Nitrogen (N) deficiency is a common problem for apple (Malus×domestica) production in arid regions of China.  However, N utilization efficiency (NUE) of different apple cultivars grown under low N conditions in arid regions has not been evaluated. In this study, NUE was assessed for one-year-old seedlings of six apple cultivars, Golden Delicious, Qinguan, Jonagold, Honeycrisp, Fuji and Pink Lady, grafted onto Malus hupehensis Rehd. rootstocks.  Four treatments were used, including control water with control N (CWCN), limited water with control N (LWCN), control water with low N (CWLN) and limited water with low N (LWLN).  Our results showed that growth indices such as biomass, plant height and stem diameter, and photosynthetic rate of all cultivars decreased in the order CWCN>CWLN>LWCN>LWLN.  When subjected to LWLN treatment, Qinguan showed better growth and photosynthetic characters than other tested cultivars.  Additionally, Qinguan and Pink Lady had higher NUE, while Honeycrisp and Jonagold had lower NUE, based on the determination of biomass, photosynthetic parameters, chlorophyll content, the maximal photochemical efficiency of PSII (F_v/F_m), ¹⁵N and N contents.

 

White-brown complex (WBC) transporters, also called half-size ATP binding cassette G (ABCG) transporters, are involved in many biological processes, including seed development; however, the WBC transporters in grapevines received less attention to date.  To reveal the molecular characteristics of WBCs and the connection between WBCs and agronomic traits of stenospermocarpic (seedless) grapevine, we carried out a genomic census and analysis of ovule-associated expression for VvWBC genes in grapevine.  We identified 30 VvWBC genes and cloned full-length complementary DNAs (cDNAs) for 20 of these.  The tissue or organ-specific expression analysis showed that several VvWBCs exhibited distinct expression patterns with some showing tissue specificity.  Twelve VvWBC genes were found to be expressed in the developing ovules.  Moreover, the results of quantitative real-time PCR (qRT-PCR) suggested that four of twelve ovule-expressed VvWBCs have distinct expression profiles during the development of ovules between seeded and stenospermocarpic grapevines.  These four genes might be involved in ovule abortion.  Meanwhile, chromosome mapping, multiple sequence alignments, exon/intron structure analyses and synteny analyses were preformed on VvWBC genes.  Our experiments provide a new perspective on the mechanism of stenospermocarpic seedlessness and put forward a framework for further study of WBC transporters.