Nodule study in Albizia chinensis in relation to nitrogen metabolism,morphology and biomass

Morphology,biomass,nitrate reductase(NR)and nitrogenase activity in Albizia chinensis(Osb.)Merr.nodules were assessed on monthly and seasonal basis for 1 year.Average NR and nitrogenase activity was higher during the rainy season,reaching a maximum in August.Thereafter,activity decreased through autumn and reached a minimum value during winter.Fresh and dry biomass of nodules increased gradually from summer to the rainy season and then started decreasing with the onset of winter as nodules began to senesce.Among four developmental stages of the nodules that correspond to their increasing age,NR and nitrogenase activity remained low in stage 1 nodules and peaked in stage 2.The activity of both enzymes further decreased with increasing age(stage 2 to stage 4).Morphological features such as shape,diameter and color varied considerably among the developmental stages.Stage 1 nodules were cream-colored,oval to heartshaped with smallest average diameter whereas at stage 2,they became bilobed to tetralobed.On the other hand,stage 3 nodules had the largest average diameter and were multilobed in structure.Stage 4 nodules that correspond to the senescing stage were dark brown to black,multilobed,flattened and hollow due to degeneration of nodular tissue.

Staying hungry:a roadmap to harnessing central regulators of symbiotic nitrogen fixation under fluctuating nitrogen availability

Legumes have evolved specific inventions to enhance nitrogen(N)acquisition by establishing symbiotic interactions with N-fixing rhizobial bacteria.Because symbiotic N fixation is energetically costly,legumes have developed sophisticated mechanisms to ensure carbon-nitrogen balance,in a variable environment,both locally and at the whole plant level,by monitoring nodule number,nodule development,and nodular nitrogenase activity,as well as controlling nodule senescence.Studies of the autoregulation of nodulation and regulation of nodulation by nodule inception(NIN)and NIN-LIKE PROTEINs(NLPs)have provided great insights into the genetic mechanisms underlying the nitrateinduced regulation of root nodulation for adapting to N availability in the rhizosphere.However,many aspects of N-induced pleiotropic regulation remain to be fully explained,such as N-triggered senescence in mature nodules.Wang et al.determined that this process is governed by a transcriptional network regulated by NAC-type transcription factors.Characterization and dissection of these soybean nitrogenassociated NAPs(SNAPs)transcription factor-mastered networks have yielded a roadmap for exploring how legumes rewire nodule functions across a range of N levels,laying the foundation for enhancing the growth of N-deprived crops in agricultural settings.