Lys-63-linked multiubiquitin chains play important roles in signal transduction in yeast and in mammals, but the functions for this type of chain in plants remain to be defined. The RING domain protein RGLG2 (for RING domain Ligase2) from Arabidopsis thaliana can be N-terminally myristoylated and localizes to the plasma membrane. It can form Lys-63-linked multiubiquitin chains in an in vitro reaction. RGLG2 has overlapping functions with its closest sequelog, RGLG1, and single mutants in either gene are inconspicuous. rglg1 rglg2 double mutant plants exhibit loss of apical dominance and altered phyllotaxy, two traits critically influenced by the plant hormone auxin. Auxin and cytokinin levels are changed, and the plants show a decreased response to exogenously added auxin. Changes in the abundance of PIN family auxin transport proteins and synthetic lethality with a mutation in the auxin transport regulator BIG suggest that the directional flow of auxin is modulated by RGLG activity. Modification of proteins by Lys-63-linked multiubiquitin chains is thus important for hormoneregulated, basic plant architecture.

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Abstraet-1. R-I1 is a U.V. induced mutant of cyanidilrrn caldarium which lacks the major accessory pigment phycocyanin. 2.Loss of phycocyanin does not impair photosynthesis or the Hill reaction. 3.The action spectrum for the quantum yield indicates an efficiently operating photosynthetic mechanism which is shifted in peak efficiency toward longer wavelengths when compared to the wild-type spectrum. The red drop is also shifted toward the far red in R-11. 4.Although 30 per cent enhancement was obtained in wild-type Cyanidiurn, no enhancement was observed when phycocyanin was absent. .A pigment absorbing at 720 nm has been observed and may possibly represent a chlorophyll-phycocyanin complex.

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