Proline Accumulation and the Adaptation of Cultured Plant Cells to Water Stress

Abstract

The transfer of cultured tomato cells (Lycopersicon esculentum cv VFNT-Cherry) to a low water potential environment resulted in an increased dry weight to fresh weight ratio accompanied by a rapid accumulation of proline. Proline content continued to increase as osmotic adjustment and growth occurred. The initial increase in proline concentration was accompanied by a drop in turgor. However, proline levels continued to increase with a gain in turgor during osmotic adjustment. Thus, the accumulation of proline depended not only on cell water potential, or on the initial loss of turgor but more closely on cell osmotic potential. The ultimate level of proline depended on the level of adaptation. Proline levels remained high after more than 100 cell generations in low water potential media, but declined rapidly after transfer to media with a less negative water potential. Addition of exogenous proline to the medium during water stress and during osmotic downshock alleviated the normally resulting inhibition of growth. The results suggest a positive role for proline accumulation in adaptation of cells to changing external water potentials.It has been suggested for some time that the often observed accumulation of proline by plant tissues during water stress is an adaptive response even though investigators have obtained varying results relating proline accumulation to enhanced survival or tolerance under stress (4,6,7,13,16,27,29). Although the relationship between proline levels and osmotic adjustment has rarely been determined, the most common interpretation of proline accumulation is that proline at high levels acts as a cytoplasmic osmotic solute.The relationship between proline accumulation and osmotic adjustment of plant cells during a prolonged period of exposure to a constant low water potential (t)2 has not been determined before. Also, the water status parameter which is primarily associated with the initiation of the accumulation of proline in response to water stress has not been determined, i.e. whether it is the turgor (tp), osmotic potential (4's), or 4,6 of the cell. factors, such as stomatal physiology and morphology, plant and leaf size, root characteristics, etc. It is possible to circumvent such problems by using cultured plant cells where tolerance to water or salt stress must involve osmotic adjustment to prevent permanent loss of turgor and subsequent cell dehydration. Since cultured cells are in A equilibrium with the medium, it is possible to keep the cells at a constant over an extended period of time and eliminate the possibility that changes in growth which occur under imposed low external A are the result of an altered balance of water availability and loss.The objective of the present investigation was to determine the relationship between proline accumulation and the adaptation of cultured plant cells to water stress through osmotic adjustment. An attempt has been made also to assess which aspect of cell water relations is involved in the initiation of the accumulation of prolin...

In vitro selection and characterization of polyethylene glycol (PEG) tolerant callus lines and regeneration of plantlets from the selected callus lines in sugarcane (Saccharum officinarum L.)

“…A similar trend in proline levels is reported in tobacco (Gangaopadhyay 1997) sunflower (Hassan et al 2004). Increase in the proline accumulation on exposing calli to PEG is reported in Sorghum (Bhaskaran et al 1985) rice (Aqeel-Ahmad et al 2007) Proline accumulation under water deficit has been mainly recognized as an osmotic agent (Handa et al 1986). Selected calli exhibited osmotic adjustment in response to PEG stress through the synthesis of solutes like proline.…”

Effects of Salt and Water Stress on Plant Growth and on Accumulation of Osmolytes and Antioxidant Compounds in Cherry Tomato

“…Proline is generally considered as a good indicator of environmental stress in tomato (Clausen, 2005) and there are many reports describing an increase in Pro contents as a response to water or salt stress in this species (Babu et al, 2012;Ghorbanli et al, 2013;Giannakoula and Ilias, 2013;Inal, 2002;Handa et al, 1986;Nahar and Gretzmacher, 2002;Umebese et al, 2009;Yokas et al, 2008), although it should be mentioned that data specific for cherry tomatoes are rather scarce (Maggio et al, 2007;Rosales et al, 2007). What is not so clear is the possible contribution of Pro accumulation to the (relative) resistance of tomato to salinity.…”

“…Osmolytes are 'compatible solutes', very soluble, low-molecular-weight organic compounds that do not interfere with normal metabolism even when present at high concentrations. While toxic inorganic ions are sequestered in vacuoles, organic osmolytes accumulate predominantly in the cytoplasm, preventing or limiting cellular dehydration (Büssis and Heineke, 1998;Handa et al, 1986;Stewart and Lee, 1974). Reduction of the osmotic potential due to accumulation of osmolytes in response to stress improves the ability of the plant cells to maintain turgor pressure at low water potentials, which is essential for biological processes such as photosynthesis or cell expansion, as well as for maintaining enzymatic activities (Tyree and Jarvis, 1982).…”

Plant water relations and proline accumulation on two cowpea (Vigna unguiculata (L.) Walp.) cultivars as a response to water stress

“…Earlier studies showed that proline accumulated as a response to a decrease in water potentials (Handa et al, 1986;Ober & Sharp, 1994;Bussis & Heineke, 1998) and or RWC (Rajagopal et al, 1977;Argandona & Pahlich, 1991). This response in proline content caused some osmotic adjustment (Handa et aI., 1986;Bussis & Heineke, 1998), which enabled the plant to re-acquire turgidity under water shortage.…”

“…Proline content has been reported to increase in response to a decrease in water potential (Handa et al, 1986;Ober & Sharp, 1994;Bussis & Heineke, 1998) or RWC (Rajagopal, Balasubramanian & Sinha, 1977;Argandona & Pahlich, 1991). Proline accumulation affects osmotic potential (Bussis & Heineke, 1998) and is therefore regarded as an important criterion for selecting drought tolerant crops (Singh, Aspinall & Paleg, 1972).…”