Cytokinin activity during early kernel development corresponds positively with yield potential and later stage ABA accumulation in field-grown wheat (Triticum aestivum L.).

MAIN CONCLUSION: Early cytokinin activity and late abscisic acid dynamics during wheat kernel development correspond to cultivars with higher yield potential. Cytokinins represent prime targets for marker development for wheat breeding programs. Two major phytohormone groups, abscisic acid (ABA) and cytokinins (CKs), are of crucial importance for seed development. Wheat (Triticum aestivum L.) yield is, to a high degree, determined during the milk and dough stages of kernel development. Therefore, understanding the hormonal regulation of these early growth stages is fundamental for crop-improvement programs of this important cereal. Here, we profiled ABA and 25 CK metabolites (including active forms, precursors and inactive conjugates) during kernel development in five field-grown wheat cultivars. The levels of ABA and profiles of CK forms varied greatly among the tested cultivars and kernel stages suggesting that several types of CK metabolites are involved in spatiotemporal regulation of kernel development. The seed yield potential was associated with the elevated levels of active CK levels (tZ, cZ). Interestingly, the increased kernel cZ levels were followed by higher ABA production, suggesting there is an interaction between these two phytohormones. Furthermore, we analyzed the expression patterns of representatives of the four main CK metabolic gene families. The unique transcriptional patterns of the IPT (biosynthesis) and ZOG (reversible inactivation) gene family members (GFMs) in the high and low yield cultivars additionally indicate that there is a significant association between CK metabolism and yield potential in wheat. Based on these results, we suggest that both CK metabolites and their associated genes, can serve as important, early markers of yield performance in modern wheat breeding programs.

Changes in cytokinin form and concentration in developing kernels correspond with variation in yield among field-grown barley cultivars.

The aim of the present study was to determine if relationships between cytokinin (CK) profiles and corresponding enzymatic regulation were consistent with differences in kernel yield among commercial barley (Hordeum vulgare L.) cultivars, differing in parameters relating to productivity and grown under agronomically-relevant field conditions. Quantification of the CKs at six distinct stages of kernel development by high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) revealed a significant increase in CKs, especially trans-zeatin (tZ), during the stage when grain filling occurs, with a greater CK concentration observed in the cultivar with the greatest number of kernels per spike, which was also the highest yielding cultivar. High levels of the cis-zeatin (cZ) CK form were observed at the first developmental stage, indicating a possible role in early embryo development and viability. Cytokinin oxidase (CKX; EC 1.5.99.12) activity was evaluated at each stage through a colorimetric assay, as the enzyme provides a primary mechanism for the irreversible degradation and, thus, regulation of CKs. However, no peaks in CKX activity were observed and no differences were detected at the particular stages examined. Isopentenyl transferase (IPT) gene expression was also examined and suggests that biosynthesis contributes to regulation of CK concentrations in developing barley kernels.