Phloem development

Abstract

The evolution of the plant vascular system is a key process in Earth history because it enabled plants to conquer land and transform the terrestrial surface. Among the vascular tissues, the phloem is particularly intriguing because of its complex functionality. In angiosperms, its principal components are the sieve elements, which transport phloem sap, and their neighboring companion cells. Together, they form a functional unit that sustains sap loading, transport, and unloading. The developmental trajectory of sieve elements is unique among plant cell types because it entails selective organelle degradation including enucleation. Meticulous analyses of primary, so-called protophloem in the Arabidopsis thaliana root meristem have revealed key steps in protophloem sieve element formation at single-cell resolution. A transcription factor cascade connects specification with differentiation and also orchestrates phloem pole patterning via noncell-autonomous action of sieve element-derived effectors. Reminiscent of vascular tissue patterning in secondary growth, these involve receptor kinase pathways, whose antagonists guide the progression of sieve element differentiation. Receptor kinase pathways may also safeguard phloem formation by maintaining the developmental plasticity of neighboring cell files. Our current understanding of protophloem development in the A. thaliana root has reached sufficient detail to instruct molecular-level investigation of phloem formation in other organs.

Sucrose-responsive osmoregulation of plant cell size by a long non-coding RNA

“…It is still unclear what CANAR’s role in the xylem is. Water exchange between the xylem and phloem is necessary to load and transport phloem content ( 2 ). Xylem-expressed CANAR could potentially help to facilitate this exchange.…”

“…The phloem route transports carbon assimilates, amino acids, RNAs, and hormones from source tissues (e.g. mature leaves) into sink tissues (such as juvenile leaves, roots, meristems, and reproductive organs) ( 1 , 2 ). The hydrostatic pressure differences between source and sink drive the flow of the phloem content ( 3 ).…”

Genome-Wide Identification of TLP Gene Family in Populus trichocarpa and Functional Characterization of PtTLP6, Preferentially Expressed in Phloem

“…Arabidopsis mrf1 mutants have shown the delayed flowering phenotype and, conversely, MRF1 -overexpressing plants exhibited early flowering [ 45 ]. It has been reported that the maturity of the phloem affects the transportation of water and nutrients in plants, which could impact their growth and flowering [ 46 ]. The more mature the phloem is, the more effectively the plants are able to transport water and nutrients to the growing parts, which could promote plant growth and development.…”

Enhancing plant photosynthesis through activating cells deficient in photosynthetic apparatus

“…The main function of vascular tissue include transport of water, ions, photoassimilates and other nutrients (Hardtke 2023). Bundle sheath cells, which surround vascular bundle, are specialized in the water transport and sulfur transport in rice (Lei Hua 2021), or glucosinolate biosynthesis and sulfur in Arabidopsis (Sylvain Aubry 2014).…”