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    Öğe
    Possible mechanisms for graft incompatibility between melon scions and pumpkin rootstocks
    (International Society for Horticultural Science, 2008) Aloni, Beny; Karni, Leah; Deventurero, Gila; Levin, Ziv; Cohen, Ron; Katzir, Nurit; Lotan-Pompan, Maya
    The successful application of the grafting technique depends on the identification of stress and pathogen-resistant rootstock (RS), and on the compatibility of the grafted union in terms of fast formation of the vascular connections between the rootstock and the scion and rapid resumption of root and shoot growth. A series of studies, using compatible and incompatible Cucurbita rootstocks, grafted with melon (Cucumis melo L.) scion ('Arava'), were conducted in order to identify metabolic and physiological factors which may be associated with the level of grafting compatibility. In order to increase the differential compatibilities, the grafted seedlings were exposed to either control (22/28°C) or high (28/35°C) temperature conditions starting at 7 days after grafting. Grafting compatibility was dependent on temperature conditions. Twenty days from grafting the rootstock part collapsed only in the non-compatible grafted seedlings under high temperatures but not under normal temperatures. Water uptake and sugar distribution between plant canopy and root measured 14 days under these conditions, and before incompatible transplants collapsed, were not correlated with the differential compatibility. At that stage histo-chemical staining showed that reactive oxygen species (ROS) generation was enhanced under high temperatures in the grafting zone in both compatible and incompatible graft combinations. In this paper we describe a mechanism which may be responsible for grafting incompatibility between Cucurbita RS and melon scion. We suggest that upon formation of the RS-scion continuum, the hormonal balance, especially of auxin and ethylene, required for proper root development, is impaired in incompatible grafting union. This impairment is initiated by the auxin, transported from the scion to the root, which in incompatible RS, triggers ethylene production, ROS generation and root growth inhibition and degeneration. In compatible RS, a variety of mechanisms may operate to either reduce auxin activity in the RS and/or reduce ROS production and activity.
  • [ X ]
    Öğe
    The suppression of salinity-associated oxygen radicals production, in pepper (Capsicum annuum) fruit, by manganese, zinc and calcium in relation to its sensitivity to blossom-end rot
    (2005) Aktas, Hakan; Karni, Leah; Chang, Dong-Chil; Turhan, Ece; Bar-Tal, Asher; Aloni, Beny
    We investigated the possibility that oxidative stress contributes to blossom-end rot (BER) initiation in bell pepper (Capsicum annuum L.) grown under high salinity. Pepper plants (cv. Mazurka, Rijk Zwaan, the Netherlands) were grown in a greenhouse and irrigated with nutrient solution made up with either desalinated water (control - rising from E.C. 1.9 to 2.4 dS m-1) or saline water (salinity - rising from E.C. 3.2 to 7.0 dS m-1). Irrigation was by a circulation system. BER symptoms were observed throughout the experiment but were highly enhanced in the salinity-grown plants during the spring and summer. The fruit calcium concentration was not affected by salinity, but manganese concentrations in both leaves and fruits were significantly reduced under these conditions. Under salinity there was an enhancement of apoplast reactive oxygen species (ROS) production, which was partly a result of increase in NAD(P)H oxidase activity in the pericarp of pepper fruit at the stage that it was most sensitive to BER. Apoplast ROS production and extracted NAD(P)H oxidase activity were inhibited by manganese, zinc and to a lesser extent by calcium. These cations also negated the enhancement of ROS production caused by incubation of fruit pericarp discs in NaCl solutions. Manganese, zinc and calcium also inhibited NAD(P)H oxidase activity, extracted following their infiltration into fruit pericarp discs. The results suggest that generation and scavenging of oxygen free radicals in the apoplast may contribute to the appearance of BER symptoms in pepper fruits under saline conditions. It is suggested that manganese may serve as antioxidant in pepper fruit and that manganese addition to peppers grown under salinity may alleviate BER symptoms in the fruits.