Chloroplast ultrastructure regeneration with protection of photosystem II is responsible for the functional ‘stay‐green’ trait in wheat

Abstract

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.

Mapping QTL for stay-green and agronomic traits in wheat under diverse water regimes

“…In crop plants species, stay-green enables a plant to maintain greenness and continue photosynthesising even under stress (Borrell et al 2014). Staygreen is associated with antioxidant status and photosystem II of the mesophyll cells (De Simone et al 2014;Luo et al 2013b). In many cereal crops, staygreen plants generally have higher chlorophyll contents and are more tolerant to abiotic stresses during grain filling.…”

In silico cloning and chromosomal localization of EST sequences that are related to leaf senescence using nulli-tetrasomes in wheat

“…In a recent study, 32 expression sequence tags (ESTs) were identified in CN17 during the delayed leaf senescence stage; these tags, which were up-regulated in stay-green CN17, and showed high homology with known or annotated genes that are associated with senescence-related processes in wheat, rice, barley, pea, and Arabidopsis. Among these ESTs, 31.3% were directly related to photosynthesis and leaf senescence processes, whereas the other ESTs were indirectly related to these processes (Luo et al 2013). However, the greatest shortage of this study is the unknown chromosomal locations of the ESTs.…”

“…During senescence, leaf cells experience dramatic changes in the expression of genes that are involved in photosynthesis, hydrolase activity, oxidoreduction, cellular processes, photorespiration, lipid transport, and biosynthesis pathways (Buchanan-Wollaston et al 2005;Luo et al 2013); because of the genetic variations, significant differences in the rate and degree of leaf senescence are observed during the important growth stages (e.g., the grain-filling period) both among species and within species (Thomas and Howarth 2000). Previous studies have reported stay-green phenotypes that result from delayed leaf senescence in many species, which includes several crop species such as wheat (Hortensteiner 2009;Luo et al 2013). Staygreen cultivars are divided into two principal categories: functional stay-green with photosynthetic activity and cosmetic stay-green without photosynthetic activity (Hortensteiner 2009).…”

“…Further studies on the levels of chlorophylls a and b, soluble proteins, and unsaturated fatty acids and on the chloroplast ultrastructure, chloroplast number, and differences in gene expression have provided strong evidence to support that chloroplast ultrastructure regeneration is responsible for the functional stay-green trait of CN17 (Luo et al 2013). In fact, plants have also evolved sophisticated response mechanisms to adapt to different developmental events during different growth stages and to reprogram gene expression at the transcriptional level (Smart 1994).…”

“…In fact, plants have also evolved sophisticated response mechanisms to adapt to different developmental events during different growth stages and to reprogram gene expression at the transcriptional level (Smart 1994). Therefore, transcript profiling has been widely used to determine how plants transcriptionally respond to developmental events during leaf senescence (Luo et al 2013). Much progress has been made in elucidating the complex transcriptional regulation mechanism that is responsible for developmental adaption.…”