Improving heavy metal stress tolerance in tomato by grafting
Author(s)
Pradeep, Kumar
Date Issued
July 7, 2015
Type
Doctoral Thesis
Abstract
Among the heavy metals, Cadmium (Cd) and nickel (Ni) are the most hazardous metals
and their excess level in soil or irrigation water causes considerable damage to crop plants.
Grafting has become an effective and sustainable tool in providing plant tolerance to various
abiotic stresses, in particular of fruiting vegetables. In present research program, grafting
potential was explored in mitigating adverse effects of elevated level of Cd or Ni in tomato
(Solanum lycopersicum L.). The aim of this PhD dissertation was to improve tomato plants
tolerance to heavy metals stress, in particular of Cd and Ni by grafting onto appropriate
rootstock(s). In addition, the rootstock mediated plant tolerance mechanisms were studied at
cellular and molecular level. The role of candidate genes (LeNRAMP3 and LeFER) function in
Cd tolerance was also studied. Furthermore, in next step, the integrated response of grafting with
arbuscular mycorrhizal (AM; Rhizophagus irregularis) inoculation in further enhancement of Cd
tolerance was investigated.
Tomato plants whether non-grafted, self-grafted or grafted onto rootstocks of tomato
(Maxifort and Unifort) or eggplant (Black Beauty) were adversely affected by excess
concentration (i.e, 25 and 50 μM) of Cd or Ni in growing medium as evident by reduced plant
growth and fruit yield. However, plants grafted onto tomato rootstocks, especially onto Maxifort
shown better performance to mitigate adverse effects of heavy metals as shown by higher fruit yield and plant biomass, compared to others. We herein, demonstrate that the higher yield and
biomass production in tomato rootstocks grafted plants, especially onto Maxifort was due to
better ability of rootstock in particular of translocation of nutrient elements to shoot, higher leaf
pigments contents, SPAD index and photochemical efficiency of PSII. In addition, their better
ability to reduce oxidative stress, evident by lipid peroxidation and ion leakage, by induction of
antioxidants- enzymes (CAT, APX or GPX) and -non-enzymes like carotenoid, proline and
certain other metabolites. The over expression of LeNRAMP3 gene in leaves support Maxifort
grafted plants ability to Cd stress tolerance by providing higher availability of certain nutrient
elements under Cd stress. Moreover, Maxifort rootstock could also efficiently limit the
translocation of toxic metals, especially of Cd to the aerial plant parts (leaf + stem + fruit).
Moreover, the expected positive response of AM fungi in providing plant tolerance to Cd stress
especially under given moderate level of Cd stress (25μM), in later phase of study, could not be
observed. Finally, from these investigations it can be concluded that tomato grafting onto
appropriate rootstock such as Maxifort could alleviate Cd or Ni stress
Additional information
Dottorato di ricerca in Ortoflorofrutticoltura
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