CN17 is a functional stay-green wheat variety that exhibits delayed leaf senescence and enhanced photosynthetic competence. To better understand these valuable traits, levels of chlorophyll a and b, soluble proteins, unsaturated fatty acids, and other components of CN17 were assayed. In addition, chloroplast ultrastructure, chloroplast number, and differences in gene expression between CN17 and a control variety, MY11, were examined. By 21 d postanthesis (DPA), CN17 leaves exhibited a significantly higher maximal photochemical efficiency for photosystem II (PSII) (Fv/Fm) and a significantly higher efficiency of excitation capture by open PSII reaction centres (FvЈ/FmЈ). In addition, chlorophyll degradation in CN17 was delayed by approximately 14 d, and was not blocked as observed in cosmetic stay-green phenotypes. The soluble protein content (Ps) of CN17 was higher than MY11 at all timepoints assayed, and the ratio of unsaturated to saturated fatty acids was significantly higher. CN17 also exhibited isolated granal lamellae associated with vesicles and diminished peroxidation, and between 35 and 42 DPA, a sharp decrease in chloroplast number was detected. Taken together, these results strongly support the hypothesis that chloroplast ultrastructure regeneration is responsible for the functional stay-green trait of CN17, and gene expression data provide insight into the mechanistic details.

ABSTRACT. Tobacco is an economically important crop, and its potassium content can greatly affect the quality of tobacco leaves. However, the molecular mechanism involved in potassium starvation in tobacco has not been elucidated to date. In this study, Illumina (Solexa) sequencing technology was used to analyze the transcriptome of tobacco seedlings under low-potassium stress for 6, 12, and 24 h. After analysis, 107,824 assembled unigenes were categorized into 57 GO functional groups, and 31,379 unigenes (29.08%) were clustered into 25 COG categories. A total of 9945 genes were classified into 233 KEGG pathways, and 15,209 SSRs were found among the 107,824 unigenes. Between the two samples, 1034 genes were differentially expressed. Twelve randomly selected gene expression levels were analyzed by quantitative RT-PCR, and the results were highly consistent with those