Root-to-shoot signaling positively mediates source-sink relation in late growth stages in diploid and tetraploid wheat.

Non-hydraulic root source signaling (nHRS) is a unique positive response to soil drying in the regulation of plant growth and development. However, it is unclear how the nHRS mediates the tradeoff between source and sink at the late growth stages and its adaptive mechanisms in primitive wheat. To address this issue, a root-splitting design was made by inserting solid partition in the middle of the pot culture to induce the occurrence of nHRS using four wheat cultivars (MO1 and MO4, diploid; DM22 and DM31, tetraploid) as materials. Three water treatments were designed as 1) both halves watered (CK), 2) holistic root system watered then droughted (FS), 3) one-half of the root system watered and half droughted (PS). FS and PS were designed to compare the role of the full root system and split root system to induce nHRS. Leaves samples were collected during booting and anthesis to compare the role of nHRS at both growth stages. The data indicated that under PS treatment, ABA concentration was significantly higher than FS and CK, demonstrating the induction of nHRS in split root design and nHRS decreased cytokinin (ZR) levels, particularly in the PS treatment. Soluble sugar and proline accumulation were higher in the anthesis stage as compared to the booting stage. POD activity was higher at anthesis, while CAT was higher at the booting stage. Increased ABA (nHRS) correlated with source-sink relationships and metabolic rate (i.e., leaf) connecting other stress signals. Biomass density showed superior resource acquisition and utilization capabilities in both FS and PS treatment as compared to CK in all plants. Our findings indicate that nHRS-induced alterations in phytohormones and their effect on source-sink relations were allied with the growth stages in primitive wheat.

Response of source-sink relationship to progressive water deficit in the domestication of dryland wheat.

It is crucial to clarify the physiological responses of wheat (T. aestivum) plants to source-sink manipulation and assimilation transportation under drought stress during domestication of dryland wheat. In this research, a two-year field experiment was conducted using nine wheat cultivars in a semiarid site of northwest China. The source-sink manipulation treatments including defoliation of flag leaves and 50% removal of ears were applied at the anthesis stage under two levels of drought stress conditions i.e. progressive water supply (PWS) and rainfed drought treatment (RDT). Our results indicated that drought stress reduced the dry weight of leaves, sheaths and stems, as well as caused a significant yield reduction. High ploidy wheat exhibits a greater capacity to sustain higher grain yields when subjected to drought stress, primarily due to its stronger buffer capacity between source supply and sink demand. All wheat species with different ploidy levels had a certain degree of source limitation and sink restriction. During the domestication of wheat, the type of source and sink might be ploidy-dependent with progressive water deficit, but similar interactive relationships. The source-sink ratio of tetraploid species was the largest, while that of hexaploid species was the lowest.