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D Schneider - One of the best experts on this subject based on the ideXlab platform.

  • Ethephon induced oxidative stress in the olive Leaf Abscission zone enables development of a selective Abscission compound
    BMC Plant Biology, 2017
    Co-Authors: S. Goldental-cohen, C. Burstein, Y. Mugira, S. Ben-sasson, Hanita Zemach, Ithay Biton, Adi Doron-faigenboim, Yair Many, Avi Sadeh, D Schneider
    Abstract:

    BackgroundTable olives (Olea europaea L.), despite their widespread production, are still harvested manually. The low efficiency of manual harvesting and the rising costs of labor have reduced the profitability of this crop. A selective Abscission treatment, inducing Abscission of fruits but not leaves, is crucial for the adoption of mechanical harvesting of table olives. In the present work we studied the anatomical and molecular differences between the three Abscission zones (AZs) of olive fruits and leaves.ResultsThe fruit Abscission zone 3 (FAZ3), located between the fruit and the pedicel, was found to be the active AZ in mature fruits and is sensitive to ethephon, whereas FAZ2, between the pedicel and the rachis, is the flower active AZ as well as functioning as the most ethephon induced fruit AZ. We found anatomical differences between the Leaf AZ (LAZ) and the two FAZs. Unlike the FAZs, the LAZ is characterized by small cells with less pectin compared to neighboring cells. In an attempt to differentiate between the fruit and Leaf AZs, we examined the effect of treating olive-bearing trees with ethephon, an ethylene-releasing compound, with or without antioxidants, on the detachment force (DF) of fruits and leaves 5 days after the treatment. Ethephon treatment enhanced pectinase activity and reduced DF in all the three olive AZs. A transcriptomic analysis of the three olive AZs after ethephon treatment revealed induction of several genes encoding for hormones (ethylene, auxin and ABA), as well as for several cell wall degrading enzymes. However, up-regulation of cellulase genes was found only in the LAZ. Many genes involved in oxidative stress were induced by the ethephon treatment in the LAZ alone. In addition, we found that reactive oxygen species (ROS) mediated Abscission in response to ethephon only in leaves. Thus, adding antioxidants such as ascorbic acid or butyric acid to the ethephon inhibited Leaf Abscission but enhanced fruit Abscission.ConclusionOur findings suggest that treating olive-bearing trees with a combination of ethephon and antioxidants reduces the detachment force (DF) of fruit without weakening that of the leaves. Hence, this selective Abscission treatment may be used in turn to promote mechanized harvest of olives.

  • Ethephon induced oxidative stress in the olive Leaf Abscission zone enables development of a selective Abscission compound.
    BMC plant biology, 2017
    Co-Authors: S. Goldental-cohen, C. Burstein, Y. Mugira, Hanita Zemach, Ithay Biton, Adi Doron-faigenboim, Yair Many, S. Ben Sasson, Amit Sadeh, D Schneider
    Abstract:

    Table olives (Olea europaea L.), despite their widespread production, are still harvested manually. The low efficiency of manual harvesting and the rising costs of labor have reduced the profitability of this crop. A selective Abscission treatment, inducing Abscission of fruits but not leaves, is crucial for the adoption of mechanical harvesting of table olives. In the present work we studied the anatomical and molecular differences between the three Abscission zones (AZs) of olive fruits and leaves. The fruit Abscission zone 3 (FAZ3), located between the fruit and the pedicel, was found to be the active AZ in mature fruits and is sensitive to ethephon, whereas FAZ2, between the pedicel and the rachis, is the flower active AZ as well as functioning as the most ethephon induced fruit AZ. We found anatomical differences between the Leaf AZ (LAZ) and the two FAZs. Unlike the FAZs, the LAZ is characterized by small cells with less pectin compared to neighboring cells. In an attempt to differentiate between the fruit and Leaf AZs, we examined the effect of treating olive-bearing trees with ethephon, an ethylene-releasing compound, with or without antioxidants, on the detachment force (DF) of fruits and leaves 5 days after the treatment. Ethephon treatment enhanced pectinase activity and reduced DF in all the three olive AZs. A transcriptomic analysis of the three olive AZs after ethephon treatment revealed induction of several genes encoding for hormones (ethylene, auxin and ABA), as well as for several cell wall degrading enzymes. However, up-regulation of cellulase genes was found only in the LAZ. Many genes involved in oxidative stress were induced by the ethephon treatment in the LAZ alone. In addition, we found that reactive oxygen species (ROS) mediated Abscission in response to ethephon only in leaves. Thus, adding antioxidants such as ascorbic acid or butyric acid to the ethephon inhibited Leaf Abscission but enhanced fruit Abscission. Our findings suggest that treating olive-bearing trees with a combination of ethephon and antioxidants reduces the detachment force (DF) of fruit without weakening that of the leaves. Hence, this selective Abscission treatment may be used in turn to promote mechanized harvest of olives.

Shimon Meir - One of the best experts on this subject based on the ideXlab platform.

  • re evaluation of ethylene role in arabidopsis cauline Leaf Abscission induced by water stress and rewatering
    bioRxiv, 2021
    Co-Authors: Shimon Meir, Sonia Philosophhadas, Shoshana Salim, Adi Segev, Joseph Riov
    Abstract:

    Patharkar and Walker (2016) reported that cauline Leaf Abscission in Arabidopsis is induced by a cycle of water stress and rewatering, which is regulated by the complex of INFLORESCENCE DEFICIENT IN Abscission (IDA), HAESA (HAE), and HAESA-LIKE2 (HSL2) kinases. However, they stated without presenting experimental results that ethylene is not involved in this process. Since this statement contradicts the well-established role of ethylene in organ Abscission induced by a cycle of water stress and rewatering, our present study was aimed to re-evaluate the possible involvement of ethylene in this process. For this purpose, we examined the endogenous ethylene production during water stress and following rewatering, as well as the effects of exogenous ethylene and 1-methylcyclopropene (1-MCP), on cauline Leaf Abscission of Arabidopsis wild type. Additionally, we examined whether this stress induces cauline Leaf Abscission in ethylene-insensitive Arabidopsis mutants. The results of the present study demonstrated that ethylene production rates increased significantly in cauline leaves at 4 h after rewatering of stressed plants, and remained high for at least 24 h in plants water-stressed to 40 and 30% of system weight. Ethylene treatment applied to well-watered plants induced cauline Leaf Abscission, which was inhibited by 1-MCP. Cauline Leaf Abscission was also inhibited by 1-MCP applied during a cycle of water stress and rewatering. Finally, no Abscission occurred in two ethylene-insensitive mutants, ein2-1 and ein2-5, following a cycle of water stress and rewatering. Taken together, these results clearly indicate that ethylene is involved in Arabidopsis cauline Leaf Abscission induced by water stress. One sentence summaryUnlike Patharker and Walker (2016), our results show that ethylene is involved in Arabidopsis cauline Leaf Abscission induced by water stress and rewatering, similar to Leaf Abscission in other plants.

  • chilling induced Leaf Abscission of ixora coccinea plants iii enhancement by high light via increased oxidative processes
    Physiologia Plantarum, 2001
    Co-Authors: Rina Michaeli, Sonia Philosophhadas, Joseph Riov, Yosepha Shahak, Kira Ratner, Shimon Meir
    Abstract:

    The role of increased oxidation induced by successive stresses of chilling and high light in the induction of Leaf Abscission was studied in Ixora coccinea plants in relation to auxin metabolism and oxidative processes. Exposure of plants following dark chilling (7 degrees C for 3 days) to high light (500-700 mmol m-2 s-1 photosynthetically active radiation) for 5 h at 20-25 degrees C enhanced chilling-induced Leaf Abscission. This Abscission was inhibited by pretreatment with the antioxidant butylated hydroxyanisole, alpha-naphthaleneacetic acid or the ethylene action inhibitor, 1-methylcyclopropene. The oxidative processes initiated during the low light period following the dark chilling period, such as indoleacetic acid (IAA) decarboxylation and lipid peroxidation, were further enhanced by subsequent exposure to high light. Photoinhibition, expressed by the reduction of the chlorophyll fluorescence parameter Fv/Fm, was evident following exposure to high light, irrespective of the temperature of the pretreatment, but this reduction persisted only in chilled plants. This suggests that oxidative processes generated during and after the chilling period might have inhibited the recovery from photoinhibition. The chilling stress under darkness induced a 60% reduction in superoxide dismutase (SOD) activity and significant increases (130-600%) in the activities of several other antioxidative enzymes. These data suggest that the chilling-induced reduction in SOD activity may well be responsible for the increase in the oxidative stress induced by the subsequent light treatment, as expressed by the increased enzymatic activities. Taken together, this study provides further support for the involvement of oxidative processes in the events occurring in tissues exposed to sequential chilling and light stresses, leading to reduction in free IAA content in the Abscission zone and to Leaf Abscission.

  • chilling induced Leaf Abscission of ixora coccinea plants i induction by oxidative stress via increased sensitivity to ethylene
    Physiologia Plantarum, 1999
    Co-Authors: Rina Michaeli, Joseph Riov, Sonia Philosophhadas, Shimon Meir
    Abstract:

    Exposing ixora (Ixora coccinea) plants to chilling temperatures (3–9°C for 3 days) resulted in increased Leaf Abscission, initiated 3 days after transfer to 20°C. Exposure to chilling also induced a 7-fold increase in ethylene production rates of Abscission zone (AZ) tissue during the initial 5 h after chilling. The ethylene burst resulted from the high levels of 1-aminocyclopropane-1-carboxylic acid (ACC) accumulated in the AZ during the chilling period. ACC levels following chilling decreased also due to enhanced conjugation to 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC). Treating plants prior to chilling with antioxidants, such as butylated hydroxyanisole (BHA), n-propyl gallate (PG), and vitamin E, significantly reduced chilling-induced Leaf Abscission. This effect was obtained despite the fact that ethylene production in the treated plants resembled that of chilled plants receiving no BHA. In addition, exposure of plants to ethylene (0.5–10 μl l−1) for 1–3 days significantly enhanced Leaf Abscission only when they had been pre-chilled. These data imply that chilling-induced Leaf Abscission was closely correlated with increased sensitivity of the AZ to ethylene rather than with the chilling-induced ethylene burst. Based on the findings that the ethylene action inhibitor, 1-methylcyclopropene (1-MCP), and the antioxidant BHA inhibited both the chilling-induced and the ethylene-enhanced Leaf Abscission, it is concluded that: (1) although ethylene is essential for chilling-induced Abscission, it is not the triggering factor; (2) oxidative processes derived from the chilling stress seem to be the trigger of chilling-induced Leaf Abscission, operating via increased sensitivity to ethylene.

  • chilling induced Leaf Abscission of ixora coccinea plants ii alteration of auxin economy by oxidative stress
    Physiologia Plantarum, 1999
    Co-Authors: Rina Michaeli, Joseph Riov, Sonia Philosophhadas, Shimon Meir
    Abstract:

    Chilling-induced Leaf Abscission of ixora (Ixora coccinea) plants was almost completely inhibited by α-naphthaleneacetic acid (NAA), even in the presence of exogenous ethylene, which enhanced the chilling effect on Leaf Abscission. Chilling reduced free indoleacetic acid (IAA) content, quantified immediately after chilling, in the Abscission zone (AZ) and Leaf blade. Free IAA content in chilling-treated plants continued to decrease gradually with time after chilling. Application of the antioxidant butylated hydroxyanisole (BHA) before or after chilling not only prevented the post-chilling decline in free IAA content, but also restored free IAA level during 6-48 h of the post-chilling period almost to the control level. No significant effect of chilling on the endogenous content of ester- and amide-conjugates of IAA or the metabolism of exogenous labeled IAA were observed. Chilling enhanced the decarboxylation of IAA, particularly in the AZ tissue. Auxin transport capacity was significantly inhibited by chilling, and this effect was counteracted by BHA applied before chilling. The data indicate that chilling reduces free IAA content in the AZ, an effect that may lead to increased sensitivity to ethylene. The chilling-induced reduction in IAA content in the AZ seems to result, at least in part, from increased IAA decarboxylation and reduced auxin transport capacity. These processes seem to be triggered by the oxidative stress imposed on the tissues by chilling.

S. Goldental-cohen - One of the best experts on this subject based on the ideXlab platform.

  • Ethephon induced oxidative stress in the olive Leaf Abscission zone enables development of a selective Abscission compound
    BMC Plant Biology, 2017
    Co-Authors: S. Goldental-cohen, C. Burstein, Y. Mugira, S. Ben-sasson, Hanita Zemach, Ithay Biton, Adi Doron-faigenboim, Yair Many, Avi Sadeh, D Schneider
    Abstract:

    BackgroundTable olives (Olea europaea L.), despite their widespread production, are still harvested manually. The low efficiency of manual harvesting and the rising costs of labor have reduced the profitability of this crop. A selective Abscission treatment, inducing Abscission of fruits but not leaves, is crucial for the adoption of mechanical harvesting of table olives. In the present work we studied the anatomical and molecular differences between the three Abscission zones (AZs) of olive fruits and leaves.ResultsThe fruit Abscission zone 3 (FAZ3), located between the fruit and the pedicel, was found to be the active AZ in mature fruits and is sensitive to ethephon, whereas FAZ2, between the pedicel and the rachis, is the flower active AZ as well as functioning as the most ethephon induced fruit AZ. We found anatomical differences between the Leaf AZ (LAZ) and the two FAZs. Unlike the FAZs, the LAZ is characterized by small cells with less pectin compared to neighboring cells. In an attempt to differentiate between the fruit and Leaf AZs, we examined the effect of treating olive-bearing trees with ethephon, an ethylene-releasing compound, with or without antioxidants, on the detachment force (DF) of fruits and leaves 5 days after the treatment. Ethephon treatment enhanced pectinase activity and reduced DF in all the three olive AZs. A transcriptomic analysis of the three olive AZs after ethephon treatment revealed induction of several genes encoding for hormones (ethylene, auxin and ABA), as well as for several cell wall degrading enzymes. However, up-regulation of cellulase genes was found only in the LAZ. Many genes involved in oxidative stress were induced by the ethephon treatment in the LAZ alone. In addition, we found that reactive oxygen species (ROS) mediated Abscission in response to ethephon only in leaves. Thus, adding antioxidants such as ascorbic acid or butyric acid to the ethephon inhibited Leaf Abscission but enhanced fruit Abscission.ConclusionOur findings suggest that treating olive-bearing trees with a combination of ethephon and antioxidants reduces the detachment force (DF) of fruit without weakening that of the leaves. Hence, this selective Abscission treatment may be used in turn to promote mechanized harvest of olives.

  • Ethephon induced oxidative stress in the olive Leaf Abscission zone enables development of a selective Abscission compound.
    BMC plant biology, 2017
    Co-Authors: S. Goldental-cohen, C. Burstein, Y. Mugira, Hanita Zemach, Ithay Biton, Adi Doron-faigenboim, Yair Many, S. Ben Sasson, Amit Sadeh, D Schneider
    Abstract:

    Table olives (Olea europaea L.), despite their widespread production, are still harvested manually. The low efficiency of manual harvesting and the rising costs of labor have reduced the profitability of this crop. A selective Abscission treatment, inducing Abscission of fruits but not leaves, is crucial for the adoption of mechanical harvesting of table olives. In the present work we studied the anatomical and molecular differences between the three Abscission zones (AZs) of olive fruits and leaves. The fruit Abscission zone 3 (FAZ3), located between the fruit and the pedicel, was found to be the active AZ in mature fruits and is sensitive to ethephon, whereas FAZ2, between the pedicel and the rachis, is the flower active AZ as well as functioning as the most ethephon induced fruit AZ. We found anatomical differences between the Leaf AZ (LAZ) and the two FAZs. Unlike the FAZs, the LAZ is characterized by small cells with less pectin compared to neighboring cells. In an attempt to differentiate between the fruit and Leaf AZs, we examined the effect of treating olive-bearing trees with ethephon, an ethylene-releasing compound, with or without antioxidants, on the detachment force (DF) of fruits and leaves 5 days after the treatment. Ethephon treatment enhanced pectinase activity and reduced DF in all the three olive AZs. A transcriptomic analysis of the three olive AZs after ethephon treatment revealed induction of several genes encoding for hormones (ethylene, auxin and ABA), as well as for several cell wall degrading enzymes. However, up-regulation of cellulase genes was found only in the LAZ. Many genes involved in oxidative stress were induced by the ethephon treatment in the LAZ alone. In addition, we found that reactive oxygen species (ROS) mediated Abscission in response to ethephon only in leaves. Thus, adding antioxidants such as ascorbic acid or butyric acid to the ethephon inhibited Leaf Abscission but enhanced fruit Abscission. Our findings suggest that treating olive-bearing trees with a combination of ethephon and antioxidants reduces the detachment force (DF) of fruit without weakening that of the leaves. Hence, this selective Abscission treatment may be used in turn to promote mechanized harvest of olives.

Joseph Riov - One of the best experts on this subject based on the ideXlab platform.

  • re evaluation of ethylene role in arabidopsis cauline Leaf Abscission induced by water stress and rewatering
    bioRxiv, 2021
    Co-Authors: Shimon Meir, Sonia Philosophhadas, Shoshana Salim, Adi Segev, Joseph Riov
    Abstract:

    Patharkar and Walker (2016) reported that cauline Leaf Abscission in Arabidopsis is induced by a cycle of water stress and rewatering, which is regulated by the complex of INFLORESCENCE DEFICIENT IN Abscission (IDA), HAESA (HAE), and HAESA-LIKE2 (HSL2) kinases. However, they stated without presenting experimental results that ethylene is not involved in this process. Since this statement contradicts the well-established role of ethylene in organ Abscission induced by a cycle of water stress and rewatering, our present study was aimed to re-evaluate the possible involvement of ethylene in this process. For this purpose, we examined the endogenous ethylene production during water stress and following rewatering, as well as the effects of exogenous ethylene and 1-methylcyclopropene (1-MCP), on cauline Leaf Abscission of Arabidopsis wild type. Additionally, we examined whether this stress induces cauline Leaf Abscission in ethylene-insensitive Arabidopsis mutants. The results of the present study demonstrated that ethylene production rates increased significantly in cauline leaves at 4 h after rewatering of stressed plants, and remained high for at least 24 h in plants water-stressed to 40 and 30% of system weight. Ethylene treatment applied to well-watered plants induced cauline Leaf Abscission, which was inhibited by 1-MCP. Cauline Leaf Abscission was also inhibited by 1-MCP applied during a cycle of water stress and rewatering. Finally, no Abscission occurred in two ethylene-insensitive mutants, ein2-1 and ein2-5, following a cycle of water stress and rewatering. Taken together, these results clearly indicate that ethylene is involved in Arabidopsis cauline Leaf Abscission induced by water stress. One sentence summaryUnlike Patharker and Walker (2016), our results show that ethylene is involved in Arabidopsis cauline Leaf Abscission induced by water stress and rewatering, similar to Leaf Abscission in other plants.

  • chilling induced Leaf Abscission of ixora coccinea plants iii enhancement by high light via increased oxidative processes
    Physiologia Plantarum, 2001
    Co-Authors: Rina Michaeli, Sonia Philosophhadas, Joseph Riov, Yosepha Shahak, Kira Ratner, Shimon Meir
    Abstract:

    The role of increased oxidation induced by successive stresses of chilling and high light in the induction of Leaf Abscission was studied in Ixora coccinea plants in relation to auxin metabolism and oxidative processes. Exposure of plants following dark chilling (7 degrees C for 3 days) to high light (500-700 mmol m-2 s-1 photosynthetically active radiation) for 5 h at 20-25 degrees C enhanced chilling-induced Leaf Abscission. This Abscission was inhibited by pretreatment with the antioxidant butylated hydroxyanisole, alpha-naphthaleneacetic acid or the ethylene action inhibitor, 1-methylcyclopropene. The oxidative processes initiated during the low light period following the dark chilling period, such as indoleacetic acid (IAA) decarboxylation and lipid peroxidation, were further enhanced by subsequent exposure to high light. Photoinhibition, expressed by the reduction of the chlorophyll fluorescence parameter Fv/Fm, was evident following exposure to high light, irrespective of the temperature of the pretreatment, but this reduction persisted only in chilled plants. This suggests that oxidative processes generated during and after the chilling period might have inhibited the recovery from photoinhibition. The chilling stress under darkness induced a 60% reduction in superoxide dismutase (SOD) activity and significant increases (130-600%) in the activities of several other antioxidative enzymes. These data suggest that the chilling-induced reduction in SOD activity may well be responsible for the increase in the oxidative stress induced by the subsequent light treatment, as expressed by the increased enzymatic activities. Taken together, this study provides further support for the involvement of oxidative processes in the events occurring in tissues exposed to sequential chilling and light stresses, leading to reduction in free IAA content in the Abscission zone and to Leaf Abscission.

  • chilling induced Leaf Abscission of ixora coccinea plants i induction by oxidative stress via increased sensitivity to ethylene
    Physiologia Plantarum, 1999
    Co-Authors: Rina Michaeli, Joseph Riov, Sonia Philosophhadas, Shimon Meir
    Abstract:

    Exposing ixora (Ixora coccinea) plants to chilling temperatures (3–9°C for 3 days) resulted in increased Leaf Abscission, initiated 3 days after transfer to 20°C. Exposure to chilling also induced a 7-fold increase in ethylene production rates of Abscission zone (AZ) tissue during the initial 5 h after chilling. The ethylene burst resulted from the high levels of 1-aminocyclopropane-1-carboxylic acid (ACC) accumulated in the AZ during the chilling period. ACC levels following chilling decreased also due to enhanced conjugation to 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC). Treating plants prior to chilling with antioxidants, such as butylated hydroxyanisole (BHA), n-propyl gallate (PG), and vitamin E, significantly reduced chilling-induced Leaf Abscission. This effect was obtained despite the fact that ethylene production in the treated plants resembled that of chilled plants receiving no BHA. In addition, exposure of plants to ethylene (0.5–10 μl l−1) for 1–3 days significantly enhanced Leaf Abscission only when they had been pre-chilled. These data imply that chilling-induced Leaf Abscission was closely correlated with increased sensitivity of the AZ to ethylene rather than with the chilling-induced ethylene burst. Based on the findings that the ethylene action inhibitor, 1-methylcyclopropene (1-MCP), and the antioxidant BHA inhibited both the chilling-induced and the ethylene-enhanced Leaf Abscission, it is concluded that: (1) although ethylene is essential for chilling-induced Abscission, it is not the triggering factor; (2) oxidative processes derived from the chilling stress seem to be the trigger of chilling-induced Leaf Abscission, operating via increased sensitivity to ethylene.

  • chilling induced Leaf Abscission of ixora coccinea plants ii alteration of auxin economy by oxidative stress
    Physiologia Plantarum, 1999
    Co-Authors: Rina Michaeli, Joseph Riov, Sonia Philosophhadas, Shimon Meir
    Abstract:

    Chilling-induced Leaf Abscission of ixora (Ixora coccinea) plants was almost completely inhibited by α-naphthaleneacetic acid (NAA), even in the presence of exogenous ethylene, which enhanced the chilling effect on Leaf Abscission. Chilling reduced free indoleacetic acid (IAA) content, quantified immediately after chilling, in the Abscission zone (AZ) and Leaf blade. Free IAA content in chilling-treated plants continued to decrease gradually with time after chilling. Application of the antioxidant butylated hydroxyanisole (BHA) before or after chilling not only prevented the post-chilling decline in free IAA content, but also restored free IAA level during 6-48 h of the post-chilling period almost to the control level. No significant effect of chilling on the endogenous content of ester- and amide-conjugates of IAA or the metabolism of exogenous labeled IAA were observed. Chilling enhanced the decarboxylation of IAA, particularly in the AZ tissue. Auxin transport capacity was significantly inhibited by chilling, and this effect was counteracted by BHA applied before chilling. The data indicate that chilling reduces free IAA content in the AZ, an effect that may lead to increased sensitivity to ethylene. The chilling-induced reduction in IAA content in the AZ seems to result, at least in part, from increased IAA decarboxylation and reduced auxin transport capacity. These processes seem to be triggered by the oxidative stress imposed on the tissues by chilling.

Rina Michaeli - One of the best experts on this subject based on the ideXlab platform.

  • chilling induced Leaf Abscission of ixora coccinea plants iii enhancement by high light via increased oxidative processes
    Physiologia Plantarum, 2001
    Co-Authors: Rina Michaeli, Sonia Philosophhadas, Joseph Riov, Yosepha Shahak, Kira Ratner, Shimon Meir
    Abstract:

    The role of increased oxidation induced by successive stresses of chilling and high light in the induction of Leaf Abscission was studied in Ixora coccinea plants in relation to auxin metabolism and oxidative processes. Exposure of plants following dark chilling (7 degrees C for 3 days) to high light (500-700 mmol m-2 s-1 photosynthetically active radiation) for 5 h at 20-25 degrees C enhanced chilling-induced Leaf Abscission. This Abscission was inhibited by pretreatment with the antioxidant butylated hydroxyanisole, alpha-naphthaleneacetic acid or the ethylene action inhibitor, 1-methylcyclopropene. The oxidative processes initiated during the low light period following the dark chilling period, such as indoleacetic acid (IAA) decarboxylation and lipid peroxidation, were further enhanced by subsequent exposure to high light. Photoinhibition, expressed by the reduction of the chlorophyll fluorescence parameter Fv/Fm, was evident following exposure to high light, irrespective of the temperature of the pretreatment, but this reduction persisted only in chilled plants. This suggests that oxidative processes generated during and after the chilling period might have inhibited the recovery from photoinhibition. The chilling stress under darkness induced a 60% reduction in superoxide dismutase (SOD) activity and significant increases (130-600%) in the activities of several other antioxidative enzymes. These data suggest that the chilling-induced reduction in SOD activity may well be responsible for the increase in the oxidative stress induced by the subsequent light treatment, as expressed by the increased enzymatic activities. Taken together, this study provides further support for the involvement of oxidative processes in the events occurring in tissues exposed to sequential chilling and light stresses, leading to reduction in free IAA content in the Abscission zone and to Leaf Abscission.

  • chilling induced Leaf Abscission of ixora coccinea plants i induction by oxidative stress via increased sensitivity to ethylene
    Physiologia Plantarum, 1999
    Co-Authors: Rina Michaeli, Joseph Riov, Sonia Philosophhadas, Shimon Meir
    Abstract:

    Exposing ixora (Ixora coccinea) plants to chilling temperatures (3–9°C for 3 days) resulted in increased Leaf Abscission, initiated 3 days after transfer to 20°C. Exposure to chilling also induced a 7-fold increase in ethylene production rates of Abscission zone (AZ) tissue during the initial 5 h after chilling. The ethylene burst resulted from the high levels of 1-aminocyclopropane-1-carboxylic acid (ACC) accumulated in the AZ during the chilling period. ACC levels following chilling decreased also due to enhanced conjugation to 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC). Treating plants prior to chilling with antioxidants, such as butylated hydroxyanisole (BHA), n-propyl gallate (PG), and vitamin E, significantly reduced chilling-induced Leaf Abscission. This effect was obtained despite the fact that ethylene production in the treated plants resembled that of chilled plants receiving no BHA. In addition, exposure of plants to ethylene (0.5–10 μl l−1) for 1–3 days significantly enhanced Leaf Abscission only when they had been pre-chilled. These data imply that chilling-induced Leaf Abscission was closely correlated with increased sensitivity of the AZ to ethylene rather than with the chilling-induced ethylene burst. Based on the findings that the ethylene action inhibitor, 1-methylcyclopropene (1-MCP), and the antioxidant BHA inhibited both the chilling-induced and the ethylene-enhanced Leaf Abscission, it is concluded that: (1) although ethylene is essential for chilling-induced Abscission, it is not the triggering factor; (2) oxidative processes derived from the chilling stress seem to be the trigger of chilling-induced Leaf Abscission, operating via increased sensitivity to ethylene.

  • chilling induced Leaf Abscission of ixora coccinea plants ii alteration of auxin economy by oxidative stress
    Physiologia Plantarum, 1999
    Co-Authors: Rina Michaeli, Joseph Riov, Sonia Philosophhadas, Shimon Meir
    Abstract:

    Chilling-induced Leaf Abscission of ixora (Ixora coccinea) plants was almost completely inhibited by α-naphthaleneacetic acid (NAA), even in the presence of exogenous ethylene, which enhanced the chilling effect on Leaf Abscission. Chilling reduced free indoleacetic acid (IAA) content, quantified immediately after chilling, in the Abscission zone (AZ) and Leaf blade. Free IAA content in chilling-treated plants continued to decrease gradually with time after chilling. Application of the antioxidant butylated hydroxyanisole (BHA) before or after chilling not only prevented the post-chilling decline in free IAA content, but also restored free IAA level during 6-48 h of the post-chilling period almost to the control level. No significant effect of chilling on the endogenous content of ester- and amide-conjugates of IAA or the metabolism of exogenous labeled IAA were observed. Chilling enhanced the decarboxylation of IAA, particularly in the AZ tissue. Auxin transport capacity was significantly inhibited by chilling, and this effect was counteracted by BHA applied before chilling. The data indicate that chilling reduces free IAA content in the AZ, an effect that may lead to increased sensitivity to ethylene. The chilling-induced reduction in IAA content in the AZ seems to result, at least in part, from increased IAA decarboxylation and reduced auxin transport capacity. These processes seem to be triggered by the oxidative stress imposed on the tissues by chilling.