Tillering is a crucial trait closely associated with yield potential and environmental adaptation in cereal crops, regulated by the synergy of endogenous (genetic) and exogenous (environmental) factors.  The physiological and molecular regulation of tillering has been intensively studied in rice and wheat.  However, tillering research on barley is scarce.  This review used the recent advances in bioinformatics to map all known and potential barley tiller development genes with their chromosomal genetic and physical positions.  Many of them were mapped for the first time.  We also discussed tillering regulation at genetic, physiological, and environmental levels.  Moreover, we established a novel link between the genetic control of phytohormones and sugars with tillering.  We provided evidence of how environmental cues and cropping systems help optimize the tiller number.  This comprehensive review enhances the understanding of barley’s physiological and genetic mechanisms controlling tillering and other developmental traits.

Development of the new crop cultivars with high yield under low nitrogen (N) input is a fundamental approach to enhance agricultural sustainability, which is dependent on the exploitation of the elite germplasm.  In the present study, four barley genotypes (two Tibetan wild and two cultivated), differing in N use efficiency (NUE), were characterized for their physiological and biochemical responses to different N levels.  Higher N levels significantly increased the contents of other essential nutrients (P, K, Ca, Fe, Cu and Mn), and the increase was more obvious for the N-efficient genotypes (ZD9 and XZ149).  The observation of ultrastructure showed that chloroplast structure was severely damaged under low nitrogen, and the two high N efficient genotypes were relatively less affected.  The activities of the five N metabolism related enzymes, i.e.,  nitrate reductase (NR), glutamine synthetase (GS), nitrite reductase (NiR), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH) all showed the substantial increase with the increased N level in the culture medium.  However the increased extent differed among the four genotypes, with the two N efficient genotypes showing more increase in comparison with the other two genotypes with relative N inefficiency (HXRL and XZ56).  The current findings showed that a huge difference exists in low N tolerance among barley genotypes, and improvement of some physiological traits (such as enzymes) could be helpful for increasing N utilization efficiency. 

Arabinoxylan (AX) content in barley grains is an important quality determinant when barley is used as raw material of malt or beer production. The cultivar and environmental variations of total arabinoxylan (TAX), water extractable arabinoxylan (WEAX) and endoxylanase activity (EA) were investigated using eight barley cultivars growing at seven locations with diverse environmental conditions. The results showed that both barley cultivar and location significantly affected the TAX, WEAX and EA levels, but the variations of TAX content and EA were mainly attributed to cultivar, while the impact of location on WEAX content was greater than that of cultivar. Correlation analysis indicated that TAX was significantly correlated to WUAX.

The alleviatory effect of silicon (Si) on chromium (Cr) toxicity to rice plants was investigated using a hydroponic experimentwith two Cr levels (0 and 100 μmol L-1), three Si levels (0, 1.25, and 2.5 mmol L-1) and two rice genotypes, differing in grainCr accumulation (Dan K5, high accumulation and Xiushui 113, low accumulation). The results showed that 100 μmol L-1 Crtreatment caused a marked reduction of seedling height, dry biomass, soluble protein content, and root antioxidantenzyme activity, whereas significantly increased Cr concentration and TBARS (thiobarbituric acid reactive substances)content. However, the reductions of seedling height, dry biomass, and soluble content were greatly alleviated due to Siaddition to the culture solution. Compared with the plants treated with Cr alone, Si addition markedly reduced Cr uptakeand translocation in rice plants. No significant differences were observed between the two Si treatments (1.25 and 2.5 mmolL-1) in shoot Cr concentration and Cr translocation factor. Under the treatment of 100 μmol L-1 Cr+2.5 mmol L-1 Si, higherroot Cr concentration but lower shoot Cr concentration and Cr translocation factor were observed in Dan K5 than thosein Xiushui 113, indicating that the beneficial effect of Si on inhibiting Cr translocation was more pronounced in Dan K5than in Xiushui 113. Si addition also alleviated the reduction of antioxidative enzymes (superoxide dismutase (SOD) andascorbate peroxidase (APX) in leaves; catalase (CAT) and APX in roots) and the increase of TBARS content in the Crstressedplants. Furthermore, the beneficial effects of Si on activities of antioxidative enzymes under Cr stress weregenotype-dependent. The highest activities of SOD, POD (guaiacol peroxidase), CAT, and APX in leaves occurred in thetreatment of 100 μmol L-1 Cr+2.5 mmol L-1 Si for Xiushui 113 and in the treatment of 100 μmol L-1 Cr+1.25 mmol L-1 Si for DanK5. The beneficial effect of Si on alleviating oxidative stress was much more pronounced in Dan K5 than in Xiushui 113.It may be concluded that Si alleviates Cr toxicity mainly through inhibiting the uptake and translocation of Cr andenhancing the capacity of defense against oxidative stress induced by Cr toxicity.

Tiller angle is very important for plant architecture and canopy structure in rice (Oryza sativa L.). Physiological and ecological characteristics of three rice genotypes with different tiller angle habits were compared in the paper. DI508, a genotype with changing tiller angle during the growth, has semi-erect tillers at early tillering stage, similar to genotype M09, and had erect tillers at late stage, similar to genotype 9308. In terms of dry biomass per plant, DI508 was consistently higher than those of M09 and 9308 throughout the growth. It was also a distinct difference of leaf area per plant that DI508 was larger than two others. From booting stage, DI508 and 9308 maintained higher photosynthetic ability of the topmost three leaves, while M09 showed rapid decline in photosynthesis during grain filling. It may be concluded that the genotype DI508 with dynamic tiller angle habit has a comprehensive advantage of fast growth and high weed competition at early stage and slow decline in photosynthesis at late stage.