Effects of Drought Stress on Growth and Yield of Rice (Oryza sativa L.) Cultivars and Accumulation of Proline and Soluble Sugars in Sheath and Blades of Their Different Ages Leaves

One of the main problems of rice cultivation and production is the lack of water resources, especially during periods of low rainfall which affect the vegetative growth rate and the amount of yield. In this study the effect of low water supply on the number of heading per hill, number of grain per hill, dry weight of vegetative tissues and panicle and 1000 grain weight in three new cultivars of rice including 216, 829 and Zayandeh-Rood were measured under submerged and non-submerged conditions in a randomize complete block design with three replicates. Simultaneously, the variation in proline and total sugars in sheaths and blades of leaves at different ages was determined. The data indicated that Zayandeh-Rood cultivar showed the lowest reduction in shoot dry weigh and the number of tillers per hill under non-submerged conditions. Furthermore, the panicle weight and the number of filled grains per spike were higher in Zayandeh-Rood cultivar than the other cultivars. In addition, the result of this study show that Zayandeh-Rood cultivar in which originated from local cultivars, have higher ability in solute accumulation such as proline and total carbohydrates than the other new lines. Due to correlation between drought tolerance of Zayandeh-Rood and solute accumulation, it may be suggested that the solute accumulation is one of the mechanisms for drought tolerance in rice. Key word: Rice (Oryza sativa L.) Drought stress Proline Carbohydrate Yield components Grain filling INTRODUCTION encounter drought [8, 9]. One mechanisms utilized by the Drought is the most important limiting factor for crop accumulation of compatible osmolytes, such as proline production and it is becoming an increasingly severe [10, 11], soluble sugars [12]. Production and accumulation problem in many regions of the world [1, 2]. According of free amino acids, especially proline by plant tissue to statistics, the percentage of drought affected land areas during drought, salt and water stress is an adaptive more than doubled from the 1970s to the early 2000s in the response. Proline has been proposed to act as a world [3]. Drought is a world-spread problem seriously compatible solute that adjusts the osmotic potential in influencing grain production and quality and with the cytoplasm. Thus, proline can be used as a metabolic increasing population and global climate change making marker in relation to stress [13]. Moreover, under drought the situation more serious [4]. Rice (Oryza sativa L.) as a stress the accumulation of total soluble sugars in different paddy field crop is particularly susceptible to water stress plant parts would be increased [14]. However the rate of [5, 6]. It is estimated that 50% of the world rice production additional production or accumulation of proline and is affected more or less by drought [7]. soluble sugar is different in different plant parts. To improve crop productivity, it is necessary to Although plant’s leaf would monitor the osmolytes understand the mechanism of plant responses to drought components more compared to the other plant parts, conditions with the ultimate goal of improving crop sheaths account for more contents rather than blades. Of performance in the vast areas of the world where course, the sensitivity of leaves toward drought stress rainfall is limiting or unreliable. In addition to the depends on their ages and segments of plants [15, 16]. complexity of drought itself [1, 2], plant’s behavior A rice leaf is composed of sheath, lamina joint and responses to drought are complex and different blade, acropetally in the longitudinal axis [17]. The leaf mechanisms are adopted by plants when they sheath is the main part of the plant that plays a major role plants for overcome the water stress effects might be via Am-Euras. J. Agric. & Environ. Sci., 5 (2): 264-272, 2009 265 in transporting all essential elements with water from the parts such as vegetative tissues, panicle and grains. roots to aerial portions of the plant. The leaf sheath Then, different plant parts were incubated at 70oC and supports and stiffens the plant against environmental their dry weights were calculated. Afterward, the amount conditions. of proline and total sugars in young and old leaves and Drought stress during vegetative growth, flowering also sheaths and blades were determined and compared and terminal period of rice cultivation, can interrupt in various ages (young and old leaves) and different parts floret initiation (which cause spikelet sterility) and grain (sheath and blade) in all three cultivars. filling, respectively [18, 19]. On the other hand, it has been proposed that grain filling is closely linked to the Determination of Proline and Soluble Sugars: Proline whole-plant senescence process [20, 21]. Usually, water accumulation in fresh leaves was determined according stress at grain filling process induces early senescence to the method of Bates et al. [24]. Free proline was and shortens the grain filling period but increases extracted from the leaves of plants using aqueous remobilization of assimilates (are reserved in the stems sulfosalicylic acid. The filtrate (1 ml) was mixed with equal and sheaths of rice and contribute 10-40% of the final volumes of glacial acetic acid and ninhydrin reagent grain weight) from the straw to the grains [22, 23]. (1.25 g ninhydrin, 30 ml of glacial acetic acid, 20 ml 6 Therefore, soil drying is unfavorable to plant growth but NH PO ) and incubated for 1 h at 100°C. The reaction may not be unfavorable to production of grain if the plant was stopped by placing the test tubes in cold water. is tolerant to drought stress and is capable to cope with The samples were rigorously mixed with 3 ml toluene. the stress condition prior to grain filling process. The light absorption of toluene phase was estimated The present study was conducted to determine how at 520 nm using Pharmacia LKBNovaspec II model drought affects grain yield and the process of grain filling spectrophotometer. The proline concentration was in three new cultivars of rice and also test the hypothesis determined using a standard curve. Free proline content that differential drought tolerance in new rice seedlings was expressed as μmol lit of plant parts. was related to quantitative aspects of the leaf osmolytes status such as proline and soluble carbohydrates in the Determination of Soluble Sugars Content: Soluble leaves. sugars were determined based on the method of MATERIALS AND METHODS homogenized with deionized water, extract was filtered This experiment was conducted in late April 2005 acid, mixture remained for 1h and then absorbance at in glass house of Biology Department, University of 485 nm was determined by spectrophotometer (Pharmacia Isfahan, Iran. Three new cultivars of rice including LKBNovaspec II model).