Protein metabolism plays an important role in plant adaptation to heat stress. This study was designed to identify heat-responsive proteins in roots associated with thermotolerance for two C3 grass species contrasting in heat tolerance, thermal Agrostis scabra and heat-sensitive Agrostis stolonifera L. Plants were exposed to 20 °C (control), 30 C (moderate heat stress), or 40 °C (severe heat stress) in growth chambers. Roots were harvested at 2 d and 10 d after temperature treatment. Proteins were extracted and separated by two-dimensional polyacrylamide gel electrophoresis. Seventy protein spots were regulated by heat stress in at least one species. Under both moderate and severe heat stress, more proteins were down-regulated than were up-regulated, and thermal A. scabra roots had more up-regulated proteins than A. stolonifera roots. The sequences of 66 differentially expressed protein spots were identified using mass spectrometry. The results suggested that the up-regulation of sucrose synthase, glutathione S-transferase, superoxide dismutase, and heat shock protein Sti (stress-inducible protein) may contribute to the superior root thermotolerance of A. scabra. In addition, phosphoproteomic analysis indicated that two isoforms of fructose-biphosphate aldolase were highly phosphorylated under heat stress, and thermal A. scabra had greater phosphorylation than A. stolonifera, suggesting that the aldolase phosphorylation might be involved in root thermotolerance.
Symbiotic nitrogen fixation is commonly inhibited by N fertilization in intensive farming systems. We hypothesized that intercropping alleviates the inhibitory effect of N fertilization on nodulation and N 2 fixation of legumes. Two years of field experiments (2006)(2007) with different Nfertilizer rates (0, 75, 150, 225, 300 kg N ha −1 ) were carried out to test the hypothesis in a faba bean (Vicia faba L.)/maize (Zea mays L.) intercropping system in the north-western part of China. The results show that both the nodule biomass and nitrogen derived from the atmosphere (Ndfa) in intercropped faba bean were increased by 7-58% and 8-33% at the start of flowering, 8-72% and 54-61% at peak flowering, 4-73% and 18-50% at grain filling, and 7-62% and −7-72% at maturity, respectively, compared with sole faba bean. Intercropping with maize significantly alleviated the inhibitory effect of N fertilization on nodulation and N 2 fixation, and improved the productivity of intercropping.
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