Evidence for the function of the free radical gas - nitric oxide (NO center dot) - as an endogenous maturation and senescence regulating factor in higher plants

The hypothesis that endogenously-produced nitric oxide (NO.) gas is a natur al plant growth regulator was experimentally tested. Experimentation encomp assed a wide spectrum of both climacteric and non-climacteric varieties of fruits, flowers, vegetables and legume sprout species. Specific NO. probe m onitoring of both vegetative and generative plant organs revealed that temp oral progress of maturation and senescence goes hand in hand with a signifi cant decrease of NO. emission. Conversely, exogenous application of the gas either by direct fumigation in an O-2-free atmosphere or by means of NO. r eleasing biochemicals such as N-tert-butyl-alpha-phenylnitrone and 3 morpho linosyl-nonimine, markedly delayed senescence and maturation. NO. decrease was moreover stoichiometrically related to ethylene upsurge, this phenomeno n also being geared to ethylene increment under short-term heat stress. Fur thermore, a classic foliage expansion bioassay indicated a concentration-de pendent growth effect evidenced as a typical growth regulator-like response where low concentrations promote, and high concentrations inhibit growth. Regarded together, experimental data lends support to the possible role of NO. as a natural senescence-delaying plant growth regulating agent acting p rimarily, but not solely, by down regulating ethylene emission. (C) Elsevie r, Paris.