Xanthomonas campestris pv. glycines (Xcg), an etiological agent of the bacterial pustule disease of soybean, displayed nutritionally regulated caspase-dependent programmed cell death (PCD). Experiments showed that Xcg was under metabolic stress during PCD, as evident from the intracellular accumulation of NADH and ATP. Further, the accumulation of reactive oxygen species (ROS), as confirmed by 2',7'-dichlorofluorescein diacetate labeling, electron spin resonance spectroscopy, and scopoletin assay, was also observed along with the activation of caspase-3. ROS scavengers such as dimethylsulfoxide, glutathione, n-propyl gallate, and catalase significantly inhibited caspase biosynthesis as well as its activity, eventually leading to the inhibition of PCD. The presence of a sublethal concentration of an electron transport chain uncoupler, 2,4-dinitrophenol, was found to reduce the ROS generation and the increase in the cell survival. These results indicated that Xcg cells grown in a protein-rich medium experienced metabolic stress due to electron leakage from the electron transport chain, leading to the generation of ROS and the expression as well as the activation of caspase-3, and resulting in PCD. A bacterial DNA gyrase inhibitor, nalidixic acid, was also found to inhibit PCD. Gyrase, which regulates DNA superhelicity, and consequently DNA replication and cell multiplication, appears to be involved in the process.

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A dose of 0.5 kGy of gamma radiation in combination with low temperature storage (4C) helped in extending the shelf life of two Indian litchi (Litchi chinensis) cultivars (“Shahi” and “China”) up to 28 days. However, during storage, pericarp browning in litchi was observed. Hence, in the current study to understand the mechanism of pericarp browning, total phenolics and the activities of polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonia lyase (PAL) were evaluated. The PPO activity and phenolics were found to be higher in “China” than in “Shahi,” whereas POD and PAL activities were higher in “Shahi.” PPO and phenolics played a major role in the pericarp browning. Radiation treatment increased the PAL activity and hence the level of total phenolics, whereas PPO and POD activities were inhibited. This may explain reduction in browning in irradiated fruits compared with nonirradiated fruits. PRACTICAL APPLICATIONS Browning of litchi pericarp affects the appeal of the fruit and is one of the main problems encountered by the cultivators and traders, leading to significant economic losses. Understanding the role of different enzymes and level of phenolics in the process of browning will help find suitable postharvest methods for the control of browning. As the radiation treatment is being used as a mandatory quarantine treatment in many countries for export, further understanding the effect of radiation treatment on the browning and related enzyme activities will help in postharvest management and improving international trade of litchi.