ULTRAVIOLET-B-RESPONSIVE ANTHOCYANIN PRODUCTION IN A RICE CULTIVAR ISASSOCIATED WITH A SPECIFIC PHASE OF PHENYLALANINE AMMONIA-LYASE BIOSYNTHESIS

Seedlings of 17 rice (Oryza sativa L.) cultivars were classified on th e basis of anthocyanin pigmentation into three groups: an acyanic grou p with 9 cultivars, a moderately cyanic group with 5 cultivars, and a cyanic group with 3 cultivars. Seedlings of the cyanic group were deep purple in color, possessing copious amounts of anthocyanin in shoots. Sunlight (SL)-mediated anthocyanin and phenylalanine ammonia lyase (P AL) induction in a cyanic cultivar, purple puttu, was compared with an acyanic cultivar, black puttu. A brief exposure of dark-grown purple puttu seedlings to SL induced anthocyanin formation during a subsequen t dark period with a peak at 24 h. The magnitude of SL-mediated anthoc yanin induction is age dependent, the 4-d-old seedlings being the most responsive to SL. The anthocyanin induction in purple puttu seedlings is mediated exclusively by the ultraviolet-B (UV-B) component of SL. The SL-triggered anthocyanin induction was reduced by about 30% by a t erminal far-red light pulse and was restored by a red light pulse, ind icating the role of phytochrome in modulation of anthocyanin level. Th e SL-mediated induction of PAL showed two peaks, one at 4 h and the ot her at 12 h. Whereas the first PAL peak (4 h) was induced by phytochro me and was seen in both cultivars, the second PAL peak (12 h) was indu cible by UV-B only in the cyanic purple puttu cultivar.