Developmental Changes in Cell and Tissue Water Relations Parameters in Storage Parenchyma of Sugarcane

Abstract

The osmotic pressure of the cell sap of stalk storage parenchyma of sugarcane (Saccharum spp. hybrids) increases by an order of magnitude during ontogeny to reach molar concentrations of sucrose at maturity. Stalk parenchyma cells must either experience very high turgor at maturation or have an ability to regulate turgor. We tested this hypothesis by using pressure probe techniques to quantify parameters of cell and tissue water relations of sugarcane storage parenchyma during ontogeny. The largest developmental change was in the volumetric elastic modulus, which increased from 6 bars in immature tissue to 43 bars in mature tissue. Turgor was maintained relatively low during sucrose accumulation by the partitioning of solutes between the cell and wall compartments. Membrane hydraulic conductivity decreased from about 12 x 10-7 centimeters per second per bar down to 4.4 x 10-7 centimeters per second per bar. The 2.7-fold decrease in membrane hydraulic conductivity during tissue maturation was accompanied by a 7.8-fold increase in wall elasticity. Integration of the cell wall and membrane properties appears to be by the opposing effects of turgor on hydraulic conductivity and elastic modulus. The changes in these properties during development of sugarcane stalk tissue may be a way for parenchyma cells to develop a capacity for expansive growth and still serve as a strong sink for storing high concentrations of sucrose.Storage parenchyma of sugarcane, beet, and certain fruits, such as grape, accumulate molar concentrations of sugars during maturation (10,17,25). This corresponds to osmotic pressures in excess of 20 bars, yet the few measurements that have been made in such tissues (14,25) indicate that turgor pressures are in the same range as nonstorage parenchyma with much lower osmotic pressures, i.e. in the range of 2 to 8 bars (7,11,16,17,23,24 12 months of age were excised, cut into 1 -m segments, enclosed in a plastic bag, and taken to the field laboratory where they were recut to obtain two experimental segments. The younger segment contained partially to fully expanded internodes numbered 3 to 8 counting down from the node subtending the youngest fully expanded leaf blade. The older segment contained internodes exhibiting near maximum sucrose content (internodes No. 13-18). The ends of each segment were dipped in molten paraffin to reduce moisture loss. The segments were then wrapped in a moist paper towel, sealed in a plastic bag, and shipped by air to Pennsylvania State University where experiments commenced within 60 h of harvest. Turgor and osmotic pressures of the 60-h material were similar to those of fresh tissue.Storage parenchyma tissue was excised from the central portion of internodes held within a humidified chamber or from internodes held on damp paper towels in the open laboratory. Typically, the central 3-to 4-cm length of a given internode was excised, then a sharp razor blade was used to remove the sclerified rind. The remaining core ofparenchyma was split into six or eight pie-sha...

Polarity of Water Transport across Epidermal Cell Membranes in Tradescantia virginiana

“…stem cells: (1) the most commonly used pressure relaxation (PR) method, in which cell turgor pressure (P cell ) changes during the measurement, and (2) the more technically demanding pressure clamp (PC) method, in which P cell is maintained constant. Consistent with other studies in higher plant cells, Moore and Cosgrove (1991) Cosgrove and Steudle (1981) reported that a substantial (6-fold) and rapid (within 20 s) reduction in L p could occur in the same cell, and in hindsight, this presumably reflected the influence of aquaporins. Cosgrove and Steudle (1981) did not consider the lower L p as indicative of the L p in situ, and Wan et al (2004) reported that a reduction in L p was associated with perturbations to P cell on the order of 0.1 MPa.…”

“…A similar degree of L p polarity, in the same direction, has been reported for stem parenchyma in Saccharum species (Moore and Cosgrove, 1991), although in their case L p OUT /L p IN was greater for PR (1.65) than for PC (1.16) methods, and we found the opposite (1.11 for PR and 1.27 for PC methods). Moore and Cosgrove (1991) suggested that the greater polarity found for the PR method may have been due to the fact that this method imposed larger changes in P cell than the PC method, but in our case, the P cell changes for both methods were small and similar (Fig.…”

“…Moore and Cosgrove (1991) suggested that the greater polarity found for the PR method may have been due to the fact that this method imposed larger changes in P cell than the PC method, but in our case, the P cell changes for both methods were small and similar (Fig. 3).…”

“…In the PC method, first developed by Wendler and Zimmermann (1982), V o (and, given reasonable assumptions about cell geometry, A) is estimated without the need for optical measurements, and L p can be measured without the need to determine dP/dV or «. However, this method is technically more demanding because it requires precise P control as well as a continuous record of the volume flow of water across the cell membrane (as measured by changes in the position of the cell solution/oil meniscus within the glass capillary over time) and has rarely been used Zimmermann, 1982, 1985;Cosgrove et al, 1987;Moore and Cosgrove, 1991;Zhang and Tyerman, 1991;Murphy and Smith, 1998). Since volume (V) is continuously changing over time, this approach may also be influenced by the hydraulic conductance of the capillary tip (K h ) used to make the measurements as well as surface tension effects due to the progressive changes in capillary diameter with meniscus position, and these influences have not been quantitatively addressed.…”

“…However, in higher plant cells, an analysis of the data presented by Steudle et al (1980Steudle et al ( , 1982 and Tomos et al (1981) indicates the opposite polarity, with L p OUT / L p IN averaging from 1.2 to 1.4. Moore and Cosgrove (1991) used two contrasting hydrostatic methods to measure L p in sugarcane (Saccharum spp.) stem cells: (1) the most commonly used pressure relaxation (PR) method, in which cell turgor pressure (P cell ) changes during the measurement, and (2) the more technically demanding pressure clamp (PC) method, in which P cell is maintained constant.…”