Abstract
Grafting is widely used to increase plant defense responses to various stresses. Grafting-induced cold tolerance is associated with the increase of the antioxidant potential of plants; however, the underlying mechanisms remain unclear. Here, we found that pumpkin rootstocks promote antioxidant enzyme activities and alleviate cold-induced oxidative damage, accompanied by increased abscisic acid (ABA), melatonin, and methyl jasmonate (MeJA) levels in leaves. Increased ABA accumulation in leaves was attributed partly to the increased ABA levels in rootstocks. ABA induced antioxidant enzymes activities and the accumulation of melatonin and MeJA, while inhibition of ABA synthesis blocked the rootstock-induced antioxidant activity and the accumulation of melatonin and MeJA under cold stress. Melatonin and MeJA application also enhanced ABA accumulation in leaves after cold exposure, whereas inhibition of melatonin or MeJA synthesis attenuated the rootstock-induced increase of ABA. Moreover, melatonin and MeJA application alleviated cold-induced oxidative stress, but inhibition of melatonin or MeJA synthesis lowered the rootstock- or ABA-induced antioxidant potential and tolerance to cold. These findings indicate that ABA plays an important role in the grafting-induced cold tolerance by promoting the accumulation of melatonin and MeJA, which in turn, promote ABA accumulation, forming a positive feedback loop.
Highlights
As sessile organisms, plants frequently suffer a variety of environmental stresses throughout their life
We investigated the effects of the pumpkin rootstock on the antioxidant potential and oxidative damage in watermelon plants in response to cold
Our results show that grafting onto pumpkin increased the activities of Superoxide dismutase (SOD), POD, and CAT and alleviated cold-induced accumulation of O2·− and H2O2 and oxidative damage in watermelon shoots
Summary
Plants frequently suffer a variety of environmental stresses throughout their life. One of the most severe abiotic stresses, adversely affects plant growth and development. When the ambient temperature drops, air temperature declines faster than soil temperature and the above-ground parts of plants are more vulnerable to cold stress. Excess ROS can cause oxidative stress leading to lipid peroxidation damage, DNA strand breakage, protein denaturation, enzyme deactivation, and, ABA in Grafting-Induced Cold Tolerance cell death (Bose et al, 2014). To ensure their adaptation and fitness under cold stress, plants have evolved sophisticated defense mechanisms
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