Passage:
In 1916, botanist Ubaldo Ricca published findings proposing that rapid leaf movements in *Mimosa pudica*—the swift folding of pinnules following mechanical stimulation—were mediated entirely by an endogenous chemical stimulant transported through the plant’s transpiration stream. Ricca demonstrated that when an internodal stem segment was excised and bridged via a water-filled glass tube, mechanical wounding below the junction still triggered leaf closure above it, albeit with a latency proportional to the rate of xylem sap convection. This putative circulating substance, termed "Ricca’s factor," appeared to refute earlier nineteenth-century speculations by Jagadish Chandra Bose, who had posited that rapid thigmonastic responses were governed by electrical impulses propagating along specialized conductive tissues.
For several decades, Ricca's hydraulic-chemical paradigm predominated, largely because the open lumen of xylem vessels provided an intuitive route for bulk fluid movement. However, subsequent microelectrode investigations initiated in the 1930s by Karl Umrath, and substantially expanded in the late twentieth century, revealed that electrical phenomena play an indispensable and primary role. Researchers discovered that mechanical perturbation directly elicits an all-or-nothing action potential originating in the phloem parenchyma and protoxylem cells. Unlike the sodium-driven action potentials characteristic of metazoan neural transmission, the depolarization phase in *Mimosa* is driven by a massive efflux of chloride ions through voltage-gated and stretch-activated anion channels, followed immediately by an efflux of potassium ions to repolarize the membrane.
Crucially, this electrical depolarization propagates symplasmically across plasmodesmata lining the phloem sieve-tube complex at velocities reaching several centimeters per second—substantially outpacing passive fluid convection. Upon arriving at the pulvinus, the specialized motor organ located at the base of each petiole and leaflet, the action potential triggers a rapid redistribution of osmolytes. Chloride and potassium ions are abruptly expelled from the abaxial extensor motor cells into the surrounding apoplastic space, thereby raising the intracellular water potential and driving a rapid efflux of water through membrane aquaporins. The resulting precipitous loss of hydrostatic turgor within the extensor cells, contrasted with the maintained turgidity of opposing adaxial flexor cells, forces the immediate mechanical collapse of the pulvinar hinge. While modern botanists concede that Ricca's factor can mediate secondary, delayed contractions under catastrophic tissue wounding, high-resolution recording has conclusively demonstrated that the primary, fast signaling mechanism is an electrical action potential that alters pulvinar cell turgor via selective ion fluxes.
Statement:
Based on the passage, the mechanical collapse of a *Mimosa pudica* leaf hinge occurs because hydrostatic turgor pressure decreases within the extensor motor cells while being preserved within the opposing flexor cells.
Cevap: Cevap