Effects of a Stay‐green Mutation on Plant Nitrogen Relations in Lolium perenne During N Starvation and after Defoliation.

The stay‐green mutation of the nuclear gene sid results in inhibition of chlorophyll degradation during leaf senescence in grasses, reducing N remobilization from senescing leaves. Effects on growth of Lolium perenne L. were investigated during N starvation (over 18 d) and after severe defoliation, when leaf growth depends on the remobilization of internal N. Rates of dry matter production, partitioning between shoots and roots, and re‐partitioning of N from shoots to roots were very similar in stay‐green and normal plants under N starvation. Km and Vmax for net uptake of NH4+ were also similar for both genotypes, and Vmax increased with the duration of N deprivation. The mutation had little effect on recovery of leaf growth following severe defoliation, but stay‐green plants recommenced NO3– and K+ uptake 1 d later than normal plants. Import of remobilized N into new leaves was generally similar in both lines. However, stay‐green plants remobilized less N from stubble compared with normal plants. It was concluded that the sid locus stay‐green mutation has no significant adverse effect on the growth of L. perenne during N starvation, or recovery from severe defoliation when plants are grown under an optimal regime of NO3– supply both before and after defoliation. The absence of any effect on leaf dry matter production implies that the difference in foliar N availability attributable to this mutation has little bearing on productivity, at least in the short to medium term. [ABSTRACT FROM PUBLISHER]