Gerd Vogg

The Developmental Pattern of Tomato Fruit Wax Accumulation and Its Impact on Cuticular Transpiration Barrier Properties: Effects of a Deficiency in a β-Ketoacyl-Coenzyme A Synthase (LeCER6)

Cuticular waxes play a pivotal role in limiting transpirational water loss across the primary plant surface. The astomatous fruits of the tomato (Lycopersicon esculentum) ‘MicroTom’ and its lecer6 mutant, defective in a β-ketoacyl-coenzyme A synthase, which is involved in very-long-chain fatty acid elongation, were analyzed with respect to cuticular wax load and composition. The developmental course of fruit ripening was followed. Both the ‘MicroTom’ wild type and lecer6 mutant showed similar patterns of quantitative wax accumulation, although exhibiting considerably different water permeances. With the exception of immature green fruits, the lecer6 mutant exhibited about 3- to 8-fold increased water loss per unit time and fruit surface area when compared to the wild type. This was not the case with immature green fruits. The differences in final cuticular barrier properties of tomato fruits in both lines were fully developed already in the mature green to early breaker stage of fruit development. When the qualitative chemical composition of fruit cuticular waxes during fruit ripening was investigated, the deficiency in a β-ketoacyl-coenzyme A synthase in the lecer6 mutant became discernible in the stage of mature green fruits mainly by a distinct decrease in the proportion of n-alkanes of chain lengths > C28 and a concomitant increase in cyclic triterpenoids. This shift in cuticular wax biosynthesis of the lecer6 mutant appears to be responsible for the simultaneously occurring increase of water permeance. Changes in cutin composition were also investigated as a function of developmental stage. This integrative functional approach demonstrates a direct relationship between cuticular transpiration barrier properties and distinct chemical modifications in cuticular wax composition during the course of tomato fruit development.

What Do Microbes Encounter at the Plant Surface? Chemical Composition of Pea Leaf Cuticular Waxes

In the cuticular wax mixtures from leaves of pea (Pisum sativum) cv Avanta, cv Lincoln, and cv Maiperle, more than 70 individual compounds were identified. The adaxial wax was characterized by very high amounts of primary alcohols (71%), while the abaxial wax consisted mainly of alkanes (73%). An aqueous adhesive of gum arabic was employed to selectively sample the epicuticular wax layer on pea leaves and hence to analyze the composition of epicuticular crystals exposed at the outermost surface of leaves. The epicuticular layer was found to contain 74% and 83% of the total wax on adaxial and abaxial surfaces, respectively. The platelet-shaped crystals on the adaxial leaf surface consisted of a mixture dominated by hexacosanol, accompanied by substantial amounts of octacosanol and hentriacontane. In contrast, the ribbon-shaped wax crystals on the abaxial surface consisted mainly of hentriacontane (63%), with approximately 5% each of hexacosanol and octacosanol being present. Based on this detailed chemical analysis of the wax exposed at the leaf surface, their importance for early events in the interaction with host-specific pathogenic fungi can now be evaluated. On adaxial surfaces, approximately 80% of Erysiphe pisi spores germinated and 70% differentiated appressoria. In contrast, significantly lower germination efficiencies (57%) and appressoria formation rates (49%) were found for abaxial surfaces. In conclusion, the influence of the physical structure and the chemical composition of the host surface, and especially of epicuticular leaf waxes, on the prepenetration processes of biotrophic fungi is discussed.

Frost hardening and photosynthetic performance of Scots pine (Pinus sylvestris L.) needles: I. Seasonal changes in the photosynthetic apparatus and its function

Abstract.Photosynthetic CO2 uptake, the photochemical efficiency of photosystem II, the contents of chlorophyll and chlorophyll-binding proteins, and the degree of frost hardiness were determined in three-year-old Scots pine (Pinus sylvestris L.) trees growing in the open air but under controlled daylength. The following conditions were compared: 9-h light period (short day), 16-h light period (long day), and natural daylength. Irrespective of induction by short-day photoperiods or by subfreezing temperatures, frost hardening of the trees was accompanied by a long-lasting pronounced decrease in the photosynthetic rates of one-year-old needles. Under moderate winter conditions, trees adapted to a long-day photoperiod, assimilated CO2 with higher rates than the short-day-treated trees. In the absence of strong frost, photochemical efficiency was lower under short-day conditions than under a long-day photoperiod. Under the impact of strong frost, photochemical efficiency was strongly inhibited in both sets of plants. The reduction in photosynthetic performance during winter was accompanied by a pronounced decrease in the content of chlorophyll and of several chlorophyll-binding proteins [light-harvesting complex (LHC)IIb, LHC Ib, and a chlorophyll-binding protein with MW 43 kDa (CP 43)]. This observed seasonal decrease in photosynthetic pigments and in pigment-binding proteins was irrespective of the degree of frost hardiness and was apparantly under the control of the length of the daily photoperiod. Under a constant 9-h daily photoperiod the chlorophyll content of the needles was considerably lower than under long-day conditions. Transfer of the trees from short-day to long-day conditions resulted in a significantly increased chlorophyll content, whereas the chlorophyll content decreased when trees were transferred from a long-day to a short-day photoperiod. The observed changes in photosynthetic pigments and pigment-binding proteins in Scots pine needles are interpreted as a reduction in the number of photosynthetic units induced by shortening of the daily light period during autumn. This results in a reduction in the absorbing capacity during the frost-hardened state.

Assimilation, allocation and utilization of carbon by 3-year-old Scots pine (Pinus sylvestris L .) trees during winter and early spring

Abstract The photosynthetic capacity of frost-hardy and frost-sensitive needles of 3-year-old Scots pines and the allocation and utilization of assimilated carbon was examined during winter and early spring. The photosynthates of the whole trees were labelled by 14CO2 fixation and after chase periods of from 7 days to 4 months under natural climatic conditions, the distribution of radiocarbon in the various tissues of the trees was determined. During winter maximal photosynthetic rates of 1-year-old needles were considerably lower than in summer when calculated on a leaf area basis. However, when related to the chlorophyll content these discrepancies disappeared. The decrease of the photosynthetic capacity upon frost-hardening could be attributed to a two- to three-fold reduction in the chlorophyll content of the needles. The pulse-chase experiments showed that photosynthesis during the cold season preferentially provides substrates for respiration. Half of the assimilated 14C was respired during the first week, and after chase periods of 3 – 4 months the trees contained not more than 10 – 20% of the radiocarbon. The carbon, which was exported by the needles, was translocated basipetally via the twigs and the stem to the roots. Whereas in the axial system incorporation of radiocarbon into storage compounds, like starch, and into cell wall material was almost negligible during the cold season, in the roots one-third of the radiocarbon was recovered from starch 2 months after the 14C-pulse. In contrast to the above-ground parts of the trees, where starch content was very low during winter, in the roots considerable amounts of starch, up to 450 μmol hexose units · g– 1 DW, were found even during mid-winter. In early spring the radiocarbon in the cell wall-, lipid-, and starch-fraction accounted for more than 80% of the 14C recovered at that time from the axial system. Incorporation of minor quantities into the cell wall fraction of the roots during winter and early spring indicate continuous root growth during the cold period as well as in early spring. Whereas during winter the buds did not attract freshly assimilated carbon, in spring just before bud break substantial amounts of carbon were translocated from the needles into the buds. In contrast, remobilization of carbon, which had been assimilated during autumn of the previous year, and import into the sprouting buds could not be demonstrated.

The positional sterile (ps) mutation affects cuticular transpiration and wax biosynthesis of tomato fruits.

Cuticular waxes are known to play a pivotal role in limiting transpirational water loss across primary plant surfaces. The astomatous tomato fruit is an ideal model system that permits the functional characterization of intact cuticular membranes and therefore allows direct correlation of their permeance for water with their qualitative and quantitative composition. The recessive positional sterile (ps) mutation, which occurred spontaneously in tomato (Solanum lycopersicum L.), is characterized by floral organ fusion and positional sterility. Because of a striking phenotypical similarity with the lecer6 wax mutant of tomato, which is defective in very-long-chain fatty acid elongation, ps mutant fruits were analyzed for their cuticular wax and cutin composition. We also examined their cuticular permeance for water following the developmental course of fruit ripening. Wild type and ps mutant fruits showed considerable differences in their cuticular permeance for water, while exhibiting similar quantitative wax accumulation. The ps mutant fruits showed a five- to eightfold increase in water loss per unit time and surface area when compared to the corresponding wild type fruits. The cuticular waxes of ps mutant fruits were characterized by an almost complete absence of n-alkanes and aldehydes, with a concomitant increase in triterpenoids and sterol derivatives. We also noted the occurrence of alkyl esters not present in the wild type. Quantitative and qualitative cutin monomer composition remained largely unaffected. The significant differences in the cuticular wax composition of ps mutant fruits induced a distinct increase of cuticular water permeance. The fruit wax compositional phenotype indicates the ps mutation is responsible for effectively blocking the decarbonylation pathway of wax biosynthesis in epidermal cells of tomato fruits.

Photosynthetic performance and adaptation of sugarcane at suboptimal temperatures

Summary Cultivation of sugarcane is limited by moderate chilling temperatures of 15° in subtropical areas of the world, whereas high temperatures seem to pose less problems. To obtain an overview of the physiological parameters affected, sugarcane plants were grown at 15, 27, and 45° for up to 10 months and photosynthetic parameters of the leaves were determined, namely chlorophyll content, Hill reaction, chlorophyll fluorescence parameters concerning photosystem II and electron transport activity, and critical temperature of chloroplast membrane organization. In all cases plants grown at 27° were superior to those grown at 15 or 45°. The photosynthetic performance of plants grown at 45° was superior to those grown at 15° in all parameters, when the plants were young (3 months old). With age some adaptation to the unfavourable temperatures proceeded, indicated by a change of photosynthetic properties in the direction of plants grown at optimal temperature (27°). The adaptation was especially strong for the plants grown at 15°, so that after 9 months their performance was better than that of 45° plants. The conclusions for breeding of more temperature adapted sugarcane plants are discussed.

Frost hardening and photosynthetic performance of Scots pine {Pinus sylvestris L.). II. Seasonal changes in the fluidity of thylakoid membranes

Abstract. The fluidity of chloroplast thylakoid membranes of frost-tolerant and frost-sensitive needles of␣three- to four-year-old Scots pine (Pinus sylvestris L.) trees, of liposomes produced from the lipids of the thylakoids of these needles, and of liposomes containing varying amounts of light-harvesting complex (LHC) II protein was investigated by means of electron paramagnetic resonance (EPR) measurements using spin-labelled fatty acids as probes. Broadening of the EPR-resonance signals of 16-doxyl stearic acid in chloroplast membranes of frost-sensitive needles and changes in the amplitudes of the peaks were observed upon a decrease in temperature from +30 °C to −10 °C, indicating a drastic loss in rotational mobility. The lipid molecules of the thylakoid membranes of frost-tolerant needles exhibited greater mobility. Moderate frost resistance could be induced in Scots pine needles by short-day treatment (Vogg et al., 1997, Planta, this issue), and growth of the trees under short-day illumination (9 h) resulted in a higher mobility of the chloroplast membrane lipids than did growth under long-day conditions (16 h). The EPR spectrum of thylakoids from frost-tolerant needles at −10 °C was typical of a spin label in highly fluid surroundings. However, an additional peak in the low-field range appeared in the subzero temperature range for the chloroplast membranes of frost-sensitive needles, which represents spin-label molecules in a motionally restricted surrounding. The EPR spectra of thylakoids and of liposomes of thylakoid lipids from frost-hardy needles were identical at +30 °C and −10 °C. The corresponding spectra from frost-sensitive plants revealed an additional peak for the thylakoids, but not for the pure liposomes. Hence, the domains with restricted mobility could be attributed to protein-lipid interactions in the membranes. Broadening of the spectrum and the appearance of an additional peak was observed with liposomes of pure distearoyl phosphatidyl glycerol modified to contain increasing amounts of LHC II. These results are discussed with respect to a loss of chlorophyll and chlorophyll-binding proteins in thylakoids of Scots pine needles under winter conditions.

Abscisic acid mediates the formation of a suberized stem scar tissue in tomato fruits

During harvest, fleshy berry tomato fruits (Solanum lycopersicum) were wounded at their stem scar. Within 3 d, this wound was rapidly sealed by a process covering the wound site with a membranous layer which effectively protects the tomato fruit from excessive water loss, nutrient elution and the entry of pathogens. Chemical analysis of the de novo synthesized stem scar tissue revealed the presence of aromatic and aliphatic components characteristic of the biopolyester suberin. Gene expression patterns associated with suberization were identified at the stem scar region. Changes in the relative abundance of different transcripts suggested a potential involvement of the plant hormone abscisic acid (ABA) in the wound-healing processes. The amount of ABA present in the stem scar tissue showed a significantly increased level during wound healing, whereas ABA-deficient mutants notabilis, flacca and sitiens were largely devoid of this rise in ABA levels. The mutant fruits showed a retarded and less efficient suberization response at the stem scar wound, whereas the rate and strength of this response were positively correlated with ABA content. These results clearly indicate in vivo the involvement of ABA in the suberization-based wound-healing processes at the stem scar tissue of tomato fruits.

Evidence for loss of D1 protein during photoinhibition of Chenopodium rubrum L. culture cells.

The effects of high-light stress on chlorophyllfluorescence parameters, D1-protein turnover and the actual level of this protein were analysed in nitrogen-deficient and nitrogen-replete cells of Chenopodium rubrum L. Changes in the number of atrazine-binding sites and in the D1-protein immunoblot signal indicated that a net loss of D1 protein occurred in high light and was partly reversible in low light. Nitrogen deficiency did not exacerbate these changes. The involvement of D1-protein turnover was shown in pulse-chase experiments with [35S]-methionine and by the application of a chloroplastic protein-synthesis inhibitor (chloramphenicol). The slowly reversible non-photochemical fluorescence quenching increased pronouncedly when D1 protein was lost at high irradiances, but its increase was only small when a net loss of D1 protein was produced at moderate irradiances by addition of chloramphenicol. The ratio of variable to maximum fluorescence, Fv/Fm, and the number of atrazine-binding sites were correlated but a proportionality between these parameters could not be observed. We conclude from these results that (i) degradation of D1 protein was not always coupled to its resynthesis, (ii) the actual level of D1 protein reflected the balance between degradation and resynthesis of D1 protein and (iii) changes in the level of D1 protein did not depend on a pronounced increase of the slowly reversible non-photochemical quenching.