Effect of 2,4-D and light quality on callus production and differentiationfrom in vitro cultured quince leaves

The effects of 2,4-dichlorophenoxyacetic acid (2,4-D) concentration, length of induction period and light quality on leaf regeneration of quince clone BA 29 were investigated. After 2, 4 or 6 days of induction with 2.5 mg l(- 1) or 5.0 mg l(-1) 2,4-D, leaves were cultured under red, blue, red+blue, f ar-red+blue, white, far-red light or darkness conditions. Leaves thereby tr eated showed different responses, with respect to somatic embryogenesis, ca llus, red-nodular structures or roots. Callus production increased with inc reasing 2,4-D concentration and induction period, although it was not influ enced by light quality; the only exception was far-red+blue light, which re duced callusing response. This result suggested involvement of the blue-abs orbing photoreceptor system in the callus formation processes. A high regen eration of red-nodular structures with a meristematic appearance was also o bserved; from some histological characterizations, we presumed they were ad ventitious buds that were arrested at an early developmental stage. Red-nod ular structures increased with decreasing 2,4-D concentration and induction period. In the regeneration of such structures, the blue-absorbing photore ceptor system appeared to have a negative effect but only at a low photoequ ilibrium value. In contrast, light quality which activated phytochrome indu ced an increment in regeneration, but the response did not vary for photoeq uilibrium values ranging from 0.43 to 0.86. For root regeneration, phytochr ome seemed to be the only photoreceptor involved.