Effects of nutrient limitations on three species of zooplankton

Nutrient imbalance—a mismatch in nutrient ratios between the available food supply and the demands of consumers—has the potential to be transported up food chains,exposing zooplankton to nutrient limitations.In this study,the response of Calanus sinicus（copepod）,Moina mongolica（cladocera）,and Brachionus plicatilis（rotifer） to nutrient-limited（no-limited,P-limited,and N-limited） food were evaluated from the perspective of growth,reproduction,and stoichiometric homoeostasis.The results indicated that the growth of three species was suppressed under nutrient-limited（especially P-limited） conditions.However,the effect of nutrient limitations on their reproduction was species-specific.For C.sinicus,the dietary UFA（unsaturated fatty acid） as a major phospholipid component affected their egg production and total FA supporting energy promoted the hatchability of eggs.Furthermore,excess carbon in the diet promoted egg production but reduced hatching success.For M.mongolica,nutritional（P and UFA） and energy（total FA） support affected their fecundity.B.plicatilis fecundity exhibited the same pattern of growth（no-limited〉N-limited〉P-limited）.In terms of stoichiometric homeostasis,B.plicatilis＇ s elemental compositions were less likely to be affected by nutrient limitations than M.mongolica.We suggest that the effects of nutrient imbalances could potentially become an evolutionary force affecting ecosystem structure and stability in eutrophic waters.

Abscisic acid receptors maintain abscisic acid homeostasis by modulating UGT71C5 glycosylation activity

Uridine diphosphate-glucosyltransferases(UGTs)maintain abscisic acid(ABA)homeostasis in Arabidopsis thaliana by converting ABA to abscisic acid-glucose ester(ABA-GE).UGT71C5 plays an important role in the generation of ABA-GE.Abscisic acid receptors are crucial upstream components of the ABA signaling pathway,but how UGTs and ABA receptors function together to modulate ABA levels is unknown.Here,we demonstrated that the ABA receptors RCAR12/13 and UGT71 C5 maintain ABA homeostasis in Arabidopsis following rehydration under drought stress.Biochemical analyses show that UGT71C5 directly interacted with RCAR8/12/13 in yeast cells,and the interactions between UGT-71C5 and RCAR12/13 were enhanced by ABA treatment.Enzyme activity analysis showed that ABA-GE contents were significantly elevated in the presence of RCAR12 or RCAR13,suggesting that these ABA receptors enhance the activity of UGT71C5.Determination of the content of ABA and ABA-GE in Arabidopsis following rehydration under drought stress revealed that ABA-GE contents were significantly higher in Arabidopsis plants overexpressing RCAR12 and RCAR13 than in nontransformed plants and plants overexpressing RCAR11 following rehydration under drought stress.These observations suggest that RCAR12 and RCAR13 enhance the activity of UGT71C5 to glycosylate excess ABA into ABA-GE following rehydration under drought stress,representing a rapid mechanism for regulating plant growth and development.