Effect of Senescence Phenotypes and Nitrate Availability on Wheat Leaf Metabolome during Grain Filling

Elmien Heyneke,Rainer Hoefgen,Malcolm John Hawkesford,Dirk Walther,Guangyou Duan,Joachim Kopka,Mutsumi Watanabe,Alexander Erban,Peter Buchner

doi:10.3390/agronomy9060305

Abstract

The capacity for optimising grain yield depends largely on the timing of senescence and the processes underlying efficient remobilisation and cycling of nutrients from source tissues to the developing grain. This study describes how metabolism is adjusted during senescence in response to varying nitrogen application rates after anthesis. A comprehensive metabolite analysis was performed in field-grown Avalon/Cadenza using segregating doubled haploid wheat genotypes having contrasting traits relating to timing of the onset of senescence. Correlative matrices of metabolites and yield parameters determined the metabolic networks that underlie these phenotypes, and were helpful for identifying unique metabolites that are indicative of timing of senescence. They also revealed robust correlations between steady increases in hexose levels, a late senescence phenotype and high straw yield associated with low N fertiliser levels. Tryptophan, cis-aconitate, phosphate and 1-kestose demonstrated strong perturbations in response to nitrogen availability and progression towards developmental senescence. A comprehensive metabolic map of wheat leaf primary metabolites yielded a cumulative readout of processes that occur during developmental ripening and contribute to grain filling in plants with differential senescence timing.

Highlights

Wheat is the most widely grown crop in the world, being cultivated on an estimated 220 million hectares of cropland yearly, and providing a major share of the world’s caloric demands [1]
Since chlorophyll content is often regarded as a proxy of leaf N content and senescence progression [36,37], chlorophyll contents and SPAD meter readings were recorded weekly to monitor the progression of senescence after anthesis, comparing genotypes with contrasting traits to one another; i.e., early senescence; AxC181 to late senescence; AxC112 (Table 1)
Chlorophyll contents at N100, N200 and N350 were maintained at higher levels up to 3 wpa in the late senescing line compared to the early senescing line, which showed a reduction in chlorophyll contents (Table 1)

Summary

Introduction

Wheat is the most widely grown crop in the world, being cultivated on an estimated 220 million hectares of cropland yearly, and providing a major share of the world’s caloric demands [1]. To obtain maximum grain yield potential, metabolic activity must coincide with maximum photosynthetic activity in the source leaves, and high yielding cultivars may possess leaves with an extended. Agronomy 2019, 9, 305 photosynthetic activity that stretches maximally into the grain filling period [2,3,4]. Grain yields are based on both grain number, which is determined at 30 days before flowering until shortly after anthesis, and grain size, which is determined during grain filling [5]. Environmental perturbations that contribute to damage of the photosynthetic apparatus and accelerate leaf senescence towards the end of the growing season shorten the duration of grain filling and reduce seed size significantly, which may be ascribed to the accelerated leaf senescence [6]

Methods

Results

Discussion

Conclusion