Melatonin Alleviates Low-Temperature Stress via ABI5-Mediated Signals During Seed Germination in Rice (Oryza sativa L.)

With increasing areas of direct sowing, low-temperature (LT) stress drastically affects global rice production. Exogenous applications of melatonin (MT) serve as one of the effective ways to improve seed germination under various stress conditions. In this study, we found that MT treatment greatly improved the LT stress-induced loss of germination percentage and the weak performance of seedlings under LT of constant 20°C (LT20). This was largely dependent on the activated antioxidant system and enhanced activities of storage substance utilization-associated enzymes. Moreover, we also detected that exogenous feeding of MT significantly increased the biosynthesis of gibberellin (GA) and endogenous MT but simultaneously inhibited the accumulation of abscisic acid (ABA) and hydrogen peroxide (H2O2) under LT20 stress. These results suggested that MT had antagonistic effects on ABA and H2O2. In addition, MT treatment also significantly enhanced the expression of CATALYSE 2 (OsCAT2), which was directly regulated by ABA-INSENSITIVE 5 (OsABI5), a core module of ABA-stressed signals, and thus promoting the H2O2 scavenging to reach reactive oxygen species (ROS) homeostasis, which consequently increased GA biosynthesis. However, in abi5 mutants, OsCAT2 failed in response to LT20 stress irrespective of MT treatment, indicating that OsABI5 is essential for MT-mediated seed germination under LT20 stress. Collectively, we now demonstrated that MT showed a synergistic interaction with an ABI5-mediated signal to mediate seed germination, partially through the direct regulation of OsCAT2.

Survival, Growth, and Development in the Early Stages of the Tropical Gar Atractosteus tropicus: Developmental Critical Windows and the Influence of Temperature, Salinity, and Oxygen Availability

Alterations in fish developmental trajectories occur in response to genetic and environmental changes, especially during sensitive periods of development (critical windows). Embryos and larvae of Atractosteus tropicus were used as a model to study fish survival, growth, and development as a function of temperature (28 °C control, 33 °C, and 36 °C), salinity (0.0 ppt control, 4.0 ppt, and 6.0 ppt), and air saturation (control ~95% air saturation, hypoxia ~30% air saturation, and hyperoxia ~117% air saturation) during three developmental periods: (1) fertilization to hatch, (2) day 1 to day 6 post hatch (dph), and (3) 7 to 12 dph. Elevated temperature, hypoxia, and hyperoxia decreased survival during incubation, and salinity at 2 and 3 dph. Growth increased in embryos incubated at elevated temperature, at higher salinity, and in hyperoxia but decreased in hypoxia. Changes in development occurred as alterations in the timing of hatching, yolk depletion, acceptance of exogenous feeding, free swimming, and snout shape change, especially at high temperature and hypoxia. Our results suggest identifiable critical windows of development in the early ontogeny of A. tropicus and contribute to the knowledge of fish larval ecology and the interactions of individuals × stressors × time of exposure.

Organization of the cephalic lateral-line canals in Electrophorus varii de Santana, Wosiacki, Crampton, Sabaj, Dillman, Mendes-Júnior & Castro e Castro, 2019 (Gymnotiformes: Gymnotidae)

Electrophorus spp. generate high-voltage electric discharges for defense and hunting, and low-voltage electric discharges (as other Gymnotiformes) for electrolocation and communication. Despite intense interest in the unusual electrogenic and electroreceptive capacities of electric eels, the other sensory systems of Electrophorus spp. are relatively poorly known. Here we describe the ontogenetic development and organization of the cephalic lateral-line canals in the lowland electric eel, Electrophorus varii. Preserved specimens of larvae, juveniles, and adults were examined to describe the spatial distribution of the canals and pores. Ontogenetic shifts of the cephalic lateral line formation were observed for each canal and support a hypothesis of non-synchronized development. The morphogenesis of cephalic canals in larvae and juveniles begins just before the onset of exogenous feeding. In adults, the cephalic sensory canals are formed separately from the skull and overlay cranial and mandibular bones and muscles. This study provides the first detailed description of the development and organization of the cephalic lateral-line system in Electrophorus varii.

Histo-morphological development of the digestive tract of larval hybrid Malaysian mahseer (Barbonymus gonionotus ♀ × Tor tambroides ♂)

New carp hybrids are being developed for the aquaculture industry to support rising seafood demands. The present study was carried out to observe the changes in digestive tract, histology and functional capabilities of the new hybrid carp larvae for a better understanding of its digestive capability and the prediction of its best weaning time to a compound diet. A tubal digestive tract was elongated to the anus and buccal cavity by 3 DAH that coincided with the mouth opening and the start of exogenous feeding. A functional stomach was observed at 7 DAH with the relative gut index (RGI) of 10.7 ± 0.06. A layer of supranuclear protein was observed with lipoprotein at the outer layer of the digestive tract at 7 DAH. The morpho-histological results of this study indicated that hybrid Malaysian mahseer larvae should be able to digest, ingest and absorb an artificial diet beginning from 7 DAH. At this stage, the hybrid larvae could be gradually or perhaps totally weaned to an artificial diet of a suitable particle size.

Mutation of OsGUN4 Uncoupled the Sugar-dependent Signals to Regulate Starch Biosynthesis in Rice

Background Starch biosynthesis requires plastid-to-nucleus signals to ordinate the flow of carbon, which is partly mediated by tetrapyrrole intermediates. We previously revealed that mutation of the Genomes Uncoupled 4 (OsGUN4) would affect tetrapyrrole intermediates, but the underlying mechanisms for regulatory roles of OsGUN4 on starch biosynthesis remains largely unknown. Results In this study, we revealed that the OsGUN4 mutation not only retarded the carbon flow from sucrose to starch but also disabled the sensitive response to exogenous feeding sucrose. Moreover, extra addition of norflurazon (NF) would aggravate insensitivity to the sucrose-dependent induction in gun4epi, especially exhibiting collapse declines of the starch biosynthetic enzymes’ activities. However, genes encoding starch synthetic enzymes performed discordance with the activities of starch biosynthesis associated enzymes upon on the scarce expression of OsGUN4 in gun4epi. These results indicated that OsGUN4 played regulatory roles on biosynthetic genes and enzyme activity in starch biosynthesis. Furthermore, we also concluded that 1O2 derived from GUN4/protoporphyrin IX (proto) might be responsible for the sugar-dependent signals to regulate starch biosynthesis, due to positive correlations between the singlet oxygen (1O2) and many starch biosynthetic genes that were subjected to the control of three reported transcriptional factors (TFs) during starch biosynthesis. Eventually, the OsGUN4 mutation would also relieve the repression of glucose on Snf1-related protein kinases (SnRK1) but seem to negatively mediate the functioning of ADP-Glc pyrophosphorylase (AGPase). Conclusion In summary, we demonstrated that OsGUN4 serve as a broker to activate 1O2-mediated signals in the sugar signaling cascade, possibly functioning upstream through TFs, and that OsGUN4 played roles in the SnRK1A-mediated signals, partly through the accumulations of sugars, e.g. glucose or sucrose.

Histological Studies on Digestive System Development and Early Feeding Activity of Pangasius Hybrid Larvae

This study was conducted to investigate the digestive system development and early feeding activity of Pangasius hybrid larvae. Four crossbreeding program in triplicate were examined between Pangasius hypopthalmus and Pangasius nasutus. Results showed that the digestive systems of both hybrid larvae were poorly developed immediately after hatching. The digestive system of the newly hatched larvae consisted of straight undifferentiated tube and anus still closed. The gastro intestinal tract, liver and pancreas were formed and developed by 2-dAH. The zymogen granules were also observed in the pancreas and thus imply that function of pancreas started before the exogenous feeding period. Gastric glands were only present and started to secrete enzyme on 6-dAH. Artemia were first seen in digestive tract of the larvae at 54-hAH. However, onset of exogenous feeding was detected at 60-hAH, whereas stomach became enlarged with isometric epithelium cells, which were different from the elongated cells in the intestinal part. Keywords: Pangasius, hybrid, digestive system, histology

Peculiarities of Hypophthalmichthys molitrix (Valenciennes, 1844) Embryonic Development Under Conditions of Artificial Reproduction in Uzbekistan

Embryonic development of Silver Carp (Hypophthalmichthys molitrix) was studied; the species was introduced from China to Uzbekistan in the early 1960s. More than 10 generation changes were taken place in local conditions. Artificial reproduction by using gonadotropic stimulation of ripening and eggs incubation is main method to provide reproduction of the species in the country. Embryonic development passed normally. A larvae hatching occurs after 32 hours after fertilization at water temperature 21–23 °C, transition to mixed feeding of larvae after 4 days, to exogenous feeding after 5 days. Embryonic development rate is some higher than in 1960–1980s in local conditions and higher than in the river Yangtze. Construction of water supply in hatchery provides more stable water temperature without noticeable changing in night.