Abstract
Summary The effect of white (WL) and red (RL) light on organogenesis in vitro was studied using explants isolated from seedlings of wild-type (WT) and two photomorphogenic mutants of tomato ( Lycopersicon esculentum Mill.) - aurea ( au ) and high pigment ( hp ). Explants excised from hypocotyls and cotyledons of green and etiolated seedlings were cultured on shoot or root inducing media. It was observed that both continuous white (CWL) and red light (CRL) stimulate shoot formation on hypocotyl explants isolated from green seedlings of WT and hp plants compared with control ones cultured in darkness. On the other hand, au mutant shows very low organogenetic response in spite of light conditions applied. Explants isolated from both green and etiolated seedlings were not able to form shoots when they were cultured in darkness. In contrast to green explants, etiolated ones formed roots in spite of being grown on a shoot inducing medium. Root regeneration from etiolated explants was stimulated by short, 5-min-long daily pulses of RL. This effect was reversed by subsequent far-red light (FRL) irradiation. Stimulation of shoot regeneration from etiolated explants was found when 2-h-long daily irradiation with WL or RL was applied. The highest and the lowest shoot regeneration response was obtained from hp and au explants, respectively, with an intermediate response from WE Under the same growth conditions shoot formation was accompanied by root formation, which also occurred in a light dependent manner. The highest number of roots regenerated from au -derived explants. The results that we have obtained may suggest that shoot formation is strongly dependent on the light sensitivity of plants and light conditions applied. It also seems that the pattern of organ (shoot and root) development in tomato is affected by the etiolated/deetiolated phenotype of explant. Therefore, we believe that the organogenetic response of tomato in vitro is at least partly regulated by phytochrome.
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