Light hypocotyl elongation

In contrast to the paucity of biochemical data on the photosensory functions of cryptochromes, there are extensive genetic and cell biology data on the roles of cryptochromes in blue light, photoreception in plants and animals, and circadian clock regulation in animals (Gashmore, 2003 Lin and Shalitin, 2003 Sancar, 2003). In Arabidopsis, blue light inhibits elongation of hypocotyls in a cryptochrome-dependent manner. In animals. 

White light inhibits hypocotyl elongation in a variety of seedlings. In some cases this can be overcome by GA. In hypocotyls of Lupinus albus, lAA largely overcomes white light inhibition of hypocotyl growth while GA is ineffective (Acton and Murray 1974). 

Together with the even distribution of lAA (Table 1), these data lead to the conclusion that the phototropic movement of the radish hypocotyl is caused by a light-induced lateral distribution of three substances that differentially inhibit the auxin-regulated cell elongation at the two flanks. 

The experiment therefore confirms the conclusion obtained from the other experiments on oat coleoptiles and radish and sunflower hypocotyls, viz that phototropic curvature is caused by the light-induced, local accumulation of substances that inhibit cell elongation at an unchanged level of auxin. Sixty years after Wuchsstoff und Wachstum it has become Hemmstoff und Wachstum , at least for phototropism. 

In light-grown hypocotyls of dwarf watermelon seedlings benzyladenine (BA) enhances ethylene production and promotes cell elongation (Loy and Pollard 1977). Prevention of BA-induced ethylene production prevents BA-induced elongation, an indication that ethylene is necessary for BA-induced growth promotion. 

Van Oostveldt P, Van Goethem G, Van Parijs R (1976) Effect of light on cell elongation, nucleic acid and protein synthesis in hypocotyls of Lupinus angustifolius. Planta 129 259-263... 

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