Colony enlargement in Phaeocystis globosa has been considered as an induced defense strategy that reduces its susceptibility to grazers, but allocation costs inflicted by this plastic morphological defense are poorly understood. We conducted experiments in which P. globosa cultures were exposed to chemical cues from copepods, ciliates and heterotrophic dinoflagellates, respectively, under nutrient sufficient and deficient conditions to evaluate allocation costs associated with induced defense. Phaeocystis globosa responded to chemical cues from grazers by increasing colony diameter irrespective of nutrient conditions. We did not find trade-offs between induced defense and growth rate under nutrient sufficient conditions. Instead, induced defensive P. globosa had higher growth rates than non-induced P. globosa. When nutrient became limited, P. globosa exposed to grazing cues from copepods and dinoflagellates had significantly decreased growth rates when compared with non-induced P. globosa. We suggested that the decreased growth revealed allocation costs associated with induced defense that may influence on the trophic interactions between Phaeocystis and consumers.

Phaeocystis globosa has become one of the primary causes of harmful algal bloom in coastal areas of southern China in recent years, and it poses a serious threat to the marine environment and other activities depending upon on it (e.g., aquaculture, cooling system of power plants), especially in the Beibu Gulf. We found colonies of P. globosa collected form Guangxi (China) were much larger than those obtained from Shantou cultured in lab. To better understand the causes of giant colonies formation, colonial cells collected from P. globosa GX strain (GX-C) and ST strain (ST-C) were separated by filtration. Morphological observations, phylogenetic analyses, rapid light-response curves, fatty acid profiling and transcriptome analyses of two type cells were performed in the laboratory. Although no differences in morphology and 18S rRNA sequences of these cells were observed, the colonies of GX strain (4.7 mm) are 30 times larger than those produced by the ST strain (300 μm). The rapid light-response curve of GX-C was greater than that of ST-C, consistent with the upregulated photosynthetic system, while the fatty acid content of GX-C was lower than that of ST-C, also consistent with the downregulated synthesis of fatty acids and the upregulated degradation of fatty acids. In summary, the increased energy generated by GX-C is allocated to promote the secretion of extracellular polysaccharides for colony formation. We performed a physiological and molecular assessment of the differences between the GX-C and ST-C strains, providing insights into the mechanisms of giant colonies formation in P. globosa.

Plant response to light is a complex and diverse phenomenon. Several studies have elucidated the mechanisms via which light and hormones regulate hypocotyl growth. However, the hormone-dependent ultraviolet-B (UV-B) response in plants remains obscure. Involvement of gibberellins (GAs) in UV-B-induced hypocotyl inhibition and its mechanisms in Arabidopsis thaliana were investigated in the present research. UV-B exposure remarkably decreased the endogenous GA₃ content through the UV RESISTANCE LOCUS 8 (UVR8) receptor pathway, and exogenous GA₃ partially restored the hypocotyl growth. UV-B irradiation affected the expression levels of GA metabolism-related genes (GA20ox1, GA2ox1 and GA3ox1) in the hy5-215 mutant, resulting in increased GA content.ELONGATED HYPOCOTYL 5 (HY5) promoted the accumulation of DELLA proteins under UV-B radiation; HY5 appeared to regulate the abundance of DELLAs at the transcriptional level under UV-B. As a result, the GA₃ content decreased, which eventually led to the shortening of the hypocotyl. To conclude, the present study provides new insight into the regulation of plant photomorphogenesis under UV-B.

Transparent exopolymer particles (TEP) are sticky polymeric substances that are commonly found in the periphery of microbial cells or colonies. They can naturally flocculate smaller suspended particles into larger aggregates and thus play a crucial role in the biological pump and the global carbon cycle. Phytoplankton are the major contributors to marine TEP production, whereas the way TEP production interacts with abiotic factors at the species level is generally unknown but critical for estimating carbon fluxes. In this study, the effects of temperature on TEP production and carbon allocation were studied in two representative diatom species (Nitzschia closterium and Chaetoceros affinis) and two model dinoflagellate species (Prorocentrum micans and Scrippisella trichoidea). The results showed that temperature had a significant impact on TEP production in all species. First, increased temperature promoted the TEP production of all four species. Second, elevated temperature affected the carbon pool allocation, with enhanced dissolved organic carbon (DOC) exudation in the form of TEP in all species. The TEP-C/DOC percentages of N. closterium and P. micans were 93.42 ± 5.88% and 82.03 ± 21.36% at the highest temperature (24 °C), respectively, which was approximately two to five times higher than those percentages at 16 °C. In contrast, TEP’s contribution to the POC pool is lower than that to the DOC pool, ranging from 6.74 ± 0.79% to 28.31 ± 1.79% for all species. Moreover, phytoplankton TEP production may be related to cellular size and physiology. The TEP content produced by the smallest N. closterium (218.96 ± 15.04 fg Xeq./μm³) was ~5 times higher compared to P. micans, S. trichoidea, or C. affinis. In conclusion, TEP production is temperature sensitive and species specific, which should be taken into consideration the regarding TEP-mediated oceanic carbon cycle, particularly in the context of global warming.