Carbon nanoparticles influence photomorphogenesis and flowering time in <italic>Arabidopsis thaliana</italic>.

Key message: Inclusion of carbon nanoparticles in growth medium accelerates timing to flower by down-regulating phytochrome B in a CONSTANS-independent but photoperiod-dependent manner in <italic>Arabidopsis thaliana</italic>.Abstract: Despite the recognized importance of nanoparticles in plant development over the last decade, the effect of carbon nanoparticles (CNPs) on plant processes such as photomorphogenesis and flowering time control is poorly understood. We explored the uptake, accumulation and effect of CNPs on seedling development and flowering time control in <italic>Arabidopsis thaliana</italic> (<italic>At</italic>). CNPs uptake was demonstrated using Raman spectroscopy and light microscopy that affected <italic>At</italic> seedling growth and flowering time in a dose-dependent manner. The highest accumulation of CNPs was observed in leaves followed by stem and root tissues. CNPs treatment enhanced seed germination, showed elongated hypocotyl, larger cotyledon area and increased chlorophyll content in <italic>At</italic> seedlings. CNPs treatment induced early flowering in both long-day and short-day growth conditions indicating a photoperiod-dependent effect. CNPs-treated seedlings showed a drastic reduction in the relative abundance of <italic>phytochrome B</italic> (<italic>PHYB</italic>) transcript. Further, we analyzed the transcript abundance of at least one major component involved in various pathways that regulate flowering such as (1) photoperiod, (2) gibberellic acid (GA), (3) vernalization and (4) autonomous. An up-regulation of transcript levels of <italic>PHYTOCHROME INTERACTING FACTOR 4 (PIF4), GIGANTEA (GI), REPRESSOR OF GIBBERELLIC ACID 1 (RGA1)</italic> and <italic>LEAFY (LFY)</italic> were observed, however, there were no changes in the transcript levels of <italic>CONSTANS (CO), VERNALIZATION 1</italic> (<italic>VRN1)</italic> and <italic>FLOWERING CONTROL LOCUS A (FCA)</italic>. Despite the up-regulation of <italic>RGA1</italic>, we conclude that the earlier flowering is most likely GA-independent. Here, we demonstrated that the early flowering in CNPs-treated seedlings was <italic>PHYB</italic> and photoperiod-dependent. [ABSTRACT FROM AUTHOR]