Deficit irrigation combined with nitrogen application in the early growth stage of sugar beet increases the production capacity of canopy and avoids yield loss

BACKGROUND

Properly reduced irrigation combined with nitrogen (N) application can be used to improve crop water use efficiency (WUE) in arid regions, but its effect on sugar beet is unknown at present. A two-year field experiment was conducted to evaluate the effects of N application (N0, 0; N1, 150; N2, 225 kg N ha-1 ) on the canopy production capacity (CPC), yield and WUE of sugar beet under normal irrigation (W1, 70% of field capacity (FC)) and deficit irrigation (DI) (W2, 50% FC) in the early growth stage (EGS).

RESULTS

The results showed that the W2 treatment reduced the CPC by reducing gas exchange, leaf area index (LAI) and chlorophyll content (SPAD value) of sugar beet leaves compared to the W1 treatment. However, DI combined with N application increased these parameters. Specifically, N application increased the net photosynthetic rate by 40.7% by increased gas exchange, SPAD and LAI compared to the N0 treatment. In addition, N application increased WUE by 12.5% by increasing thickness of upper surface, stomatal aperture and cross-sectional area of petiole. This ultimately led to a significant increase in taproot yield (TY; 19.7%) and sugar yield (SY; 57.6%). Although the TY of the N2 treatment was higher than that of the N1 treatment, the SY and WUE did not increase significantly and the harvest index decreased significantly by 9.3%.

CONCLUSION

DI combined with 150 kg N ha-1 in the EGS of sugar beet increases the WUE in arid areas while avoiding yield loss by improving the CPC. © 2023 Society of Chemical Industry.

japonicum (Asteraceae)

Farfugium japonicum (L.) Kitam. var. japonicum grows mainly in the coastal areas of Japan. Meteorological recording data from natural habitats were used to investigate the factors associated with the laminas and petioles of radical leaves of F. japonicum var. japonicum to avoid or resist higher wind stress. Our morphological and mechanical results indicated that petiole length and petiole cross-sectional area had a weak correlation with wind speed and breaking strength, and the petiole second area moment of inertia did not differ significantly among populations. However, both lamina area and petiole length per petiole cross-sectional area decreased with increasing wind speed, indicating that F. japonicum var. japonicum resisted or avoided an increase in wind speed outdoors by reducing the lamina area and petiole length per petiole cross-sectional area without qualitative changes in their petioles. The results of this study indicated that densely distributed recording stations of the Automated Meteorological Data Acquisition System (AMeDAS) by the Japan Meteorological Agency can be used for environmental adaptation studies of plants in the field using nearby plant populations.

SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 9 and 13 repress BLADE-ON-PETIOLE 1 and 2 directly to promote adult leaf morphology in Arabidopsis

The juvenile-to-adult phase transition during vegetative development is a critical decision point in a plant's life cycle. This transition is mediated by a decline in levels of miR156/157 and an increase in the activities of its direct targets, SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) proteins. In Arabidopsis, the juvenile-to-adult transition is characterized by an increase in the length to width ratio of the leaf blade (a change in the distal region of a leaf), but what mediates this change in lamina shape is not known. Here, we show that ectopic expression of SPL9 and SPL13 produces enlarged and elongated leaves, resembling leaves from the blade-on-petiole1 (bop1) bop2 double mutant. The expression of BOP1/BOP2 is down-regulated in successive leaves, correlating with the amount of miR156 and antagonistic to the expression of SPL9 and SPL13 in leaves. SPL9 and SPL13 bind to the promoters of BOP1/BOP2 directly to repress their expression, resulting in delayed establishment of proliferative regions in leaves, which promotes more blade outgrowth (the distal region of a leaf) and suppresses petiole development (the proximal region of a leaf). Our results reveal a mechanism for leaf development along the proximal-distal axis, a heteroblastic character between juvenile leaves and adult leaves.

Two MYB activators of anthocyanin biosynthesis exhibit specialized activities in petiole and fruit of diploid strawberry

The R2R3-MYB transcription factor FveMYB10 is a major regulator of anthocyanin pigmentation in the red fruits of strawberry. fvemyb10 loss-of-function mutants form yellow fruits but still accumulate purple-colored anthocyanins in the petioles, suggesting that anthocyanin biosynthesis is under distinct regulation in fruits and petioles. From chemical mutagenesis in the diploid wild strawberry Fragaria vesca, we identified a green petioles (gp)-1 mutant that lacks anthocyanins in petioles. Using mapping-by-sequencing and transient functional assays, we confirmed that the causative mutation resides in a FveMYB10-Like (FveMYB10L) gene and that FveMYB10 and FveMYB10L function independently in the fruit and petiole, respectively. In addition to their tissue-specific regulation, FveMYB10 and FveMYB10L respond differently to changes in light quality, produce distinct anthocyanin compositions, and preferentially activate different downstream anthocyanin biosynthesis genes in their respective tissues. This work identifies a new regulator of anthocyanin synthesis and demonstrates that two paralogous MYB genes with specialized functions enable tissue-specific regulation of anthocyanin biosynthesis in fruit and petiole tissues.

Functional Mapping of Genes Modulating Plant Shade Avoidance Using Leaf Traits

Shade avoidance syndrome (SAS) refers to a set of plant responses that increases light capture in dense stands. This process is crucial for plants in natural and agricultural environments as they compete for resources and avoid suboptimal conditions. Although the molecular, biochemical, and physiological mechanisms underlying the SAS response have been extensively studied, the genetic basis of developmental variation in leaves in regard to leaf area, petiole length, and leaf length (i.e., their allometric relationships) remains unresolved. In this study, with the recombinant inbred line (RIL) population, the developmental traits of leaves of Arabidopsis were investigated under two growth density conditions (high- and low-density plantings). The observed changes were then reconstructed digitally, and their allometric relationships were modelled. Taking the genome-wide association analysis, the SNP genotype and the dynamic phenotype of the leaf from both densities were combined to explore the allometry QTLs. Under different densities, leaf change phenotype was analyzed from two core ecological scenarios: (i) the allometric change of the leaf area with leaf length, and (ii) the change of the leaf length with petiole length. QTLs modulating these two scenarios were characterized as 'leaf shape QTLs' and 'leaf position QTLs'. With functional mapping, results showed a total of 30 and 24 significant SNPs for shapeQTLs and positionQTLs, respectively. By annotation, immune pathway genes, photosensory receptor genes, and phytohormone genes were identified to be involved in the SAS response. Interestingly, genes modulating the immune pathway and salt tolerance, i.e., systemic acquired resistance (SAR) regulatory proteins (MININ-1-related) and salt tolerance homologs (STH), were reported to mediate the SAS response. By dissecting and comparing QTL effects from low- and high-density conditions, our results elucidate the genetic control of leaf formation in the context of the SAS response. The mechanism with leaf development × density interaction can further aid the development of density-tolerant crop varieties for agricultural practices.

Sources and consequences of mismatch between leaf disc and whole-leaf leaf mass per area (LMA)

PREMISE

Leaf mass per area (LMA), which is an important functional trait in leaf economic spectrum and plant growth analysis, is measured from leaf discs or whole leaves. Differences between the measurement methods may lead to large differences in the estimates of LMA values.

METHODS

We examined to what extent estimates of LMA based on whole leaves match those based on discs using 334 woody species from a wide range of biomes (tropics, subtropics, savanna, and temperate), whether the relationship varied by leaf morphology (tissue density, leaf area, leaf thickness), punch size (0.6- and 1.0-cm diameter), and whether the extent of intraspecifc variation for each species matches.

RESULTS

Disc-based estimates of species mean LMA matched the whole-leaf estimates well, and whole-leaf LMA tended to be 9.69% higher than leaf-disc LMA. The ratio of whole-leaf LMA to leaf-disc LMA was higher for species with higher leaf tissue density and larger leaves, and variance in the ratio was greater for species with lower leaf tissue density and thinner leaves. Estimates based on small leaf discs also inflated the ratio. The extent of the intraspecific variation only weakly matched between whole-leaf and disc-based estimates (R²  = 0.08).

CONCLUSIONS

Our results suggest that simple conversion between whole-leaf and leaf-disc LMA is difficult for species obtained with a small leaf punch, but it should be possible for species obtained with a large+ leaf punch. Accurately representing leaf traits will likely require careful selection between leaf-disc and whole-leaf traits depending on the objectives. Quantifying intraspecific variation using leaf discs should be also considered with caution.

Acclimation to wind loads and/or contact stimuli? A biomechanical study of peltate leaves of Pilea peperomioides

Plants are exposed to various environmental stresses. Leaves immediately respond to mechano-stimulation, such as wind and touch, by bending and twisting or acclimate over a longer time period by thigmomorphogenetic changes of mechanical and geometrical properties. We selected the peltate leaves of Pilea peperomioides for a comparative analysis of mechano-induced effects on morphology, anatomy, and biomechanics of petiole and transition zone. The plants were cultivated for 6 weeks in a phytochamber divided into four treatment groups: control (no stimulus), touch stimulus (brushing every 30 s), wind stimulus (constant air flow of 4.6 m s-1), and a combination of touch and wind stimuli. Comparing the four treatment groups, neither the petiole nor the transition zone showed significant thigmomorphogenetic acclimations. However, comparing the petiole and the transition zone, the elastic modulus (E), the torsional modulus (G), the E/G ratio, and the axial rigidity (EA) differed significantly, whereas no significant difference was found for the torsional rigidity (GK). The twist-to-bend ratios (EI/GK) of all petioles ranged between 4.33 and 5.99, and of all transition zones between 0.67 and 0.78. Based on the twist-to-bend ratios, we hypothesize that bending loads are accommodated by the petiole, while torsional loads are shared between the transition zone and petiole.

Microscopic characterization of petiole anatomy of Asteraceous taxa of Western Himalaya-Pakistan

Petiole anatomy of 15 species of family Asteraceae was examined which aimed to investigate petiolar anatomical structures for species level identification. Shandon Microtome was used for petiole histological preparations. Both qualitative and quantitative features were studied under microscope which showed significant variation in petiole, collenchyma, parenchyma shape/size, vascular bundles arrangement/size, and vessel elements quantity. Artemisia japonica Thunb., Cirsium vulgare (Savi) Ten., Myriactis nepalensis Less., Seriphidium brevifolium Ling & Y.R.Ling, Taraxacum officinale (L.) Weber ex F.H.Wigg., and Xanthium strumarium L. showed winged petioles. Maximum length and width of upper and lower epidermis was found in Tagetes erecta L. which is 23.05 ± 0.89 μm, 24.9 ± 1.257 μm length and 21.75 ± 1.38067 μm, 22.75 ± 0.467 μm width, respectively. Petioles of Parthenium hysterophorus L. was longest one with 9.85 ± 10.45 μm while A. japonica Thunb. showed highest number of vessel elements. Maximum size of vascular bundles was found in T. erecta L. with 5.05 ± 14.25 μm. Artemisia annua L., C. vulgare (Savi) Ten, Cyanthillium cinereum (L.) H.Rob., Helianthus annus L., M. nepalensis Less., P. hysterophorus L., Senecio chrysanthemoides DC. have trichomes while Tussilago farfara L. has highest number of vascular bundles. All species have angular collenchyma type except M. nepalensis Less., P. hysterophorus L., S. brevifolium Ling & Y.R.Ling, Tagetes minuta L., T. officinale L., S. chrysanthemoides DC., and T. farfara L. Cluster analysis implemented that distinct plant species in cluster. Petiolar anatomical structures and taxonomic key will helpful for distinguishing Asteraceous taxa at genus and species level. This taxonomic significant investigation will also provide baseline to taxonomists for other Asteraceae studies and phylogenetic research.

Complexity untwined: The structure and function of cucumber (Cucumis sativus L.) shoot phloem

Cucurbit phloem is complex, with large sieve tubes on both sides of the xylem (bicollateral phloem), and extrafascicular elements that form an intricate web linking the rest of the vasculature. Little is known of the physical interconnections between these networks or their functional specialization, largely because the extrafascicular phloem strands branch and turn at irregular angles. Here, export in the phloem from specific regions of the lamina of cucumber (Cucumis sativus L.) was mapped using carboxyfluorescein and ¹⁴ C as mobile tracers. We also mapped vascular architecture by conventional microscopy and X-ray computed tomography using optimized whole-tissue staining procedures. Differential gene expression in the internal (IP) and external phloem (EP) was analyzed by laser-capture microdissection followed by RNA-sequencing. The vascular bundles of the lamina form a nexus at the petiole junction, emerging in a predictable pattern, each bundle conducting photoassimilate from a specific region of the blade. The vascular bundles of the stem interconnect at the node, facilitating lateral transport around the stem. Elements of the extrafascicular phloem traverse the stem and petiole obliquely, joining the IP and EP of adjacent bundles. Using pairwise comparisons and weighted gene coexpression network analysis, we found differences in gene expression patterns between the petiole and stem and between IP and EP, and we identified hub genes of tissue-specific modules. Genes related to transport were expressed primarily in the EP while those involved in cell differentiation and development as well as amino acid transport and metabolism were expressed mainly in the IP.

Petiole-Lamina Transition Zone: A Functionally Crucial but Often Overlooked Leaf Trait

Although both the petiole and lamina of foliage leaves have been thoroughly studied, the transition zone between them has often been overlooked. We aimed to identify objectively measurable morphological and anatomical criteria for a generally valid definition of the petiole-lamina transition zone by comparing foliage leaves with various body plans (monocotyledons vs. dicotyledons) and spatial arrangements of petiole and lamina (two-dimensional vs. three-dimensional configurations). Cross-sectional geometry and tissue arrangement of petioles and transition zones were investigated via serial thin-sections and µCT. The changes in the cross-sectional geometries from the petiole to the transition zone and the course of the vascular bundles in the transition zone apparently depend on the spatial arrangement, while the arrangement of the vascular bundles in the petioles depends on the body plan. We found an exponential acropetal increase in the cross-sectional area and axial and polar second moments of area to be the defining characteristic of all transition zones studied, regardless of body plan or spatial arrangement. In conclusion, a variety of terms is used in the literature for describing the region between petiole and lamina. We prefer the term "petiole-lamina transition zone" to underline its three-dimensional nature and the integration of multiple gradients of geometry, shape, and size.

Strengthening Structures in the Petiole-Lamina Junction of Peltate Leaves

Peltate- or umbrella- shaped leaves are characterised by a petiole more or less centrally attached to the lamina on the abaxial side. The transition from the petiole to lamina in peltate leaves resembles a significant and abrupt geometrical change from a beam to a plate in a very compact shape. Since these leaves have not been subject of many studies, the distribution of that specific leaf morphology in the plant kingdom was investigated. Furthermore, the connection between the petiole and lamina of several peltate species was studied anatomically and morphologically, focusing on the reinforcing fibre strands. We found peltate leaves in 357 species representing 25 orders, 40 families and 99 genera. The majority are herbaceous perennials growing in shady, humid to wet habitats mainly distributed in the subtropical–tropical zones. Detailed anatomical investigation of 41 species revealed several distinct principles of how the transition zone between the petiole and lamina is organised. In-depth analysis of these different types accompanied by finite element-modelling could serve as inspiration for supporting structures in lightweight construction.

Twist-to-Bend Ratios and Safety Factors of Petioles Having Various Geometries, Sizes and Shapes

From a mechanical viewpoint, petioles of foliage leaves are subject to contradictory mechanical requirements. High flexural rigidity guarantees support of the lamina and low torsional rigidity ensures streamlining of the leaves in wind. This mechanical trade-off between flexural and torsional rigidity is described by the twist-to-bend ratio. The safety factor describes the maximum load capacity. We selected four herbaceous species with different body plans (monocotyledonous, dicotyledonous) and spatial configurations of petiole and lamina (2-dimensional, 3-dimensional) and carried out morphological-anatomical studies, two-point bending tests and torsional tests on the petioles to analyze the influence of geometry, size and shape on their twist-to-bend ratio and safety factor. The monocotyledons studied had significantly higher twist-to-bend ratios (23.7 and 39.2) than the dicotyledons (11.5 and 13.3). High twist-to-bend ratios can be geometry-based, which is true for the U-profile of Hosta x tardiana with a ratio of axial second moment of area to torsion constant of over 1.0. High twist-to-bend ratios can also be material-based, as found for the petioles of Caladium bicolor with a ratio of bending elastic modulus and torsional modulus of 64. The safety factors range between 1.7 and 2.9, meaning that each petiole can support about double to triple the leaf's weight.

Pathways of Photosynthesis in Non-Leaf Tissues

Plants have leaves as specialised organs that capture light energy by photosynthesis. However, photosynthesis is also found in other plant organs. Photosynthesis may be found in the petiole, stems, flowers, fruits, and seeds. All photosynthesis can contribute to the capture of carbon and growth of the plant. The benefit to the plant of photosynthesis in these other tissues or organs may often be associated with the need to re-capture carbon especially in storage organs that have high respiration rates. Some plants that conduct C3 photosynthesis in the leaves have been reported to use C4 photosynthesis in petioles, stems, flowers, fruits, or seeds. These pathways of non-leaf photosynthesis may be especially important in supporting plant growth under stress and may be a key contributor to plant growth and survival. Pathways of photosynthesis have directionally evolved many times in different plant lineages in response to environmental selection and may also have differentiated in specific parts of the plant. This consideration may be useful in the breeding of crop plants with enhanced performance in response to climate change.

Celery and Celeriac: A Critical View on Present and Future Breeding

Cultivated for the crispy petioles and round, fleshy, and flavored hypocotyl celery and celeriac have over two centuries of breeding history in Europe. In this review paper we summarized the most recent advances touching when necessary the historical context of celery and celeriac breeding. In the post genomic era of research, the genome sequence of celery is only partially available. We comprised however in this paper the most important aspects of celery genetics that are available today and have applicability in celery modern cultivars development. We discussed the problems and traits that drive the main celery and celeriac breeding goals, like hybrid seed production, disease resistance, and interesting enlarged hypocotyl and petiole characteristics. Besides the classical breeding traits we covered the potential of integration of existing cultivars as sources for consumer oriented traits like nutraceuticals and health promoting substances. Sustainability is a subject that is continuously growing in popularity and we looked at the genetic base of celery and celeriac that makes them sources for abiotic stress resistance and candidates for phytoremediation. We explored the fundamental concepts gained in various fields of celery and related species research, as resources for future improvement of celery and celeriac germplasm. We forecast what the next years will bring to Apium breeding.

Scaling relationships and vessel packing in petioles

PREMISE OF THE STUDY

While tradeoffs among mechanical and conductive functions have been well investigated in woody stems, these tradeoffs are relatively unexplored in petioles, the structural link between stems and laminas. We investigated size-independent scaling relationships between cross-sectional areas of structural and vascular tissues, relationships between tissue areas of xylem and phloem, vessel packing within xylem, and scaling of vascular and structural tissues with lamina traits.

METHODS

We examined allometric relationships among petiole tissues and as a function of lamina and petiole size variation on eleven species of Pelargonium. From transverse sections of methacrylate-embedded tissue, we measured the cross-sectional areas of all tissues within the petiole and vessel lumen, and cell wall areas of each vessel. Allometric scaling relationships were analyzed using standardized major axis regressions.

KEY RESULTS

Pelargonium petiole vessels were packed as predicted by Sperry's packing rule for woody stems. In contrast to woody stems, there was no evidence of a tradeoff between vessel area and fiber area. Within cross-sections, more xylem was produced than phloem. Among bundles, xylem and phloem scaling relationships varied with bundle position. Except for lamina dry mass and petiole fiber cross-sectional area, petiole and lamina traits were independent.

CONCLUSIONS

Petioles share vascular tissue traits with stems despite derivation from leaf primordia. We did not find evidence for a tradeoff between structural and vascular tissues, in part because fibers occur outside the xylem. We propose this separation of conduction and support underlies observed developmental and evolutionary plasticity in petioles.

Fabrication of iron oxide nanocolloids using metallosurfactant-based microemulsions: antioxidant activity, cellular, and genotoxicity toward Vitis vinifera

The present work aims at the fabrication of iron oxide nanocolloids using biocompatible microemulsion and their cytotoxic, genotoxic effect on Vitis vinifera plant has been evaluated. The three iron-based metallosurfactant complexes were synthesized. Nanosuspensions (Ns) were prepared using microemulsion technique and for the purpose, the microemulsion was prepared using oleic acid, butanol, tween 80 and as synthesized iron metallosurfactant. In this technique, no additional capping agent and/or reducing agent was added. Tween 80 which is a biocompatible surfactant acted as a reducing agent as well as stabilizing for the iron oxide Ns. Characterization of Ns's was done using TEM, FESEM, EDX, XRD, AFM, and zeta potential. Mixed type of iron oxide nanoparticles i.e. magnetite (Fe₃O₄), and maghemite (Fe₂O₃) with a size range of 1-16 nm was found to be present in the nanosuspensions prepared from all the three precursors. The antioxidant activity of the Fe Ns was also confirmed using DPPH assay, with order of activity FeDDA > FeCTAC > FeHEXA. The cellular toxicity of Ns was evaluated by observing the morphological changes on V. vinifera plant (petiole) using a light microscope. Further, the interactions of iron oxide Ns with V. vinifera's DNA (plant-DNA) was assessed using circular dichroism (CD) and gel electrophoresis. For the case of FeCTAC Ns, a decrease in the intensity of bands was observed indicating fragmentation or adduct formation resulting in DNA damage. In the case of FeDDA, a modest decrease in the intensity of bands was observed. However, for FeHEXA Ns, complete neutralization of bands was confirmed implying maximum damage to the plant DNA. CD, gel electrophoresis and antioxidant activity confirmed that FeHEXA Ns were most toxic and FeDDA Ns were safest among the three as-fabricated nanosuspensions.

Delivery of Hairpin RNAs and Small RNAs Into Woody and Herbaceous Plants by Trunk Injection and Petiole Absorption

Since its discovery, RNA interference has been widely used in crop protection. Recently, transgene-free procedures that were based on exogenous application of RNA molecules having the capacity to trigger RNAi in planta have been reported. Yet, efficient delivery of such RNA molecules to plants and particularly to trees poses major technical challenges. Here, we describe simple methods for efficient delivery of hairpin RNAs (hpRNAs) and small interfering RNAs (siRNAs) to Malus domestica, Vitis vinifera, and Nicotiana benthamiana that are based on trunk injection and/or petiole absorption. The applied RNA molecules were efficiently taken up and systemically transported. In apical leaves, the RNA was already detectable 1 day post-application (dpa) and could be detected at least up to 10 dpa, depending on the method of application. Confocal microscopy revealed that the uptaken and systemically transported RNA molecules were strictly restricted to the xylem and apoplast which may illustrate why the applied hpRNAs were not processed into siRNAs by plant DICER-LIKE (DCL) endonucleases. These innovative methods may have great impact in pest management against chewing and/or xylem sap-feeding vectors and eukaryotic pathogens that reside in the xylem.

A Comparison of Petiole Hydraulics and Aquaporin Expression in an Anisohydric and Isohydric Cultivar of Grapevine in Response to Water-Stress Induced Cavitation

We report physiological, anatomical and molecular differences in two economically important grapevine (Vitis vinifera L.) cultivars cv. Grenache (near-isohydric) and Chardonnay (anisohydric) in their response to water-stress induced cavitation. The aim of the study was to compare organ vulnerability (petiole and stem) to cavitation by measuring ultrasonic acoustic emissions (UAE) and percent loss of conductance of potted grapevines subject to the onset of water-stress. Leaf (ψL) and stem water potential (ψS), stomatal conductance (gs), transpiration (E), petiole hydraulics (KPet), and xylem diameter were also measured. Chardonnay displayed hydraulic segmentation based on UAE, with cavitation occurring at a less negative ψL in the petiole than in the stem. Vulnerability segmentation was not observed in Grenache, with both petioles and stems equally vulnerable to cavitation. Leaf water potential that induced 50% of maximum UAE was significantly different between petioles and stems in Chardonnay (ψ50Petiole = -1.14 and ψ50Stem = -2.24 MPa) but not in Grenache (ψ50Petiole = -0.73 and ψ50Stem = -0.78 MPa). Grenache stems appeared more susceptible to water-stress induced cavitation than Chardonnay stems. Grenache displayed (on average) a higher KPet likely due to the presence of larger xylem vessels. A close relationship between petiole hydraulic properties and vine water status was observed in Chardonnay but not in Grenache. Transcriptional analysis of aquaporins in the petioles and leaves (VvPIP1;1, VvPIP2;1, VvPIP2;2 VvPIP2;3, VvTIP1;1, and VvTIP2;1) showed differential regulation diurnally and in response to water-stress. VvPIP2;1 showed strong diurnal regulation in the petioles and leaves of both cultivars with expression highest predawn. Expression of VvPIP2;1 and VvPIP2;2 responded to ψL and ψS in both cultivars indicating the expression of these two genes are closely linked to vine water status. Expression of several aquaporin genes correlated with gas exchange measurements, however, these genes differed between cultivars. In summary, the data shows two contrasting responses in petiole hydraulics and aquaporin expression between the near-isohydric cultivar, Grenache and anisohydric cultivar, Chardonnay.

FLEXURAL STIFFNESS ALLOMETRIES OF ANGIOSPERM AND FERN PETIOLES AND RACHISES: EVIDENCE FOR BIOMECHANICAL CONVERGENCE

Evidence for convergence in biomechanical and anatomical features of leaves (elastic modulus E, second moment of area I, taper of petioles, the longitudinal distribution of petiolar and laminar weight, and volumes of tissues) is presented based on a survey of 22 species (distributed among dicots, monocots, and ferns). In general, regardless of taxonomic affinity, petioles were found to be mechanically constructed in one of two ways: Type I petioles-as cantilevered, end-loaded beams with relatively uniform flexural stiffness (EI) (simple and palmate leaves); and Type II petioles-as tapered cantilevered beams whose static loadings (biomass) and EI increase basipetally (pinnate leaves). In general, collenchyma and sclerenchyma were found to be peripherally located in transections through Type I and II petioles, respectively. Statistical analyses within each species and among species with either type of petiole indicated that EI ≈ k₁ Lp^2.98 and EI ≈ k₂ Lp^2.05 for Type I and II petioles, respectively, where k₁ and k₂ are dimensional constants and Lp is petiolar length. The data are interpreted to indicate that Type I and II petioles mechanically operate to deal with static loadings in two distinct ways, such that Type II petioles function in an analogous manner to branches supporting separate leaves (leaflets). The convergence in mechanical "designs" among taxonomically distinct lineages (angiosperms and ferns) is interpreted as evidence for selection on mechanical attributes of load supporting structures (petioles).

Long-term impact of Ophiostoma novo-ulmi on leaf traits and transpiration of branches in the Dutch elm hybrid 'Dodoens'

To better understand the long-term impact of Ophiostoma novo-ulmi Brasier on leaf physiology in 'Dodoens', a Dutch elm disease-tolerant hybrid, measurements of leaf area, leaf dry mass, petiole anatomy, petiole hydraulic conductivity, leaf and branch water potential, and branch sap flow were performed 3 years following an initial artificial inoculation. Although fungal hyphae were detected in fully expanded leaves, neither anatomical nor morphological traits were affected, indicating that there was no impact from the fungal hyphae on the leaves during leaf expansion. In contrast, however, infected trees showed both a lower transpiration rate of branches and a lower sap flow density. The long-term persistence of fungal hyphae inside vessels decreased the xylem hydraulic conductivity, but stomatal regulation of transpiration appeared to be unaffected as the leaf water potential in both infected and non-infected trees was similarly driven by the transpirational demands. Regardless of the fungal infection, leaves with a higher leaf mass per area ratio tended to have a higher leaf area-specific conductivity. Smaller leaves had an increased number of conduits with smaller diameters and thicker cell walls. Such a pattern could increase tolerance towards hydraulic dysfunction. Measurements of water potential and theoretical xylem conductivity revealed that petiole anatomy could predict the maximal transpiration rate. Three years following fungal inoculation, phenotypic expressions for the majority of the examined traits revealed a constitutive nature for their possible role in Dutch elm disease tolerance of 'Dodoens' trees.

Plant Responses to Vegetation Proximity: A Whole Life Avoiding Shade

In high density of vegetation, plants detect neighbors by perceiving changes in light quality through phytochrome photoreceptors. Close vegetation proximity might result in competition for resources, such as light. To face this challenge, plants have evolved two alternative strategies: to either tolerate or avoid shade. Shade-avoiding species generally adapt their development by inducing hypocotyl, stem, and petiole elongation, apical dominance and flowering, and decreasing leaf expansion and yield, a set of responses collectively known as the shade avoidance syndrome (SAS). The SAS responses have been mostly studied at the seedling stage, centered on the increase of hypocotyl elongation. After compiling the main findings about SAS responses in seedlings, this review is focused on the response to shade at adult stages of development, such as petioles of adult leaves, and the little information available on the SAS responses in reproductive tissues. We discuss these responses based on the knowledge about the molecular mechanisms and components with a role in regulating the SAS response of the hypocotyls of Arabidopsis thaliana. The transcriptional networks involved in this process, as well as the communication among the tissues that perceive the shade and the ones that respond to this stimulus will also be briefly commented.

Linking Expression of Fructan Active Enzymes, Cell Wall Invertases and Sucrose Transporters with Fructan Profiles in Growing Taproot of Chicory (Cichorium intybus): Impact of Hormonal and Environmental Cues

In chicory taproot, the inulin-type fructans serve as carbohydrate reserve. Inulin metabolism is mediated by fructan active enzymes (FAZYs): sucrose:sucrose 1-fructosyltransferase (1-SST; fructan synthesis), fructan:fructan-1-fructosyltransferase (1-FFT; fructan synthesis and degradation), and fructan 1-exohydrolases (1-FEH1/2a/2b; fructan degradation). In developing taproot, fructan synthesis is affected by source-to-sink sucrose transport and sink unloading. In the present study, expression of FAZYs, sucrose transporter and CWI isoforms, vacuolar invertase and sucrose synthase was determined in leaf blade, petiole and taproot of young chicory plants (taproot diameter: 2 cm) and compared with taproot fructan profiles for the following scenarios: (i) N-starvation, (ii) abscisic acid (ABA) treatment, (iii) ethylene treatment (via 1-aminoyclopropane-1-carboxylic acid [ACC]), and (iv) cold treatment. Both N-starvation and ABA treatment induced an increase in taproot oligofructans. However, while under N-starvation this increase reflected de novo synthesis, under ABA treatment gene expression profiles indicated a role for both de novo synthesis and degradation of long-chain fructans. Conversely, under ACC and cold treatment oligofructans slightly decreased, correlating with reduced expression of 1-SST and 1-FFT and increased expression of FEHs and VI. Distinct SUT and CWI expression profiles were observed, indicating a functional alignment of SUT and CWI expression with taproot fructan metabolism under different source-sink scenarios.

Effect of drought stress on bending stiffness in petioles of Caladium bicolor (Araceae)

PREMISE OF THE STUDY

Cell turgor plays an important role in the mechanical stability of herbaceous plants. This study on petioles of Caladium bicolor 'Candyland' analyzes the correlation between flexural rigidity and cell turgor. The results offer new insights into the underlying form-structure-function relationship and the dependency of mechanical properties from water availability.

METHODS

Bending modulus E of petioles is calculated from two-point bending tests, taking into account the tapering mode. The corresponding turgor of parenchyma cells during wilting is investigated by pressure probe tests.

KEY RESULTS

Wilting petioles show highly significant lower values of E than petioles with sufficient water supply. These differences are also found when comparing well-watered petioles to drought-stressed petioles having parenchyma turgor values in the same range. These results indicate an additional mechanical system sensitive to drought stress. On the basis of analyses of the contribution of different petiolar tissues toward the axial second moment of area and by using experimentally determined and literature values of E for the different tissues, we were able to (1) recalculate E of the intact petiole and to compare it with experimental data and (2) quantitatively estimate the importance of the different tissues for flexural rigidity and E of the petiole.

CONCLUSIONS

Our results show that the decrease in flexural rigidity of petioles of Caladium bicolor 'Candyland' during wilting results from (1) a water-loss-induced decrease in mechanical efficiency of collenchyma fibers and (2) turgor loss of parenchyma cells.

Regeneration of multiple shoots from petiole callus of Viola serpens Wall

Experiments were conducted to develop methodology for in vitro propagation and rapid multiplication of Viola serpens Wall. using petiole explant. The MS medium supplemented with 2, 4-D (6.78 μm) was found most suitable for callus induction in petiole explant. The best growth response and higher rate of shoot regeneration from petiole callus was observed on MS medium containing BAP (11.10 μm) as the average number of shoots could be increased to 36.4 on fourth successive subculturing. Higher rooting response with larger number of roots were observed in shoots inoculated on the half-strength MS medium supplemented with IBA (19.68 μm).

The unique function of the Arabidopsis circadian clock gene PRR5 in the regulation of shade avoidance response

Shade avoidance response (S.A.R) is regulated by light and circadian clock. Circadian clock controls S.A.R by the transcriptional regulation of positive regulators of S.A.R, PIF4 and PIF5, to prevent plants from responding to 'light' of dark period. Thus, in many cases, deficits in circadian clock appear in abnormalities of hypocotyl and/or petiole elongation. Previously, interesting phenomena were reported that the triple mutants of PSEUDO RESPONSE REGULATORS9, 7 and 5, which are clock components, show longer petioles and smaller leaves under light/dark cycle than those under continuous lighting. These S.A.R-like phenotypes cannot be explained by their hyposensitivity to red light. We demonstrated detailed analyses of this mutant to reveal the leaf-specific S.A.R regulated by circadian clock. Expression analyses of S.A.R-related genes suggested that PRR5 functions as a repressor of S.A.R. Morphological analyses of leaves under different light condition revealed that PRR5 is involved in the inhibition of leaf expansion in S.A.R.

Early gene expression events in the laminar abscission zone of abscission-promoted citrus leaves after a cycle of water stress/rehydration: involvement of CitbHLH1

Leaf abscission is a common response of plants to drought stress. Some species, such as citrus, have evolved a specific behaviour in this respect, keeping their leaves attached to the plant body during water stress until this is released by irrigation or rain. This study successfully reproduced this phenomenon under controlled conditions (24h of water stress followed by 24h of rehydration) and used it to construct a suppression subtractive hybridization cDNA library enriched in genes involved in the early stages of rehydration-promoted leaf abscission after water stress. Sequencing of the library yielded 314 unigenes, which were spotted onto nylon membranes. Membrane hybridization with petiole (Pet)- and laminar abscission zone (LAZ)-enriched RNA samples corresponding to early steps in leaf abscission revealed an almost exclusive preferential gene expression programme in the LAZ. The data identified major processes such as protein metabolism, cell-wall modification, signalling, control of transcription and vesicle production, and transport as the main biological processes activated in LAZs during the early steps of rehydration-promoted leaf abscission after water stress. Based on these findings, a model for the early steps of citrus leaf abscission is proposed. In addition, it is suggested that CitbHLH1, the putative citrus orthologue of Arabidopsis BIGPETAL, may play major roles in the control of abscission-related events in citrus abscission zones.

Auxin perception and polar auxin transport are not always a prerequisite for differential growth

Using time-lapse photography, we studied the response kinetics of low light intensity-induced upward leaf-movement, called hyponastic growth, in Arabidopsis thaliana. This response is one of the traits of shade avoidance and directs plant organs to more favorable light conditions. Based on mutant- and pharmacological data we demonstrated that among other factors, functional auxin perception and polar auxin transport (PAT) are required for the amplitude of hyponastic growth and for maintenance of the high leaf angle, upon low light treatment. Here, we present additional data suggesting that auxin and PAT antagonize the hyponastic growth response induced by ethylene treatment. We conclude that ethylene- and low light-induced hyponastic growth occurs at least partly via separate signaling routes, despite their strong similarities in response kinetics.

Leaf investment and light partitioning among leaves of different genotypes of the clonal plant Potentilla reptans in a dense stand after 5 years of competition

BACKGROUND AND AIMS

While within-species competition for light is generally found to be asymmetric - larger plants absorbing more than proportional amounts of light - between-species competition tends to be more symmetric. Here, the light capture was analysed in a 5-year-old competition experiment that started with ten genotypes of the clonal plant Potentilla reptans. The following hypotheses were tested: (a) if different genotypes would do better in different layers of the canopy, thereby promoting coexistence, and (b) if leaves and genotypes with higher total mass captured more than proportional amounts of light, possibly explaining the observed dominance of the abundant genotypes.

METHODS

In eight plots, 100 leaves were harvested at various depths in the canopy and their genotype determined to test for differences in leaf biomass allocation, leaf characteristics and the resulting light capture, calculated through a canopy model using the actual vertical light and leaf area profiles. Light capture was related to biomass to determine whether light competition between genotypes was asymmetric.

KEY RESULTS

All genotypes could reach the top of the canopy. The genotypes differed in morphology, but did not differ significantly in light capture per unit mass (Phi(mass)) for leaves with the laminae placed at the same light levels. Light capture did increase disproportionately with leaf mass for all genotypes. However, the more abundant genotypes did not capture disproportionately more light relative to their mass than less-abundant genotypes.

CONCLUSIONS

Vertical niche differentiation in light acquisition does not appear to be a factor that could promote coexistence between these genotypes. Contrary to what is generally assumed, light competition among genetic individuals of the same species was size-symmetric, even if taller individual leaves did capture disproportionately more light. The observed shifts in genotype frequency cannot therefore be explained by asymmetric competition for light.

Ethylene-induced differential gene expression during abscission of citrus leaves

The main objective of this work was to identify and classify genes involved in the process of leaf abscission in Clementina de Nules (Citrus clementina Hort. Ex Tan.). A 7 K unigene citrus cDNA microarray containing 12 K spots was used to characterize the transcriptome of the ethylene-induced abscission process in laminar abscission zone-enriched tissues and the petiole of debladed leaf explants. In these conditions, ethylene induced 100% leaf explant abscission in 72 h while, in air-treated samples, the abscission period started later and took 240 h. Gene expression monitored during the first 36 h of ethylene treatment showed that out of the 12 672 cDNA microarray probes, ethylene differentially induced 725 probes distributed as follows: 216 (29.8%) probes in the laminar abscission zone and 509 (70.2%) in the petiole. Functional MIPS classification and manual annotation of differentially expressed genes highlighted key processes regulating the activation and progress of the cell separation that brings about abscission. These included cell-wall modification, lipid transport, protein biosynthesis and degradation, and differential activation of signal transduction and transcription control pathways. Expression data associated with the petiole indicated the occurrence of a double defensive strategy mediated by the activation of a biochemical programme including scavenging ROS, defence and PR genes, and a physical response mostly based on lignin biosynthesis and deposition. This work identifies new genes probably involved in the onset and development of the leaf abscission process and suggests a different but co-ordinated and complementary role for the laminar abscission zone and the petiole during the process of abscission.

A novel mechanism important for the alignment of microtubules

Using a live-cell imaging approach to study individual micro-tubules, we have compared microtubule behavior between net-like and aligned cortical arrays. In contrast to previous studies, a steep angled collision between the growing end of a microtubule and a preexisting microtubule was found to favor crossover. Frequencies of microtubule crossovers, bundling and catastrophes are similar regardless of whether the cell exhibited a net-like or aligned microtubule array. In the predominantly aligned array of petiole cells, severing occurs at the sites of microtubule crossovers and serves to remove unaligned microtubules and to increase microtubule density. Severing was observed to be rare in net-like arrays. Microtubule severing is carried out by the katanin enzyme. In this addendum, we present new insights into the possible mechanism of crossing over and preliminary data looking at organization of the array in a katanin mutant.

Unusual metaxylem tracheids in petioles of Amorphophallus (Araceae) giant leaves

BACKGROUND AND AIMS

Petioles of huge solitary leaves of mature plants of Amorphophallus resemble tree trunks supporting an umbrella-like crown. Since they may be 4 m tall, adaptations to water transport in the petioles are as important as adaptations to mechanical support of lamina. The petiole is a cylindrical shell composed of compact unlignified tissue with a honeycomb aerenchymatous core. In both parts numerous vascular bundles occur, which are unique because of the scarcity of lignified elements. In the xylemic part of each bundle there is a characteristic canal with unlignified walls. The xylem pecularities are described and interpreted.

MATERIAL

Vascular bundles in mature petioles of Amorphophallus titanum and A. gigas plants were studied using light and scanning electron microscopy.

KEY RESULTS

The xylemic canal represents a file of huge metaxylem tracheids (diameter 55-200 microm, length >30 mm) with unlignified lateral walls surrounded by turgid parenchyma cells. Only their end walls, orientated steeply, have lignified secondary thickenings. The file is accompanied by a strand of narrow tracheids with lignified bar-type secondary walls, which come into direct contact with the wide tracheid in many places along its length.

CONCLUSIONS

The metaxylem tracheids in A. petioles are probably the longest and widest tracheids known. Only their end walls have lignified secondary thickenings. Tracheids are long due to enormous intercalary elongation and wide due to a transverse growth mechanism similar to that underlying formation of aerenchyma cavities. The lack of lignin in lateral walls shifts the function of 'pipe walls' to the turgid parenchyma paving the tracheid. The analogy to carinal canals of Equisetum, as well as other protoxylem lacunas is discussed. The stiff partitions between the long and wide tracheids are interpreted as structures similar to the end walls in vessels.