Role of Carbohydrates in Proline Accumulation in Wilted Barley Leaves

Abstract

The effect of wilting on proline synthesis, proline oxidation, and protein synthesis-all of which contribute to proline accumulation-was deter- Wilting caused an increased conversion of glutamate to other products. In nonstarved leaves, conversion to organic acids as well as to proline was increased. In starved leaves, wilting caused an increase in the conversion of glutamate to glutamine, aspartate, asparagine, and organic acids.The carbohydrate requirement for proline accumulation in wilted leaves was originally observed in turnip leaves (18) and later in barley (8). Those results were interpreted to mean that carbon and hydrogen atoms for proline accumulation were supplied by carbohydrate and the supply of these was lacking in starved leaves. However, no direct evidence for this interpretation is available. In bean leaves, the carbohydrate requirement also has been observed (14) but in bean leaves carbohydrates inhibit proline oxidation and there is a smaller requirement for precursors because proline accumulation is about 10-fold slower (15) than in barley. Thus, the carbohydrate requirement for proline accumulation in bean can be attributed to its role in inhibiting proline oxidation (12,14).Proline accumulation in wilted barley leaves is primarily due to the stimulation of proline synthesis from glutamate (4, 17). Water stress also causes an inhibition of proline oxidation (17) and decreased protein synthesis both of which contribute to proline accumulation but cannot' be solely responsible for it. Wilting causes a loss of end product inhibition by proline (2) and a loss of compartmentation separating proline synthesis from proline oxidation is apparent (16). The experiments reported in this paper were done to determine which of the effects of water stress require carbohydrate in contributing to proline accumulation in barley.

The Mechanism of Abscisic Acid-induced Proline Accumulation in Barley Leaves

“…The oxidation rates in the control leaves were considerably lower than previously reported rates (18,19). This difference could be due to the sparing effect of added sugars, which has been observed in bean leaves (15) and, to a much lesser extent, in barley leaves (16). Because ABA-induced proline accumulation may be dependent on sugars, it is difficult to separate the effects of ABA from the effect of sugar on proline oxidation.…”

“…The ABA-induced proline accumulation at the rate of about ytmol/h .g fresh weight is comparable to the rate of proline accumulation in barley leaves wilted to 75% of the original fresh weight (16). This accumulation does not always occur, but I have found it in all experiments in which leaves were allowed to t.ke up sucrose and glutamate prior to ABA treatment.…”

“…Soluble proline accumulates in plant tissues under several types of stresses including drought (4,13,(16)(17)(18)(19), and references cited therein), salinity (8), and low temperature (7). Treatment with ABA also causes proline to accumulate (2).…”

NITROGEN METABOLISM IN POTERIUM SANGUISORBA DURING WATER STRESS

“…In many species of higher plants a decrease in leaf water potential is accompanied hy an extensive accumulation of the imino acid, proline (Stewart and Larher, 1980), perhaps mainly due to a stimulation of proline synthesis (Stewart, 1978). A high capacity to assimilate nitrogen to provide the carbon and nitrogen precursors for proline biosynthesis may therefore be important during periods of water deficit.…”

Farklı fusarik asit ve bor konsantrasyonları altında in vitro da kültüre alınan patates (Solanum tuberosum cv. Agria) sürgünlerinin gelişimi ve antioksidan tepkileri

“…Proline is an amino acid, which the plant produced under stress conditions and played a role in defense mechanism (Yashu et al 1997) Proline accumulation is a symptom of adaptation towards the environmental stresses such as temperature, nutritional deficiency, exposure to heavy metals, and high level of acidity (Barnett and Naylor 1966, Stewart and Lee 1974, Stewart et al 1977, Stewart 1978, Aspinall and Paleg 1981, Öncel 1988, Ergün 2005. It has been determined that there are some changes in enzyme activities that protect the plants that are under biotic and abiotic stress from the threat of reactive oxygen species (ROS) (O'Brien et al 2012).…”