LEAF SENESCENCE IN A NONYELLOWING MUTANT OF FESTUCA-PRATENSIS - IMPLICATIONS OF THE STAY-GREEN MUTATION FOR PHOTOSYNTHESIS, GROWTH AND NITROGEN NUTRITION

Mutation of the nuclear gene sid disables chlorophyll degradation duri ng leaf senescence in the pasture grass Festuca pratensis. This study investigated the effect of the mutation on photosynthesis and on leaf and whole plant growth under a range of nitrogen regimes, When plants were cultivated in a static hydroponic system, the chlorophyll content of fourth leaves of the stay-green mutant Bf993 remained virtually un changed from full expansion to complete senescence, while tissue of th e wild-type (cv. Rossa) became completely yellow, The retention of chl orophyll in Bf993 was not associated with maintenance of photosyntheti c activity as shown by rates of light-saturated CO2 fixation and appar ent quantum efficiency, Higher levels of total N in senescing leaves o f Bf993 than in Rossa indicated reduced nitrogen remobilization in the mutant, When using a range of [NH4NO3], dry matter production and til lering were lower for Bf993 at all but the highest [NH4NO3], which was supra-optimal for the wild type, In contrast to the static system, wh ere fluctuations in N supply occurred, growth and NO(3)(-)uptake were similar in mutant and wild type when [NO3-] was continuously maintaine d by a flowing solution culture system. The results are discussed in r elation to the role of N supply and the effect of the stay-green mutat ion on N recycling.