Water Water deficit especially after heading is one of the most effective factors of wheat yield loss in Iran and across the world and identifying the physiological traits related to plant resilience is of great importance in screening for tolerant varieties. The objective of this study was to evaluate the variation in stem reserves accumulation capacity and its relationship with remobilization in some wheat cultivars. 22 wheat cultivars were cultivated in a split plot design with three replications, full irrigation and 40% of field capacity being main plots. The amount of accumulation and remobilization was estimated by measuring internodes weight and stem soluble Carbohydrates content (WSC). Significant genotypic variation among cultivars was observed under both normal and drought conditions. Maximum accumulation was found in lower internodes followed by peduncle and penultimate using dry weight measurement method. In WSC measurement method, however, maximum accumulation was observed in penultimate followed by lower internodes and peduncle. Cultivars ranking based on accumulation was also different in two methods. Drought stress caused decline in internodes weight, WSC and yield and remobilization efficiency. The specific stem weight had the highest correlation with remobilization. Significant correlation was found between grain yield and remobilization, specific stem weight and WSC.

Introduction: In semiarid regions with a Mediterranean climate, grain-filling period of barley (Hordeum vulgare L. ) faces different kinds of biotic and abiotic stresses including water deficit, heat stress and foliar diseases. Current assimilation as a carbon source for grain filling is dependent on light absorptive green surfaces after anthesis. This source decreases normally due to natural senescence and different stresses. Simultaneously, demand of growing grain increases in addition to the demand of maintenance and respiration of live plant biomass. So stem reserves are one of the important carbon reserves for grain filling. (Blum, 1998). Stem reserves are mainly in the form of WSC (Kuhbauch and Thome, 1989; Przulj and Momcivilic, 2001; Schnyder, 1993). The final grain weight is one of the main determinant components of yield, which is determined by two factors: grain filling rate and grain filling period (Blum, 1998, Yang and Zhang, 2005). These two components are influenced by environmental and genetic factors and are physiologically completely independent of each other. Ehdaie et al. (2008) studied grain growth in 11 wheat genotypes. Under drought stress, 26% grain weight reduction was due to 29 percent reduction in grain filling rate and 50 percent grain filling period. The aim of this experiment was to investigate the changes in grain weight and Carbohydrate concentration of four barley cultivars under end of season drought stress, and to investigate the role of stem reserves and current photosynthesis in grain weight stability under drought stress. Materials and methods: A pot experiment was carried out in a factorial design with three replicates at the faculty of Agronomy, University of Shahid Chamran in the duration of 2010-2011 growing seasons. Four spring barley cultivars (Hordeum vulgare L. ) selected from preliminary experiment including Nimruz, Jonub, Nosrat and Torkaman were grown under two water treatments including water stress vs. fully irrigation. The chlorophyll Content of flag leaf was assessed from anthesis to maturity at 5-day intervals from the same-age plants. Sampling was done from anthesis to maturity at 5-day intervals from the same-age plants. The spikes were removed and the weight of nine middle grain was measured. The linear rate of grain growth was estimated by The linear regression analysis for each cultivar in well-watered and droughted treatment. The penultimate internodes were separated from stems and then frozen in liquid nitrogen after removing leaf sheet. Five main spikes at maturity were harvested for assessment of main spike grain yield, the number of grains and grain weight. WSC were extracted based on Sonnewald et al. (1992) and measured according to Dubois et al. (1956). Results are expressed as milligrams of WSC per gram of fresh weight for WSC concentration. The mobilized WSC (MWSC) in penultimate internode was estimated as the difference between postanthesis maximum and minimum WSC concentration. remobilization efficiency (Re) of WSC was estimated by the proportion (%) of postanthesis maximum WSC concentration of penultimate internode that mobilized. Result and discussion: Significant difference was observed among cultivars in WSCc at anthesis. Jonub showed the highest and Nosrat showed the lowest concentrations. Inspite of lower WSC concentration (WSCc) at anthesis, Torkaman and Nimruz could be set in the same group with Jonub, based on maximum WSCc (Fig. 1). The ratio of preanthesis WSC to total reserved WSC was different among cultivars. Jonub had the highest ratio, while Torkaman had the lowest ratio. Water withholding elevated remobilisation efficiency by 10%. Nosrat was affected the most by water-stressed conditions by increase of 47% in mobilised Carbohydrates and increase of 44% in remobilisation efficiency. On the other hand, Nimruz and Jonub had high level of WSC remobilisation in both conditions and these cultivars weren’ t highly affected by drought. Water withholding increased the rate of chlorophyll loss by 66%. Nosrat and Nimruz showed the highest and the lowest rate of chlorophyll loss in both circumstances respectively. On the other hand, Jonub and Nosrat showed the highest and the lowest increase in this feature by entering drought. Drought decreased grain filling rate by 35 that resulted in decrease of 15% in grain weight. Reduction by 17% was observed for yield of main spike by entering drought that was mainly due to the decrease of grain weight, Because grains per spike didn’ t change. Conclusion: Cultivars were different in WSC-related traits such as WSC concentration at anthesis, maximum WSC concentration and rate of WSC accumulation in ten-day period after anthesis. Water withholding elevated WSC remobilisation efficiency. Water withholding increased the rate of chlorophyll loss by 66%. Drought decrease the the rate of grain filling by 35%. The decrease of 15% in grain weight led to decrease of 17% in grain yield of main stem. Cultivars showed different manner about use of current photoassimilates and reserved WSC in the second phase of grain filling that led to different changes in grain weight by entering drought conditions.

Side transportation of storage Carbohydrates is one of the most important physiological indices in yield formation. In order to study potassium variation levels (200, 300 and 400 mg kg-1) on side transportation and soluble Carbohydrate contents in two wheat cultivars with different maturity period (Veerynak and Chamran as early and medium maturity types, respectively), a pot experiment was carried out in the glasshouse using a factorial experiment based on a randomized complete block design with three replications in Shahid Chamran University of Ahvaz. The stem soluble Carbohydrate in both cultivars was higher at 300 mg kg-1 from flowering to maturity stages at this potassium level. Total soluble Carbohydrate was higher at 300 mg kg-1 than two other potassium levels. Leaf soluble Carbohydrate in both cultivars was higher at 200 mg kg-1, although the potassium level was lower. Potassium was also caused to increase grain starch during the grain filling period. In general, due to lower leaf area duration in both cultivars, remobilization was lower at 200 mg kg-1 than other levels

To evaluate the capability of different spring bread wheat genotypes for storage and remobilization of stem water soluble Carbohydrates (WSC) and their response to heat stress conditions during grain filling period, a field experiment was carried out as factorial arrangement in randomized complete block design with three replications in 2010-2011 growing season under Ahwaz conditions in Iran. The experimental factors consisted of 10 medium maturity spring bread wheat genotypes (Chamran, Atrak, Aflak, Dez, Falat, Darab-2, Kavir, Pishtaz, S-78-11, S-83-3) and two sowing dates; optimum (12 November) and the late sowing date (21 December). Results showed that spring bread wheat genotypes were significantly different in stem specific weight, WSC concentration and content, stem WSC remobilization and its efficiency. In heat stress conditions in the late sowing date, the amount of WSC remobilization from stem to grain and its efficiency increased by 29% and 33%, respectively. In both sowing dates, maximum stem specific weight had significant association with maximum WSC concentration and the amount of remobilized WSC, and it was considered as a suitable criteria for selecting genotypes with maximum storage and remobilization capability of stem reserves. In the late sowing date, grains.pike-1 was positively correlated with WSC remobilization. This implies the effect of sink strength on increasing water soluble remobilization. However, there was no simple relationship between grain yield and stem reserves remobilization under heat stress conditions during grain filling period. Some genotypes supported grain growth either by maintaining green leaf area and current photosynthesis or by increasing remobilization of more stem reserves, under heat stress conditions.

In order to evaluate the morphological characteristics and lodging related traits and Carbohydrate content of culm and Carbohydrate remobilization in traditional and improved rice cultivars, a field experiment was laid out in randomized complete block design with three replications at Rice Research Institute of Iran ) Rasht (in 2012 and 2013. Rice genotypes included three native rice cultivars (Hashemi, Sangjo and Alikazemi) and six improved (Kadous, Gohar, Khazar, Sepidrood, Deylam and Dorfak) and three promising lines (831, 841 and 416). On the basis of this results, the greatest amount of breaking resistance were observed in third and fourth internods of Khazar. Furthermore, significant positive correlation were observed between average diameter of internode, fresh weight/length of internode and unsoluble Carbohydrate content of culm in anthesis and maturity stages with breaking resistance of third and forth internods. Also, significant positive correlation was observed between number of parenchyma cells and unsoluble Carbohydrate content of culm in anthesis and maturity stages. On the other hand, there was significant negative correlation between Carbohydrate remobilization and breaking resistance of third and forth internods. Principal component analysis classified plant characteristics to two groups. The first factor was named as lodgigng resistance factor and included 71.01 percent of total variation. The second factor with 19.74 percent of total variation was named as morphological lodging sensitivity factor. According to the results of this experiment, it seems that average diameter, thikness and weight/length of internode, have major roles in rice plant resistance to lodging.

remobilization of internal resources is an important mechanism enabling plants to be partly independent of environmental conditions and external nutrient availability. Therefore, in this study the enhancement of nonstructural Carbohydrate remobilization of two barley (Hordeum vu/gore L.) cultivars, Walfajr and Reihan, was assessed by pre-anthesis nitrogen usage and a controlled drought stress during grain filling stage. The experiment was conducted as factorial split plot based on randomized complete blocks in both pot and field experiments. Three levels of nitrogen (60, 120 and 180 kgha-1) and three irrigation levels (>80, 55-65 and 35-45 percent of field capacity) were applied at heading and 10 days after anthesis respectively. Soil water was controlled by pot weighing and determination of soil moisture, in pot and field experiments, respectively. Maximum nonstructural Carbohydrate (NSC) at anthesis, NSC residue at maturity, NSC translocation, and NSC translocation efficiency measured in leaf, sheath, peduncle, two internodes under peduncle, and stem base. Then, the contribution of these parts to grain filling was determined. Pre-an thesis Carbohydrate reserves were increased in the high nitrogen condition, but NSC reserves translocation, and translocation efficiency from anthesis to maturity were decreased. In severe soil drying condition, NSC reserves translocation and remobilization efficiency were increased. Two internodes under peduncle and stem base had greatest Carbohydrate translocation efficiency. Evaluation of each part indicated that NSC reserves in two internodes under peduncle had the highest contribution to grain filling. No. considerable differences were observed between the two, cultivars (Walfajr and Reihan). 

In order to evaluate the effects of leaf defoliation on assimilate remobilization in wheat under water deficit stress, a field experiment was carried out as a split split plot based on randomized complete block design with three replications at College of Agriculture, Shiraz University during 2013-2014 growing season. The treatments included water stress: normal irrigation and cutting-off irrigation at anthesis as main plot, wheat cultivars: Pishtaz, Chamran and Marvdasht as sub plot, and levels of source manipulation: non-defoliation, defoliation at mid-stem elongation or mid-anthesis as sub sub plots. The results showed that leaf defoliation, especially at stem elongation reduced grain yield significantly (Pishtaz 19. 2%, Chamran 24. 7% and Marvdasht 24. 9%). The highest remobilization was also obtained from leaf defoliation treatment at stem elongation, so that defoliation at stem elongation increased proportion of stem and ear in grain yield by 1. 6 and 1. 4 times, respectively; however, it could not compensate yield loss resulted from leaf defoliation. Pishtaz and Marvdasht cultivars had the highest and the lowest remobilization, respectively. Water deficit enhanced remobilization and relative proportion of stem and ear in yield, so that mean of relative proportion of stem and ear in grain yield were 9. 1% and 6. 8% under normal and 15. 2% and 26. 3% under water stress conditions, respectively, meanwhile relative proportion was greater for Pishtaz cultivar. In general, water deficit stress and leaf defoliation, especially at early growth season increased remobilization before flowering and proportion of ear and stem storage in grain yield.

Pre-anthesis stored dry matter in vegetative tissues of barley (Hordeum vulgare L.) are important, because grain filling and yield frequently depend on the remobilization of pre-anthesis assimilates. In this work that was conducted in the University of Tabriz in 2004 and 2005 (pot and field experiments, respectively), the contribution of leaf, stem and sheath in grain filling were determined in two cultivars of barley, Walfajr and Reihan. Influence of three levels of nitrogen (60, 120 and 180 Kgha-1) and drought stress (>80, 55-65 and 35-45 percentage of field capacity) on accumulation and remobilization of assimilates and their contribution in grain filling were investigated. Maximum pre-anthesis stored dry matter (including non structural Carbohydrates and nitrogen) increased in high N treatment. Nitrogen and non structural Carbohydrates had the highest values in leaf and sheath, respectively. A significant enhancement of remobilization was observed under drought stress particularly in high N.treatment. Under severe drought stress, harvest index was increased 10% in both pot and field experiments. remobilization efficiency was higher in flag leaf, peduncle, internode 1 and sheath 4. Prean thesis application of high and normal nitrogen in pot and field experiments, respectively, increased contribution of stem internodes and sheath reserves to grain filling especially, when plants were confronted with drought stress. Peduncle with 3.9% and internode beneath peduncle with 6% and their respective sheaths had the highest contribution to grain filling in pot and field experiments respectively, which was related to the length of these parts. Generally, application of controlled water stress during grain filling period causes a higher remobilization from vegetative tissues before onset of water stress at the end of growing season.