Abstract Continuous and intensive selective breeding reduces the genetic diversity of cultivated Pyropia stock, thereby increasing its susceptibility to diseases, and hindering the sustainable development of the Pyropia industry. To develop new Pyropia germplasms with desirable agronomic traits, a new Pyropia yezoensis strain, “Huangyou No. 1” was bred from a wild subtidal population. In this study, the genetic diversity of this strain was analyzed using AFLP. Totally, 249 loci were obtained, of which 248 were polymorphic with a polymorphism rate of 99.6%, using seven primer pairs. The intra-population polymorphism rates of the populations Wild 1 and Wild 2 were the highest (47.39% and 59.44%, respectively), while they were relatively low (20.88–24.5%) in the cultivated populations. The genetic distances between the breeding Pyropia populations cultivated in the same aquaculture farm were low. Specifically, the F 2 offspring of “Huangyou No. 1” and the control cultivar, cultivated using the “never-drying” protocol, were genetically distant from the other populations, including that from the same seedlings, yet cultivated using the “periodic-drying” protocol. The never-drying cultivation protocol had a high likelihood of influencing genetic diversity of Pyropia yezoensis .
Abstract As a temperate‐cold species, S accharina japonica often suffers heat stress when it is transplanted to temperate and subtropical zones. Study the heat stress response and resistance mechanism of S accharina is of great significance for understanding the acclimation to heat stress under domestication as well as for breeding new cultivars with heat stress resistance. In this study, we identified a set of heat stress‐responsive miRNAs and analysed their regulation during the heat stress response. CO (control) and heat stress ( HS ) sRNA libraries were constructed and sequenced. Forty‐nine known miRNAs and 75 novel miRNAs were identified, of which seven known and 25 novel miRNAs were expressed differentially under heat stress. Quantitative PCR of six selected miRNAs confirmed that these loci were responsive to heat stress. Thirty‐nine and 712 genes were predicted to be targeted by the seven known miRNAs and 25 novel miRNAs , respectively. Gene function and pathway analyses showed that these genes probably play important roles in S . japonica heat stress tolerance. The miRNAs identified represent the first set of heat‐responsive miRNAs identified from S . japonica , and their identification can help elucidate the heat stress response and resistance mechanisms in S . japonica .
Sargassum thunbergii is an economically important brown alga that is used as a perferred food for sea cucumber in China. However, reports on the reproductive biology of S. thunbergii are limited. This study observed the characteristics of mature receptacles. The effects of different temperatures, light intensities, and photoperiods on the egg release of mature S. thunbergii receptacles were investigated. A liquid-phase oxygen electrode system was used to obtain light saturation and light compensation points of egg and young thalli of S. thunbergii. Results showed that temperature was the key factor for the egg release of mature receptacles. The conditions most conducive to egg release were 20°C to 23°C temperature and 50 μmol photons m-2·s-1 to 200 μmol photons m-2·s-1 light intensity. In addition, the light saturation and compensation points of unfertilized eggs or young thalli at 2 d or 3 d postfertilization ranged from 90 μmol photons m-2·s-1 to 120 μmol photons m-2·s-1 and 14 μmol photons m-2·s-1 to 22 μmol photons m-2·s-1, respectively. The combined results provide a reference for the sporeling culture of S. thunbergii.
For clarifying the physiological and ecological adaptability of leaves of Sargassum thunbergii,the photosynthesis and respiration were investigated by using liquid-phase oxygen measurement system.The major results included two aspects:(1) The differences of maximal net photosynthetic rate(Pnmax),saturation irradiance(Isat),light compensation point(Ic),initial quantum yield α,dark respiration rate(Rd),pigment content,specific leaf area and microstructure of heteromorphism leaf(broad leaf,narrow leaf,pneumathode) were analyzed to reveal the probable reason about the change of leaf shape of S.thunbergii.(2) Effects of different temperatures and different salinities stress on Pn and Rd of broad leaves of newborn branch of S.thunbergii were researched.The preliminary analysis of the newborn branch about resistance physiology could provide reference for the artificial cultivation of S.thunbergii based on vegetative reproduction.The results are shown as follows: The optimum temperature for growth of newborn branch is 15-24 ℃ under the experimental conditions in this paper.Pn had significant reduction when temperature was 5 ℃ or higher than 30 ℃ and Rd was significantly affected by low temperature(10 ℃ or below) or high temperature(higher than 30 ℃) stress for one hour treatment.However,Pn or Rd of low temperature stress groups could nearly recover to normal level after 24 h under standard culture condition.Short-term high or low salinity tests,especially salinity 0 and salinity 60 stress,had significant influence on Pn of broad leaves.However,Pn of salinity 0 group could recover to normal level after a 24 h recovery period,but Pn could not recover after exposure to salinity 60 for 9 h.During the whole stress process,Rd of salinity 40 and salinity 50 treatments both showed high values.And salinity 0 and salinity 60 stress both had significant influence on Rd.However,Rd could recover to normal level after a 24 h recovery period after exposure to different salinities for 9 h.
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