The initial hours of post-excision light are critical for adventitious root regeneration from Arabidopsis thaliana (L.) Heynh. cotyledon explants

Abstract

How light exposure of excised plant tissues impacts the success of subsequent adventitious root regeneration is poorly understood. Here, exposure to high light intensity was observed to inhibit root regeneration from Arabidopsis thaliana (L.) Heynh. cotyledon explants. Transfers to dark followed by high-intensity light (or reciprocal) were used to define when the explants were most light-sensitive and when adventitious root formation was most inhibited. Exposure of explants to light during the first 6–48 h after excision strongly inhibited root regeneration. Mutants and chemical inhibitors were used to identify modulators of this light-induced response. During the first 48 h post excision, reduction in photoprotective xanthophylls or application of chemicals known to promote reactive oxygen species caused the cotyledon explants to become light-hypersensitive, and decreased adventitious root regeneration. Filtering out blue/ultraviolet-A wavelengths reduced the negative effects of light, while mutants defective in phytochrome A or light-activated transcription factor ELONGATED HYPOCOTYL 5 were hypersensitive to early light exposure. A mutant defective in chalcone synthase (transparent testa 4) showed reduced root regeneration, regardless of early light or dark exposure. Application of a polar auxin transport inhibitor, 1-N-naphthylphthalamic acid, during the first 24 h post excision reduced explant light sensitivity and increased the percentage that successfully induced adventitious roots. These results indicated a critical role for light during the initial post-excision hours on root regeneration in Arabidopsis. The data suggested that complex interactions between light, photoreceptor signaling, reactive oxygen species, photoprotective pigments, and auxin act upon adventitious root induction in A. thaliana cotyledon explants.