LWR1andLWR2Are Required for Osmoregulation and Osmotic Adjustment in Arabidopsis

Abstract

With the goal of identifying molecular components of the low-water-potential response, we have carried out a two-part selection and screening strategy to identify new Arabidopsis mutants. Using a system of polyethylene glycol-infused agar plates to impose a constant low-water-potential stress, putative mutants impaired in low-water-potential induction of the tomato (Lycopersicon esculentum) le25 promoter were selected. These lines were then screened for altered accumulation of free Pro. The seedlings of 22 mutant lines had either higher or lower Pro content than wild type when exposed to low water potential. Two mutants, designated low-water-potential response1 (lwr1) and lwr2, were characterized in detail. In addition to higher Pro accumulation, lwr1 seedlings had higher total solute content, greater osmotic adjustment at low water potential, altered abscisic acid content, and increased sensitivity to applied abscisic acid with respect to Pro content. lwr1 also had altered growth and morphology. lwr2, in contrast, had lower Pro content and less osmotic adjustment leading to greater water loss at low water potential. Both lwr1 and lwr2 also had altered leaf solute content and water relations in unstressed soil-grown plants. In both mutants, the effects on solute content were too large to be explained by the changes in Pro content alone, indicating that LWR1 and LWR2 affect multiple aspects of cellular osmoregulation.Drought exposes plants to a decrease in soil water content, quantified as a decrease in soil water potential (c w ), which decreases the ability of plants to absorb water from the soil (Boyer, 1982(Boyer, , 1985. Osmotic adjustment functions to avoid excessive dehydration through the accumulation of intercellular solutes, which lowers cellular c w and maintains a favorable c w gradient for water movement into the plant (Morgan, 1984;Zhang et al., 1999). Osmotic adjustment is defined as the amount of solute accumulated in response to low c w excluding any increase in solute concentration that occurs solely because of cellular water loss (Morgan, 1984) and is a specific example of the more general process of osmoregulation, the mechanisms that control cellular solute and water content, and turgor. In plants at constant high c w , solute content and turgor remain relatively stable (Silk et al., 1986;Kutschera, 1991). Net deposition of new solutes occurs mainly in growing tissue where it is needed to drive the uptake of water necessary for cell expansion (Silk et al., 1986). Thus, solute deposition is closely coordinated with growth and solute content subject to tight homeostatic regulation. Exposure to low c w alters this regulation and leads to the accumulation of additional solutes throughout much of the plant. The increase in solute content involves many solute species including K 1 , sugars, and various types of compatible solutes (Morgan, 1984;Sharp et al., 1990;Zhang et al., 1999). The upstream sensing and signaling mechanisms involved in perceiving external c w and controlling cellular solute con...

RETRACTED: HOS10 encodes an R2R3-type MYB transcription factor essential for cold acclimation in plants

“…7F). MYP transcription factors comprise a large gene family in Arabidopsis that are involved in numerous functions, including response to stresses (18,19). The HOS10 gene is constitutively expressed (Fig.…”

“…17. For measurement of low water potentialinduced ABA accumulation, 5-d-old seedlings grown on halfstrength Murashige and Skoog medium (PhytoTechnology Laboratories, Lenexa, KS) (without addition of sugar) containing 2.5 mM Mes buffer were transferred using nylon mesh overlaid on the agar surface to Ϫ1.2-MPa, polyethylene glycol (PEG)-infused plates (18). Control seedlings were transferred to halfstrength Murashige and Skoog medium plates.…”

Nonspecific Phospholipase C NPC4 Promotes Responses to Abscisic Acid and Tolerance to Hyperosmotic Stress inArabidopsis

“…Murashige and Skoog plates were infused with polyethylene glycol (PEG) to a water potential of 20.25 or 20.45 MPa (Verslues and Bray, 2004 Figure 9C). …”

“…These solutions were added to the surface of 20 mM ABA agar plates (200 mL of 100 mM). For NaCl (0 to 150 mM) and PEG (20.25 and 20.45 MPa) experiments, 5-d-old seedlings were transferred and grown under cool white fluorescent light of 100 ;mol m 21 s 21 under 12-h-light/12-h-dark and 238C/228C cycles for 10 d. PEG plates were prepared as described by Verslues and Bray (2004). Briefly, 1.5% agar plates containing 0.53 Murashige and Skoog medium were solidified and then were overlayed with a solution containing 6 mM MES with 0 or 170 g/L PEG (molecular weight, 8000; Sigma-Aldrich), which gave rise to an MPa of 20.25 and 20.45, respectively.…”

A Lipid-Anchored NAC Transcription Factor Is Translocated into the Nucleus and Activates Glyoxalase I Expression during Drought Stress

“…The sterilized seeds of wild-type plants were plated on 0.8% agarose medium and grown for 3 d at 4°C, followed by growth in darkness for 1 d at 24°C. The germinated seedlings were subsequently transferred to the agar-solidified half-strength Murashige and Skoog (MS) basal salt medium or 10% (w/v), 35% (w/v), and 70% (w/v) PEG-infused agar plates for 14 d. The PEG-infused plate system was described previously (Verslues and Bray, 2004). Then, the plants were transferred to half-strength MS salts for recovery for 14 d, and the relative length of the primary root and numbers of lateral roots were quantified.…”