Direct measurement of the break-out ^(19)F(p,γ)^(20)Ne reaction in the China Jinping underground laboratory(CJPL)

Calcium production and the stellar evolution of first-generation stars remain fascinating mysteries in astrophysics.As one possible nucleosynthesis scenario,break-out from the hot carbon–nitrogen–oxygen(HCNO)cycle was thought to be the source of the calcium observed in these oldest stars.However,according to the stellar modeling,a nearly tenfold increase in the thermonuclear rate ratio of the break-out ^(19)F(p,γ)^(20) Ne reaction with respect to the competing ^(19)F(p,α)^(16) O back-processing reaction is required to reproduce the observed calcium abundance.We performed a direct measurement of this break-out reaction at the China Jinping underground laboratory.The measurement was performed down to the low-energy limit of E_(c.m.)=186 keV in the center-of-mass frame.The key resonance was observed at 225.2 keV for the first time.At a temperature of approximately 0.1 GK,this new resonance enhanced the thermonuclear ^(19)F(p,γ)^(20) Ne rate by up to a factor of≈7.4,compared with the previously recommended NACRE rate.This is of particular interest to the study of the evolution of the first stars and implies a stronger breakdown in their“warm”CNO cycle through the ^(19)F(p,γ)^(20) Ne reaction than previously envisioned.This break-out resulted in the production of the calcium observed in the oldest stars,enhancing our understanding of the evolution of the first stars.

The action of enhancing weak light capture via phototropic growth and chloroplast movement in plants

To cope with fluctuating light conditions,terrestrial plants have evolved precise regulation mechanisms to help optimize light capture and increase photosynthetic efficiency.Upon blue light-triggered autophosphorylation,acti-vated phototropin(PHOT1 and PHOT2)photoreceptors function solely or redundantly to regulate diverse responses,including phototropism,chloroplast movement,stomatal opening,and leaf positioning and flattening in plants.These responses enhance light capture under low-light conditions and avoid photodamage under high-light conditions.NON-PHOTOTROPIC HYPOCOTYL 3(NPH3)and ROOT PHOTOTROPISM 2(RPT2)are signal transducers that function in the PHOT1-and PHOT2-mediated response.NPH3 is required for phototropism,leaf expansion and positioning.RPT2 regulates chloroplast accumulation as well as NPH3-mediated responses.NRL PROTEIN FOR CHLOROPLAST MOVE-MENT 1(NCH1)was recently identified as a PHOT1-interacting protein that functions redundantly with RPT2 to medi-ate chloroplast accumulation.The PHYTOCHROME KINASE SUBSTRATE(PKS)proteins(PKS1,PKS2,and PKS4)interact with PHOT1 and NPH3 and mediate hypocotyl phototropic bending.This review summarizes advances in phototropic growth and chloroplast movement induced by light.We also focus on how crosstalk in signaling between phototro-pism and chloroplast movement enhances weak light capture,providing a basis for future studies aiming to delineate the mechanism of light-trapping plants to improve light-use efficiency.