Plants grown in far red (FR) light deficient environments are typically shorter because of short internodes, resembling plants treated with GA biosynthesis inhibitors. The role of GAs in the reduction of stem elongation of `Bright Golden Anne' chrysanthemum [Dendranthem ×grandiflora (Ramat.) Kitam. (syn. Chrysanthemum ×morifolium Ramat.)] grown in FR light deficient (-FR) environment was investigated by following the response of chrysanthemums grown in - FR environment to exogenous application of GA1, GA19, or GA20, and the metabolism of GA12 and GA19 in -FR or +FR environment. FR light deficient environment resulted in 25% to 30% shorter plants than in +FR environment. Final height of GA1- and GA20-treated plants followed a quadratic pattern while that of GA19 treated plants followed a linear pattern as the dosage increased from 0 to 50 μg/apex. The response to GA1 was the greatest followed by GA20 and GA19, regardless of the light environment. Application of GA1 (50 μg/apex) increased final height by 65% compared with no GA (0 μg/apex) application under either +FR or -FR light environment, suggesting the response to GA1, which is the active form, remained the same. Responses to GA19 and GA20 declined under -FR light. [14 C]GA12 and [14C]GA19 metabolized slowly in the -FR environment suggesting that the turnover of GAs may have caused in part the lower response to GA19. Although metabolism of GA1 under -FR environments was not investigated, observations with GA1 application experiments support that -FR environment may have enhanced inactivation of GA1. Chemical name used: gibberellic acid (GA).
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