From physics to fixtures to food:current and potential LED efficacy

Overview Light-emitting diodes(LEDs)have enabled a historic increase in the conversion of electric energy to photons,but this is approaching a physical limit.The theoretical maximum efficiency occurs when all input energy is converted to energy in photosynthetic photons.Blue LEDs can be 93%efficient,phosphor-converted“whites”76%efficient,and red LEDs 81%efficient.These improvements open new opportunities for horticultural lighting.

RETHINKING ACCLIMATION OF GROWTH AND MAINTENANCE RESPIRATION OF TOMATO IN ELEVATED CO_2:EFFECTS OF A SUDDEN CHANGE IN LIGHT AT DIFFERENT TEMPERATURES

Aims Changes in light and temperature are among the most common and most profound environmental perturbations. The independent effects of light and temperature on photosynthesis and respiration are well studied in single leaves, but are less well studied in whole plants. The short and long term influence of light and temperature on carbon use efficiency is also poorly understood, and is commonly modeled to remain constant over a wide range of conditions. We sought to determine the primary effects of changing light at two growth temperatures on photosynthesis, respiration, and their balance, as defined by carbon use efficiency. Methods We separated respiration into growth and maintenance components using whole-canopy gas-exchange in an elevated CO2 environment in a controlled environment, and supplemented that information with tissue analysis. Important findings Decreases in light level decreased carbon use efficiency through a reduction in the maintenance coefficient, increased the growth coefficient, and reduced partitioning of N in protein. Growth temperature did not significantly affect either maintenance or growth respiration coefficients, suggesting that long-term temperature responses can differ greatly from short-term observations.

AtPEPTIDE RECEPTOR_2 mediates the AtPEPTIDE1‐induced cytosolic Ca^(2+) trise, which is required for the suppression of Glutamine Dumper gene expression in Arabidopsis roots

AtPEPTIDE RECEPTOR2 （AtPEPR2） is a member of leucine-rich repeat receptor-like kinase family and binds to a group of AtPROPEP gene-encoded endogenous peptides, AtPeps. Previously, we found that AtPEPR2 plays a moderate role in the AtPep1-mediated innate immunity responses in Arabidopsis leaf. In this study, we found that AtPEPR2 promoter has strong activity in the vascular tissues of the roots and the atpepr2 mutants showed a moderate but significantly shorter root phenotype. AtPEPR2 partial y mediated AtPep1-induced root elongation inhibition. AtPep1-triggered cytosolic Ca2t transient rise in roots showed partial dependence on AtPEPR2 and ful y on extracellular Ca2t （[Ca2t]ext）. Transcriptional profiling analysis found that expression of 75% of AtPep1-modulated genes in roots was ful y dependent on AtPEPR2, of which two dramatical y induced genes showed partial dependence on the [Ca2t]ext. Arabidopsis genome contains seven Glutamine Dumpers genes （AtGDUs）, encoding amino acid exporters. Three of them （AtGDU2, 3, 5） were among the top 10 genes that were＆amp;nbsp;downregulated by AtPep1 through AtPEPR2 ful y dependent pathway. Treatment with AtPep1 strongly suppressed pro-moter activity of AtGDU3 in roots, which was relieved by chelating [Ca2t]ext. Arabidopsis overexpressing AtGDU3 showed a shorter root phenotype and decreased sensitivity to the AtPep1-mediated inhibition of root elongation. Taken together, this study demonstrated a significant role of AtPEPR2 in the AtPep1-mediated signaling in the roots.