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Morphogenesis of the reproductive structure of buckwheat and the impact of light conditions on flowering time and duration have been investigated using the variety 'La Harpe'. Inflorescences were initiated acropetally, in leaf axils, by the shoot apical meristem until its arrest of functioning which was accompanied by the abortion of the last inflorescence produced. The buckwheat inflorescence is a compound raceme that produces laterally flowered cymose clusters, the number of which was affected by the position of the inflorescence along the main stem. Similarly, the number of flowers in a lateral cluster was dependent on the inflorescence's position on the stem. The development of each inflorescence was stopped as its meristem stopped functioning and, in a situation reminiscent of the shoot apical meristem, the latest initiated cyme aborted. The development of each cyme was also terminated with the abortion of a few young flowers. The variety 'La Harpe' is a facultative short-day plant: the number of nodes generated before the initiation of the first inflorescence and the number of days from sowing to macroscopic appearance of this inflorescence were reduced in 8 h days as compared with 16 h days. The number of inflorescences, and thus flowering duration, was also strongly reduced by short days. It was unaffected by light irradiance in 8 h days while, in 16 h days, it was prolonged when light intensity was increased, suggesting the interaction of two different mechanisms for its regulation. Buckwheat is a distylous species, but inflorescence structure and flowering behaviour were not affected by floral morph.

Rutin is an antioxidant with many interesting pharmacological effects. It can also be found in buckwheat (Fagopyrum esculentum Moench). UV radiation stimulates the activity of enzymes of the phenylpropanoid pathway and there is some evidence that it influences the rutin content in plants. The aim of the present research was (1) to examine the influence of different levels of UV-B radiation on rutin content and (2) to compare the results obtained by three analytical methods. The plants were grown under three UV-B levels: reduced, ambient and enhanced, simulating 17% ozone depletion. Analyses were performed by HPLC and two spectrophotometric methods. In one, the absorbancies were measured at 420 nm with and without the addition of AlCl(3). In another method the concentration was calculated from absorbancies at 352.5 nm and 366.5 nm according to the Official Methods of Analysis of AOAC International. The highest amounts of rutin were found in flowers, followed by leaves and stems. A comparison of the different treatments revealed that the highest amounts of rutin were in plants grown under ambient radiation, followed by the plants cultivated under enhanced UV-B and then under reduced UV-B radiation. Treatments caused more effect on leaves than on flowers. Leaves developed under ambient light conditions contained 97% more rutin than leaves grown under reduced UV-B radiation. In flowers, the contents differed by 19% only. The results obtained using the three methods showed a good correlation, but the absolute differences were surprisingly high. The AOAC and the AlCl(3) methods gave, on average, 140% and 30% higher results than HPLC, respectively.