Shanmugaraj, N. | Search bioRxiv

bioRxiv2026

Spatial metabolomics links polyamine turnover and vascular lipid remodeling to barley spikelet fate

Local metabolic programs can determine whether developing organs maintain growth, differentiate, or degenerate. However, the spatial establishment of such programs during reproductive development remains poorly understood. In cereal inflorescences, this question is closely tied to grain number because the fate of initiated floral primordia is shaped by the developmental position, metabolic support, genotype, and environmental stress. To understand the metabolic logic underlying floral fate in barley (Hordeum vulgare L.), we mapped the spatial distribution of metabolites across the inflorescence in wild-type Bowman and in hvcmf4, a mutant that undergoes premature apical inflorescence degeneration. Amino acid-, carbohydrate-, and chlorophyll-associated metabolites form clear developmental gradients along the inflorescence axis. These gradients are progressively remodeled during developmental pre-anthesis tip degeneration but are both accelerated and spatially distorted in hvcmf4. Within this broader metabolic landscape, two discrete domains stand out. First, spermidine-associated domains specifically marked reproductive meristems, a pattern corroborated by the meristem-enriched expression of polyamine biosynthetic genes. This polyamine-rich meristem state declined as developmental tip degeneration proceeded and was prematurely lost in hvcmf4, where polyamine metabolism appeared to shift toward oxidative breakdown via the polyamine oxidase pathway. Second, lysophosphatidylcholine accumulated specifically at floral attachment and vascular supply zones. The developmental reduction of this bioactive lysophospholipid-associated domain in the apical regions, and its stronger disruption in hvcmf4, coincided with the reprogramming of lipid-remodeling and auxin transport-associated genes, suggesting impaired coordination of lipid signaling, auxin canalization, and vascular support. Together, our study reveals spatial polyamine and lysophospholipid domains that couple meristem maintenance with vascular support, providing a metabolic framework for the fate of developing cereal inflorescences.

plant biology↗

bioRxiv2023

Anatomical insights into the vascular lay-out of the barley rachis: implications for transport and spikelet connection

Background and aimsVascular patterning is intimately related to plant form and function. However, morphologic a l studies on the vascular anatomy of cereal crops, and inflorescences in particular, are scarce despite their importance for grain yield determination. Here, using barley (Hordeum vulgare) as a model, we study the vascular anatomy of the spike-type inflorescence. Our goal is to clarify the relationship between rachis (spike axis) vasculature and spike size, the implications for transport capacity and its interaction with the spikelets. MethodsWe employed serial transversal internode sections in multiple barley lines with different spike size, and investigated the internode diameter, vascular area and vein number size along the mature barley rachis. We then modeled the vascular dynamics along the main spike axis, and analyzed their relationship with spike size. Key resultsInternode diameter and total vascular area have a clear positive correlation with spike size whereas vascular number is only weakly correlated. While the lateral periphery of the rachis contains large mature veins of constant diameter the central part is occupied by a staggered array of small immature veins. This underlines the importance of minimizing transport resistance and suggests that transport and distribution of nutrients are spatially separated. Spikelet-derived veins enter the rachis either in the central area, where they often merge with the immature rachis veins, or in the periphery where they do not merge with the large mature veins. An increase in floret fertility through the conversion of a two-rowed barley into an isogenic six-rowed line, as well a decrease in floret fertility due to enhanced pre-anthesis tip degeneration caused by the mutation tip sterile 2.b (tst2.b) significantly affected vein size, but had limited to no effects on vein number or rachis diameter. Comparative analysis of a wild barley accession suggests that the domestication of barley may have favored plants with enhanced rachis transport capacity. ConclusionsThe rachis vasculature is the result of a two-step process involving an initial lay-out followed by size adjustment according to floret fertility/spike size. The functional processes of long distance transport and local supply to spikelets are spatially separated while a vascular continuity between rachis and spikelets appears non-essential.

plant biology↗