**1. Introduction**

Plant cells can cope up with fluctuating environments by modulation of different cellular processes [1]. Programmed cell death (PCD) is the process in which the cell(s) voluntarily commit suicide on several occasions among which the most prominent reasons are morphogenic or developmental changes and stress responses. In plants and animals, PCD plays significant role during development, structure formation, or removing unwanted tissues [2, 3]. It has been also reported that PCD act as a defense mechanism of an organism to prevent the pathogen spread from the infected cell [4].

In general, PCD is grouped into three broad categories; *viz.* apoptosis, autophagy (vacuolar PCD), and necrosis [5]. The detailed cellular mechanism of apoptosis is

well studied in the animal system but current knowledge of the execution processes leading to PCD in plants is very scarce [6, 7]. In general, the fundamental mechanism of apoptosis involves chromatin condensation followed by nuclear fragmentation and the formation of the apoptotic body [8]. Besides that, autophagy involves the formation of vacuoles and rupture of vacuoles that results from the release of hydrolyses enzyme and sudden disappearance of cytoplasm [9]. Such autophagic vacuoles contain degenerating organelles and cytosolic content [10]. Lastly, the process of necrosis is an energy-independent process that results in cytoplasmic swelling and rupture of the plasma membrane [5].

Our present study emphasized on current understanding of plant PCD in different dimensions such as understanding the PCD response towards stress, types of PCDs occurs, cellular-hormones signaling mechanism, and proteases involved in different stress conditions and developmental processes. Additionally, our comparative studies showed that the process of true apoptosis is absent in plants but has several similarities, hence this process is termed apoptosis-like PCD (AL-PCD). The *cys*-protease which is responsible for triggering animal PCD is absent in plants but similar kinds of proteases particularly vacuolar processing enzymes (VPEs) and papain-like cysteine proteases (PLCPs), known as metacaspase play the main roles in PCD [6, 11, 12].
