The Halophyte Seashore Paspalum Uses Adaxial Leaf Papillae for Sodium Sequestration

Salinity is a growing issue worldwide, with nearly 30% of arable land predicted to be lost due to soil salinity in the next 30 years. Many grass crops that are vital to sustain the world’s caloric intake are salt sensitive. Studying mechanisms of salt tolerance in halophytic grasses, plants that thrive in salt conditions, may be an effective approach to ultimately improve salt-sensitive grass crops. Seashore paspalum (Paspalum vaginatum) is a halophytic Panicoid grass able to grow in salt concentrations near that of seawater. Despite its widespread cultivation as a sustainable turfgrass, the mechanism underlying its ability to retain high Na⁺ concentrations in photosynthetic tissue while maintaining growth remains unknown. We examined the leaf structure and ion content in P. vaginatum ‘HI10’, which shows increased growth under saline conditions, and Paspalum distichum ‘Spence’, which shows reduced growth under salt, to better understand the superior salt tolerance of cv HI10. A striking difference between cv HI10 and cv Spence was the high steady-state level of K⁺ in cv HI10. Imaging further showed that the adaxial surface of both cv HI10 and cv Spence contained dense costal ridges of papillae. However, these unicellular extensions of the epidermis were significantly larger in cv HI10 than in cv Spence. The cv HI10 papillae were shown to act as Na⁺ sinks when plants were grown under saline conditions. We provide evidence that leaf papillae function as specialized structures for Na⁺ sequestration in P. vaginatum, illustrating a possible path for biotechnological improvement of salt-sensitive Panicoid crops with analogous leaf structures.

About 20% of irrigated land is considered saline, with the amount of saline soils increasing worldwide (Mayak et al., 2004). This is due to increased irrigation in agricultural fields necessitated by more frequent droughts due to climate change. This trend is alarming due to the high salt sensitivity of most crop species that we rely on for vital resources. Yield reduction in crops in saline soils amounts to losses on the order of 12 to 27.3 billion U.S. dollars annually (Qadir et al., 2014). Thus, the improvement of salt tolerance in plants will become key in the coming decades. Breeding salt-tolerant crops is a cost-effective approach to improve growth in saline soils. Although much work has focused on breeding salt-tolerant species, progress in this area has been slow due to the complex genetic and physiological nature of the salt response. Furthermore, most research has been conducted on glycophytic model systems that are salt sensitive (Munns and Gilliham, 2015). Unraveling the salt-tolerance mechanisms in halophytes, species that can complete their life cycle in 200 mm salt concentrations, and transferring these pathways into glycophytes is therefore of great interest (Rajalakshmi and Parida, 2012; Roy and Chakraborty, 2014).Both glycophytes and halophytes have evolved a multitude of salt-tolerance mechanisms, including sodium (Na⁺) exclusion, sequestration, and secretion; osmolyte production; ion homeostasis; and reactive oxygen species (ROS) detoxification (Meng et al., 2018). Often, mechanisms present in glycophytes, such as osmolyte production and Na⁺ exclusion, are utilized in halophytes at higher efficiency (Wyn Jones and Storey, 1981; Grieve and Maas, 1984). However, halophytes also use mechanisms that are absent in glycophytes. Salt sequestration and secretion via salt glands is a halophyte-specific mechanism of coping with salt (Flowers and Colmer, 2008). Salt glands are found in over 50 species in 14 angiosperm families with four subtypes: epidermal bladder cells, complex multicellular glands, bicellular glands, and unicellular glands (Dassanayake and Larkin, 2017). The Poales order contains ∼8% of all halophytes (Flowers et al., 2010) and has therefore been the focus of much salt-gland-focused work (Ceccoli et al., 2015). As salt tolerance has independently evolved >70 times in grass lineages (Bennett et al., 2013), studying these salt sequestering/secreting structures in grasses is an excellent approach to better understand salt tolerance mechanisms in halophytes.Most structural and physiological work on salt glands in grasses has been conducted in the Chloridoideae and Oryzoideae subfamilies. Grasses carry either unicellular or bicellular glands, often referred to as glandular trichomes or microhairs, on the leaf surface (Dassanayake and Larkin, 2017). Microhairs have been observed on the leaf surface in all grass subfamilies except the Pooideae, and have evolved diverse functions including the sequestration or secretion of substances such as callose and heavy metals (Burke et al., 2000; Ceccoli et al., 2015). Unicellular structures on the adaxial leaf side able to secrete salt are only found in the Oryzoideae wild rice species Porteresia coarctata (Flowers et al., 1990; Sengupta and Majumder, 2009). Salt glands in the Chloridoideae are bicellular, consisting of a cap cell and a lower basal cell, both of which are dense in cytoplasm and mitochondria (Ceccoli et al., 2015). The cuticle is thickened above the cap cell in some species, forming a cuticular chamber used for storing secreted salts (Amarasinghe and Watson, 1988). In the Panicoideae, a few cases of Na⁺ secretion have been reported (McWhorter et al., 1995; Ramadan and Flowers, 2004), but to date, no sequestration structures have been identified.The Panicoideae subfamily includes the agronomically important food crops maize (Zea mays) and sorghum (Sorghum bicolor) in addition to the biofuel grasses miscanthus (Miscanthus sinensis), switchgrass (Panicum virgatum), and sugarcane (Saccharum officinarum). One of the most salt-tolerant species in the Panicoideae is the halophyte seashore paspalum (Paspalum vaginatum). It is cultivated as a turfgrass worldwide and derives its popularity from its ability to be irrigated with brackish water. P. vaginatum can survive in salt concentrations near that of seawater (Uddin et al., 2012) and uses osmolyte production, ion homeostasis, and Na⁺ exclusion to cope with salt stress (Peacock and Dudeck, 1985; Lee et al., 2008; Guo et al., 2016). However, its ability to maintain growth while accumulating high levels of Na⁺ in leaf tissue remains perplexing.Here, we studied the leaf structure and Na⁺ sequestration in ‘HI10’, a P. vaginatum cultivar, and ‘Spence’, a Paspalum distichum cultivar. P. vaginatum and P. distichum are closely related (and possibly the same species; Eudy et al., 2017), and constitute group “Disticha” in the tribe Paspaleae. P. distichum is less salt tolerant than P. vaginatum and is typically found in freshwater habitats (Leithead et al., 1971). P. vaginatum and P. distichum therefore represent a useful species pair to study salt tolerance. Furthermore, their salt responses can be compared with those of sorghum, a Panicoid glycophyte. Our main research objective was to identify the phenotypic and physiological factors that contribute to the differential tolerance to salt stress of the two Paspalum spp. cultivars and sorghum ‘BTx623’. We show that both Paspalum species contain dense rows of translucent papillae on the adaxial surface. The papillae are unicellular protrusions from epidermal cells and are much larger in cv HI10 than in cv Spence. We further demonstrate that the papillae sequester Na⁺ under salt stress. This study thus provides evidence of Na⁺ sequestration in specialized leaf-borne organs within the Panicoideae.     

Localization and transport of lipids in the avian ovarian follicular layers and the structural relationship of theca and granulosa to the basement membrane

We describe the localization of lipids in the wall and superficial ooplasm of the largest avian ovarian follicles by the use of different fixatives and light and electron microscopy. We demonstrate that each yolk globule is always accompanied by one or more highly osmiophilic and sudanophilic alcohol insoluble yolk masses, which we have called satellite yolk. Together with the protein containing yolk globule it forms an integral morphological part of a compartmentalized, bipartite yolk system. Cytochemical, histoautoradiographic, biochemical, and light and electron microscopical aspects of satellite yolk were studied. At the start of satellite yolk formation in the 3–4 mm diameter follicle (when the oocyte begins to yellow) the distribution of the microcirculation of the follicle wall becomes printed on the underlying superficial ooplasm of the oocyte. The oocyte then presents so-called yolk mountains (containing satellite yolk), only localized below the thecal capillary sinus and not below the efferent and radially perforating thecal veins (black hole regions). We also describe the structural continuity between the thecal intercellular spaces and the microvilli-associated extracellular spaces of the granulosa cells via the basement membrane. The thecal cells present centripetal extensions into the basement membrane and the basement membrane material extends centripetally into the granulosa microvillar channels. Therefore, at least two cellular barriers are crossed when fat or fat precursors are transported from the thecal capillary sinus to the ooplasm.     

Galactomannan detection in nonserum specimens: Where do we stand?

Aspergillus species have emerged as a cause of devastating infections in immunocompromised patients. A circulating antigen in aspergillosis is galactomannan (GM), a cell wall constituent released during growth. GM can be detected in serum of neutropenic patients at an early stage of disease, often before clinical signs become apparent. Until recently, data regarding performance of the test in other fluids were lacking. It was suggested that, in absence of neutropenia, viable fungi can endure in lung tissue, whereas circulating markers remained undetectable because of clearance by circulating neutrophils. Indeed, bronchoalveolar lavage (BAL) fluid proved to be a better specimen for the diagnosis of invasive aspergillosis in critically ill patients. The published clinical experience with GM in BAL fluid in solid organ transplant recipients also showed promising results. The evidence for using GM in other body fluids, such as cerebrospinal fluid and urine, is based on case reports. The objective of this review is to summarize the current evidence for GM detection in nonserum fluids.     

Drought affects the rate and duration of organ growth but not inter-organ growth coordination

Drought at flowering and grain filling greatly reduces maize (Zea mays) yield. Climate change is causing earlier and longer-lasting periods of drought, which affect the growth of multiple maize organs throughout development. To study how long periods of water deficit impact the dynamic nature of growth, and to determine how these relate to reproductive drought, we employed a high-throughput phenotyping platform featuring precise irrigation, imaging systems, and image-based biomass estimations. Prolonged drought resulted in a reduction of growth rate of individual organs—though an extension of growth duration partially compensated for this—culminating in lower biomass and delayed flowering. However, long periods of drought did not affect the highly organized succession of maximal growth rates of the distinct organs, i.e. leaves, stems, and ears. Two drought treatments negatively affected distinct seed yield components: Prolonged drought mainly reduced the number of spikelets, and drought during the reproductive period increased the anthesis-silking interval. The identification of these divergent biomass and yield components, which were affected by the shift in duration and intensity of drought, will facilitate trait-specific breeding toward future climate-resilient crops.

When affected by drought, the plant responds by adjusting the growth of individual organs but not the coordination between the organs.     

X chromosomal mutations and spermatogenic failure

The X and Y chromosomes, the sex chromosomes, are important key players in germ cell development. Both chromosomes contain genes that are uniquely expressed in male spermatogenesis. Furthermore, these chromosomes are special because men only have a single copy of them. These features make the sex chromosomes interesting for studying in view of spermatogenesis defects. The role of the Y chromosome, together with the presence of Yq microdeletions, in male infertility is well established. Less well-understood are the X-linked genes, their expression patterns and potential impact on male infertility. This review provides an overview of the current knowledge on potential spermatogenesis genes that are located on the mouse and human X chromosomes. A summary is given on knock-out mice models in which X-linked genes have been shown to alter spermatogenesis, and on genes that have been studied in humans. Finally, new research areas like miRNA analysis, Genome Wide Association Studies (GWAS) and array comparative genomic hybridisation (CGH) studies are discussed. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.     

Factors Influencing Nodule Occupancy by Inoculant Rhizobia

Inoculation of legumes under field conditions with superior nitrogen-fixing rhizobia does not always result in the desired yield increase. Often it is observed that the inoculum strain fails to occupy a significant proportion of the nodules. The introduced inoculant strains have to compete with the indigenous, often ineffective, nitrogen-fixing rhizobial population at different levels. The success of inoculation depends to a large extent on the ratio of the inoculant cells to indigenous rhizobia. However, intrinsic characteristics of the inoculant and indigenous rhizobia, and their responses to abiotic and biotic environmental variables, also influence the outcome of inoculation. In this review, the genetic basis for “efficient host-bacteria interaction” is reviewed. In addition, environmental factors that influence competition and saprophytic competence of rhizobia are discussed.     

The in vitro effects of benzodiazepines on the rat diaphragm. Structure-activity relationships

The effect of three different subgroups of benzodiazepines on the indirectly evoked twitch tension was investigated in the in vitro rat phrenic nerve - hemidiaphragm preparation. Two effects were observed: an initial increase in twitch tension at lower concentrations with some benzodiazepines, and a concentration-dependent depression at higher concentrations with all benzodiazepines. Significant differences for these effects were observed among the three subgroups of benzodiazepines and additionally within the subgroup of the 1,4-benzodiazepine-2-ketones. Structural requirements for both effects were different. For the increase of twitch tension a --CH3 substitution at R1 and a --F substitution at R2' were beneficial. For the twitch depression an --OH substitution at R3 and a --C1 substitution at R2' were optimal. An interaction between substituents at different substitution sites occurred. The potency of twitch depression showed a good correlation with literature reports of pKa values and a poor-to-inverse correlation with lipophilicity indices. A benzodiazepines antagonist, Ro 15-1788, caused no change in twitch tension in the concentration range of the investigated benzodiazepines nor did it prevent the twitch depression caused by benzodiazepines.     

Resource allocation in a simultaneously hermaphroditic slug with phally polymorphism

The theory of resource allocation assumes that a resource not allocated to one function may be reallocated to another. Thus, in hermaphroditic species, an individual that suppresses the use of one sex function may free resources for the other sex function. We determined the relative importance of male copulatory organs in terms of their fraction of the total dry body weight and tested whether in the pulmonate land slug Deroceras laeve (Müller), individuals that lack the male copulatory organs (aphallics) reallocate this resource towards the female structures and/or towards life-history traits. To this end, we raised 13 families under uniparental reproduction and compared growth, length of the juvenile period, number of eggs produced, percentage of hatched eggs and hatching time among a- and euphallics. We also measured the reproductive and sex allocation of all individuals. Six out of 13 families contained no euphallic individuals. In the other seven families, the proportion of euphallic individuals ranged from 0.13 to 0.43. There was an enormous variation in life-history traits and reproductive and sex allocation among individuals, even among individuals of the same family. Allocation to the male function was very low in euphallic slugs (i.e. 1.35% of the total body dry mass and 12.33% of the total reproductive dry mass). Our results did not reveal a reallocation from the lost male function towards the female function, nor towards one of the life-history traits. Finally, we propose a scenario that could explain the maintenance of phally polymorphism in D. laeve.