Osmotic Adjustment in Expanding and Fully Expanded Leaves of Sunflower in Response to Water Deficits

Abstract

Sunflower plants were grown in large volumes of soil and slowly water-stressed by withholding water. The tissue water relationships of leaves at various stages of stress and of leaves of equivalent well watered controls were studied by the pressure chamber technique. Plants were stressed either when leaf 17 was expanding or when it was fully expanded. When expanding leaves reached a moderate level of stress (predawn leaf water potential of -0.9 MPa), the osmotic potentials at full turgor and zero turgor were lower than the control values by 0.1 MPa and 0.2 MPa, respectively. When fully expanded leaves were stressed to a similar degree (predawn leaf water potential of - 1.1 MPa), the osmotic potentials at full turgor and zero turgor were lower than the control values by 0.2 MPa and 0.3 MPa, respectively. The development of more severe stress in the fully expanded leaves was not accompanied by any further osmotic adjustment. However, when the expanding leaves reached a predawn leaf water potential of -2.3 MPa, the values of leaf osmotic potential at full turgor and zero turgor were lower than the values for the well watered plants by 0.4 MPa and 0.6 MPa, respectively. In expanding leaves prestressed to a predawn leaf water potential of -2.3 MPa, the osmotic potential at full turgor was significantly less than the control values for at least 7 days after rewatering. Stress had no effect on the bulk modulus of elasticity. It is concluded that both expanding and fully expanded sunflower leaves show osmotic adjustment.

The effect of salinity stress on ions and soluble sugars distribution in leaves, leaf sheaths and roots of rice (Oryza sativa L.) seedlings

“…Many of physiological processes in plants were suppressed with the increase in Na + concentration. Jones and Turner (1980) reported that K + is an important ion for osmotic adjustment, especially in old leaves, and participates in Mn 2+ 1 *P < 0.05; **P < 0.01; ns not significant osmotic adjustment till 30-50%. Reduction in K + concentration probably caused a reduction of plant ability for osmotic adjustment and drought stress, which led to plant growth reduction.…”

Osmotic Adjustment in Sorghum

“…The objective of this experiment was to determine the relative contribution of passive versus active mechanisms involved in diurnal 'II changes Loss of water from turgid leaf tissue in response to transpiration results in not only a significant decline in 'I',' but also a decline in 'In, to a lesser extent. As the leaf tissue 'I,, declines even more in response to soil water deficits, 'I' declines accordingly as reported in a large number of crop species (2,(13)(14)(15)(16)19). A decline in measured 'I' can result from a simple passive concentration of solutes due to dehydration or due to net solute accumulation.…”

Combined effects of excess boron and salinity on root histology of Zea mays L. amylacea from the Lluta Valley (Arica, Chile)

“…This increase in the number of rows of cells in the pericycle is accompanied by the presence of smaller cell sizes, a behavior that probably increases the resistance of cells against collapsing under conditions of stress (Oertli 1990). This would also increase the ability of plants to maintain turgor, especially under conditions of water stress (Jones & Turner 1980). This resistance can be increased by around 20 times when the cells forming the pericycle are smaller compared to larger cells (Bosabalidis & Kofidis 2002).…”