Biology subjects

Losada, J. M.

Publications and source records attributed to Losada, J. M..

9 recordsLinked to original sources

bioRxiv2026

Phloem conductance from leaf to fruits in avocado during development

Reproductive function in seed plants depends on efficiently allocating nutrients from sources to developing fruits. Hydraulic transport of carbohydrates largely depends on phloem architecture, but how phloem structure in fruit pedicels changes with development remains unexplored for most seed plants. Using the one-year phenology of avocado trees, we quantified water content, dry matter, and non-structural carbohydrates (NSCs) in mature leaves, flowers, young fruits, and fully developed fruits. Concomitantly, we measured phloem conduit geometry in different vein orders of leaves and in flower-fruit pedicels over time, including sieve tube numbers in cross sections. NSCs were below 5% in leaves and fruits but reached the highest concentrations in flowers, especially fructose (20%) and glucose (35%), and the pedicels of these flowers showed the smallest conduits. While sieve tube elements in leaves scaled their geometry from the minor veins to the petioles, in fruit pedicels, their geometry changed only from flower to initial fruit set, increasing their number linearly up to fruit maturation. Our models show that phloem transport toward the flowers is impaired, but total conductance increases gradually due to phloemogenesis.

plant biology↗

bioRxiv2026

Continuous monitoring of deficit irrigation in avocado across two contrasting rainfall years using sensor networks, telemetry, and machine learning

Water scarcity and increasingly irregular rainfall threaten avocado production in Mediterranean regions, yet the long term physiological responses of mature trees to sustained deficit irrigation remain poorly understood. We conducted a two-year field study integrating continuous monitoring of the soil plant atmosphere continuum, drone-based multispectral imaging, canopy structural analysis, and fruit phenotyping in a mature avocado orchard subjected to three irrigation regimes. The two study years differed markedly in rainfall, providing a unique opportunity to evaluate how environmental conditions modulate tree responses to water limitation. Trees under severe deficit irrigation showed depletion of water in deeper soil layers and a flattened physiological profile, with near-zero diel variation in leaf thickness and trunk water potential, indicating minimal transpiration and decoupling of tree water status from environmental demand. Drone telemetry via NDVI detected stress during fruit growth and maturation, but not during flowering or the new summer leaf flush, revealing greater drought sensitivity at later maturation stages. Although canopy area did not differ among irrigation treatments, canopy surface roughness increased significantly under deficit irrigation, thereby identifying a novel structural indicator of drought stress. Despite large physiological differences among treatments, fruit number remained stable, while fruit weight decreased significantly under severe deficit irrigation, particularly in the wetter year, suggesting that annual rainfall modulates the trade-off between fruit retention and fruit growth. This study provides the first continuous, multi-scale characterization of avocado performance under sustained deficit irrigation in Mediterranean conditions. By integrating plant-based sensors, remote sensing, and artificial intelligence, we reveal previously undescribed stress dynamics and identify new indicators for precision irrigation management in fruit crops.

plant biology↗

bioRxiv2025

Secreting salt glands constrain cuticle fracture to enhance desalination efficiency

Plants responding to excessive soil salinity by discharging brine onto their leaf surface risk dehydration through the osmotic continuity between the living tissue and the surface brine, which further enriches with evaporation. Cuticle cracks have long been identified as essential for salt to reach the leaf surface but provide the potentially desiccating continuity between the brine and the gland interior. Using the secreting salt gland of Nolana mollis as a model system, we integrate mathematical modeling, imaging, and physiological measurements to examine the mechanical and biochemical processes required for efficient desalination. We find that the subcuticular space between the concentrated surface brine and the more dilute secreting cell eases the energetic limits of active desalination by reducing the concentration gradient of salt across the cell membrane. We show that crack size plays a critical role in balancing the osmotic and pressure gradients required for salt removal without runaway foliar desiccation.

plant biology↗

bioRxiv2022

Hydraulic tradeoffs underlie enhanced performance of polyploid trees under soil water scarcity

O_LIPolyploid trees are excellent candidates to reduce crop water footprint and mitigate the increasingly reduced availability of freshwater for irrigation in many regions of the world due to climate change. Yet, the relationships between aerial organ morpho-anatomy of woody polyploids with their functional hydraulics under water stress remain understudied. C_LIO_LIWe evaluated growth-associated traits, aerial organ xylem anatomy, and physiological parameters of diploid, triploid, and tetraploid genotypes of the woody perennial genus Annona (Annonaceae), testing their performance under long-term soil water reduction. C_LIO_LIPolyploids displayed contrasting phenotypes, vigorous triploids and dwarf tetraploids, but consistently showed stomatal size-density trade-off. The vessel elements in aerial organs were [~]1.5 times wider in polyploids compared with diploids, but triploids displayed the lowest vessel density. Sap flow velocity, measured in vivo through a novel method, was 10-fold faster in flower carpels than in second leaf vein orders. Triploid leaves displayed the slowest velocity in the leaves but the fastest in the carpels. Plant hydraulic conductance was higher in well-irrigated diploids at the cost of consuming more belowground water, but diploids showed less tolerance than polyploids to soil water deficit. C_LIO_LIThe phenotypic disparity of atemoya polyploids associates with contrasting leaf and stem xylem porosity traits that coordinate to regulate water balances between the trees and the belowground and aboveground environment. Polyploid trees displayed a better performance under soil water scarcity, opening the possibility for deeper research on the factors underlying this behaviour and use them for a more sustainable agricultural and forestry production. C_LI

plant biology↗

bioRxiv2021

Sieve tube structural variation in Austrobaileya scandens and its significance for lianescence

Lianas are characterized by large leaf areas and slender stems, a combination of features that require an efficient vascular system. The only extant member of the Austrobaileyaceae, is an endemic twining liana of the tropical Australian forests with well-known xylem hydraulic traits. However, the vascular phloem continuum through aerial organs remains understudied. We analyzed the structure of phloem conduits across leaf veins and stems of A. scandens, combining topological data obtained through light and electron microscopy, with current models of phloem transport. Leaves displayed a low xylem to phloem ratio compared with leaves of other angiosperms, with vascular elements invariant in diameter along the midrib, but tapered across vein hierarchies. Sieve plate pore radii were extremely small: 0.08 {micro}m in minor veins, increasing to 0.12{micro}m in the petiole and only to 0.20{micro}m at the base of the stem, tens of meters away. Searcher branches contained tube shaped phloem conduits with a pectin-rich wall, whereas twining stems displayed sieve elements with tangential connections that displayed a greater fraction of the tubes populated with an astonishing number of sieve plates. Hydraulic segmentation of the leaves in Austrobaileyaceae correlate with vesseless leaves that benefit photoassimilate export through volumetric scaling of the sieve tube elements. Yet, compared with canopy dominant trees, the geometrical properties of the sieve tube in twining stems, restrict considerably energy distribution in the sub-canopy layers, potentially favoring the allocation of assimilates toward the elongating branches. Thus, the conductive xylem of twining stems contrasts with a poorly conductive phloem that meets the mechanical constraints of lianescence.

plant biology↗

bioRxiv2021

Changes In Ploidy Affect Vascular Allometry And Hydraulic Function In Trees

O_LIThe enucleated vascular elements of the xylem and the phloem offer an excellent system to test the effect of ploidy on plant function because variation in vascular geometry has a direct influence on transport efficiency. However, evaluations of conduit sizes in polyploid plants have remained elusive, most remarkably in woody species. C_LIO_LIWe used a combination of molecular, physiological, and microscopy techniques to model the hydraulic resistance between source and sinks in tetraploid and diploid mango trees. C_LIO_LITetraploids exhibited larger chloroplasts, mesophyll cells, and stomatal guard cells, resulting in higher leaf elastic modulus and lower dehydration rates despite the high water potentials of both ploidies in the field. Both the xylem and the phloem displayed a scaling of conduits with ploidy, revealing attenuated hydraulic resistance in tetraploids. C_LIO_LIConspicuous wall hygroscopic moieties in the cells involved in processes of transpiration and transport advocates a role in volumetric adjustments due to turgor change in polyploids, which, together with the enlargement of organelles, cells, and tissues that are critical for water and photo assimilate transport at long distances, imply major physiological novelties of polyploidy. C_LI

plant biology↗

bioRxiv2021

Conductivity of the phloem in Mangifera indica L.

Mangifera indica is the fifth most consumed fruit worldwide, and the most important in tropical regions, but its anatomy is quite unexplored. Previous studies examined the effect of chemicals on the xylem structure in the stems of mango, but the anatomy of the phloem has remained elusive, leaving the long distance transport of photo assimilates understudied. In this work, we used a combination of fluorescence and electron microscopy to evaluate in detail the structure of the sieve tube elements composing the phloem tissue in the tapering branches of mango trees. We then used this information to better understand the hydraulic conductivity of the sieve tubes following current models of fluid transport in trees. Our results revealed that the anatomy of the phloem in the stems changes from current year branches, where it was protected by pericyclic fibers, to older ones, where the lack of fibers was concomitant with laticiferous canals embedded in the phloem tissue. Callose was present in the sieve plates, but also in the walls of the phloem conduits, making them discernible from other phloem cells in fresh sections. A scaling geometry of the sieve tube elements, including the number of sieve areas and the pore size across tapering branches resulted in an exponential conductivity from current year branches to the base of the tree. Our measurements of the phloem in mango fit with measurements of the phloem architecture in the stems of forest woody species, and imply that, despite agronomic pruning practices, the sieve conduits of the phloem scale with the tapering branches. As a result, the pipe model theory applied to the continuous tubing system of the phloem appears as a good approach to understand the "long distance" hydraulic transport of photoassimilates in fruit trees.

plant biology↗

bioRxiv2019

Idioblasts as pathways for distributing water absorbed by leaf surfaces to the mesophyll in Capparis odoratissima

Capparis odoratissima is a tree species native to semi-arid environments of the northern coast of South America where low soil water availability coexists with frequent nighttime fog. Previous work with this species demonstrated that C. odoratissima is able to use water absorbed through its leaves at night to enhance leaf hydration, photosynthesis, and growth. Here, we combine detailed anatomical evaluations of the leaves of C. odoratissima, with water and dye uptake experiments in the laboratory. We used immunolocalization of pectin and arabinogalactan protein epitopes to characterize the chemistry of foliar water uptake pathways. The abaxial surfaces of C. odoratissima leaves are covered with overlapping, multicellular peltate hairs, while the adaxial surfaces are glabrous but with star-shaped "structures" at regular intervals. Despite these differences in anatomy, both surfaces are able to absorb condensed water, but this ability is most significant on the upper surface. Rates of evaporative water loss from the upper surface, however, are coincident with cuticle conductance. Numerous idioblasts connect the adaxial leaf surface and the adaxial peltate hairs, which contain hygroscopic substances such as arabinogalactan proteins and pectins. The highly specialized anatomy of the leaves of C odoratissima fulfills the dual function of avoiding excessive water loss due to evaporation, while maintaining the ability to absorb liquid water. Cell-wall related hygroscopic compounds present in the peltate hairs and idioblasts create a network of microchannels that maintain leaf hydration and promote the uptake of aerial water.

plant biology↗

bioRxiv2018

Phloem structure and development in Illicium parviflorum, a basal angiosperm shrub

Recent studies in canopy-dominant trees revealed a structure-function scaling of the phloem. However, whether axial scaling is conserved in woody plants of the understory, the environments of most basal-grade angiosperms, remains mysterious. We used seedlings and adult plants of the shrub Illicium parviflorum to explore the anatomy and physiology of the phloem in their aerial parts, and possible changes through ontogeny. Adult plants maintain a similar proportion of phloem tissue across stem diameters, but scaling of conduit dimensions and number decreases the hydraulic resistance towards the base of the plant. Yet, the small sieve plate pores resulted in an overall higher sieve tube hydraulic resistance than has been reported in other woody angiosperms. Sieve elements scaled from minor to major leaf veins, but were shorter and narrower in petioles. The low carbon assimilation rates of seedlings and mature plants contrasted with a three-fold higher phloem sap velocity in seedlings, suggesting that phloem transport velocity is modulated through ontogeny. While the overall architecture of the phloem tissue in basal-angiosperm understory shrubs scales in a manner consistent with trees, modification of conduit connections may have allowed woody angiosperms to extend beyond their understory origins.

physiology↗