Abstract
Alternative pathway (AP) has been widely accepted to be involved in enhancing tolerance to various environmental stresses. In this study, the role of AP in response to cadmium (Cd) stress in two barley varieties, highland barley (Kunlun14) and barley (Ganpi6), was investigated. Results showed that the malondialdehyde (MDA) content and electrolyte leakage (EL) level under Cd stress increased in two barley varieties. The expressions of alternative oxidase (AOX) genes (mainly AOX1a), AP capacity (Valt), and AOX protein amount were clearly induced more in Kunlun14 under Cd stress, and these parameters were further enhanced by applying sodium nitroprussid (SNP, a NO donor). Moreover, H2O2 and O2− contents were raised in the Cd-treated roots of two barley varieties, but they were markedly relieved by exogenous SNP. However, this mitigating effect was aggravated by salicylhydroxamic acid (SHAM, an AOX inhibitor), suggesting that AP contributes to NO-enhanced Cd stress tolerance. Further study demonstrated that the effect of SHAM application on reactive oxygen species (ROS)-related scavenging enzymes and antioxidants was minimal. These observations showed that AP exerts an indispensable function in NO-enhanced Cd stress tolerance in two barley varieties. AP was mainly responsible for regulating the ROS accumulation to maintain the homeostasis of redox state.
Highlights
Cadmium (Cd), one of the most toxic heavy metals to the environment, has drawn great attention worldwide
The results showed that NaN3 in Ganpi6 and Kunlun14 roots nearly abolished Cd-induced Nitric oxide (NO) accumulation, whereas applying L-NNA had almost no impact on Cd-induced NO accumulation (Figure 3A), indicating that the Cd-induced NO production originated from the Nitrate Reductase (NR)-dependent pathway
We found that the activities of reactive oxygen species (ROS)-related scavenging enzymes and antioxidant molecules were enhanced in two barley roots under normal and stressed conditions in the presence of sodium nitroprussid (SNP), which is in line with the previous study in barley seedlings [64]
Summary
Cadmium (Cd), one of the most toxic heavy metals to the environment, has drawn great attention worldwide. It inhibits plant growth, and pollutes the food chain, seriously threatening human health [1,2]. Over-accumulated Cd affects enzyme activity and changes protein structure [4,6,7]. Cellular redox homoeostasis is disturbed, and reactive oxygen species (ROS) burst, which further leads to oxidative stresses. Activating antioxidant enzymes and non-enzymatic antioxidants to counteract the oxidative stress has been widely accepted [8,9]. Even though great effort has been made in the past, the protective mechanisms against
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