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This study focuses on the role of the qualitative leaf wax composition in modulating the cuticular water loss using a Populus × canescens cer6 mutant line, which accumulates C34–C46 wax ester dimers and is reduced in wax monomers >C24. The two literature‐based hypotheses to be tested were the importance of the amount of wax esters and the weighted mean carbon chain length in restricting cuticular water loss. The main results were acquired by chemical analysis of cuticular wax and gravimetric cuticular transpiration measurements. Besides additional physiological measurements, the leaf surface properties were characterised by scanning electron microscopy and spectrophotometric light reflectance quantification. Mutation of the CER6 gene resulted in striking changes in qualitative wax composition but not quantitative wax amount. Based on the strong accumulation of dimeric wax esters, the relative proportion of esters increased to >90%, and the weighted mean carbon chain length increased by >6 carbon atoms. These qualitative alterations were found to increase the cuticular transpiration of leaves by twofold. Our results do not support the hypotheses that enhanced amounts of wax esters or increased weighted mean carbon chain lengths of waxes lead to reduced cuticular transpiration. Summary statement: Mutation of the CER6 gene in Populus × canescens significantly increased the proportion of wax esters and the weighted mean carbon chain length of the cuticular wax. However, in contrast to literature‐based expectations, these alterations increased the cuticular transpiration by twofold. [ABSTRACT FROM AUTHOR]

Experimental approaches to isolate drivers of variation in the carbon‐bound hydrogen isotope composition (δ2H) of plant cellulose are rare and current models are limited in their application. This is in part due to a lack in understanding of how 2H‐fractionations in carbohydrates differ between species. We analysed, for the first time, the δ2H of leaf sucrose along with the δ2H and δ18O of leaf cellulose and leaf and xylem water across seven herbaceous species and a starchless mutant of tobacco. The δ2H of sucrose explained 66% of the δ2H variation in cellulose (R2 = 0.66), which was associated with species differences in the 2H enrichment of sucrose above leaf water (εsucrose : −126% to −192‰) rather than by variation in leaf water δ2H itself. εsucrose was positively related to dark respiration (R2 = 0.27), and isotopic exchange of hydrogen in sugars was positively related to the turnover time of carbohydrates (R2 = 0.38), but only when εsucrose was fixed to the literature accepted value of −171 ‰. No relation was found between isotopic exchange of hydrogen and oxygen, suggesting large differences in the processes shaping post‐photosynthetic fractionation between elements. Our results strongly advocate that for robust applications of the leaf cellulose hydrogen isotope model, parameterization utilizing δ2H of sugars is needed. With new capacity to measure the hydrogen isotope composition (δ2H) of leaf sucrose we show that the majority of variation in cellulose δ2H is driven by a species‐specific isotope offset between leaf water and leaf sucrose, which has previously been assumed constant. [ABSTRACT FROM AUTHOR]

Carbonic anhydrase (CA) performs the first enzymatic step of C4 photosynthesis by catalysing the reversible hydration of dissolved CO2 that diffuses into mesophyll cells from intercellular airspaces. This CA‐catalysed reaction provides the bicarbonate used by phosphoenolpyruvate carboxylase to generate products that flow into the C4 carbon‐concentrating mechanism (CCM). It was previously demonstrated that the Zea mays ca1ca2 double mutant lost 97% of leaf CA activity, but there was little difference in the growth phenotype under ambient CO2 partial pressures (pCO2). We hypothesise that since CAs are among the fastest enzymes, minimal activity from a third CA, CA8, can provide the inorganic carbon needed to drive C4 photosynthesis. We observed that removing CA8 from the maize ca1ca2 background resulted in plants that had 0.2% of wild‐type leaf CA activity. These ca1ca2ca8 plants had reduced photosynthetic parameters and could only survive at elevated pCO2. Photosynthetic and carbon isotope analysis combined with modelling of photosynthesis and carbon isotope discrimination was used to determine if ca1ca2ca8 plants had a functional C4 cycle or were relying on direct CO2 diffusion to ribulose 1,5‐bisphosphate carboxylase/oxygenase within bundle sheath cells. The results suggest that leaf CA activity in ca1ca2ca8 plants was not sufficient to sustain the C4 CCM. Summary Statement: Zea mays plants containing 0.2% of wild‐type leaf carbonic anhydrase activity had low photosynthesis rates and a 1% CO2‐dependent growth phenotype. The depleted leaf 13C isotopic composition and high CO2 compensation point suggest that these plants had a disrupted C4 carbon‐concentrating mechanism. [ABSTRACT FROM AUTHOR]

Our understanding of the regulation of respiration in C4 plants, where mitochondria play different roles in the different types of C4 photosynthetic pathway, remains limited. We examined how leaf dark respiration rates (Rdark), in the presence and absence of added malate, vary in monocots representing the three classical biochemical types of C4 photosynthesis (NADP‐ME, NAD‐ME and PCK) using intact leaves and extracted bundle sheath strands. In particular, we explored to what extent rates of Rdark are associated with mitochondrial number, volume and ultrastructure. Based on examination of a single species per C4 type, we found that the respiratory response of NAD‐ME and PCK type bundle sheath strands to added malate was associated with differences in mitochondrial number, volume, and/or ultrastructure, while NADP‐ME type bundle sheath strands did not respond to malate addition. In general, mitochondrial traits reflected the contributions mitochondria make to photosynthesis in the three C4 types. However, despite the obvious differences in mitochondrial traits, no clear correlation was observed between these traits and Rdark. We suggest that Rdark is primarily driven by cellular maintenance demands and not mitochondrial composition per se, in a manner that is somewhat independent of mitochondrial organic acid cycling in the light. SUMMARY STATEMENT: We found distinct anatomical, ultrastructural and functional differences in mitochondria of leaves using the three classical biochemical types of C4 photosynthesis. Such differences reflect the roles of mitochondria in photosynthesis. However, we found no clear correlation between mitochondrial composition and leaf dark respiration rates, suggesting leaf dark respiration is likely driven by cellular maintenance demands but not mitochondrial composition. [ABSTRACT FROM AUTHOR]

An expression was earlier derived for the non‐steady state isotopic composition of a leaf when the composition of the water entering the leaf was not necessarily the same as that of the water being transpired (Farquhar and Cernusak 2005). This was relevant to natural conditions because the associated time constant is typically sufficiently long to ensure that the leaf water composition and fluxes of the isotopologues are rarely steady. With the advent of laser‐based measurements of isotopologues, leaves have been enclosed in cuvettes and time courses of fluxes recorded. The enclosure modifies the time constant by effectively increasing the resistance to the one‐way gross flux out of the stomata because transpiration increases the vapour concentration within the chamber. The resistance is increased from stomatal and boundary layer in series, to stomata, boundary layer and chamber resistance, where the latter is given by the ratio of leaf area to the flow rate out of the chamber. An apparent change in concept from one‐way to net flux, introduced by Song, Simonin, Loucos and Barbour (2015) is resolved, and shown to be unnecessary, but the value of their data is reinforced. The transient responses of isotopic composition of water in leaves and transpiration depends on the leaf water content and the one way flux of water vapour out of the leaves, not the net transpiration rate. [ABSTRACT FROM AUTHOR]

H218O enrichment develops when leaves transpire, but an accurate generalized mechanistic model has proven elusive. We hypothesized that leaf hydraulic architecture may affect the degree to which gradients in H218O develop within leaves, influencing bulk leaf stable oxygen isotope enrichment (ΔL) and the degree to which the Péclet effect is relevant in leaves. Leaf hydraulic design predicted the relevance of a Péclet effect to ΔL in 19 of the 21 species tested. Leaves with well‐developed hydraulic connections between the vascular tissue and the epidermal cells through bundle sheath extensions and clear distinctions between palisade and spongy mesophyll layers (while the mesophyll is hydraulically disconnected) may have velocities of the transpiration stream such that gradients in H218O develop and are expressed in the mesophyll. In contrast, in leaves where the vascular tissue is hydraulically disconnected from the epidermal layers, or where all mesophyll cells are well connected to the transpiration stream, velocities within the liquid transport pathways may be low enough that gradients in H218O are very small. Prior knowledge of leaf hydraulic design allows informed selection of the appropriate ΔL modelling framework. We show that leaf hydraulic design contributes to the development of gradients in oxygen isotope composition within leaf water, and that a priori knowledge of leaf hydraulic design can guide selection of appropriate leaf water isotope models. [ABSTRACT FROM AUTHOR]

Light gradients within tree canopies play a major role in the distribution of plant resources that define the photosynthetic capacity of sun and shade leaves. However, the biochemical and diffusional constraints on gas exchange in sun and shade leaves in response to light remain poorly quantified, but critical for predicting canopy carbon and water exchange. To investigate the CO2 diffusion pathway of sun and shade leaves, leaf gas exchange was coupled with concurrent measurements of carbon isotope discrimination to measure net leaf photosynthesis ( An), stomatal conductance ( gs) and mesophyll conductance ( gm) in Eucalyptus tereticornis trees grown in climate controlled whole-tree chambers. Compared to sun leaves, shade leaves had lower An, gm, leaf nitrogen and photosynthetic capacity ( Amax) but gs was similar. When light intensity was temporarily increased for shade leaves to match that of sun leaves, both gs and gm increased, and An increased to values greater than sun leaves. We show that dynamic physiological responses of shade leaves to altered light environments have implications for up-scaling leaf level measurements and predicting whole canopy carbon gain. Despite exhibiting reduced photosynthetic capacity, the rapid up-regulation of gm with increased light enables shade leaves to respond quickly to sunflecks. [ABSTRACT FROM AUTHOR]

The oxygen isotope composition of cellulose (δ18OCel) archives hydrological and physiological information. Here, we assess previously unexplored direct and interactive effects of the δ18O of CO2 (δ18OCO2), nitrogen (N) fertilizer supply and vapour pressure deficit (VPD) on δ18OCel, 18O-enrichment of leaf water (Δ18OLW) and cellulose (Δ18OCel) relative to source water, and pexpx, the proportion of oxygen in cellulose that exchanged with unenriched water at the site of cellulose synthesis, in a C4 grass ( Cleistogenes squarrosa). δ18OCO2 and N supply, and their interactions with VPD, had no effect on δ18OCel, Δ18OLW, Δ18OCel and pexpx. Δ18OCel and Δ18OLW increased with VPD, while pexpx decreased. That VPD-effect on pexpx was supported by sensitivity tests to variation of Δ18OLW and the equilibrium fractionation factor between carbonyl oxygen and water. N supply altered growth and morphological features, but not 18O relations; conversely, VPD had no effect on growth or morphology, but controlled 18O relations. The work implies that reconstructions of VPD from Δ18OCel would overestimate amplitudes of VPD variation, at least in this species, if the VPD-effect on pexpx is ignored. Progress in understanding the relationship between Δ18OLW and Δ18OCel will require separate investigations of pex and px and of their responses to environmental conditions. [ABSTRACT FROM AUTHOR]

Leaf water contains naturally occurring stable isotopes of oxygen and hydrogen in abundances that vary spatially and temporally. When sufficiently understood, these can be harnessed for a wide range of applications. Here, we review the current state of knowledge of stable isotope enrichment of leaf water, and its relevance for isotopic signals incorporated into plant organic matter and atmospheric gases. Models describing evaporative enrichment of leaf water have become increasingly complex over time, reflecting enhanced spatial and temporal resolution. We recommend that practitioners choose a model with a level of complexity suited to their application, and provide guidance. At the same time, there exists some lingering uncertainty about the biophysical processes relevant to patterns of isotopic enrichment in leaf water. An important goal for future research is to link observed variations in isotopic composition to specific anatomical and physiological features of leaves that reflect differences in hydraulic design. New measurement techniques are developing rapidly, enabling determinations of both transpired and leaf water δ18O and δ2H to be made more easily and at higher temporal resolution than previously possible. We expect these technological advances to spur new developments in our understanding of patterns of stable isotope fractionation in leaf water. [ABSTRACT FROM AUTHOR]

Plants synthesize phenolic compounds in response to certain environmental signals or stresses. One large group of phenolics, flavonoids, is considered particularly responsive to ultraviolet ( UV) radiation. However, here we demonstrate that solar blue light stimulates flavonoid biosynthesis in the absence of UV- A and UV- B radiation. We grew pea plants ( P isum sativum cv. Meteor) outdoors, in Finland during the summer, under five types of filters differing in their spectral transmittance. These filters were used to (1) attenuate UV- B; (2) attenuate UV- B and UV- A < 370 nm; (3) attenuate UV- B and UV- A; (4) attenuate UV- B, UV- A and blue light; and (5) as a control not attenuating these wavebands. Attenuation of blue light significantly reduced the flavonoid content in leaf adaxial epidermis and reduced the whole-leaf concentrations of quercetin derivatives relative to kaempferol derivatives. In contrast, UV- B responses were not significant. These results show that pea plants regulate epidermal UV- A absorbance and accumulation of individual flavonoids by perceiving complex radiation signals that extend into the visible region of the solar spectrum. Furthermore, solar blue light instead of solar UV- B radiation can be the main regulator of phenolic compound accumulation in plants that germinate and develop outdoors. [ABSTRACT FROM AUTHOR]

ABSTRACT Methionine (Met) in proteins can be oxidized to two diastereoisomers of methionine sulfoxide, Met- S-O and Met- R-O, which are reduced back to Met by two types of methionine sulfoxide reductases (MSRs), A and B, respectively. MSRs are generally supplied with reducing power by thioredoxins. Plants are characterized by a large number of thioredoxin isoforms, but those providing electrons to MSRs in vivo are not known. Three MSR isoforms, MSRA4, MSRB1 and MSRB2, are present in Arabidopsis thaliana chloroplasts. Under conditions of high light and long photoperiod, plants knockdown for each plastidial MSR type or for both display reduced growth. In contrast, overexpression of plastidial MSRBs is not associated with beneficial effects in terms of growth under high light. To identify the physiological reductants for plastidial MSRs, we analyzed a series of mutants deficient for thioredoxins f, m, x or y. We show that mutant lines lacking both thioredoxins y1 and y2 or only thioredoxin y2 specifically display a significantly reduced leaf MSR capacity (-25%) and growth characteristics under high light, related to those of plants lacking plastidial MSRs. We propose that thioredoxin y2 plays a physiological function in protein repair mechanisms as an electron donor to plastidial MSRs in photosynthetic organs. [ABSTRACT FROM AUTHOR]

ABSTRACT Nitrogen isotope composition ( δ15N) in plant organic matter is currently used as a natural tracer of nitrogen acquisition efficiency. However, the δ15N value of whole leaf material does not properly reflect the way in which N is assimilated because isotope fractionations along metabolic reactions may cause substantial differences among leaf compounds. In other words, any change in metabolic composition or allocation pattern may cause undesirable variability in leaf δ15N. Here, we investigated the δ15N in different leaf fractions and individual metabolites from rapeseed ( Brassica napus) leaves. We show that there were substantial differences in δ15N between nitrogenous compounds (up to 30‰) and the content in (15N enriched) nitrate had a clear influence on leaf δ15N. Using a simple steady-state model of day metabolism, we suggest that the δ15N value in major amino acids was mostly explained by isotope fractionation associated with isotope effects on enzyme-catalysed reactions in primary nitrogen metabolism. δ15N values were further influenced by light versus dark conditions and the probable occurrence of alternative biosynthetic pathways. We conclude that both biochemical pathways (that fractionate between isotopes) and nitrogen sources (used for amino acid production) should be considered when interpreting the δ15N value of leaf nitrogenous compounds. [ABSTRACT FROM AUTHOR]

Dew formation, a common meteorological phenomenon, is expected to intensify in the future. Dew can influence the H218O and HDO isotopic compositions of leaf water ( δL), but the phenomenon has been neglected in many experimental and modelling studies. In this study, the dew effect on δL was investigated with a dark plant chamber in which dew formation was introduced. The H218O and HDO compositions of water vapour, dew water and leaf water of five species were measured for up to 48 h of dew exposure. Our results show that the exchanges of H218O and HDO in leaf water with the air continued in the darkness when the net H216O flux was zero. Our estimates of the leaf conductance using the isotopic mass balance method ranged from 0.035 to 0.087 mol m−2 s−1, in broad agreement of the night-time stomatal conductance reported in the literature. In our experiments, the conductance of the C4 species was 0.04 ± 0.01 mol m−2 s−1 and that of the C3 plants was 0.10 ± 0.04 mol m−2 s−1. At the end of 16 h dew exposure, 72 (±17) and 94 (±11)% of the leaf water came from dew according to the 18O and D tracer, respectively. [ABSTRACT FROM AUTHOR]

We investigated the individual effect of null mutations of each of the four sucrose-phosphate synthase (SPS) genes in Arabidopsis ( SPSA1, S PSA2, SPSB and SPSC) on photosynthesis and carbon partitioning. Null mutants spsa1 and spsc led to decreases in maximum SPS activity in leaves by 80 and 13%, respectively, whereas null mutants spsa2 and spsb had no significant effect. Consistently, isoform-specific antibodies detected only the SPSA1 and SPSC proteins in leaf extracts. Leaf photosynthesis at ambient [CO] was not different among the genotypes but was 20% lower in spsa1 mutants when measured under saturating [CO] levels. Carbon partitioning at ambient [CO] was altered only in the spsa1 null mutant. Cold treatment of plants (4 °C for 96 h) increased leaf soluble sugars and starch and increased the leaf content of SPSA1 and SPSC proteins twofold to threefold, and of the four null mutants, only spsa1 reduced leaf non-structural carbohydrate accumulation in response to cold treatment. It is concluded that SPSA1 plays a major role in photosynthetic sucrose synthesis in Arabidopsis leaves, and decreases in leaf SPS activity lead to increased starch synthesis and starch turnover and decreased Ribulose 1,5-bisphosphate regeneration-limited photosynthesis but not ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco)-limited photosynthesis, indicating a limitation of triose-phosphate utilization (TPU). [ABSTRACT FROM AUTHOR]

This study focuses on the spatial patterns of transpiration-driven water isotope enrichment (Δlw) along monocot leaves. It has been suggested that these spatial patterns are the result of competing effects of advection and (back-)diffusion of water isotopes along leaf veins and in the mesophyll, but also reflect leaf geometry (e.g. leaf length, interveinal distance) and non-uniform gas-exchange parameters. We therefore developed a two-dimensional model of isotopic leaf water enrichment that incorporates new features, compared with previous models, such as radial diffusion in the xylem, longitudinal diffusion in the mesophyll, non-uniform gas-exchange parameters and non-steady-state effects. The model reproduces well all published measurements of Δlw along monocot leaf blades, except at the leaf tip and given the uncertainties on measurements and model parameters. We show that the longitudinal diffusion in the mesophyll cannot explain the observed reduction in the isotope gradient at the leaf tip. Our results also suggest that the observed differences in Δlw between C3 and C4 plants reflect more differences in mesophyll tortuosity rather than in leaf length or interveinal distance. Mesophyll tortuosity is by far the most sensitive parameter and different values are required for different experiments on the same plant species. Finally, using new measurements of non-steady-state, spatially varying leaf water enrichment we show that spatial patterns are in steady state around midday only, just as observed for bulk leaf water enrichment, but can be easily upscaled to the whole leaf level, regardless of their degree of heterogeneity along the leaf. [ABSTRACT FROM AUTHOR]

The specificity factor of Rubisco is a measure of the relative capacities of the enzyme to catalyse carboxylation and oxygenation of ribulose 1,5-bisphosphate and hence to control the relative rates of photosynthetic carbon assimilation and photorespiration. Specificity factors of purified Rubisco from 24 species of C3 plants found in diverse habitats with a wide range of environmental growth limitations by both water availability and temperature in the Balearic Islands were measured at 25 °C. The results suggest that specificity factors are more dependent on environmental pressure than on phylogenetic factors. Irrespective of phylogenetic relationships, higher specificity factors were found in species characteristically growing in dryer environments and in species that are hemideciduous or evergreen. Effects of temperature on specificity factor of the purified enzyme from 14 species were consistent with the concept that higher specificity factors were associated with an increase in the activation energy for oxygenation compared to carboxylation of the 2,3-enediolate of RuBP to the respective transition state intermediates. The results are discussed in terms of selection pressures leading to the differences in specificity factors and the value of the observations for identifying useful genetic manipulation to change Rubisco polypeptide subunits. [ABSTRACT FROM AUTHOR]

The cellular and subcellular distribution of Ni within leaves of Hybanthus floribundus (Lindley) F. Muell, a hyperaccumulator of Ni, was investigated at relatively high spatial resolution using energy-dispersive X-ray microanalysis (EDAX). Elemental distribution maps showed that Ni was predominantly localized in the vacuoles of epidermal cells in the leaves. Quantification of Ni revealed concentrations up to 275 mmol kg−1 (embedded tissue) in some epidermal vacuoles. The accumulation of Ni in these cells was associated with a decrease in the concentration of Na and K. There was no indication that Ni was associated with P, S or Cl in the vacuoles. Ni was also concentrated on the outside of cell walls throughout the leaves, indicating that apoplastic compartmentation is also involved in Ni tolerance and accumulation in this plant. [ABSTRACT FROM AUTHOR]

ABSTRACT A model has been derived for the enrichment of heavy isotopes of water in leaves, including progressive enrichment along the leaf. In the model, lighter water is preferentially transpired leaving heavier water to diffuse back into the xylem and be carried further along the leaf. For this pattern to be pronounced, the ratio of advection to diffusion (Péclet number) has to be large in the longitudinal direction, and small in the radial direction. The progressive enrichment along the xylem is less than that occurring at the sites of evaporation in the mesophyll, depending on the isolation afforded by the radial Péclet number. There is an upper bound on enrichment, and effects of ground tissue associated with major veins are included. When transpiration rate is spatially nonuniform, averaging of enrichment occurs more naturally with transpiration weighting than with area-based weighting. This gives zero average enrichment of transpired water, the modified Craig–Gordon equation for average enrichment at the sites of evaporation and the Farquhar and Lloyd (In Stable Isotopes and Plant Carbon-Water Relations , pp. 47–70. Academic Press, New York, USA, 1993) prediction for mesophyll water. Earlier results on the isotopic composition of evolved oxygen and of retro-diffused carbon dioxide are preserved if these processes vary in parallel with transpiration rate. Parallel variation should be indicated approximately by uniform carbon isotope discrimination across the leaf. [ABSTRACT FROM AUTHOR]

ABSTRACT The objective of this study was to test whether elevated [CO2], [O3] and nitrogen (N) fertility altered leaf mass per area (LMPA), non-structural carbohydrate (TNC), N, lignin (LTGA) and proanthocyanidin (PA) concentrations in cotton (Gossypium hirsutum L.) leaves and roots. Cotton was grown in 14 dm3 pots with either sufficient (0·8 g N dm-3) or deficient (0·4 and 0·2 g N dm-3) N fertilization, and treated in open-top chambers with either ambient or elevated (+ 175 and + 350 μmol mol-1) [CO2] in combination with either charcoal-filtered air (CF) or non-filtered air plus 1·5 times ambient [O3]. At about 50 d after planting, LMPA, starch and PA concentrations in canopy leaves were as much as 51–72% higher in plants treated with elevated [CO2] compared with plants treated with ambient [CO2], whereas leaf N concentration was 29% lower in elevated [CO2]-treated plants compared with controls. None of the treatments had a major effect on LTGA concentrations on a TNC-free mass basis. LMPA and starch levels were up to 48% lower in plants treated with elevated [O3] and ambient [CO2] compared with CF controls, although the elevated [O3] effect was diminished when plants were treated concurrently with elevated [CO2]. On a total mass basis, leaf N and PA concentrations were higher in samples treated with elevated [O3] in ambient [CO2], but the difference was much reduced by elevated [CO2]. On a TNC-free basis, however, elevated [O3] had little effect on tissue N and PA concentrations. Fertilization treatments resulted in higher PA and lower N concentrations in tissues from the deficient N fertility treatments. The experiment showed that suppression by elevated [O3] of LMPA and starch was largely prevented by elevated [CO2], and that interpretation of [CO2] and [O3] effects should include comparisons on a TNC-free basis. Overall, the experiment indicated that allocation to starch and PA may be related to how environmental factors affect source–sink relationships in plants, although the effects of elevated [O3] on secondary metabolites differed in this respect. [ABSTRACT FROM AUTHOR]

ABSTRACT The composition and spatial arrangement of cuticular waxes on the leaves of Prunus laurocerasus were investigated. In the wax mixture, the triterpenoids ursolic acid and oleanolic acid as well as alkanes, fatty acids, aldehydes, primary alcohols and alcohol acetates were identified. The surface extraction of upper and lower leaf surfaces yielded 280 mg m-2 and 830 mg m-2, respectively. Protocols for the mechanical removal of waxes from the outermost layers of the cuticle were devised and evaluated. With the most selective of these methods, 130 mg m-2 of cuticular waxes could be removed from the adaxial surface before a sharp, physically resistant boundary was reached. Compounds thus obtained are interpreted as ‘epicuticular waxes’ with respect to their localization in a distinct layer on the surface of the cutin matrix. The epicuticular wax film can be transferred onto glass and visualized by scanning electron microscopy. Prunus laurocerasus epicuticular waxes consisted entirely of aliphatic compounds, whereas the remaining intracuticular waxes comprised 63% of triterpenoids. The ecological relevance of this layered structure for recognition by phytotrophic fungi and herbivorous insects that probe the surface composition for sign stimuli is discussed. [ABSTRACT FROM AUTHOR]

Photosynthetic acclimation to elevated CO2 cannot presently be predicted due to our limited understanding of the molecular mechanisms and metabolic signals that regulate photosynthetic gene expression. We have examined acclimation by comparing changes in the leaf content of RuBP carboxylase/oxygenase (Rubisco) with changes in the transcripts of Rubisco subunit genes and with leaf carbohydrate metabolism. When grown at 1000 mm3 dm–3 CO2, 12 of 16 crop species at peak vegetative growth had a 15–44% decrease in leaf Rubisco protein, but with no specific association with changes in transcript levels measured at midday. Species with only modest reductions in Rubisco content (10–20%) often had a large reduction in Rubisco small subunit gene mRNAs (> 30%), with no reduction in large subunit gene mRNAs. However, species with a very large reduction in Rubisco content generally had only small reductions in transcript mRNAs. Photosynthetic acclimation also was not specifically associated with a change in the level of any particular carbohydrate measured at midday. However, a threshold relationship was found between the reduction in Rubisco content at high CO2 and absolute levels of soluble acid invertase activity measured in plants grown at ambient or high CO2. This relationship was valid for 15 of the 16 species examined. There also occurred a similar, albeit less robust, threshold relationship between the leaf hexose/sucrose ratio at high CO2 and a reduced photosynthetic capacity ≥ 20%. These data indicate that carbohydrate repression of photosynthetic gene expression at elevated CO2 may involve leaf sucrose cycling through acid invertase and hexokinase. [ABSTRACT FROM AUTHOR]

The indole-3-acetic acid (IAA) concentration in leaves and stamens of the normal and a temperature-sensitive male sterile 'stamenless-2' (sI-2/sl-2) mutant of tomato (Lycopersicon esculentum Mill.), grown under three temperature conditions, was measured by gas chromatography - mass spectrometry - selected ion monitoring (GC-MS-SIM) and by enzyme-linked immunosorbant assay (ELISA). At low (LTR, 18°C day/15°C night), intermediate (ITR, 23°C day/18°C night), and high temperatures (HTR, 28°C day/23°C night), the mutant leaves had approximately 10 to 20 times higher IAA concentrations, respectively, than the normal leaves under these temperature regimes. Similarly, the stamens of mutant flowers had approximately five and eight times higher IAA concentration at ITR and HTR, respectively, than the normal flowers. In the low temperature reverted mutant stamens, however, the level of IAA was similar to that in normal stamens. Also, with an increase in temperature, there was an increase in the level of IAA in the leaves and stamens of mutant plants. However, different temperatures had no appreciable effect on the IAA content of leaves and stamens of normal plants. It is suggested that the high IAA content in leaves and stamens of the stamenless-2 mutant is one of the factors associated with male sterility and carpellization of stamens in this mutant. [ABSTRACT FROM AUTHOR]