Changes in osmotic and turgor pressure in response to sugar accumulation in barley source leaves

Abstract

Pressure-probe measurements and single-cell sampling and analysis techniques were used to determine the effect of photosynthetic production and accumulation of sugars on osmotic and turgor pressures of individual cells of barley ( Hordeum vulgare L.) source leaves. In control plants, the changes in osmotic pressure in individual cells during the photoperiod were different for mesophyll (increase of 276 mOsmol/kg), parenchymatous bundle sheath (PBS; increase of 100 mOsmol/kg) and epidermis (remains constant). There was also an increase in osmotic pressure at the tissue level. Cooling of roots and the shoot apical meristem restricted the export of sugars from leaves, and the resulting changes in osmotic and turgor pressure were monitored. In contrast to the control leaves, mesophyll, PBS, and epidermal cells showed a similar increase in osmotic pressure (up to 500 mOsmol/kg). Cooling also increased the turgor pressure in epidermal and (to a greater extent) PBS cells. The difference in turgor pressure between epidermal and PBS cells is consistent with the presence of a water potential gradient within the leaf, from the vascular bundles towards the leaf surface.

Glucosinolate-accumulating S-cells in Arabidopsis leaves and flower stalks undergo programmed cell death at early stages of differentiation

“…Single‐cell samples were isolated from flower stalks of intact plants under a stereomicroscope, using a glass microcapillary as previously described (Koroleva et al. , 1998; 2000; 2002), and shown in Figure S1.…”

“…The single‐cell sampling procedure relies on the high turgor pressure in a cell. Under normal growing conditions, epidermal cells in Arabidopsis leaf have a turgor pressure of 0.5 ± 0.1 MPa (in nine leaves from three plants), as measured using a pressure probe as previously described (Koroleva et al. , 2002).…”

The Plant Vascular System: Evolution, Development and FunctionsF

“…In general, it would appear that phloem loading of major osmotic species (sugars and K + ) does not constrain phloem transport under optimal growth conditions. During periods of abiotic stress, phloem loading can minimize the impact of water/salt stress through osmoregulatory activities of cells comprising the phloem‐loading pathway(s) (Koroleva et al 2002; Pommerrenig et al 2007). Interestingly, and perhaps surprisingly, both apoplasmic (Wardlaw and Bagnall 1981) and symplasmic (Hoffman‐Thom et al 2001) loaders undergo maintenance of phloem loading activities in cold‐adapted plants.…”

Phloem Transport of Resources

“…In this context, decreased sink demand slows export (Minchin et al 2002) accompanied by an increase in mesophyll sucrose concentrations (Koroleva et al 2002). Elevated sugar levels in sugarcane leaves coordinately act to repress expression of photosynthetic and sugar transporter genes (McCormick et al 2008b).…”