Photomorphogenic control of shoot regeneration from etiolated and light-grown hypocotyls of tomato

Abstract

We have investigated the role of phytochrome in the photocontrol of shoot regeneration from hypocotyls of tomato ( Lycopersicon esculentum Mill.) by comparing the regenerative capability of explants obtained from etiolated and light grown seedlings of an aurea ( au) mutant and its isogenic wild type. No shoot regeneration was displayed by etiolated aurea hypocotyls. While significant regeneration was shown by etiolated wild type explants. De-etiolated explants of both genotypes were able to regenerate shoots if cultured in presence of 16 h light/8 h dark cycles. When cultured in darkness on a medium devoid of hormones no one explant regenerated shoots. Out of more than 500 aurea explants, only one differentiated a shoot under continuous red and far red light, while significant shoot regeneration from wild type hypocotyl explants was induced by both the wavebands. Hypocotyl cultures under constant red, far red and blue light showed a position-dependent capability of regenerate shoots. We propose that the phytochrome play a crucial role in shoot regeneration from hypocotyl explants of tomato. Furthermore we provide evidence that a gradient in phytochrome content between the different segments of the hypocotyl is involved in the position-dependent capability of hypocotyl cells of regenerate shoots.