Modelling the effect of environmental factors on the “trade-off” between growth and defensive compounds in young apple trees

The allocation of plant internal resources to growth processes (primary metabolism) and to defensive compounds (secondary metabolism) is determined by plant internal competition for common substrates and energy. In order to contribute to the discussion about environmental impacts on this trade-off between demands for growth and defence, we extended a complex plant growth model to simulate the formation of defensive compounds on the whole plant level, depending on the dynamics of the environmental conditions light, nutrients and water. In this paper, we present and apply the model to simulate the effects of different N fertilizer applications on growth and resistance of young apple trees (cv Golden Delicious). The results show that model predictions are able to describe the observed relation between growth rate and phenylpropanoid concentrations in young leaves of apple trees, and can assist in the interpretation of experimental findings. Finally, we estimate costs and benefits of investment into defence in a scenario, in which an attack by the leaf pathogen Venturia inaequalis is simulated.     

Girdling induces oxidative damage and triggers enzymatic and non-enzymatic antioxidative defences in Citrus leaves

The effects of girdling on oxidative damage, antioxidant enzyme activity, antioxidant metabolites and proline (Pro) were studied in leaves arising from different shoot types of potted 2-year-old ‘Loretina’ mandarin (Citrus reticulata Blanco) trees during the spring flush period. Girdling increased malonyldialdehyde (MDA) and basal chlorophyll (Chl) a fluorescence (F_o) in young leaves 30 days after girdling but not in the mature leaves (ML) suggesting a disruption of photosynthetic apparatus and oxidative damage in young leaves. This phenomenon was accompanied by increasing levels of Pro. Paralleling these changes, an increase of all antioxidant enzyme activities occurred in leaves from vegetative (VG) and multiflowered leafy shoots (MLY) of girdled trees. Similarly, in ML of girdled trees, ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) activity also increased. However, dehydroascorbate reductase (DHAR) activity decreased and superoxide dismutase (SOD) activity remained unchanged. Total leaf carbohydrate content and starch also increased as a result of girdling in all shoot types. Whilst soluble sugars increased markedly in young leaves, they increased only slightly in ML. In conclusion, this study provides evidence that girdling gives rise to oxidative damage in Citrus during carbohydrate accumulation, triggering enzymatic and non-enzymatic defence mechanisms.     

Girdling induces oxidative damage and triggers enzymatic and non-enzymatic antioxidative defences in Citrus leaves

The effects of girdling on oxidative damage, antioxidant enzyme activity, antioxidant metabolites and proline (Pro) were studied in leaves arising from different shoot types of potted 2-year-old ‘Loretina’ mandarin (Citrus reticulata Blanco) trees during the spring flush period. Girdling increased malonyldialdehyde (MDA) and basal chlorophyll (Chl) a fluorescence (F_o) in young leaves 30 days after girdling but not in the mature leaves (ML) suggesting a disruption of photosynthetic apparatus and oxidative damage in young leaves. This phenomenon was accompanied by increasing levels of Pro. Paralleling these changes, an increase of all antioxidant enzyme activities occurred in leaves from vegetative (VG) and multiflowered leafy shoots (MLY) of girdled trees. Similarly, in ML of girdled trees, ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) activity also increased. However, dehydroascorbate reductase (DHAR) activity decreased and superoxide dismutase (SOD) activity remained unchanged. Total leaf carbohydrate content and starch also increased as a result of girdling in all shoot types. Whilst soluble sugars increased markedly in young leaves, they increased only slightly in ML. In conclusion, this study provides evidence that girdling gives rise to oxidative damage in Citrus during carbohydrate accumulation, triggering enzymatic and non-enzymatic defence mechanisms.     

Effects of different N fertilizers on the activity of <Emphasis Type="Italic">Glomus mosseae</Emphasis> and on grapevine nutrition and berry composition

Grapevine N fertilization may affect and be affected by arbuscular mycorrhizal (AM) fungal colonization and change berry composition. We studied the effects of different N fertilizers on AM fungal grapevine root colonization and sporulation, and on grapevine growth, nutrition, and berry composition, by conducting a 3.5-year pot study supplying grapevine plants with either urea, calcium nitrate, ammonium sulfate, or ammonium nitrate. We measured the percentage of AM fungal root colonization, AM fungal sporulation, grapevine shoot dry weight and number of leaves, nutrient composition (macro- and micronutrients), and grapevine berry soluble solids (total sugars or °Brix) and total acidity. Urea suppressed AM fungal root colonization and sporulation. Mycorrhizal grapevine plants had higher shoot dry weight and number of leaves than non-mycorrhizal and with a higher growth response with calcium nitrate as the N source. For the macronutrients P and K, and for the micronutrient B, leaf concentration was higher in mycorrhizal plants. Non-mycorrhizal plants had higher concentration of microelements Zn, Mn, Fe, and Cu than mycorrhizal. There were no differences in soluble solids (°Brix) in grapevine berries among mycorrhizal and non-mycorrhizal plants. However, non-mycorrhizal grapevine berries had higher acid content with ammonium nitrate, although they did not have better N nutrition and vegetative growth.     

Remobilised nitrogen and root uptake of nitrate for spring leaf growth,flowers and developing fruits of pear (Pyrus communis L.) trees

Both uptake of fertiliser N and remobilisation of stored N were quantified for the early growth of spur and shoot leaves, flowers and fruit development of pear trees. One-year old Abbé F. trees grafted on quince C rootstocks were fertilised with a generous N supply for one year and while dormant during the winter, transferred to sand cultures. Each tree received 3 g of labelled nitrate-N at the end of winter and in early spring. Leaves, flowers and fruit were sampled on 5 separate occasions and the recovery of labelled N used to distinguish the remobilisation of N and the root uptake of nitrate. Remobilisation of stored N accounted for most of the N present in leaves and flowers during blossoming. Remobilisation of nitrogen stopped between petal fall and the beginning of fruit development. Root uptake of nitrate linearly increased over time and at the last sampling, 55 days after bud burst, fertiliser N contributed approximately half of the total N recovered in both spur and shoot leaves, the remainder coming from remobilisation. Flowers and fruits based their N metabolism more on remobilisation as compared to the leaves. This pattern of internal cycling of N is discussed in relation to fertilisation strategies for pear trees.     

结果初期黄冠梨对春施15N-尿素的吸收、分配与利用

以3年生黄冠梨为材料,探讨了早春施用¹⁵N尿素后,树体在萌芽期-新梢缓慢生长期和新梢缓慢生长期-果实成熟期对氮素的吸收、分配与利用特性。结果表明: 梨树在萌芽期-新梢缓慢生长期主要以新梢和叶片等营养器官生长为核心;在新梢缓慢生长期-果实成熟期则以根系等贮藏器官生长为主,果实产量品质形成为辅,且树体尤其是贮藏器官的生物量成倍增加。由于各器官尤其是新梢和叶片生长旺盛、新梢缓慢生长期吸收的标记氮量相对较多,各器官吸收的肥料氮(Ndff)值相对较高;果实成熟期除粗根外各器官的Ndff值均低于新梢缓慢生长期。萌芽期到新梢缓慢生长期吸收的标记氮主要分配在新梢和叶片营养器官中,新梢缓慢生长期到果实成熟期吸收的标记氮则主要分配在贮藏器官中;整个生育期间,植株吸收的标记氮在贮藏器官中分配率最高,营养器官次之,生殖器官中分配率最低。3年生梨树从萌芽期-新梢缓慢生长期、新梢缓慢生长期-果实成熟期吸收的肥料氮分别占当年总吸氮量的31.1%和21.0%,而两个时期内吸收的土壤氮占比分别达68.9%和79.0%。     

Gibberellins in Diffusates from Shoots of Apple Trees

Excised shoot apices, leaves and internodes from shoots of apple trees (Malus×domestica) give off gibberellins by diffusion on agar. A methanol extract of the agar was prepared, the extract separated on thin layer plates, and the gibberellin activity estimated by means of Rumex and lettuce hypocotyl bioassays. The largest amounts of gibberellin are found in diffusates from the shoot apex, the two upper leaves and the two upper internodes. Several promotive fractions are found on the chromatograms as well as growth inhibitors. Removal of young leaves retards elongation of the internodes. Probably gibberellins produced in young leaves exercise some control over this process. The growth regulators Alar and CCC also retard internode elongation. Diffusates from shoots treated with these substances were also examined. Preliminary results suggest that the amount of diffusible gibberellins from treated shoots is not reduced.     

The occurrence of auxins in the old leaves of apple trees

A relatively high auxin level was found in old leaves from the lower part of long shoots of young apple trees using the straight growth bioassay on wheat coleoptile segments. The auxin level remains almost constant during summer and autumn.     

Sampling conditions for reliable routine detection by enzyme-linked immunosorbent assay of three ilarviruses in fruit trees

Enzyme-linked immunosorbent assay (ELISA) was used to test plum trees for prune dwarf (PDV), Prunus necrotic ringspot (NRSV) and apple mosaic (ApMV) viruses, cherry trees for PDV and NRSV, and apple trees for ApMV. Optimum conditions were determined for sampling in large-scale surveys for these viruses. All three viruses were detected throughout the growing season in individual samples of young leaves, or twigs with newly formed buds. However, when single infected leaves were combined with different numbers of healthy leaves, tests were most successful for all three viruses early in the growing season. PDV was detected in 1/40 (infected/total leaves) cherry leaves in April and May and 1/40 plum leaves until July, whereas NRSV was detected in 1/20 cherry leaves until July and 1/20 plum leaves until May. ApMV was detected in 1/20 apple or plum leaves until June but was detected less readily in mature leaves after June than either NRSV or PDV. There was no evidence of uneven distribution of virus infection in the trees. The viruses were detected in leaf samples kept for 8 wk at 3°C but freezing was less reliable for storage especially with ApMV. ApMV was detected in tests on plants held for several weeks at 25°C, and PDV and NRSV in plants held at 30°C.     

The Influence of Nitrogen Supply on the Uptake and Remobilization of Stored N for the Seasonal Growth of Apple Trees

M26 apple rootstocks were grown in sand culture and suppliedwith three rates of nitrogen (N) with the irrigation: none,0·8 mol N m^–2 or 8·0 mol N m^–2. Allthe N supplied to the trees was labelled with ¹⁵N at 5·0atom percent enrichment. The effect of N supply on tree growth,N uptake and the remobilization of N from stems for the annualgrowth of the trees was measured. Increasing the N supply increasedleaf growth, but had no effect upon root mass and so alteredthe root/leaf dry matter ratio Plants receiving no fertilizer N had to rely entirely upon storedreserves of N for their seasonal growth. Initially this N wasused for leaf growth, which stopped after a few weeks. Thereafterthe N-deficient plants retranslocated some of the N from theirleaves to support root growth. Increasing the N supply had littleeffect upon the amount of N remobilized for growth, althoughwell-fertilized plants accumulated N in their leaves and didnot retranslocate any to support root growth. The partitioningof N between roots and shoots was, therefore, altered by increasingthe N supply. Amino acid analysis of stems showed that the majorforms of N remobilized during growth were protein rich in asparagineand arginine The results show the importance of internal N cycling for thegrowth of young apple trees, and are discussed in relation toother studies of N cycling in deciduous trees Malus domestica Borkh., nitrogen, remobilization, growth, partitioning, storage     

Effects of nitrogen supply on growth, contents of phenolic compounds and pathogen (scab) resistance of apple trees

The effect of long-term N-supply on growth, scab resistance and phenolic compounds in the leaves of two apple cultivars was studied. The different pools of phenylpropanoids (hydroxycinnamic acids, dihydrochalcones) and flavonoids (flavonols, catechins, procyanidins) were quanitfied by HPLC from non-infected and inoculated leaves representing different ontogenetic stages. Scab incidence was also evaluated. Strictly following the carbon-nutrient-balance hypothesis, apple trees responded to high N-supply with increased shoot growth and with a reduced accumulation of total phenolic compounds in their leaves. This was shown for the cultivar 'Golden Delicious', which is susceptible to the scab disease caused by Venturia inaequalis , and for the resistant cultivar 'Rewena'. Whereas high N-fertilization increased the susceptibility of 'Golden Delicious', it did not decrease the resistance of 'Rewena' despite of the pronounced reduction of phenolic concentrations. Thus, a simple C trade off between growth-related metabolism and secondary metabolism cannot solely explain changes in defensive potential.     

Efficient phloem remobilization of Zn protects apple trees during the early stages of Zn deficiency

Apple trees are extensively cultivated worldwide but are often affected by zinc (Zn) deficiency. Limited knowledge regarding Zn remobilization within fruit crops has hampered the development of efficient strategies for providing adequate amounts of Zn. In the present study, Zn distribution and remobilization were compared among apple trees cultivated under different Zn conditions. Without Zn application, plants showed visible symptoms of Zn deficiency at the shoot tips after 1 year but appeared to grow normally during the first 6 months (early stage of Zn deficiency). Compared with apple plants under sufficient Zn treatment, plants suffering from early‐stage Zn deficiency showed preferential Zn distribution to young leaves and higher Zn levels in phloem, demonstrating that hidden Zn deficiency triggers a highly efficient remobilization of Zn in this species. The in vivo Zn‐nicotianamine complex in phloem tissues, combined with the significant enhanced expression of MdNAS3 and MdYSL6, suggested a positive role for nicotianamine in the phloem remobilization of Zn. These results strongly suggest that a proportion of Zn in the old leaves of apple trees can be efficiently remobilized by phloem transport to the shoot tips, partially in the form of Zn‐nicotianamine, thus protecting apple trees against the early stages of Zn deficiency.     

Infestation of the coccid,Icerya seychellarum (Westw.), on the mangrove Avicennia marina (forsk.) vierh. on Aldabra Atoll,with special reference to tree age

Summary The level of infestation by the coccid Icerya seychellarum on the mangrove tree Avicennia marina was measured on a stand of ca. 670 trees on Aldabra Atoll in 1978. Trees varied in basal trunk diameter (btd) between 3 and 30 cm. Leaf infestation increased significantly with increasing btd-class and young trees (btd 3.0–4.5 cm) had a mean infestation of 0.3 mg coccids g^-1 leaf whilst the heaviest infested trees (btd 13.0–14.5 cm) supported 7.6 mg g^-1. Leaf and shoot growth were not correlated with coccid infestation but shoot vigour (leaf to green shoot ratio) declined significantly with increasing btd-class (or age). Leaves of older, heavily infested trees did not differ from those of young uninfested trees in the concentration of soluble or total nitrogen of in four other leaf elements, indicating that nutrient status was not an important factor in infestation. Field observations showed that many of the older trees were subjected to poor drainage which may have increased their susceptibility to attack and also that on the leaves of young trees salt secretion presented an effective barrier to the establishment of coccids. re19800212     

Phytophthora collar rot of apple: seasonal effects on infection and disease development

One-to three-year-old trees of the apple variety Cox's Orange Pippin were highly resistant to infection by Phytophthora cactorum except during the spring from March to May. A rapid increase in resistance occurred after this time from the commencement of shoot growth. The period of susceptibility to infection by P. syringae was from October to December, when trees were dormant. Inoculations with either fungus during the respective susceptible periods caused rapidly extending lesions which girdled and killed the trees; established lesions continued to enlarge in months when trees were resistant to infection. Similar seasonal fluctuations in resistance to infection by P. cactorum also occurred in mature (35-year-old) Cox trees but the susceptible period was longer. Lesions resulting from inoculations at the optimum time (the ‘mouseear’ to ‘pink-bud’ stages of development) extended at similar rates in both young and old trees. The infrequent incidence of collar rot in young trees is probably related to factors other than inherent resistance. In resistance and pathogenicity studies young trees gave reliable and consistent results, provided that inoculations were correctly timed in relation to bud development.     

Autumnal N storage determines the spring growth,N uptake and N internal cycling of young peach trees

Although N storage determines early spring growth in trees, the usefulness of autumn N supply remains unclear as N uptake decreases in autumn, but could be restored earlier in spring to compensate for low N cycling. We intended here to evaluate the effects of autumn N supply on N uptake, storage and cycling, and spring growth. Four levels of N fertilisation were applied to 1-year-old peach trees, between the end of shoot growth and leaf fall. In spring, N supply was ¹⁵N labelled. Organ dry weights and concentrations of ¹⁴N, ¹⁵N, starch and soluble sugars were evaluated after the first growth flush. Bud development had previously been described in the same trees by Jordan et al. (Trees-Struct Func 23:235–245, 2009). Fertilisation promoted autumn N uptake, spring N uptake and growth up to a threshold level, since no differences were evidenced between the three highest N treatments. The variability in tree ¹⁴N contents was related to the number of phytomers per tree in autumn, i.e. to tree size. In spring, the depletion of the perennial structures was independent of treatment, indicating a complete mobilisation of the N stores. Spring growth was related to the amounts of cycling N, and spring N uptake was in turn proportioned to shoot and fruit growth. The lower N uptake of the N limited trees was not due to a C shortage since these trees displayed the highest starch concentrations. We conclude that a moderate autumn fertilisation improved spring growth and fruit production (Jordan et al. in Trees-Struct Func 23:235–245, 2009) and that a deficit of N storage could not be compensated for by an increase in spring N uptake.     

The influence of the cooling of donor cultures on the in vitro adventitious regeneration and carbohydrate metabolism of four dwarfing apple rootstocks

We examined the effects of cooling applied for 4 to 20 weeks on donor cultures of four dwarfing apple rootstocks (P16, P22, P59 and M26). Our aim includes increasing their competence for in vitro adventitious shoot regeneration from the leaves. Donor cultures were maintained on a shoot multiplication medium at 4°C in the dark for 4 months, followed by subculture on a fresh medium for 4 weeks. The cooling of the cultures caused an increase in the adventitious shoot number and a decrease in the starch content and an increase in the soluble sugar content (monosaccharides, raffinose and stachyose). The accumulation of stachyose in response to cold is a new observation, and it suggests that raffinose and stachyose play important role in the acclimation of dwarf apple rootstocks to low temperatures.     

Studies on Apple Canker Disease. The Necrotic Toxins Produced by Valsa ceratosperma

Several metabolites responsible for the toxic manifestations of Valsa ceratosperma (Toda et Fries) Maire, a phytopathogenic fungus of the Japanese apple canker, have been isolated from its culture filtrate after growth on apple branch extract. Chemical and spectrometric studies revealed the products to be degradation products of phlorizin which is a dominant component distributed in leaves, stems, fruits and roots of apple. The toxic substances were identified as 3-(p-hydroxyphenyl) propionic acid, phloroglucinol, p-hydroxyacetophenone, p-hydroxybenzoic acid and protocatechuic acid. All of these compounds except p-hydroxyacetophenone were detected in the lesions of apple trees infected by V. ceratosperma. The fungus cultivated in a medium containing added phlorizin also produced the five toxic substances mentioned above. These results suggest that phlorizin is involved in the specific relationship between the host and the pathogen, indicating that the degradation products of phlorizin play important roles in the production of symptoms of infected apple trees.     

Is photosynthetic acclimation to low temperature controlled by capacities for storage and growth at low temperature? Results from comparative studies of grasses and trees

The ability of warm-grown leaves to acclimate their photosynthetic machinery to low, non-freezing temperature was compared for contrasting species of grasses and trees. All trees ( Betula pubescens , Salix sp. and Picea abies ), and young plants of one of the grasses ( Hordeum vulgare ) showed acclimation of photosynthesis while the other two grasses ( Phalaris arundinacea and Festuca ovina ) did not. It was those species that maintained leaf sugar concentrations essentially unchanged that showed acclimation. Trees maintained leaf sugar concentrations essentially unchanged by effectively converting leaf sugar surpluses into storage compounds. Grasses were, by comparison, less effective. However, very young plants of Hordeum maintained leaf sugar concentrations unchanged by continued growth rather than by increased storage. This diversity of low-temperature responses are discussed in relation to possible different priorities of trees and grasses: for grasses to undergo cold hardening by allowing sugars to rise, and for trees to store sugars to allow photosynthesis to operate independently of growth as growth varies with growth rhythm and air temperature.