Abstract:
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 photo morphogenic 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 ofWT 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 WT. 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