Veronica Angyalossy

The rise and evolution of the cambial variant in Bignonieae (Bignoniaceae)

SUMMARY Cambial variants represent a form of secondary growth that creates great stem anatomical diversity in lianas. Despite the importance of cambial variants, nothing is known about the developmental mechanisms that may have led to the current diversity seen in these stems. Here, a thorough anatomical analysis of all genera along the phylogeny of Bignonieae (Bignoniaceae) was carried out in order to detect when in their ontogeny and phylogeny there were shifts leading to different stem anatomical patterns. We found that all species depart from a common developmental basis, with a continuous, regularly growing cambium. Initial development is then followed by the modification of four equidistant portions of the cambium that reduce the production of xylem and increase the production of phloem, the former with much larger sieve tubes and an extended lifespan. In most species, the formerly continuous cambium becomes disjunct, with cambial portions within phloem wedges and cambial portions between them. Other anatomical modifications such as the formation of multiples of four phloem wedges, multiple‐dissected phloem wedges, and included phloem wedges take place thereafter. The fact that each novel trait raised on the ontogenetic trajectory appeared in subsequently more recent ancestors on the phylogeny suggests a recapitulatory history. This recapitulation is, however, caused by the terminal addition of evolutionary novelties rather than a truly heterochronic process. Truly heterochronic processes were only found in shrubby species, which resemble juveniles of their ancestors, as a result of a decelerated phloem formation by the variant cambia. In addition, the modular evolution of phloem and xylem in Bignonieae seems to indicate that stem anatomical modifications in this group occurred at the level of cambial initials.

An overview of the anatomy, development and evolution of the vascular system of lianas

Background: Lianas present many interesting structural features that are linked to their climbing habit. Having lost substantial amounts of supporting tissue, these plants depend on external structures for support. Meanwhile, during their evolutionary history, they have gained additional conductive and storage tissues. The wood of lianas generally includes wider vessels, larger amounts of axial parenchyma, larger rays, and longer fibres than those of trees. Cambial variants represent another key anatomical feature of lianas. Aims: In this paper, we review various aspects of liana biology, including those associated with their vascular system and water conduction, secondary growth and seasonal responses to environmental variability, as well as aspects related to the evolution of their cambial variants. Methods: Examples from the Bignoniaceae and Leguminosae, the two most abundant liana taxa in the Neotropics, are presented in a series of case studies, bringing new data, such as the activity of the cambium during the dry seasons; the radial conducting elements that are associated with the habit; the cambial variant of Bignonieae that has evolved in a recapitulatory fashion; and the increased specialisation for photosynthate conduction by the phloem. Conclusions: Altogether, lianas represent an excellent model for studies on the convergent evolution of plants.

A new method to obtain good anatomical slides of heterogeneous plant parts.

A new method is presented to prepare anatomical slides of plant materials including a combination of soft and hard tissues, such as stems with cambial variants, arboreal monocotyledons, and tree bark. The method integrates previous techniques aimed at softening the samples and making them thereby more homogeneous, with the use of anti-tearing polystyrene foam solution. In addition, we suggest two other alternatives to protect the sections from tearing: adhesive tape and/or Mayer’s albumin adhesive, both combined with the polystyrene foam solution. This solution is cheap and easy to make by dissolving any packaging polystyrene in butyl acetate. It is applied before each section is cut on a sliding microtome and ensures that all the tissues in the section will hold together. This novel microtechnical procedure will facilitate the study of heterogeneous plant portions, as shown in some illustrated examples.

Seasonal variation in wood formation of Cedrela fissilis (Meliaceae)

Cambial activity and periodicity of secondary xylem formation in Cedrela fissilis, a semi-ring-porous species, were studied. Wood samples were collected periodically from 1996 to 2000. The phenology was related to climate data of the region. The cambium has one active and one dormant period per year. The active period coincides with the wet season when trees leaf-out. The dormant period coincides with the dry season when trees lose their leaves. Growth rings are marked by parenchyma bands that begin to be formed, together with the small latewood vessels, just before the cambium becomes dormant at the beginning of the dry season. These bands are added to when the cambium reactivates in the wet season. At this time, the large earlywood vessels of the growth rings are also formed. As these bands consist of both terminal and initial parenchyma, we suggest the general term marginal bands be used to describe them. The growth layers vary in width among and within the trees.

Evaluating the annual nature of juvenile rings in Bolivian tropical rainforest trees

Knowledge on juvenile tree growth is crucial to understand how trees reach the canopy in tropical forests. However, long-term data on juvenile tree growth are usually unavailable. Annual tree rings provide growth information for the entire life of trees and their analysis has become more popular in tropical forest regions over the past decades. Nonetheless, tree ring studies mainly deal with adult rings as the annual character of juvenile rings has been questioned. We evaluated whether juvenile tree rings can be used for three Bolivian rainforest species. First, we characterized the rings of juvenile and adult trees anatomically. We then evaluated the annual nature of tree rings by a combination of three indirect methods: evaluation of synchronous growth patterns in the tree- ring series, 14C bomb peak dating and correlations with rainfall. Our results indicate that rings of juvenile and adult trees are defined by similar ring-boundary elements. We built juvenile tree-ring chronologies and verified the ring age of several samples using 14C bomb peak dating. We found that ring width was correlated with rainfall in all species, but in different ways. In all, the chronology, rainfall correlations and 14C dating suggest that rings in our study species are formed annually.

Evolution of disparity between the regular and variant phloem in Bignonieae (Bignoniaceae)

PREMISE OF THE STUDY The phloem is a plant tissue with a critical role in plant nutrition and signaling. However, little is still known about the evolution of this tissue. In lianas of the Bignoniaceae, two distinct types of phloem coexist: a regular and a variant phloem. The cells associated with these two phloem types are known to be anatomically different; however, it is still unclear what steps were involved in the evolution of such differences. METHODS Here we studied the anatomical development of the regular and variant phloem in representatives of all 21 genera of Bignonieae and used a phylogenetic framework to investigate the timing of changes associated with the evolution of each phloem type. KEY RESULTS We found that the variant phloem always appears in a determinate location, between the leaf orthostichies. Furthermore, the variant phloem was mostly occupied by very wide sieve tubes and generally included a higher concentration of fibers, indicating an increase in conduction and mechanical support. On the other hand, the regular phloem included much more parenchyma, more and wider rays, and tiny sieve tubes that resembled terminal sieve tubes from plants with seasonal formation of vascular tissues; these findings suggest reduced conduction and higher storage capacity in the regular phloem. CONCLUSIONS Overall, differences between the regular and variant phloem increased over time, leading to further specialization in conduction in the variant phloem and an increase in storage specialization in the regular phloem.

Wood Anatomy and Evolution: A Case Study in the Bignoniaceae

Wood (secondary xylem) is responsible for water transport and has been well-studied anatomically, ecologically, physiologically, and phylogenetically. Comparative methods can reveal patterns of evolution for xylem traits using knowledge from the phylogenetic history of the taxa and the branching pattern of phylogenies. Bignoniaceae (Lamiales) is a family of pantropical plants of various growth habits that includes trees, shrubs, and lianas, which display diverse wood anatomies and for which robust phylogenies are available. Here we review important aspects in classical wood anatomy and evolution and test hypotheses regarding patterns of wood evolution using the Bignoniaceae as a model. Altogether, 85% of the genera currently recognized in Bignoniaceae were sampled, and 30 characters were delimited and mapped onto a robust phylogeny of the family. Some patterns of wood evolution within the Bignoniaceae seem to have been shaped by ecophysiological and habit aspects in the family. For example, vessels increase in diameter in the lianoid lineages but decrease in trees and shrubs during evolution. Rays in trees have evolved from a mixture of homo- and heterocellular to exclusively homocellular and storied in some lineages, while in the lianas the opposite pattern was recorded. Other patterns are consistent with more general phylogenetic trends; for example, parenchyma increases in abundance from the most basal to the most derived nodes of the phylogeny. Other characters in the family that are delimited and discussed include growth rings, porosity, perforation plates, ray width, and height. This work provides evidence that wood evolution is rather labile and that the evolution of new habits and the occupation of new habitats greatly influence wood evolution.

Structural variations in root and stem wood of Styrax (Styracaceae) from Brazilian forest and cerrado

The genus Styrax L. (Styracaceae) has a wide distribution in Brazil, occurring in diverse ecosystems. To get a better insight into the ecologieal adaptations ofwood strueture, we studied two speeies, S. camporum and S.jerrugineus from the cerrado, and three species, S. latifolium, S. martii and S. leprosus from the Atlantie forest. For each species, the wood of root and stern was analyzed separately and observations inc1uded qualitative as well as quantitative wood characteristics. The results show that there were significant anatomical differences between the forest and cerrado species as well as between the root and stern wood within single species. Quantitatively, the most informative features in the root wood that separated the forest from the cerrado species were diameter, length and number of vessels, length of fibres, and width and frequeney of rays. In the stern wood, length and frequency of vessels, length of fibres, and width and frequency of rays were the most informative features. In contrast to the forest species, which had larger vessel diameters in their stem wood, the cerrado species had larger vessel diameters in their root wood. The ca1culated vulnerability index indicates that all Styrax species have adaptations to mesic conditions. The cerrado species had the smallest index values, which could be related to the seasonally dry condition of this environment.

Anatomy of Brazilian Cereeae (subfamily Cactoideae, Cactaceae): Arrojadoa Britton & Rose, Stephanocereus A. Berger and Brasilicereus Backeberg

(Anatomy of Brazilian Cereeae (subfamily Cactoideae, Cactaceae): Arrojadoa Britton & Rose, Stephanocereus A. Berger wâBrasilicereus Backeberg). Arrojadoa, Stephanocereus and Brasilicereus are endemic Brazilian Cereeae, occurring along the Espinhaco Range, in the campos rupestres, cerrados and caatingas, from northern Minas Gerais to southern Bahia. The genera are columnar, erect to semi-erect cacti, except for one species, A bahiensis, which is globose. This study describes the anatomy of dermal, fundamental and vascular systems, aiming to find diagnostic characters for the genera and species. Basal portions of stems were sectioned transversely and longitudinally, and stained with Astrablue and Safranin. The species share a uniseriate epidermis, with thick cuticle; well developed collenchymatic hypodermis, containing prismatic crystals; cortex with numerous mucilage cells, druses and vascular bundles; outside cortex as a palisade parenchyma; periderm composed of lignified cork cells alternating with suberized cells; pheloderm consisting of a few layers of thin-walled cells; phloem composed of solitary or multiple of two to three sieve tube elements, companion cells, axial and radial parenchyma; secondary xylem with solitary to multiple vessels, with simple perforation plates and alternate bordered to semi-bordered pits; axial parenchyma scanty vasicentric to incomplete; libriform septate fibres; large rays. Unlignified parenchyma is seen in the secondary xylem, varying from a few cells to bands among axial and radial elements. The following are considered diagnostic characters: the shape of lignified phellem cells, cubic to radially elongate, which individualizes S. leucostele; an underdeveloped hypodermis and the occurrence of sclereids in the cortex are exclusive to Brasilicereus markgrqfii.

Stem anatomy of Cipocereus (Cactaceae)

Summary: The genus Cipocereus belongs to the subfamily Cactoideae, tribe Cereeae, and includes columnar or semi-erect species, endemic of the Serra do Espinhaço of Minas Gerais, Brazil. It is composed of five species: C. bradei, C. crassisepalus, C. laniflorus, C. minensis and C. pusilliflorus. It is considered to be one of the most primitive of the tribe, due to a vascular cylinder composed of secondary xylem with heavy lignification, among other morphological characters. The aim of the present work is to verify the occurrence of diagnostic and taxonomic features. Stem and branch samples of each species were cut at apical, medium and basal portions. Sections were stained with safranin and astrablue and mounted in synthetic resin. The species share the following characters: a uniseriate epidermis, with thick cuticle; an external cortex portion differentiated to have a hypodermis, with many layers of cells with very thick walls; a well developed palisade chlorenchyma containing mucilage cells. During the secondary vascular formation, sclereid precursors are present outside the secondary phloem, that give rise to sclereids in later stages. Primary rays are formed by the interfascicular cambium and secondary rays by the fascicular cambium, among the axial elements of xylem and phloem. The secondary phloem is composed of sieve tube elements with transverse simple sieve plate, companion cells, axial and radial parenchyma. The xylem is composed of vessel elements with simple perforation plates, septate libriform fibres, large and high rays, axial scanty paratracheal parenchyma. Species differences have been found in the hypodermis structure, the presence of crystals and mucilage cells.