Browsing by Person "Mondal, Shimul"

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    Ion uptake and distribution in sweet potato genotypes subjected to salt stress is not driven by transpiration
    (2023) Mondal, Shimul; Rahaman, Ebna Habib Md Shofiur; Asch, Folkard
    Potassium is taken up actively by the plant, whereas sodium is often either competing for the same uptake mechanisms or uptake and distribution are driven by the transpirational volume flow in the shoots of plants grown under salinity. Reducing transpiration rate is regarded as an adaptation mechanism to reduce leaf tissue salt load. In combination with a high K uptake, plants may be able to maintain growth and are, thus, seen as salt‐tolerant. Little is known about these mechanisms in sweet potato (Ipomoea batatas L.). Therefore, cuttings of two sweet potato genotypes contrasting in salinity tolerance (CIP 188002.1, tolerant; CIP 189151.8, sensitive) were subjected to 0 and 50 mM NaCl root zone salinity in a hydroponic system and grown under low (0.76 kPa) and high (2.27 kPa) vapour pressure deficit (VPD) to create differences in transpiration. After 18 days of initial hydroponic growth, NaCl was added for another 33 days. Cumulative plant water loss and total uptake of Na, K and Cl were determined for all plants and treatments. Transpirational water loss was twice as high under high VPD as compared to low VPD conditions, but genotypic Na and Cl accumulation remained almost the same. In contrast to plants subjected to salt stress under low VPD conditions, genotypes under high VPD conditions differed significantly in transpiration. However, in both genotypes transpirational water loss from individual leaves and Na or Cl accumulation were not correlated, under high VPD younger leaves of CIP 188002.1 (tolerant) accumulated more than twice as much potassium than in CIP 189151.8 (sensitive). The distribution of the three ions across leaf positions and within one leaf position between petiole and leaf blade differed strongly between the two genotypes. Tolerant CIP 188002.1 accumulated up to five times more sodium and potassium in the leaf petioles in the middle‐aged and young leaf positions than in the leaf blade, whereas in sensitive CIP 189151.8 neither ion was preferentially accumulated in the petioles. This was independent of salinity treatment and VPD conditions. In contrast, hyperaccumulation of Cl in petioles only occurred under high VPD conditions in the petioles of the tolerant genotype, but not under low VPD conditions, indicating a VPD sensitivity for Cl distribution in sweet potato. While we conclude that transpirational volume flow is not a main driving force for Na and Cl uptake and distribution within the plant, we discuss potential pathways leading to the hyperaccumulation of sodium and potassium in the leaf petioles of the tolerant genotype. We suggest studies on HKT transporter activities in the petioles as an object of further studies in sweet potato.
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    Physiological mechanisms and growth responses of sweet potato subjected to salinity
    (2023) Mondal, Shimul; Asch, Folkard
    For the development of salt-tolerant sweet potato varieties, either through breeding or biotechnology, an appropriate salinity screening tool is necessary for the identification of tolerant or sensitive genotype. Our overall objectives for this study were to develop a suitable, reliable and rapid salinity screening tool in view of salt tolerance mechanism in sweet potato under salinity. To better understand the tolerance mechanisms; leaf level ion uptake and distribution patterns by transpirational water loss and leaf level ROS scavenging antioxidant enzyme activities were evaluated under salinity. Additionally, different ion extraction methods were tested which will contribute to the development of reliable salinity screening tool in sweet potato genotypes. All the experiments were conducted in the greenhouse and VPD (vapor pressure deficit) chambers of the Hans-Rutenberg Institute of Tropical Agricultural Sciences, University of Hohenheim, Germany, in a hydroponic system. Twelve genotypes of sweet potato were collected from Bangladesh Agricultural Research Institute (BARI) and used to evaluate salt thresholds with salt tolerance mechanisms for a wide range of salinity levels (0, 50, 100, and 150 mM NaCl). First, genotypic thresholds were determined for 12 sweet potato genotypes exposed to salinity, whereupon it was found that 75 mM root zone salinity (NaCl) was the threshold for sweet potato. The genotypic threshold was estimated from the dry matter accumulation that began to decrease under the influence of salinity. It was found that genotypic thresholds were negatively linearly correlated with the difference between tissue K content at 75 mM NaCl and tissue K content at controlled salinity in the root zone. This information is very important for identifying the salt tolerant and sensitive genotype of sweet potato. Second, the uptake and distribution of Na, K, and Cl ions by transpiration, across different-aged leaves, were studied to better understand the mechanisms of salt tolerance in sweet potato. Two different sweet potato genotypes were subjected to salt stress of 0 and 50 mM NaCl in artificially dry (VPD 2.27 kPa) and humid (VPD 0.76 kPa) chambers. We found that cumulative water loss per unit leaf area was twice as high at a VPD of 2.27 kPa, but Na uptake remained the same. No relationship was observed between water loss from individual leaves and Na or Cl uptake. About 30% more Na was distributed in the petioles of salt tolerant genotype compared to leaf blades, while the opposite was observed in salt sensitive sweet potato genotype and VPD had no effect on Na distribution. Third, the activities of ROS scavenging antioxidant enzymes were evaluated with respect to different leaf age, in two different genotypes of sweet potato under 100 mM salinity. In general, antioxidant enzymes in sweet potato do not respond to salt stress but are altered by the effects of leaf position, leaf age, duration of stress, and genotype. No effect of Na on antioxidant enzyme activities was found under salt stress in sweet potato leaves. However, the significant positive correlation between K concentration and the level of SOD (super oxide dismutase) in older leaves suggests that SOD contributes to the maintenance of a high K concentration to protect photosynthetic activity. In summary, this study shows that sweet potato responds differently to salinity depending on the genotype, and that the threshold beyond which yield decreases is 75 mM NaCl. Genotypic threshold strongly linked to high tissue K content under increasing salinity that suggests a salt tolerance mechanisms in sweet potato. Salt-tolerant sweet potatoes distribute significant amounts of Na and K in their petioles. Young leaves of the tolerant genotype contain more K under salt stress. GR and positive relationship between K concentration and SOD in salt tolerant genotypes indicate some tolerance mechanisms. So, a screening tool is proposed for sweet potato based on the genotypic ability to maintain high tissue K levels under increasing salinity level.
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    Potassium content is the main driver for salinity tolerance in sweet potato before tuber formation
    (2022) Mondal, Shimul; Rahaman, Ebna Habib Md Shofiur; Asch, Folkard
    Sweet potato (Ipomoea batatas L.) is mostly grown in Asia, which accounts for 86% of global production. However, its production is under threat by salinity. Little is known about genotypic responses to salinity in sweet potato. Phenotypic responses or physiological processes linked to salt tolerance that could be developed into a reliable screening tool to assist breeding have not yet been developed for sweet potato. In a hydroponic cultivation system, 12 contrasting sweet potato genotypes were subjected to 0, 50, 100 and 150 mM root zone salinity (RZS). Genotypic thresholds for dry matter accumulation and the genotypic slopes for additional dry matter reduction when the RZS increased beyond the genotypic threshold were determined. Sodium, chlorine and potassium (K) were determined from above‐ground biomass and correlated with the genotypic thresholds found. Genotypic threshold levels were linearly negatively correlated with the difference in tissue K content at 75 mM RZS and the tissue K content at control levels. Based on the genotypic ability to retain high tissue potassium levels under increasing RZS, we propose a screening tool based on these experimental data that can distinguish between salt‐tolerant and salt‐sensitive genotypes and indicate the potential yield level of the sweet potato genotypes.
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    Salinity effects on the activities of ROS scavenging enzymes in leaves of two sweet potato clones
    (2023) Mondal, Shimul; Burgert, Susane; Asch, Julia; Rahaman, Ebna Habib Md Shofiur; Asch, Folkard
    Sweet potato production, particularly in coastal areas is often prone to salinity. Salt‐tolerant clones will be needed to maintain production, but to date, little is known about salt tolerance traits in sweet potato. Salt stress may result in excessive uptake of unwanted ions into plant tissues leading to the formation of reactive oxygen species (ROS), which in turn may destroy membranes and reduce photosynthesis and growth. Antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), glutathione reductase (GR) and ascorbate peroxidase (APX) scavenge ROS and early changes in the activities of such enzymes could be used to identify salinity tolerant genotypes. Therefore, cuttings of two contrasting cultivars of sweet potato, BARI SP 8 (tolerant) and BARI SP 4 (sensitive) were greenhouse‐cultivated in nutrient solution for 21 days and then exposed to 100 mmol NaCl for 7 days. Three, five and seven days after salt application the youngest leaves were sampled individually and enzyme activities, potassium (K) and sodium (Na) concentrations, and SPAD (as a proxy for chlorophyll content) were determined. In both varieties leaf growth was not affected by salinity and young leaves grown under salinity had higher SPAD values than older leaves. Na concentration increased over time, particularly in earlier and in older leaves, whereas K was reduced in younger leaves. In general, enzyme activities were strongly affected by leaf age and leaf position. SOD and APX showed varietal but no salinity effects, CAT increased under salinity in both varieties, whereas POX was strongly reduced and GR was strongly increased under salinity in BARI SP 8 with no effect in BARI SP 4. Enzyme activities were not correlated to leaf Na, neither in relation to leaf age, nor leaf number or duration of salt stress in both varieties. However, varietal differences were observed regarding leaf K. Activities of SOD were highly positive and of CAT highly negatively correlated with leaf K under salinity in BARI SP 8 but not in BARI SP 4, whereas activities of GR and POX were strongly positively correlated with leaf K in BARI SP 4 under salinity but not in BARI SP 8. We conclude that potassium may have a strong regulating role on leaf stress levels and therefore on the activities of antioxidant enzymes. Varieties may differ in their tolerance strategy and we have shown that salinity does not generally increase levels of ROS‐scavenging enzymes in sweet potato leaves under salt stress. Confounding factors such as leaf age and leaf position as well as maintaining high leaf level K concentrations need to be considered when evaluating metabolic traits for salinity tolerance traits.