A unique pantoyllactone glycoside system is activated in rice seedlings developing aerobically in the dark

Rice (Oryza sativa L.) seedlings developing aerobically in the dark accumulated in the expanding coleoptile millimolar amounts of pantoyllactone glucoside (PLG) together with sugars and amino acids. Following leaf emergence and seedling development, the transformation of PLG into pantoyllactone primeveroside (PLP) was initiated inside the coleoptile, whose senescence was suspended in spite of the exhaustion of seed reserves and cessation of shoot growth. PLG, PLP and most of the sugars and amino acids remained inside the coleoptile. Light administration triggered shoot greening and coleoptile senescence that was accompanied by the conversion of PLG into the shoot-translocatable species PLP and by the utilization of the coleoptile-stored metabolites. Light-induced retrieval of amino acids and sugars from the coleoptile was 90% complete within 24 h while translocation of pantoyllactone glycosides started only 24–48 h after light administration. Conversely, no accumulation of PLG and PLP was detected in seedlings germinated and grown either aerobically in the light or in the dark under hypoxic conditions. The possible significance of the activation of the PLG-PLP system under specific environmental conditions is discussed.