Basal internode elongation of rice as affected by light intensity and leaf area

Short basal internodes are important for lodging resistance of rice(Oryza sativa L.).Several canopy indices affect the elongation of basal internodes,but uncertainty as to the key factors determining elongation of basal internodes persists.The objectives of this study were(1)to identify key factors affecting the elongation of basal internodes and(2)to establish a quantitative relationship between basal internode length and canopy indices.An inbred rice cultivar,Yinjingruanzhan,was grown in two split-plot field experiments with three N rates(0,75,and 150 kg N ha−1 in early season and 0,90,and 180 kg N ha−1 in late season)as main plots,three seedling densities(16.7,75.0,and 187.5 seedlings m−2)as subplots,and three replications in the 2015 early and late seasons in Guangzhou,China.Light intensity at base of canopy(Lb),light quality as determined from red/far-red light ratio(R/FR),light transmission ratio(LTR),leaf area index(LAI),leaf N concentration(NLV)and final length of second internode(counted from soil surface upward)(FIL)were recorded.Higher N rate and seedling density resulted in significantly longer FIL.FIL was negatively correlated with Lb,LTR,and R/FR(P<0.01)and positively correlated with LAI(P<0.01),but not correlated with NLV(P>0.05).Stepwise linear regression analysis showed that FIL was strongly associated with Lb and LAI(R2=0.82).Heavy N application to pot-grown rice at the beginning of first internode elongation did not change FIL.We conclude that FIL is determined mainly by Lb and LAI at jointing stage.NLV has no direct effect on the elongation of basal internodes.N application indirectly affects FIL by changing LAI and light conditions in the rice canopy.Reducing LAI and improving canopy light transmission at jointing stage can shorten the basal internodes and increase the lodging resistance of rice.

Peptide Transporter OsNPF8.1 Contributes to Sustainable Growth under Salt and Drought Stresses,and Grain Yield under Nitrogen Deficiency in Rice

Peptide transport is important for plant tissues where rapid proteolysis occurs,especially during germination and senescence,to enhance redistribution of organic nitrogen(N).However,the biological role of peptide transporters is poorly investigated in rice.We characterized the function of the peptide transporter OsNPF8.1 of rice nitrate transporter 1/peptide transporter family(NPF).Ectopic expression of OsNPF8.1 in yeast revealed that OsNPF8.1 encoded a high-affinity di-/tri-peptide transporter,and the osnpf8.1 mutants had a lower uptake rate of the fluorescent-labelled dipeptide c in leaves of rice seedlings.Histochemical assays showed that OsNPF8.1 was highly expressed in mesophyll cells and vascular parenchyma cells,but not detected in root hairs and epidermises.Expression of OsNPF8.1 was induced by N deficiency,drought,Na Cl and abscisic acid,and kept at a high level in senescing leaves.Under N deficiency conditions,compared with the wild type Zhonghua 11,the osnpf8.1 mutants grew slower at the seedling stage,and had lower grain yield and lower N content in the grains.In contrast,OsNPF8.1-over-expressing rice(OsNPF8.1-OE)grew faster at the seedling stage and had a higher grain yield.The osnpf8.1 seedlings were less tolerant to salt and drought stresses.These results suggested that stress-induced organic N transportation mediated by OsNPF8.1 might contribute to balance plant growth and tolerate to salt/drought stress and N-deficiency.

THE GENETIC DIVERSITY OF GAOZHOU WILD RICE ANALYZED BY SSR

The genetic diversity of total 240 acces- sions of common wild rice coming from Gaozhou, Shaoguan, Zhanjiang, and other places in Guang- dong, and Jiangxi, Fujian, Yunnan provinces, etc. in China and South-eastern Asia was evaluated by us- ing 24 pairs of SSR primers. The results indicated that: (i) there were 17 polymorphic loci in 24 pairs of SSR primers, and the average percentage of poly- morphic loci was 69%; the average total number of alleles, the average number of alleles per locus and the average number of alleles per polymorphic loci were 51.1, 2.04 and 2.43, respectively; (ii) the aver- age gene diversity was 0.8447. There were remark- able differentiations among 5 populations of Gaozhou wild rice. All the above-mentioned genetic parame- ters indicated that Gaozhou wild rice of Pengshan Village (or Bei Toudong) of Zhenjiang Town should be a center of genetic differentiation and diversity of Gaozhou wild rice. Gaozhou wild rice is probably the largest center of genetic differentiation and diversity of common wild rice from Guangdong Province, South China and even the whole China.