To Lead or to Follow: Contribution of the Plant Vacuole to Cell Growth

Abstract

Cell division and cell elongation are fundamental processes for growth. In contrast to animal cells, plant cells are surrounded by rigid walls and therefore loosening of the wall is required during elongation. On the other hand, vacuole size has been shown to correlate with cell size and inhibition of vacuolar expansion limits cell growth. However, the specific role of the vacuole during cell elongation is still not fully resolved. Especially the question whether the vacuole is the leading unit during cellular growth or just passively expands upon water uptake remains to be answered. Here, we review recent findings about the contribution of the vacuole to cell elongation. In addition, we also discuss the connection between cell wall status and vacuolar morphology. In particular, we focus on the question whether vacuolar size is dictated by cell size or vice versa and share our personnel view about the sequential steps during cell elongation.

The TOR–Auxin Connection Upstream of Root Hair Growth

“…Auxin levels and on-point distribution are modulated by polar auxin transport, biosynthesis, conjugation, perception, and signaling [ 14 , 25 , 90 ]. Auxin signaling events underpin the reorganization of root hair cells on a subcellular level, including cytoskeleton bundling, vacuolar morphology, cell wall properties, endomembrane trafficking, and membrane composition [ 25 , 72 , 89 , 91 , 92 , 93 , 94 , 95 ]. Polar auxin transport is characterized by active, PM protein-dependent distribution from auxin source to sink, including importers, like the AUXIN1/LIKE-AUX1 (AUX1/LAX) protein family [ 96 , 97 , 98 , 99 ] or the nitrate and auxin transporter NITRATE TRANSPORTER 1.1 (NRT1.1) [ 100 , 101 , 102 ].…”

“…The expanding root hair tip is almost fully filled with the vacuole, surrounded by a thin layer of highly polarized cytoplasm [ 8 ]. Vacuolar morphology has to date been extensively studied during the elongation processes of cells in the primary root tip, where it is crucial to maintain the expansion of the elongating cell without investing excessive resources to build up cytoplasmic content and stability [ 94 , 196 , 197 , 198 , 199 , 200 ]. It highly depends on intracellular auxin concentration [ 23 , 82 , 201 ] and signaling pathways partially regulated by FER [ 202 , 203 ].…”

Optimizing Protocols for Arabidopsis Shoot and Root Protoplast Cultivation

“…The higher Cl − content of other media, such as Kao and Michayluk ([ 22 ] and PCA [ 23 ], at 12 mM and 6.12 mM Cl − , respectively, increase Cl − sequestration in the vacuole. This Cl − sequestration could contribute to increased cell size [ 24 ] due to the increased size of vacuole with changes typical for lytic vacuole [ 25 ]. This process is the reverse of what is observed during dedifferentiation when the acidic lytic vacuole is converted to a protein storage vacuole with alkaline properties [ 26 ].…”

Light at the end of the tunnel: FRAP assay reveals that plant vacuoles start as a tubular network

“…Presence of the vacuoles in all plant cells implies that these organelles are likely to be inherited from cell to cell, but does not exclude that a subpopulation of the vacuolar structures might be possibility formed de novo. Plant vacuoles typically undergo massive structural changes during cell differentiation and growth, starting as relatively small organelles in meristematic cells and occupying up to 90% of the cellular volume in differentiated cells 1,8 . It is intriguing how such vast reorganization of the organelle is synchronized with its vital role in cellular homeostasis and responses to environmental stress stimuli.…”

“…These organelles are highly dynamic and vary greatly in size, morphology and content, depending on plant species, cell type, developmental stage and environmental conditions 4,5 . Plant vacuoles typically undergo massive structural changes during cell differentiation and growth, starting as relatively small organelles in meristematic cells and occupying up to 90% of the cellular volume in differentiated cells 3,6 . It is intriguing how such vast reorganization of the organelle is synchronized with its vital role in cellular homeostasis and responses to environmental stress stimuli.…”