivar Corindo. Similarly, increase in PO activity with NADH appeared significantly earlier in cultivar Perkoz. Apoplastic PO was separated with DEAE Sepharose and two fractions binding and non-binding were obtained. Binding PO fraction was significantly more active especially with S, TMB and NADH after B. cinerea infection. The increase in the enzyme activity was mostly observed in cultivar Perkoz. Binding PO was separated by electrophoresis on acrylamide gel and revealed six enzymatic forms from which three were much more active after infection in cultivar Perkoz. The obtained results suggest that cell wall strengthening mediated by apoplast PO is a key factor responsible for different resistance of tomato cultivars Perkoz and Corindo to B. cinerea infection.     

Synergistic effect of auxins and polyamines in hairy roots of <Emphasis Type="Italic">Cichorium intybus</Emphasis> L. during growth,coumarin production and morphogenesis

Hairy roots of Cichorium intybus obtained by infecting with different Agrobacterium rhizogenes strains (LMG-150 and A20/83) were studied for total endogenous indole-3-acetic acid (IAA) levels and indole-3-acetic acid oxidase (IAAO) activity. The roots initiated by LMG- 150 showed higher endogenous IAA levels as well as IAAO activity as compared to the roots from A20/83. Coumarin production in roots obtained by both of these strains strictly correlated with growth, with higher content in the roots obtained by LMG- 150. Moreover roots from LMG-150 showed increased growth index, length of primary roots and number of secondary and tertiary roots. The roots derived from LMG-150 were studied for total endogenous IAA and IAAO activity under the exogenous administration of polyamines and fungal elicitors. The treatment with putrescine (Put) at 1.5 mM level showed maximum endogenous IAA levels and IAAO activity as compared to the control and other polyamine administration, it also supported faster growth in terms of biomass accumulation, and total coumarin production. Of the various treatments, mycelial extract (ME) and culture media filtrate (CMF) of Pythium aphanidermatum and Phytopthora parasitica var. nicotiana, the treatment with 1 % CMF of P. parasitica var. nicotiana, resulted in maximum IAA levels and IAAO activity, which was supported by maximum biomass, coumarin production as compared to the control and other elicitor treatments. Two different regenerants of chicory obtained through A. rhizogenes LMG-150 designated as T-I and T-II, were studied for total endogenous IAA levels and IAAO activity. T-II showed higher titers of IAA with higher activity of IAAO as compared to T-I. Endogenous titer of IAA and IAAO activity was found to be maximum in transformed roots as compared to T-I, T-II, normal roots and normal plants. Our work showed a variation in endogenous auxin levels in these transformed plants. There exists a synergistic effect of endogenous IAA titers and polyamines in regulating root morphogenesis. Fungal elicitors influenced growth and coumarin production and an elicitor preparation of 1 % CMF of P. parasitica var. nicotiana gave spontaneous regeneration of shoots. The implications of these results are discussed.     

Physiology of Rice Tungro Virus Disease: Increased Cytokinin Activity in Tungro-Infected Rice Cultivars

Tungro virus infection decreased the chlorophyll content in the susceptible rice (Oryza sativa) cultivar ‘Taichung Native 1’, while it increased the pigment in the less-susceptible cultivar ‘IR 20’ during the later stages of infection. The virus was recovered from the infected susceptibile cultivar as early as 3 days after inoculation. Relatively low amounts of virus were recovered from the less-susceptible cultivar between 12 and 30 days after inoculation. The senescence of detached leaves of virus-infected less-susceptible cultivar incubated in water in darkness was considerably delayed compared to healthy leaves. The cytokinin activity in the extracts from inoculated less-susceptible cultivar was 69% higher than in the extracts from the healthy plants.     

Correlation of cytological and biochemical parameters with resistance and tolerance to Mycosphaerella graminicola in wheat

This study investigated the infection process of Mycosphaerella graminicola and enzyme activities related to reactive oxygen species (ROS) or oxylipin biosynthesis in four French wheat cultivars with variable resistance to M.?graminicola infection. At field level, cultivars Caphorn, Maxyl and Gen11 were susceptible, whereas Capnor showed high levels of quantitative resistance. Moreover, Capnor and Gen11 were tolerant, i.e., their yield was less affected by infection compared to non-tolerant Maxyl and Caphorn. These four cultivars were inoculated under laboratory conditions with the M.?graminicola IPO323 reference strain. Cytological and biochemical responses were studied on collected first plantlet leaves and several features discriminated between cultivars. However, resistance and tolerance had no impact on the fungal infection process. Levels of lipoxygenase (LOX), peroxidase (PO) and glutathione-S-transferase (GST) activities were also compared with regard to cultivar resistance or tolerance to M.?graminicola. LOX, PO and GST activities did not discriminate resistance and tolerance profiles, although a low level of PO in inoculated and non-inoculated plants could be associated with tolerance. In addition, cell necrosis correlated positively with LOX in non-tolerant cultivars, while mycelia surrounding stomata were positively correlated with PO in the resistant cultivar. GST activity presented correlations between cytological and biochemical parameters only for susceptible cultivars. Stomatal and direct penetration were positively correlated with GST activity in the susceptible non-tolerant cultivars, while these correlations were negative in the tolerant cultivar. When combining cytological and biochemical observations with resistance and tolerance profiles, for each cultivar and at each time point, cultivars could be classified in tight accordance with their previous field characterisation. Moreover, tolerance allowed us to distinguish susceptible cultivars when both biochemical and cytological parameters were considered together.     

Peroxidase Activity in Leaves of Wheat Cultivars Differing in Resistance to Erysiphe graminis DC.

The peroxidase activities in leaves from resistant and susceptible cultivars of wheat infected and non-infected by Erysiphe graminis DC were studied. In non-infected wheat, soluble and ionic bound peroxidase activity level was found to be higher in the resistant cultivar than that in the one susceptible to Erysiphe graminis DC. After infecting wheat leaves with Erysiphe graminis DC a remarkable increase in the activity of soluble and ionic bound peroxidases was detected 5 days after inoculation only in the resistant cultivar. In the susceptible cultivar a high increase in the activity of the soluble and ionic bound peroxidases occurred only 15 days after inoculation. Using ion exchange chromatography four peroxidase fractions were obtained from infected susceptible and resistant cultivars as from non-infected ones. The fraction II in non-inoculated resistant cultivars was much higher than that in the susceptible one. This fraction increased after inoculation in both cases reaching a higher level in resistant cultivars. Fraction I was higher in the susceptible cultivar. Electrofocusing profiles of peroxidase from the susceptible and resistant cultivar differed from one another. New peroxidase bands after inoculation appeared only in the resistant cultivar.     

Activation of Glycosidases as a Consequence of Infection Stress in Fusarium Wilt of Tomato

Changes of β-1,3-glucanase, chitinase, β-1,4-glucosidase and N-acetylglucosaminidase activity have been investigated in relation to the development of symptoms and colonization by the pathogen in roots, stems and leaves of susceptible (‘Improved, Pearson’) and resistant (‘Improved Pearson VF11’) tomato plants infected by Fusarium oxysporum f. sp. lycopersici. Glycosidase activities increased after inoculation to different extents depending on the plant part and cultivar. Increases were always higher in susceptible than in resistant plants. Changes in the β-1,3-glucanase activity after inoculation were particularly large in stems of infected plants. In contrast, chitinase activity increased more in roots than in stems. The β-1,3-glucosidase and chitinase activity decreased slightly from the basal to the apical third of stems. The trend of changes of the glycosidase activity generally were well related with the severity of disease symptoms and the fungal colonization of basal stem segments. There was no evidence that the increase of glycosidase activity after the infection was directly related with the resistance to Fusarium wilt in tomato.     

Influence of elevated CO2 and O3 on IAA, IAA oxidase and peroxidase in the leaves of ginkgo trees

This study examined the impacts of elevated CO₂ or O₃ on indole-3-acetic acid (IAA) content, activities of IAA oxidase (IAAO) and peroxidase (POD) in Ginkgo biloba leaves. Plants grown in open-top chambers were exposed to ambient atmosphere (control; C), elevated CO₂ and elevated O₃ from 1 June to 30 September. An increase in IAA content and decrease in IAAO and POD activities were observed in plants exposed to elevated CO₂ compared with C. Elevated O₃ had no significant effect on IAA content and IAAO activity, but increased POD activity during the early days. When trees pre-exposed to elevated CO₂ were transferred to elevated O₃ or C, the increase in IAAO activity resulted in the decrease in IAA content. When trees pre-exposed to elevated O₃ were transferred to elevated CO₂ or C, IAA content, IAAO and POD activities showed no significant changes. The influence of POD activity on the IAA activity was low.     

Physiology of Rice Tungro Virus Disease: Involvement of Abscisic Acid-Like Substance in Susceptible Host-Virus Interactions

Stunting was severe in susceptible rice (Oryza saliva L.) cultivar ‘Taichung Native 1’ infected with tungro virus (RTV) compared to less-susceptible cultivar ‘IR 20’. The senescence of detached leaves of RTV-infected susceptible cultivar incubated in water in dark was accelerated compared to the healthy leaves as measured by the loss of total chlorophyll content. The transpiration rate of RTV-infected leaves of the susceptible cultivar was much lower than the healthy and RTV-infected leaves of the less-susceptible cultivar. Partially purified extracts obtained from RTV-infected leaves effectively inhibited GA-induced α-amylase synthesis in barley endosperms, and rice seedling growth, and they accelerated senescence of detached rice leaves. In all the three bibassays the ABA-like activity was significantly greater in the extracts from the RTV-infected susceptible cultivar than in extracts from the less-susceptible cultivar.     

Feeding behaviour of Aphis craccivora (Koch) on cowpea cultivars with different levels of aphid resistance

The feeding activity of Aphis craccivora (Koch) was monitored on cowpea plants of aphid-susceptible (Vita 7) and aphid-resistant (TVu 801) cultivars, using an AC electronic feeding monitoring system. Waveforms corresponding to salivation, phloem ingestion and non-phloem ingestion were observed. Aphids probing on the resistant cultivar showed a significantly reduced ingestion of phloem sap compared with those aphids which fed on the susceptible cultivar. The insect also made more brief and repeated probes on TVu 801. In addition, the duration of non-probing activities and non-phloem ingestion was shorter on the susceptible than on the resistant cultivar.     

Phenoloxidase activity in the reproductive system and egg masses of the pulmonate gastropod,Biomphalaria glabrata

Phenoloxidase (PO) activity in the albumen gland (AG) and egg masses (EM) ofBiomphalaria glabrata was assessed using high-performance liquid chromatography combined with electrochemical detection and colorimetric techniques. Both AG and EM extracts catalyzed the hydroxylation ofl-tyrosine (monophenol oxidase activity, MPO) and oxidation ofl-dopa (diphenol oxidase activity, DPO). However, no PO activity was found in the ovotestis. Both MPO and DPO activities in AG and EM were significantly inhibited by 1-phenyl-2-thiourea and inactivated by boiling. Approximately 35% of MPO and 44% of DPO activities were detected in the soluble fraction of homogenized EM, in contrast to that of homogenized AG, which contained about 5% and 12%, respectively, of MPO and DPO activities. N-acetyl-dopamine, a diphenolic compound, enhanced the hydroxylation of tyrosine by the PO. The presence of both MPO and DPO activities also was confirmed by the accelerated accumulation of dopachrome during incubation of EM extracts withl-tyrosine in the absence of ascorbate. Temperature and pH optima for this enzyme were 30°C and 7.5, respectively. The potential roles of PO in egg formation inB. glabrata are discussed.     

Hydrolytic Activities of Fusarium solani and Fusarium solani f. sp. eumartii Associated with the Infection Process of Potato Tubers

The development of dry rot caused by Fusarium solani f. sp. eumartii was evaluated in susceptible (Huinkul) and resistant (Spunta) potato cultivars. Fungal proteolytic and polygalacturanase activities were measured at different days postinoculation either with the pathogenic F. solani f. sp. eumartii, isolate 3122 or with the non‐pathogenic F. solani, isolate 1042. After inoculation with the pathogenic fungus, proteolytic and polygalaturonase activities were higher in the susceptible than in the resistant cultivar. In addition, we found a correlation between the levels of proteolytic activity detected in the intercellular washing fluids with the size of the lesion area caused by F. solani f. sp. eumartii in Huinkul tubers. The action of the proteolytic activity over cell wall proteins of both potato cultivars was assayed. An extracellular potato protein with homology to proteinase inhibitors of the Kunitz family was identified as a substrate of the proteolytic activity in the susceptible cultivar. A microscopic study revealed differences between the potato genotypes in the rate of response to infection by F. solani f. sp. eumartii. In addition, the cell wall alteration caused by F. solani f. sp. eumartii in cortical cells of susceptible tubers was evaluated. The data with respect to the correlation between the course of cyto‐ and biochemical events of the two host–pathogen interactions were discussed.     

Polyphenol metabolism of developing apple skin of a scab resistant and a susceptible apple cultivar

During fruit development, the concentration of main polyphenols (flavonols, flavanols, dihydrochalcones, hydroxycinnamic acids, anthocyanins) and the activities of related enzymes (phenylalanine ammonia lyase, chalcone synthase/chalcone isomerase, flavanone 3-hydroxylase, dihydroflavonol 4-reductase, flavonol synthase, peroxidase) were monitored in apple (Malus domestica Borkh.). The seasonal survey was performed at five different sampling dates and included the healthy peel of the resistant cultivar ‘Florina’ and healthy peel, scab symptomatic spot and the tissue around the infected spot of the susceptible cultivar ‘Golden Delicious’. From all enzymes tested, chalcone synthase/chalcone isomerase had the highest activity in both cultivars, while phenylalanine ammonia lyase had the lowest. The healthy peels of the susceptible and the resistant cultivar did not show differences in the accumulation of the main polyphenol groups present in the apple skin. However, in the resistant cultivar ‘Florina’, an increase of polyphenol enzyme activities could be observed in late stages of fruit development, which seems to be related to the anthocyanin accumulation in ripe fruits. Significant differences in the polyphenol metabolism were observed in the three different tissues of the susceptible cultivar ‘Golden Delicious’. Increased concentrations of hydroxycinnamic acids, dihydrochalcones and flavan-3-ols were found in the scab symptomatic spots and surrounding tissues. Phenylalanine ammonia-lyase, dihydroflavonol 4-reductase, flavanone 3-hydroxylase and peroxidase showed higher activities in the scab symptomatic spot compared to other analysed tissues, whereas the activities of other enzymes remained unchanged. Highest induction of polyphenol accumulation after scab infection was observed in early developmental stages, whereas enzyme activities were increased in later stages.     

Acetylation degree of chitin in the protective response of wheat plants

Influences on the acetylation degree of chitin manifested by proteins from cultural filtrates of strains of the fungus Septoria nodorum different in aggressiveness and of extracts from leaves of the susceptible (Triticum aestivum) and resistant (Triticum timopheevii) wheat plants infected with these strains were studied. Chitin deacetylase was found among the extracellular proteins of the fungus. Its activity was higher in the aggressive strain of the fungus than in the non-aggressive one, and this suggested that this enzyme could play an important role in the further formation of compatible relationship of the pathogens with the plants. Protein extracts from the susceptible wheat seedlings infected with the septoriosis agent also contained a component decreasing the acetylation degree of chitin. Protein extracts from the resistant wheat seedlings increased the chitin acetylation degree. It is supposed that this can be a pattern of the plant counteracting the action of chitin deacetylases of the pathogen.     

Elicitor-induced metabolic changes in cell cultures of chickpea (Cicer arietinum L.) cultivars resistant and susceptible to Ascochyta rabiei

Cell-suspension cultures of two chickpea (Cicer arietinum L.) cultivars, resistant (ILC 3279) and susceptible (ILC 1929) to the fungus Ascochyta rabiei (Pass.) Lab., showed differential accumulation of the phytoalexins medicarpin and maackiain, and transient induction of related enzyme activities after application of an A. rabiei-derived elicitor. The chalcone-synthase (CHS) activity (EC 2.3.1.74) which is involved in the first part of phytoalexin biosynthesis exhibited a maximum 8–12 h after elicitation in the cells of both cultivars. Concomitant with the fivefold-higher phytoalexin accumulation, CHS activity increased twofold in the cells of the resistant cultivar. The maximum of the elicitor-induced CHS-mRNA activity was determined 4 h after onset of induction in the cultures of both cultivars, although in cells of cultivar ILC 3279 this mRNA activity was induced at a level twofold higher than that in cells of the susceptible race ILC 1929. Investigations of CHS isoenzymes by two-dimensional gel electrophoresis of immunoprecipitated in-vitro-translated protein indicated the presence of five proteins. In the cells of both cultivars only two of the isoenzymes were induced after elicitor treatment. Analysis of the total in-vitro-translated proteins by two-dimensional gel electrophoresis showed that the constitutively expressed patterns of mRNA activities in the cell cultures of the two cultivars were identical. After elicitation, considerably more translatable mRNAs were induced in the cells of cultivar ILC 3279. The few induced proteins, and their respective mRNA activities, which could be detected in the cells of the susceptible cultivar, all existed in the cells of the resistant cultivar, too. One highly induced protein (M_r 18 kDa) found in the cells of cultivar ILC 3279 reached its maximum mRNA activity 6 h after elicitor application. The amount of this protein was hardly increased in the cells of the susceptible cultivar. This protein appears to be excreted from the cells into the growth medium.Abbreviations CHS chalcone synthase - IEF isoelectric focussing - ILC international legume chickpea - PR-protein pathogenesis-related protein - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis Financial support by Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie is gratefully acknowledged. The authors thank Dr. K. Hahlbrock (Max-Planck-Institut für Züchtungsforschung, Köln, FRG) for provision of antisera and the International Centre for Agricultural Research in the Dry Areas (Aleppo, Syria) for plant material.     

Aldose reductase expression contributes in sorbitol accumulation and 4-hydroxynon-2-enal detoxification in two foxtail millet (<Emphasis Type="Italic">Setaria italic</Emphasis>a L.) cultivars with different salt stress tolerance

Salt stress is a major environmental factor in arid and semi-arid regions and influences many aspects of plant development. Salinity results in generation of various free radicals that can potentially damage the cellular constituents in plants. Plants were able to effectively reduce the damage caused by these free radicals by a way of enzymatic and non enzymatic defenses for better survival. Enhanced efficacy of antioxidative enzyme systems such as superoxide dismutase, catalase and ascarbate peroxidase was well documented in several plants subjected to salinity stress. Aldose reductase, an important enzyme is also known to detoxify free toxic aldehydes like HNE (4-hydroxynon-2-enal, a hydroxyalkenal) generated during oxidative damage of cellular components. However, the role of aldose reductase to impart tolerance to the plants under salt stress has not been studied in any detail. Therefore, we were interested to study the aldose reductase activity and its expression to gain an insight into the role of aldose reductase in imparting tolerance to foxtail millet cultivars (viz., Cv. Prasad and Lepakshi) subjected to NaCl stress. We observed that subjecting foxtail millets to increasing levels of stress significantly increased aldose reductase activity and in a way that correlated positively with elevated levels of sorbitol, an osmotic solute involved in osmotic balance. This suggests the involvement of aldose reductase in sorbitol biosynthesis in foxtail millet. Additionally, we observed higher levels of 4-hydroxynon-2-enal, a major lipid peroxidation product, in the susceptible than the tolerant cultivar indicating a higher proportion of cellular damage in former than in the latter. This high content of 4-hydroxynon-2-enal in the susceptible cultivar was negatively correlated with its aldose reductase activity, indicating the involvement of aldose reductase in detoxification of 4-hydroxynon-2-enal. 4-hydroxynon-2-enal is also known to be a catalyzed by glutathione-S-transferase. Glutathione-S-transferase activity was found higher in the tolerant foxtail millet than the sensitive cultivar: the tolerant cultivar showed a low 4-hydroxynon-2-enal content compared to the susceptible cultivar, demonstrating a possible mechanism for detoxification of 4-hydroxynon-2-enal by two enzymes, glutathione-S-transferase and aldose reductase in plants under stressful conditions.     

Changes in glucose-6-phosphate dehydrogenase and ribonucleases activities during PVY-RNA biosynthesis in infected potato plants

Changes in glucose-6-phosphate dehydrogenase, ribonucleases activities and chlorophyll content were studied in leaves of plants systemically infected by potato virus Y, necrotic strain (PVY^N). Potato cultivars Jara and Adretta differing in resistance to potato virus Y were used. No statistically significant differences were observed between healthy and infected plants of both cultivars in chlorophyll content. Activity of glucose-6-phosphate dehydrogenase slowly increased in connection with virus multiplication and reached 203.4% of the values of non-infected control in susceptible cv. Jara and 160.4% in the resistant cv. Adretta. Differences between cultivars were significant from 60 d after inoculation (P≤0.05). The activity of ribonucleases quickly increased in the initial period of the experiment and then slowly decreased. Their activities reached 195.6% in susceptible cultivar and 183.5% in the resistant one. Significant differences (P≤0.01) between susceptible and resistant cultivars was found from 18 to 35 d after inoculation. The activities of enzymes corresponded to PVY^N multiplication which was since 40 d considerably higher (P<0.01) in susceptible cultivar in comparison with the resistant one. Thus the activities of studied enzymes could be considered as markers of resistance of potato cultivars to PVY^N multiplication.     

砷胁迫下不同砷富集能力植物内源生长素与抗氧化酶的关系

采用室内土培法,研究了砷胁迫(0,50,100和200 mg/kg)对凤尾蕨属中砷超富集植物大叶井口边草(Pteris cretica var.nervosa)和非砷超富集植物剑叶凤尾蕨(Pteris ensiformis)生物量、株高、叶片内源3-吲哚乙酸(IAA)含量、IAA氧化酶(IAAO)活性、砷含量、抗氧化酶(超氧化物歧化酶SOD、过氧化物酶POD、过氧化氢酶CAT)活性以及细胞膜脂过氧化产物丙二醛(MDA)含量的影响,并用逐步回归法分析了IAA含量与砷含量、抗氧化酶活性、MDA含量之间的关系。此外,研究了100 mg/kg砷处理下IAA、IAAO、3种抗氧化酶和MDA的时间动态。结果表明,与对照(不加砷)相比,加砷处理下大叶井口边草的株高和生物量未出现显著变化,但剑叶凤尾蕨在中、高浓度砷胁迫下则显著降低;中、高浓度砷胁迫均使2种植物叶片含砷量、IAA含量显著增加和IAAO活性显著下降,但这种改变在大叶井口边草中更为显著;加砷处理使大叶井口边草叶片3种抗氧化酶活性维持或增加,剑叶凤尾蕨中SOD和CAT活性虽能维持,但POD活性则显著下降,说明砷胁迫下大叶井口边草具有更强的抗氧化能力。逐步回归分析结果显示,2种植物叶片IAA含量均与砷含量成显著正相关,但在大叶井口边草中,IAA含量还与CAT活性成显著负相关。时间动态研究表明,第13天,大叶井口边草具有最高的IAA含量、最低的IAAO活性以及最低的CAT活性,而剑叶凤尾蕨中的变化规律则不明显。因此,叶片保持较高的IAA含量、较低的IAAO和CAT活性有助于大叶井口边草超量富集砷。     

Induction of Isoperoxidases in Resistant and Susceptible Tomato Cultivars by Meloidogyne incognita

Isoperoxidases were detected in resistant Rossol and susceptible Roma VF tomato roots uninfected and infected by Meloidogyne incognita. Syringaldazine, guaiacol, p-phenylenediamine-pyrocatechol (PPD-PC), and indoleacetic acid (IAA) were used as substrates, and the corresponding peroxidative activities were detected either in cytoplasmic or in cell wall fractions, except for IAA oxidase, which was measured in soluble and microsomal fractions. Isoperoxidase activities and cellular locations were induced differently in resistant and susceptible cultivars by nematodes. Nematode infestation markedly enhanced syringaldazine oxidase activity in cell walls of the resistant cultivar. This isoperoxidase is involved in the last step of lignin deposition in plants. Conversely, the susceptible cultivar reacted to M. incognita infection with an increase in cytoplasmic PPD-PC oxidase activity, which presumedly is involved in ethylene production; no changes in cell wall isoperoxidases were observed. IAA oxidase was inhibited in susceptible plants after nematode inoculation, whereas in resistant plants this activity increased in the soluble fraction and decreased in the microsomal fraction.     

The Role of Peroxidase and Polyphenol Oxidase Isozymes in Wheat Resistance to Alternaria triticina

Polyphenol oxidase activity was higher in resistant wheat cultivar ACC-8226 than in susceptible cultivar MP-845 in control sets and after inoculation of Alternaria triticina. However, similar polyphenol oxidase isozyme pattern was found in control and inoculated sets of both the cultivars, but the band intensity was higher after inoculation. Three and four peroxidase isozymes were found in ACC-8226 and MP-845, respectively. An extra peroxidase isozyme band was observed in both the cultivars after inoculation. The results suggest an active role of peroxidase and polyphenol oxidase in defence mechanism of wheat plants.     

Manipulation of IAA-Oxidase Activity and Auxin-Deficiency Symptoms in Intact Cotton Plants with Manganese Nutrition

Cotton (Gossypium hirsutum L. cv. Deltapine 15) seedlings were grown in solution culture in which the Mn²⁺ level was varied. Following an initial period, a series of shifts in manganese nutrition were employed, each lasting 14 days. Appearance was observed and fresh weight, IAA oxidase (IAAO), peroxidase and IAAO inhibitor levels were determined. After the initial 3 weeks of treatment, growth was negatively correlated with IAAO (or peroxidase) activity. All shifts in manganese nutrition resulted in predicted changes in IAAO activity, growth and plant appearance during a second 2-week period of the experiment. Continuously deficient plants exhibited highest leaf abscission and IAA oxidase activity, and lowest growth of all treatments. Plants shifted from deficient to control levels of Mn²⁺ exhibited a marked decline in IAAO activity, increase in growth and absence of leaf abscission. Plants shifted from borderline deficiency to deficient Mn²⁺ exhibited a major increase in IAAO activity, reduction in growth and extensive leaf abscission. Control and borderline toxicity plants maintained normal IAAO activity, growth, and appearance. During a final 2-week period, symptom expression was intensified. In particular, the initial borderline deficiency plants shifted to deficient levels of Mn²⁺ abscised most of those leaves that expanded after the shift in treatment. In addition, shifts of some plants to toxic Mn²⁺ levels during the third phase of the experiment produced a complete cycle of manipulation. Plants initially deficient in Mn²⁺ with high IAAO and low growth recovered growth and declined in IAAO when shifted to control Mn²⁺ and then suffered severe inhibition of growth and toxicity symptoms when shifted to high Mn²⁺. In all cases changes in enzyme activity, growth, leaf abscission and similar symptoms were most strongly expressed in the youngest tissue or that with the greatest potential for growth during the interval of a particular treatment. Since total growth, IAAO, leaf abscission, internode length and similar symptoms were consistently manipulated in both directions (increase or decrease in intensity or degree) by raising or lowering Mn²⁺ levels in the plant culture medium, we conclude that there is a causal relationship between IAAO and these responses that involves destruction of auxin.