Calcium dynamics in tomato pollen tubes using the Yellow Cameleon 3.6 sensor.

In vitro tomato pollen tubes show a cytoplasmic calcium gradient that oscillates with the same period as growth. Pollen tube growth requires coordination between the tip-focused cytoplasmic calcium concentration ([Ca]) gradient and the actin cytoskeleton. This [Ca] gradient is necessary for exocytosis of small vesicles, which contributes to the delivery of new membrane and cell wall at the pollen tube tip.

RSL4 Takes Control: Multiple Signals, One Transcription Factor.

Root hair growth dramatically expands the root surface area, thus facilitating water and nutrient uptake. Until recently, the molecular mechanism underlying root hair growth was unknown. Recent studies have revealed that the transcription factor ROOT HAIR DEFECTIVE 6 LIKE 4 (RSL4) coordinates hormonal, environmental, and developmental factors to trigger polar growth.

Molecular link between auxin and ROS-mediated polar growth.

Root hair polar growth is endogenously controlled by auxin and sustained by oscillating levels of reactive oxygen species (ROS). These cells extend several hundred-fold their original size toward signals important for plant survival. Although their final cell size is of fundamental importance, the molecular mechanisms that control it remain largely unknown.

ROS Regulation of Polar Growth in Plant Cells.

Root hair cells and pollen tubes, like fungal hyphae, possess a typical tip or polar cell expansion with growth limited to the apical dome. Cell expansion needs to be carefully regulated to produce a correct shape and size. Polar cell growth is sustained by oscillatory feedback loops comprising three main components that together play an important role regulating this process.

Low Sugar Is Not Always Good: Impact of Specific O-Glycan Defects on Tip Growth in Arabidopsis.

Mutants of the O-glycosylation pathway of extensins as well as molecular dynamics simulations uncover the effects of the O-glycosylation machinery on root hair tip growth.

Complex regulation of prolyl-4-hydroxylases impacts root hair expansion.

Root hairs are single cells that develop by tip growth, a process shared with pollen tubes, axons, and fungal hyphae. However, structural plant cell walls impose constraints to accomplish tip growth. In addition to polysaccharides, plant cell walls are composed of hydroxyproline-rich glycoproteins (HRGPs), which include several groups of O-glycoproteins, including extensins (EXTs).

Improved ROS measurement in root hair cells.

Reactive oxygen species (ROS) are recognized as important signaling components in various processes in plants. ROS are produced for NADPH oxidase in different subcellular compartments and they are involved for a wide range of stimuli, such as cell cycle, growth, plant defenses, abiotic stress responses, and abscisic acid signaling in guard cells. In Arabidopsis, root hairs ROS also play a key role in root hair growth and they control the activity of calcium channels required for polar growth (Takeda et al.