Promotion of 5-aminolevulinic acid treatment on leaf photosynthesis is related with increase of antioxidant enzyme activity in watermelon seedlings grown under shade condition

Abstract

Watermelon [Citrullus lanatus (Thunb.) Mansfeld] is a photophilic plant, whose net photosynthetic rate was significantly decreased when seedlings were grown under low light condition. However, treatment with 100 mg kg -1 5-aminolevulinic acid (ALA) could significantly restore the photosynthetic ability under the environmental stress. The parameters of leaf gas exchange, chlorophyll modulated fluorescence and fast induction fluorescence of the ALA-treated plants were higher than that of the control. Additionally, ALA treatment increased the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX). Nevertheless, the treatment of diethyldithiocarbamate (DDC), an inhibitor of SOD activity, dramatically depressed photosynthesis of watermelon leaves, while ALA could reverse the inhibition of DDC. Therefore, it can be deduced that ALA promotion on photosynthesis of watermelon leaves under low light stress is attributed to its promotion on antioxidant enzyme activities, and the increased activities of the enzymes, which are mainly located near the reaction centers of PSI, can scavenge superoxide anions, leading to an increase of apparent electron transport rate and an alleviation of photosynthetic photoinhibition under the stressed environment.

Effect of 5-Aminolevulinic Acid (ALA) on Leaf Diurnal Photosynthetic Characteristics and Antioxidant Activity in Pear (Pyrus Pyrifolia Nakai)

“…ALA might improve the photochemical efficiency of PSII reaction center. Whether the darkadapted or light-adapted maximal photochemical efficiency, it has been reported that ALA had significant effect (Sun et al, 2009a;Wang et al, 2010). Recently, the similar effect was confirmed in the transgenic tobacco (Zhang et al, 2010).…”

“…Previous reports have demonstrated that ALA treatment can improve the net photosynthetic rate in spinach (Nishihara et al, 2003), melon (Wang et al, 2004), pakchoi (Wang et al, 2004b), radish (Hotta et al, 1997b;Wang et al, 2005b), strawberry (Liu et al, 2006) and watermelon (Sun et al, 2009a), under normal or stress conditions. The result of this work confirmed that exogenous ALA at a concentration of 0.5 mg/L could increase the net photosynthetic rate of pear leaves ( Fig.…”

“…In aspect of antioxidant enzymes, it has been suggested that ALA treatment stimulated SOD activity around PSI reaction center, which can scavenge ROS aroused from photosynthetic electron transport in electron transfer chain to improve photochemical electron transfer rate (Sun et al, 2009a, b). Diethyldithiocarbamate (DDC), an inhibitor of Cu-Zn-SOD, could eliminate ALA' effect on photochemical efficiency (Liu et al, 2006;Sun et al, 2009a), which suggested the important role of SOD on ALA promotion. In this work, ALA treatment also induced SOD activity in pear leaves (Fig.…”

“…Chlorophyll fast fluorescence transient was measured by a Plant Efficiency Analyzer (Hansatech, UK), according to methods of Strasser et al (1995) and Sun et al (2009a). All the leaves were immediately exposed to a saturating light pulse (3000 mmol·m -2 ·s -1 PFD) for 1 s after dark adapted for 20min.…”

“…All the leaves were immediately exposed to a saturating light pulse (3000 mmol·m -2 ·s -1 PFD) for 1 s after dark adapted for 20min. Each transient obtained from the dark-adapted samples was analyzed according to the JIP-test (Srivastava et al, 1997;Li et al, 2005;Sun et al, 2009a).…”