World Subtropics Research Articles

Plant regeneration from embryogenic callus-derived from immature leaves of Momordica charantia L

Bitter melon (Momordica charantia L.), a widely cultivated food and medicinal plant native to the world's subtropics and tropics, is a Cucurbitaceae rich in carotenoids. However, the low seed germination frequency and progeny variability associated with the production of this plant have a substantial impact on its growth and yield. These constraints affect the availability and exploitation of this crop, especially the fruits, which are rich in secondary metabolites such as β-carotene and α-carotene. In vitro regeneration would help overcome the obstacle linked to the germination of this plant and increase its yield and utilization. A reproducible in vitro organogenesis protocol was established using bitter melon embryogenic callus derived from immature leaf explants of in vivo grown seedlings and in vitro plantlets. Regeneration via callus was conducted on MSB5 media augmented with different plant growth regulator concentrations. The maximum frequency of callus formation (95.09 %) was produced in MSB5 media incorporated with 1.2 mg L−1 NAA augmented with 0.5 mg L−1 TDZ. MSB5 medium with no growth regulators was observed to be the most suitable for the shoot and root formation from the callus, producing a significantly high shoot percentage of 90.91 % and 21.53 shoots per explants, and the highest rooting frequency and root number of 88.92 % and 6.23 roots per explant, respectively, from leaf-derived callus of in vitro plantlets. The elongated plantlets had grown to a significantly higher average height of 12.20 cm on media added with 0.75 mg L−1 GA3. This reproducible method for regenerating bitter melon plantlets could facilitate mass multiplication, conservation, and commercial field production.

Transcript expression level analysis of phytoene synthase and phytoene desaturase associated with β-carotene content in selected Kenyan Bitter melon.

Bitter melon (Momordica charantia L.) is a widely cultivated food and medicinal plant native to the world's subtropics and tropics. Constraints affecting cultivation of Bitter melon affect productivity of β-carotene. Knowing the mechanism that controls the transcription of the β-carotene biosynthesis genes in Bitter melon will be of great value in improving the yield of this important metabolite. The expressions of β-carotene biosynthetic genes such as Phytoene Desaturase (PDS) and Phytoene Synthase (PSY) were evaluated in Bitter melon accessions 'GBK027049', 'NS1026', 'Mahy-ventura', '453B' and 'Sibuka532'. Transcript expression level analysis of PSY and PDS, and amount of β-carotene in leaf, stem, and fruit, were determined using quantitative polymerase chain reaction and high-performance liquid chromatography (HPLC). Root transcript expression was used as a negative control for determining relative fold change in other tissues. Expression of PSY in fruit (6 to 27-fold compared to the control) was higher than in the other organs for all accessions. This was also the case of PDS expression (10 to 29-fold compared to the control). Leaves had the highest β-carotene concentration (17.92-45.35µg∙g-1); there was no difference between stems (5.67-12.75µg∙g-1) and fruit (6.18-12.53µg∙g-1). The highest β-carotene content was in accessions 'GBK027049' (12.53-45.35µg∙g-1) and '453B' (6.18-32.09µg∙g-1). The PSY and PDS expressions were positively correlated with amount of β-carotene in leaves, stems, and fruits. Bitter melon leaves, especially those of 'GBK027049' and '453B' accessions, are an alternative to alleviate the β-carotene deficiencies in the world and especially in Africa.

First global molecular phylogeny and biogeographical analysis of two arachnid orders (Schizomida and Uropygi) supports a tropical Pangean origin and mid‐Cretaceous diversification

AbstractAimWe sought to illuminate the history of the arachnid orders Schizomida and Uropygi, neither of which have previously been subjected to global molecular phylogenetic and biogeographical analyses.LocationSpecimens used in this study were collected in all major tropical and subtropical areas where they are presently found, including the Americas, Africa, Australia and the Indo‐Pacific region.MethodsFrom field‐collected specimens, we sequenced two nuclear and two mitochondrial markers, combined these with publicly available data, and conducted multi‐gene phylogenetic analyses on 240 Schizomida, 24 Uropygi and 12 other arachnid outgroups. Schizomid specimens included one specimen from the small family Protoschizomidae; other schizomid specimens were in Hubbardiidae, subfamily Hubbardiinae, which holds 289 of the order's 305 named species. We inferred ancestral areas using the Dispersal‐Extinction‐Cladogenesis model of range evolution, and we used fossil calibrations to estimate divergence times.ResultsWe recovered monophyletic Schizomida and Uropygi as each other's sister group, forming the clade Thelyphonida, and terminals from the New World were usually positioned as the earliest diverging lineages. The ancestral area for schizomids reconstructed unambiguously to the region comprised of Mexico, Southern California and Florida (the xeric New World subtropics). Optimal trees suggested a single colonization of the Indo‐Pacific in both orders, although this did not receive bootstrap support. Molecular dating gave an Upper Carboniferous origin for each order, and a mid‐Cretaceous expansion of Schizomida, including the origin and initial diversification of those in the Indo‐Pacific.Main conclusionsAncestral area reconstructions, molecular dating and fossil evidence all support an Upper Carboniferous, tropical Pangean origin for Thelyphonida, Schizomida and perhaps Uropygi. Much of this region became unsuitable habitat for these arachnids during the breakup of Pangea, but they persisted in the area that is now Meso‐ and South America. From there they then expanded to the Indo‐Pacific, where schizomids today display an idiosyncratic combination of microendemism and long‐range dispersal.

Seasonal shifts in genotype frequencies in the invasive cladoceran Daphnia lumholtzi in Lake Texoma, U.S.A.

Summary1. We examined the ecological genetics of the invasive cladoceran Daphnia lumholtzi in a reservoir (Lake Texoma) in the southern USA. This species originates from the Old World subtropics and has spread across North America since the late 1980s after its inadvertent introduction to a reservoir in northeastern Texas.2. The population genetic structure of D. lumholtzi was examined seasonally on 22 dates over a 3‐year period along a natural temperature and salinity gradient.3. A two‐allele polymorphism at the phosphoglucose isomerase (PGI) locus was detected, while other loci tested showed no variation. Significant temporal heterogeneity existed in genotype frequencies with a major shift between summer and autumn.4. Results of a multiple linear regression analysis revealed that a significant amount of variation was explained by day length, temperature and conductivity. Additionally, significant spatial heterogeneity of genotype frequencies between lake stations was observed, but was restricted to the summer.5. Clonal isolates were used in controlled laboratory temperature and salinity tolerance experiments. Results suggest that salinity and temperature tolerance differed between PGI genotypes.6. Genotype × environment interactions may play a significant role in the micro‐evolutionary dynamics of this invasive species and may have facilitated its rapid expansion across the North American continent.

Intercomparison of Simulated Global Vegetation Distributions in Response to 6 kyr BP Orbital Forcing

Abstract The response of ten atmospheric general circulation models to orbital forcing at 6 kyr BP has been investigated using the BIOME model, which predicts equilibrium vegetation distribution, as a diagnostic. Several common features emerge: (a) reduced tropical rain forest as a consequence of increased aridity in the equatorial zone, (b) expansion of moisture-demanding vegetation in the Old World subtropics as a consequence of the expansion of the Afro–Asian monsoon, (c) an increase in warm grass/shrub in the Northern Hemisphere continental interiors in response to warming and enhanced aridity, and (d) a northward shift in the tundra–forest boundary in response to a warmer growing season at high northern latitudes. These broadscale features are consistent from model to model, but there are differences in their expression at a regional scale. Vegetation changes associated with monsoon enhancement and high-latitude summer warming are consistent with palaeoenvironmental observations, but the simulated sh...

Sustainable Forestry: The Role of Eucalypts and Lessons from Natural and Artificial Monoculture Systems

SYNOPSIS Throughout much of the world's subtropics, eucalypts have become favoured plantation trees for commercial forestry. The reasons for their popularity are similar to those that made Norway spruce the favoured plantation tree in Central Europe. As is well known, however, many Norway spruce stands all over Europe are now in a state of decline, suffering from mineral deficiencies. Such a fate can be predicted also for repeated eucalypt plantations. Moreover, eucalypts are in a state of decline in East Australia from Canberra to Brisbane. Here the decline is related to insects that devour eucalypts because of intensified agricultural development. High-yielding eucalypts are, of course, attainable in the short run. For long-term sustainability, however, a number of ecological parameters need to be observed. Among these is an important biological component, which will be the central theme of this paper.

XYLEM ANATOMY OF SOPHORA (LEGUMINOSAE) IN RELATION TO HABIT

CUMBIE, B. G., and DAN MERTZ. (U. Missouri, Columbia.) Xylem anatomy of Sophora (Leguminosae) in relation to habit. Amer. Jour. Bot. 49(1): 33-40. Illus. 1962.-A comparison of 8 tree, shrub, and herbaceous species of Sophora showed considerable variation in structural organization of the secondary xylem in relation to habit. A reduction in duration of cambial activity has been accompanied by a decrease in conspicuousness of storied structure, more frequent arrangement of vessels in multiples, the formation of narrower rays, and a striking reduction in amount of axial xylem parenchyma. On the other hand, relatively minor changes in size of xylem elements have resulted from decreased cambial activity, as shown by comparing the first-formed secondary xylem elements of woody and herbaceous species. In many structural features, shrubs were found to be more or less intermediate between the tree and herbaceous species, at least in the early stages of development. These observations indicate that the often repeated generalization that the organization of herbaceous stems resembles that of the first year's growth in closely related woody species is not always applicable. AN EARLIER investigation of stem anatomy in herbaceous Leguminosae (Cumbie, 1960) provided a basis for comparing the structural organization of secondary xylem among plants of different habits. Although only limited comparisons were possible, a number of differences in xylem structure between woody and herbaceous species indicated that the often repeated generalization that the organization of herbaceous stems resembles the first year's growth in closely related woody species may not always be valid. The observations suggested, however, that intensive studies of individual genera would permit the modifications accompanying decreased cambial activity to be defined more precisely. This investigation of the genus Sophora extends the earlier study. Sophora is one of several genera in the Leguminosae which includes species of widely varying habits, ranging from tall trees to small, herbaceous plants. Although usually described as a woody genus, there are a few perennial herbs among approximately 70 species (Turner, 1960) of Sophora. The species are distributed sporadically over a large part of the world, mainly the New World subtropics, warmer temperate regions of North America and Asia, and many islands in the Pacific area. Because of its widespread distribution, the genus is usually considered to be an old one (Andrews, 1914). MATERIALS AND METHODS-Since a comparison of xylem anatomy of species of different habits was the main objective of this study, 8 representative tree, shrub, and herbaceous species were included. These are listed in Table 1 with collection data cited according to the method proposed by Stern and Chambers (1960). Most of the material was pro. 1 Received for publication May 29, 1961. This investigation was supported in part by a grant to the first author while on the staff of Texas Technological College. Sincere appreciation is extended Professor Charles Heimsch for his helpful advice and constructive criticism of the manuscript. vided by Professor B. L. Turner, The University of Texas; Dr. W. L. Stern, Smithsonian Institution; and Professor R. H. Wetmore, Harvard University. The assistance of these individuals is gratefully acknowledged. Except for S. japonica, young twigs for all woody species as well as older material were available. Following the procedures outlined by Wetmore (1932), stems and blocks of wood were sectioned by the celloidin method. Sections were stained in Heidenhain's iron-alum hematoxylin and safranin. Macerations were prepared following Jeffrey's method as outlined by Johansen (1940). In the anatomical descriptions, the diagnostic features believed most significant for this investigation were selected from among those listed by Tippo (1941) . Cell dimensions were determined by measuring 100 elements for each character. Most descriptive terminology adheres to that advocated by the Committee on Nomenclature of the International Association of Wood Anatomists (1957). Since many xylem characteristics in woody plants undergo ontogenetic changes associated with growth in diameter, the development of each character was considered in plants of this habit. In referring to xylem in different stages of development, the secondary xylem at the outer margin of the primary xylem is designated as first-formed secondary xylem or wood near the pith, and the most recently formed xylem as outer or later-formed wood. It seemed inadvisable to use the term adult wood or mature wood for the outer wood in this study, because it was not possible to determine if most samples available were actually mature, and in some specimens it was readily apparent that the outer wood was not mature on the basis of cell dimensions. ANATOMICAL DESCRIPTIONS-Storied structureStorying of vessel elements and axial wood parenchyma occurs in all trees and shrubs examined