Osmoregulation in Cotton Fiber

Abstract

Kinetics and osmoregulation of cotton (Gossypium hirsutum L.) fiber growth (primarily extension) have been studied. Growth is dependent on turgor pressure in the fiber. It is inhibited when a decrease in the water potential of the culture medium due to an addition of Carbowax 6000, equals the turgor pressure of the fiber. Potassium and malate accumulate in the fiber and reach peak levels when the growth rate is highest. Maximum concentrations of potassium and malate reached in the fiber can account for over 50% of the osmotic potential of the fiber. As growth slows down, levels of potassium and malate decrease and turgor pressure declines. Cotton ovules are capable of fixing H4CO3-in the dark, predominantly into malate. Fiber growth is inhibited by the absence of potassium and/or atmospheric CO2. We suggest that potassium and malate act as osmoregulatory solutes and that malate, at least in part, arises from dark CO2 fixation reactions.

A Cotton Annexin Affects Fiber Elongation and Secondary Cell Wall Biosynthesis Associated with Ca2+ Influx, ROS Homeostasis, and Actin Filament Reorganization

“…S9D). Early field trials have shown that an increase in fiber K + concentrations led to higher turgor (Dhindsa et al, 1975) and produced longer fibers with a higher quality (Cassman et al, 1990). Ruan et al (2001) demonstrated that the transient closure of plasmodesmata and the maximal expression of the Suc and K + transporters at about 10 DPA raised the fiber turgor to drive rapid elongation.…”

Evidence That High Activity of Vacuolar Invertase Is Required for Cotton Fiber and Arabidopsis Root Elongation through Osmotic Dependent and Independent Pathways, Respectively

“…Second, compelling evidence has indicated a major role of osmotically active solutes in fiber elongation through the generation of cell turgor (Ruan et al, 2004). To this end, Suc moves into fibers symplasmically early in elongation (Ruan et al, 2001), and hexoses accumulated in the vacuole are major osmotically active solutes in the fiber sap (Dhindsa et al, 1975;Ruan et al, 1997), where VIN activity has been reported (Wäfler and Meier, 1994). These observations raise the possibility that VIN may be a central player in osmotically driven fiber expansion (Andersen et al, 2002;Ruan, 2005).…”

Unraveling mechanisms of cell expansion linking solute transport, metabolism, plasmodesmtal gating and cell wall dynamics

“…4,16,17 The observation that a number of GhPIPs and GhTIPs are soluble sugars, potassium and malate are the three major osmotic active solutes, together accounting for ~80% of fibre sap osmolality. 2,14 Potassium and sucrose are imported from the underlying seed coat cells, either symplasmically through the plasmodesmata (PD) or apoplasmically across cell wall space and plasma membrane by their respective transporters, energized by the plasma membrane and tonoplast H + -ATPases, respectively. 4,5 GhKT1, encodes a cotton K + transporter, is weakly expressed in fibers at 6 DAA when the PD are open.…”