Tomato susceptibility to Alternaria stem canker:Parameters involved in host-specific toxin-induced leaf necrosis

AAL-toxin causes severe necrosis in leaves of susceptible tomato cultivars at nanomolar concentrations. In resistant tomato cultivars harbouring the semi-dominant Alternaria stem canker resistance locus necrosis is also observed, however at much higher toxin concentrations, in both lines the percentage of the leaf area exhibiting necrosis is dependent on toxin concentration and on length of toxin exposure. However, at the same toxin concentration, periods of toxin exposure resulting in similar necrosis are much longer for the resistant than for the susceptible tomato. It was demonstrated that toxin uptake in the leaves does not imply toxin uptake in the cells since a discrepancy was observed between death of protoplasts, isolated from leaves cut for protoplast isolation immediately after incubation on AAL-toxin and necrosis in leaves when further incubated on water. However, when after exposure to AAL-toxin leaves were further incubated on water for 24 h before they were cut for protoplast isolation, a correlation was found between leaf necrosis and death of protoplasts. This suggests that further transport is needed in leaves after toxin uptake, bringing toxin to all the cells, that cannot occur in leaves cut for protoplast isolation. Light plays an important role in AAL-toxin induced necrosis and it was shown that length of light exposure controls necrosis development like toxin concentration and length of toxin exposure. The product of these 3 parameters can provide a good hint to predict the extent of leaf necrosis. The effect of light might be restricted to differentiated leaf tissue, since it was not observed in callus tissue

Swim-Training Changes the Spatio-Temporal Dynamics of Skeletogenesis in Zebrafish Larvae (Danio rerio)

Fish larvae experience many environmental challenges during development such as variation in water velocity, food availability and predation. The rapid development of structures involved in feeding, respiration and swimming increases the chance of survival. It has been hypothesized that mechanical loading induced by muscle forces plays a role in prioritizing the development of these structures. Mechanical loading by muscle forces has been shown to affect larval and embryonic bone development in vertebrates, but these investigations were limited to the appendicular skeleton. To explore the role of mechanical load during chondrogenesis and osteogenesis of the cranial, axial and appendicular skeleton, we subjected zebrafish larvae to swim-training, which increases physical exercise levels and presumably also mechanical loads, from 5 until 14 days post fertilization. Here we show that an increased swimming activity accelerated growth, chondrogenesis and osteogenesis during larval development in zebrafish. Interestingly, swim-training accelerated both perichondral and intramembranous ossification. Furthermore, swim-training prioritized the formation of cartilage and bone structures in the head and tail region as well as the formation of elements in the anal and dorsal fins. This suggests that an increased swimming activity prioritized the development of structures which play an important role in swimming and thereby increasing the chance of survival in an environment where water velocity increases. Our study is the first to show that already during early zebrafish larval development, skeletal tissue in the cranial, axial and appendicular skeleton is competent to respond to swim-training due to increased water velocities. It demonstrates that changes in water flow conditions can result into significant spatio-temporal changes in skeletogenesis

Influence of the Testa on Seed Dormancy, Germination, and Longevity in Arabidopsis

The testa of higher plant seeds protects the embryo against adverse environmental conditions. Its role is assumed mainly by controlling germination through dormancy imposition and by limiting the detrimental activity of physical and biological agents during seed storage. To analyze the function of the testa in the model plant Arabidopsis, we compared mutants affected in testa pigmentation and/or structure for dormancy, germination, and storability. The seeds of most mutants exhibited reduced dormancy. Moreover, unlike wild-type testas, mutant testas were permeable to tetrazolium salts. These altered dormancy and tetrazolium uptake properties were related to defects in the pigmentation of the endothelium and its neighboring crushed parenchymatic layers, as determined by vanillin staining and microscopic observations. Structural aberrations such as missing layers or a modified epidermal layer in specific mutants also affected dormancy levels and permeability to tetrazolium. Both structural and pigmentation mutants deteriorated faster than the wild types during natural aging at room temperature, with structural mutants being the most strongly affected

The TRANSPARENT TESTA12 Gene of Arabidopsis Encodes a Multidrug Secondary Transporter-like Protein Required for Flavonoid Sequestration in Vacuoles of the Seed Coat Endothelium

Phenolic compounds that are present in the testa interfere with the physiology of seed dormancy and germination. We isolated a recessive Arabidopsis mutant with pale brown seeds, transparent testa12 (tt12), from a reduced seed dormancy screen. Microscopic analysis of tt12 developing and mature testas revealed a strong reduction of proanthocyanidin deposition in vacuoles of endothelial cells. Double mutants with tt12 and other testa pigmentation mutants were constructed, and their phenotypes confirmed that tt12 was affected at the level of the flavonoid biosynthetic pathway. The TT12 gene was cloned and found to encode a protein with similarity to prokaryotic and eukaryotic secondary transporters with 12 transmembrane segments, belonging to the MATE (multidrug and toxic compound extrusion) family. TT12 is expressed specifically in ovules and developing seeds. In situ hybridization localized its transcript in the endothelium layer, as expected from the effect of the tt12 mutation on testa flavonoid pigmentation. The phenotype of the mutant and the nature of the gene suggest that TT12 may control the vacuolar sequestration of flavonoids in the seed coat endothelium

Tomato susceptibility to Alternaria stem canker: Parameters involved in host-specific toxin-induced leaf necrosis

AAL-toxin causes severe necrosis in leaves of susceptible tomato cultivars at nanomolar concentrations. In resistant tomato cultivars harbouring the semi-dominant Alternaria stem canker resistance locus necrosis is also observed, however at much higher toxin concentrations, in both lines the percentage of the leaf area exhibiting necrosis is dependent on toxin concentration and on length of toxin exposure. However, at the same toxin concentration, periods of toxin exposure resulting in similar necrosis are much longer for the resistant than for the susceptible tomato. It was demonstrated that toxin uptake in the leaves does not imply toxin uptake in the cells since a discrepancy was observed between death of protoplasts, isolated from leaves cut for protoplast isolation immediately after incubation on AAL-toxin and necrosis in leaves when further incubated on water. However, when after exposure to AAL-toxin leaves were further incubated on water for 24 h before they were cut for protoplast isolation, a correlation was found between leaf necrosis and death of protoplasts. This suggests that further transport is needed in leaves after toxin uptake, bringing toxin to all the cells, that cannot occur in leaves cut for protoplast isolation. Light plays an important role in AAL-toxin induced necrosis and it was shown that length of light exposure controls necrosis development like toxin concentration and length of toxin exposure. The product of these 3 parameters can provide a good hint to predict the extent of leaf necrosis. The effect of light might be restricted to differentiated leaf tissue, since it was not observed in callus tissue.

High Degree of Multiple Paternity and Reproductive Skew in the Highly Fecund Live-Bearing Fish Poecilia gillii (Family Poeciliidae)

Multiple paternity is a common phenomenon within the live-bearing fish family Poeciliidae. There is a great variety in brood sizes of at least two orders-of-magnitude across the family. However, little is known about the ramifications of this remarkable variation for the incidence and degree of multiple paternity and reproductive skew. Mollies (subgenus Mollienesia, genus Poecilia) produce some of the largest broods in the family Poeciliidae, making them an excellent model to study the effects of intra-specific variation in brood size on patterns of multiple paternity. We collected samples of the live-bearing fish Poecilia gillii from 9 locations in Costa Rica. We measured body size of 159 adult females, of which 72 were pregnant. These samples had a mean brood size of 47.2 ± 3.0 embryos, ranging from 4 to 130 embryos. We genotyped 196 field-collected specimens with 5 microsatellite markers to obtain location-specific allele frequencies. In addition, we randomly selected 31 pregnant females, genotyped all their embryos (N = 1346) and calculated two different parameters of multiple paternity: i.e., the minimum number of sires per litter using an exclusion-based method (GERUD) and the estimated number of sires per litter using a maximum likelihood approach (COLONY). Based on these two approaches, multiple paternity was detected in 22 and 27 (out of the 31) females, respectively, with the minimum number of sires ranging from 1 to 4 (mean ± SE: 2.1 ± 0.16 sires per female) and the estimated number of fathers ranging from 1 to 9 (mean ± SE: 4.2 ± 0.35 sires per female). The number of fathers per brood was positively correlated with brood size, but not with female size. Next, we calculated the reproductive skew per brood using the estimated number of sires, and found that in 21 out of the 27 multiply sired broods sires did not contribute equally to the offspring. Skew was not correlated with either female size, brood size or the number of sires per brood. Finally, we discuss several biological mechanisms that may influence multiple paternity and reproductive skew in P. gillii as well as in the Poeciliidae in general.</p

Swim-training had a differential effect on on the age at appearance of bone structures between control and trained fish.

<p><b>A,B</b>) BF50<i>_age</i> values visualized in the corresponding structures in control fish (A) and trained fish (B). The branchial region is indicated separately, ventral view. <b>C</b>) Differences in BF50<i>_age</i> values between control and trained fish. Positive values indicate that structures appear earlier in the trained fish. Structures with a difference less than twice the standard error are indicated in grey.</p