Emília Arruda

Caatinga, the Brazilian dry tropical forest: can it tolerate climate changes?

Our review focuses on the projections of climate change in the Brazilian semiarid region, the Caatinga, based on recent publications about global climate change and biology. We found several vulnerable points in the initial estimates, the main one being that the data were collected and analyzed without a multidisciplinary knowledge. This review discusses several studies that show the current knowledge in many semiarid regions around the world. Some of these studies argue for the increase in vegetation greenness responses even under severe and prolonged drought, based on the high resilience the Caatinga native species show under severe drought conditions over the years. Additionally, we include in this review recent data produced by our group on key ecophysiological variables under drought conditions. We also show successful examples of deforested areas recovery in the semiarid region of the Central America. It is critical that the recovery of semiarid areas is coupled with the implementation of socio-environmental policies, engaging the local population and providing subsidies for life wealth improvement. These are key aspects for a long-term recovery and conservation of the Brazilian dry tropical forest.

Ecophysiological leaf traits of native and exotic palm tree species under semi-arid conditions

AbstrA ct: The main goal of this study was to evaluate the performance of two palm species under semi-arid conditions during the rainy and dry periods: the semi-arid native Syagrus coronata and a native to tropical America, Acrocomia aculeata. The leaf water potential, gas exchange, leaf soluble sugars, starch, free amino acids, total soluble protein content and morphological traits were measured. The highest leaf water potential and CO 2 assimilation values in both species were achieved during the rainy period. In response to the low soil moisture content during the dry period, gas exchange decreased 72 and 92% in S. coronata and A. aculeata, respectively,

Wide-band tracheids (WBTs) of photosynthetic and non-photosynthetic stems in species of Cactaceae1

Abstract The absence of WBTs and wood polymorphisms in some species of the Caryophyllales may be related to the particular area of plant analyzed. The present research has the objective of studying the photosynthetic and non-photosynthetic stems of different species and stages of differentiation to register wood polymorphisms and to understand the distribution and occurrence of WBTs. Wood polymorphism was observed in the non-photosynthetic stem of young and adult plants of Opuntioideae and Cactoideae and is also found in the photosynthetic stem of young plants of some species of Cactoideae. Cactoideae present WBT/fibrous dimorphic wood that can be related to cambial variation associated with growth habits and plant development. As expected, in the photosynthetic stem of the adult columnar cacti the wood is monomorphic fibrous in which WBTs were not found. This wood contains a great amount of fibers due to necessity of the mechanical support. In contrast, the globular species do not possess fibers in this area of the stem in either adult or young plants. Opuntia monacantha Haw. had non-fibrous wood in which WBTs were observed in the axial system and in the inner parts of the rays. Fiber clusters were present in the axial system. This wood represents a variation in the wood types described for Opuntioideae. Also, in O. monacantha, cells similar to the WBTs were observed in the pith, which can be interpreted as variation in the morphogenic processes during the ontogeny of the plant, probably a case of homeosis. Monomorphic fibrous wood without WBTs was found along the entire stem of Pereskia bahiensis Gürke. This feature has been observed in other pereskias, and in addition to the others, indicates its proximity to the ancestral cacti.

Wide-band tracheids in Brazilian cacti

Summary: Wide-band tracheids (WBTs) were present in species with dimorphic and monomorphic wood. In all types of dimorphic wood in which WBTs were present, the phase that contains the WBTs is produced first. In seedlings of Cipocereus minensis the first phase consists of vessels and parenchyma in a matrix of wide-band tracheids and the second phase consists of a fibrous matrix with vessels and parenchyma (wide-band tracheid wood followed by fibrous wood). Adult plants of Discocactus placentiformis and Melocactus ernestii have monomorphic WBT wood which consists of parenchyma distributed in the form of small clusters between the vessels and wide-band tracheids. In all species examined a band-like secondary wall is present in the form of annular rings or a helix. We observed annularhelical thickening in D. placentiformis and M. ernestii or a double-helix in D. placentiformis.

Seasonal variability in physiological and anatomical traits contributes to invasion success of Prosopis juliflora in tropical dry forest

We investigated whether there were consistent differences in the physiological and anatomical traits and phenotypic variability of an invasive (Prosopis juliflora (Sw.) DC.) and native species (Anadenanthera colubrina (Vell.) Brenan) in response to seasonality in a tropical dry forest. The water potential, organic solutes, gas exchange, enzymes of the antioxidant system, products of oxidative stress and anatomical parameters were evaluated in both species in response to seasonality. An analysis of physiological responses indicated that the invasive P. juliflora exhibited higher response in net photosynthetic rate to that of the native species between seasons. Higher values of water potential of the invasive species than those of the native species in the dry season indicate a more efficient mechanism for water regulation in the invasive species. The invasive species exhibits a thicker cuticle and trichomes, which can reduce transpiration. In combination, the increased epidermal thickness and the decreased thickness of the parenchyma in the dry season may contribute to water saving. Our data suggest a higher variability in anatomical traits in the invasive species as a response to seasonality, whereas physiological traits did not present a clear pattern of response.

Morphology and Anatomy of Stem Mines in Cipocereus minensis (Wender.) Ritter (Cactaceae), an Endemic Species to Eastern Brazil

Abstract: Plant mines are structures with the form of a cavity caused by consumption of host plant tissue by the insects miner larvae. Plant mines are more common in leaves, but in Cipocereus minensis, a species in which the leaves are modified spines, the miner activity is restricted to the stem. The aim of this paper was to document the morphological and anatomical differences in the infected and uninfected stems of C. minensis due to the feeding habit of the mining agent. Fresh tissue samples of non-mined and mined young stem of C. minensis were collected and examined in transverse sections. We hypothesize that the infection begins following mating when the females scratch the surface of the stem or while they feed on fruits and lay eggs, which subsequently develop into larvae, invading the cactus stem. The insects miner larvae had mostly consumed the parenchyma tissue towards the center of the stem, and periderm formed along the entire path of the insect. This meristematic tissue or “wound periderm” is a common response for compartmentalization to isolate the damaged tissue, in this case the incubating chamber, in which the eggs will be placed. There were no signs of consumption of vascular tissue in the infested samples, further suggesting a compartmentalized infestation. The nest chamber was found in the stem pith region, with periderm surrounding an insects miner pupa inside identified as a member of the Cerambycidae. The mining insect depends on a host plant to complete the life cycle; however, the nature of this partnership and the long-term effects of the insect on the plant tissue are unknown. The complex mechanisms by which herbivorous insects control the morphogenesis of the plant host are discussed. We propose that C. minensis has a recognition system to identify insect attack and evaluate the effectiveness of early response triggering compartmentalized defense mechanisms by protecting the injured area with a new layer of periderm.

The odd roots of Campylocentrum (Angraeciinae-Orchidaceae): an anatomical study of its morphologically variable roots

Although some anatomical studies have been performed in Angraecinae, knowledge about the anatomy of the genus Campylocentrum is as yet incipient. The aim of this study is to anatomically characterize the structure of the different kinds of roots in the genus. Roots from 12 species were analyzed, including all the morphological variation in the genus (smooth and granulose surface). The leafless species are characterized by endovelamen, exodermal and endodermal cell walls thicker than in the leafy species. The species with terete leaves can be split in two groups: one constituting C. poeppigii, whose roots have a granulose surface produced by numerous unicellular, absorbent hairs; the second formed by six species from the Atlantic Forest. In this second group, the same granulose root appearance is produced by tufts of epivelamen in addition to the unicellular, absorbent root hairs. The other species in the genus, with conduplicate leaves, do not present a pattern for grouping. Some of them, such as C. serranum and C. micranthum, share a similar structure with the leafless species, but with thinner exodermal and endodermal cell walls. Other species, such as C. crassirhizum and C. jamaicense, are the only ones in the genus with ○-thickened cells in the exodermis.

Areolar structure in some Opuntioideae: occurrence of mucilage cells in the leaf-glochid transition forms in Opuntia microdasys (Lhem.) Pfeiff.

ABSTRACT One of the most remarkable features of Cactaceae are the areoles, axillary outgrowths, which produce trichomes, spines and leaves. The subfamily Opuntioideae K. Schum. shows the widest diversity of transition forms between leaves and spines, which represents anatomical evidence that spines and glochids are modified leaves. The purpose of this paper is to provide an anatomical description of the areolar structure in four species of Opuntioideae, in order that new anatomical homology between spines/glochids and leaves may be clarified. Different patterns of areole morphology are observed: 1) Austrocylindropuntia subulata (Muehl.) Backeb. showing terete and persistent leaves; areoles with persistent spines, glochids and trichomes; 2) Opuntia monacantha (Willd.) Haw. with terete caducous leaves and persistent spines, glochids and trichomes; 3) Opuntia rufida Engelm. with terete deciduous leaves and areoles with glochids and trichomes; and 4) Opuntia microdasys (Lhem.) Pfeiff. with early caducous leaves and areoles showing trichomes and leaf-spine and leaf-glochid transition forms. The development of the areolar structures is very similar in all species, following the description of the literature for other Cactaceae Juss. In O. microdasys is described a new anatomical character in the family: mucilage cells in the leaf-glochid transition forms, which may have functional importance for water storage in species devoid of persistent leaves.

Caracteres anatômicos do segmento caulinar em espécies da subfamília Opuntioideae (Cactaceae)

This work presents a general anatomical characterization of the stem segments of four species of Opuntioideae with emphasis on the dermal and ground tissue systems, and a review of the anatomical studies for the subfamily. Some characters are distinctive for the studied species, such as: stomata position in the same level of the remaining epidermal cells, occurrence of papillose epidermis and trichomes, stomata type, cell type of the palisade cortex, and occurrence of mucilaginous channel next to the phloem. In conclusion, our results show that some anatomical aspects on the dermal and ground systems are useful in the diagnosis of species. Furthermore, original data about distribution of medullary cells with secondary wall thickening are described in Opuntia or Opuntioideae.