Senescence-induced ectopic expression of the A. tumefaciens ipt gene in wheat delays leaf senescence, increases cytokinin content, nitrate influx, and nitrate reductase activity, but does not affect grain yield

Abstract

The manipulation of cytokinin levels by senescence-regulated expression of the Agrobacterium tumefaciens ipt gene through its control by the Arabidopsis SAG12 (senescence-associated gene 12) promoter is an efficient tool for the prolongation of leaf photosynthetic activity which potentially can affect plant productivity. In the present study, the efficiency of this approach was tested on wheat (Triticum aestivum L.)-a monocarpic plant characterized by a fast switch from vegetative to reproductive growth, and rapid translocation of metabolites from leaves to developing grains after anthesis. When compared with the wild-type (WT) control plants, the SAG12::ipt wheat plants exhibited delayed chlorophyll degradation only when grown under limited nitrogen (N) supply. Ten days after anthesis the content of chlorophyll and bioactive cytokinins of the first (flag) leaf of the transgenic plants was 32% and 65% higher, respectively, than that of the control. There was a progressive increase in nitrate influx and nitrate reductase activity. However, the SAG12::ipt and the WT plants did not show differences in yield-related parameters including number of grains and grain weight. These results suggest that the delay of leaf senescence in wheat also delays the translocation of metabolites from leaves to developing grains, as indicated by higher accumulation of ((15)N-labelled) N in spikes of control compared with transgenic plants prior to anthesis. This delay interferes with the wheat reproductive strategy that is based on a fast programmed translocation of metabolites from the senescing leaves to the reproductive sinks shortly after anthesis.

Comprehensive Dissection of Spatiotemporal Metabolic Shifts in Primary, Secondary, and Lipid Metabolism during Developmental Senescence in Arabidopsis

“…The linkage between senescence and genotype and environmental conditions is complex and dependent on the respective crop species or the environmental conditions. While delayed senescence in stay-green mutants of maize (Zea mays) and sorghum (Sorghum bicolor) increased yield, due to prolonged accumulation of carbohydrates, this is not true for all cereal crop plants, as stay-green wheat varieties do not show yield advantages, as this phenotype is probably interfering with the fast programmed translocation of metabolites from the leaves to the seeds after anthesis (Sykorová et al, 2008). Crops have usually been selected under optimal mineral nutrient conditions; thus, for example, nitrogen-depleted wheat matures faster and senesces earlier, producing lower yields and poorer seed protein quality (Gregersen, 2011).…”

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

“…This might be due to fewer known genes and QTL. Until now, the isopentenyl transferase (IPT) gene (Gan and Amasino 1995) has been the most successful application of improving stay-green traits and delayed senescence for increasing productivity in specific crops (Rivero et al 2007;Swartzberg et al 2006), but it does not affect grain yield in wheat (Sykorova et al 2008).…”

Manipulation of a Senescence-Associated Gene Improves Fleshy Fruit Yield

“…Once the expression is activated during senescence by the SAG12 promoter, the increment in cytokinin levels blocks senescence progression, thereby retaining photosynthetically active leaves. This approach has proven to successfully block or attenuate both ageand stress-related leaf senescence in different crop species like rice (Oryza sativa; Liu et al, 2010), cassava (Manihot esculenta; Zhang et al, 2010), wheat (Triticum aestivum; Sykorová et al, 2008), and tomato (Solanum lycopersicum; Swartzberg et al, 2006).…”