Light spectral composition affects metabolic response and flowering in non-vernalized Ranunculus asiaticus L

We investigated the influence of photoperiodic light spectrum, inducing different phytochrome photoequilibria (PPE) at plant level, on photosynthesis, metabolic profiling, plant growth and flowering of Ranunculus asiaticus L. hybrids, MBO and MDR with different flowering earliness, grown in glasshouse from rehydrated dry tuberous roots. Plants were exposed to three photoperiodic treatments (day extension to 14 h), compared to natural day length (NL): white fluorescent light (PPE 0.84), and LEDs Red:Far Red light at 3:1 ratio (PPE 0.84) and 1:3 ratio (PPE 0.63). We discuss the results also compared to data on plants from rehydrated and vernalized roots previously reported in Modarelli et al., 2000a. Leaf gas exchanges and quantum yield of PSII electron transport were higher in MDR than in MBO, whereas non-photochemical quenching showed the opposite behaviour. In MDR, R:FR 3:1 light was the most effective in promoting stomatal conductance, while it reduced photochemistry and increased heat dissipation compared to other treatments. Under NL, leaf area was greater in MBO while flowering earliness and flower stems were similar in the hybrids. Photoperiodic treatments did not influence the plant growth while anticipated flowering in both the hybrids. In both the hybrids, lighting did not change the content of chlorophylls, carotenoids, glucose and sucrose. The greater number and expansion of leaves in MBO, except under R:FR 3:1, was accompanied by a lower photosynthetic capacity per leaf area. Conversely, in MDR, with lower leaf number, area and DW, an interesting increase of N-containing metabolites (i.e. chlorophylls and amino acids) occurred, thus exerting a positive effect on photosynthetic rate.