The photoperiod is the period of time that a plant receives light each day. The photoperiod matters to a plant as it contains information about the progress of seasons. Plants use the changing photoperiod as a cue for the correct timing of important life history events, including flowering. Ulla Kemi and colleagues studied the effect of photoperiod on flowering in four Arabidopsis lyrata populations originating from different latitudes, as well as expression levels of candidate genes for governing the between-population differences.
Most plants in all populations formed visible flower primordia during vernalization. Further inflorescence development after vernalization was strongly inhibited by short days in the northern European population (latitude 61°N), only slightly in the central European population (49°N) and not at all in the North American populations (36°N and 42°N). In the 14 h daylength, where all plants from the three southernmost populations but only 60 % of the northernmost population flowered, the circadian expression rhythm of the A. lyrata FLOWERING LOCUS T was only detected in the southern populations, suggesting differentiation in the critical daylength for activation of the long-day pathway. However, circadian expression rhythms of A. lyrata GIGANTEA, FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 and CONSTANS were similar between populations.
The results indicate that in A. lyrata, transition to flowering can occur through pathways independent of long days, but elongation of inflorescences is photoperiodically regulated.