The shape of the maternal pericarp affects cereal grain mass and yield. Pericarp growth was analysed by magnetic resonance imaging (MRI), revealing topological maps of mobile water in developing pericarp of barley (Hordeum vulgare) and displaying tissue regions actively elongating in specific temporal-spatial patterns. Correlation analysis of MRI signals and growth rates reveals that growth in length is mediated by dorsal and also lateral rather than ventral regions. Growth in thickness is related to ventral regions. Switching from dorsal to ventral growth is associated with differential expression of axial regulators of the HD-ZipIII and Kanadi/Ettin types, and NPH3 photoreceptors, suggesting light-mediated auxin re-distribution. Auxin increases with the highest levels in the basal pericarp at 6 days after fertilization (DAF), together with transcriptionally up-regulated auxin transport and signalling. Gibberellin biosynthesis is transcriptionally up-regulated only later, and levels of bioactive gibberellins increase from 7 to 13 DAF, with higher levels in ventral than dorsal regions. Differential gene expression related to cell expansion indicates genes related to apoplast acidification, wall relaxation, sugar cleavage, water transport, and cell wall biosynthesis. Candidate genes potentially involved in pericarp extension are distinguished by their temporal expression, representing potential isoforms responsible for dorsal-mediated early growth in length or ventral-mediated late growth in thickness.

• Klíčová slova
• Auxin, barley pericarp, cell expansion, directed growth, gibberellic acid, grain length, growth dynamics, magnetic resonance imaging, transcript profiling.,
• MeSH
• gibereliny metabolismus   MeSH
• ječmen (rod) genetika   růst a vývoj   metabolismus   MeSH
• kyseliny indoloctové metabolismus   MeSH
• magnetická rezonanční tomografie MeSH
• regulace genové exprese u rostlin * MeSH
• regulátory růstu rostlin metabolismus   MeSH
• rostlinné proteiny genetika   metabolismus   MeSH
• semena rostlinná genetika   růst a vývoj   metabolismus   MeSH
• stanovení celkové genové exprese MeSH
• vývojová regulace genové exprese MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• gibereliny MeSH
• kyseliny indoloctové MeSH
• regulátory růstu rostlin MeSH
• rostlinné proteiny MeSH

In cereal grains, the maternal nucellar projection (NP) constitutes the link to the filial organs, forming a transfer path for assimilates and signals towards the endosperm. At transition to the storage phase, the NP of barley (Hordeum vulgare) undergoes dynamic and regulated differentiation forming a characteristic pattern of proliferating, elongating, and disintegrating cells. Immunolocalization revealed that abscisic acid (ABA) is abundant in early non-elongated but not in differentiated NP cells. In the maternally affected shrunken-endosperm mutant seg8, NP cells did not elongate and ABA remained abundant. The amounts of the bioactive forms of gibberellins (GAs) as well as their biosynthetic precursors were strongly and transiently increased in wild-type caryopses during the transition and early storage phases. In seg8, this increase was delayed and less pronounced together with deregulated gene expression of specific ABA and GA biosynthetic genes. We concluded that differentiation of the barley NP is driven by a distinct and specific shift from lower to higher GA:ABA ratios and that the spatial-temporal change of GA:ABA balances is required to form the differentiation gradient, which is a prerequisite for ordered transfer processes through the NP. Deregulated ABA:GA balances in seg8 impair the differentiation of the NP and potentially compromise transfer of signals and assimilates, resulting in aberrant endosperm growth. These results highlight the impact of hormonal balances on the proper release of assimilates from maternal to filial organs and provide new insights into maternal effects on endosperm differentiation and growth of barley grains.

• Klíčová slova
• Assimilate transfer, barley endosperm, gibberellin-to-abscisic acid balances, maternal–filial communication, nucellar projection, seg8 barley mutant.,
• MeSH
• buněčná diferenciace fyziologie   MeSH
• gibereliny metabolismus   MeSH
• ječmen (rod) metabolismus   MeSH
• kyselina abscisová metabolismus   MeSH
• regulace genové exprese u rostlin fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• gibereliny MeSH
• kyselina abscisová MeSH