Role of reactive oxygen species (ROS) scavengers on plant growth and shelf life of Tomato

Tomato is widely cultivated and important nutritious vegetable in the world. It deteriorates rapidly after harvesting. High reactive oxygen species (ROS) level has negative effect on growth and development through oxidative stress by affecting physiological and molecular processes. Oxidative stress can be recovered by the scavenging system which consists of enzymatic as well as non-enzymatic antioxidants. So, ROS balance and antioxidant are necessary for better growth and prolong shelf life. As an antioxidant ascorbic acid was applied several times which played key role for plant growth and stress management. This study evaluated the role of ascorbic acid on physical and physiological changes of tomato. A marked variation was observed on some parameters regarding leaf length, panicle length, flower cluster and fruits per plant, chlorophyll content, MDA content, fruit yield per plant etc. Application of ascorbic acid increased leaf length, chlorophyll content, dry matter and decreased MDA content. Flower cluster per plant as well as panicle length was maximum at 45 DAT. Number of fruits and fruit yield/plant was fluctuated slightly with the application of ascorbic acid. Thus antioxidant has played a pivotal role on growth and development of plant.


Introduction
Tomato (Lycopersicon esculentum) is used as edible vegetables belong to the family solanaceae in the world. Nutritive value of the fruit is an important aspect of quality in tomato. Tomato is usually treated as common food due to its minerals, vitamins, few antioxidants, essential amino acids, sugars as well as dietary fibers that are important ingredients for culinary and chutney, pickles, soup, juice, and puree [1]. It contains few major chemical elements such as 2.50-4.50% sugar, 15-20 mg/100g vitamin C, 0.25-0.50 g/100g calcium (Ca), 0.10-0.50g/100g magnesium (Mg), 0.20-0.80 g/100g phosphorous, and lycopene 20-50 g/100g [2]. Tomato is cultivated across Bangladesh as its adaptation to any type of soil and environment [3,4]. Tomato is an extremely perishable fruit and rapidly deteriorates after ripening [5]. Post-harvest degradation that accounts for tremendous financial losses of more than 25 percent of fresh tomato per year is a major challenge for tomato cultivation [6][7][8].
It is commercially cultivated in Bangladesh as well as in many countries around the world for its taste and nutritional status [9][10][11]. In Bangladesh, it is cultivated as winter vegetable with annual production of about 389000 metric tons [12]. The popular cultivation areas of tomato in Bangladesh include Chittagong, Comilla et al. [13][14][15]. However, tomatoes are grown extensively all over the country. In Bangladesh, tomato is mainly grown in the winter season [16]. November to February is the congenial period for tomato cultivation in Bangladesh [17,18].
Plants use O2 to generate the required energy for their own production processes. Land state O2 is reduced to water (H2O) and ROS during normal cellular metabolism that include O2ˉ, H2O2, OHand O2 [19,20]. Reactive oxygen species (ROS), like O2, H2O2, O2and HO, are highly reactive molecules, causing protein, DNA, and lipid oxidative damage [21][22][23]. In addition to being toxic molecules, however, ROS also plays a role of signaling molecules which regulate many important biological processes [24][25][26]. Since ROS plays a dual role in plants, both as key regulators for growth, development and defense pathways and as toxic aerobic metabolism by-products [27][28][29].
The accretion of ROS is allied with growth and over maturation of the fruit [29]. The high ROS levels are harmful for cells of plant and equilibrium between ROS growth and scavenging [30][31].
The fruit undergoes photosynthesis and respiration during the early expansion stages, as well as other physiological processes to satisfy its size expansion requirements [32][33][34]. ROS is produced and accumulated during these processes [35]. The application of antioxidant compounds after harvest will effectively prolong the shelf-life of tomatoes [36]. Extending the shelf-life by minimizing ROS in other crops has also proved successful. Tomato fruit ripening and over-ripening is difficult. It requires numerous changes in chemical and morphological words. The functions of antioxidants and scavenging process studied widely across all these modifications [37,38]. The fruit antioxidant system's scavenging capacity decreases during ripening and over-ripening [39]. The main factor controlling tomato fruit ripening and overripening is the balance between antioxidant activity and ROS generation [40]. Different strategies were used to prolong the shelf life. The simplest and commonly practiced is to collect tomato in green stage as well as store it at minimum temperature [41]. The fruits are subsequently subjected to ethylene to cause ripening [42]. Therefore, this study aims to determine the suitable stage of antioxidant application to lower the ROS level in plants as well as in fruits. Hence, this experiment intended to assess the effectiveness of various treatments on plant growth of tomato and increase the shelf life of tomato.

Materials and Methods
This study was done in the horticulture experimental field and

Data Analysis
The observation (data) for various growth and yield contributing factors analyzed statistically to explore the mentionable variation obtained from the treatments of the experiment. Statistic 10 program used to examine the collected data.

Results and Discussion
The results of different parameters that obtained from the present experiment have been presented and explained in this chapter. Data on different parameters were analyzed statistically and the results have been presented in different tables and figures.
The result of each parameter has been explained and possible interpretations have been made in this section.

Leaf Length (cm)
There was little difference found in the leaves length of tomato during 1 month and 2 months after transplantation due to application of different treatments ( Table 1). The longest leaf length (13.667 cm) was recorded in T4 and the lowest leaf length (13.33 cm) was observed in T2 at 30 days after transplanting (DAT).
In case of 60 days after transplanting, the highest leaf length (37.90 cm) was observed in T2 and the lowest leaf length (35.44 cm) was found in T1 treatment. At 45 days after transplanting, different treatments showed statistically significant variation in the leaves length. The longest leaf length (33.11 cm) was recorded from T4 treatment while small leaf length (28.44 cm) was found in T1 treatment. This might be due to application of antioxidant reducing ROS content of leaves which helps to extend leaves length [43]. Note: 5% level of probability. T 1 = control, T 2 =0.5 mM, T 3 =2 mM and T 4 =4 mM.

Panicle Length (cm)
There was no significant variation in case of length of panicle (cm) during 1 month and 1.5 month after transplantation due to the application of antioxidant (Figure 1). The maximum length of panicle (4.33 cm) was recorded in T1 and the minimum length of panicle (4.00 cm) was recorded in T4 at 30 days after transplanting.
At 45 DAT, the ranges varied from 11.00 cm to 11.44 cm where T4 gave the highest value (11.00 cm) and the lowest value (11.44 cm) was found in T1. Statistically significant variation was observed for panicle length at 60 days after transplanting. Among the different treatments the maximum value (13.667 cm) was found in T3 and T4 treatment which was significantly different from T1 (11.66 cm).
This might be due to the balance of network of ROS and antioxidant was higher at 60 days after transplanting.    Note: 5% level of probability. T 1 = control, T 2 =0.5 mM, T 3 =2 mM and T 4 =4 mM.

Number of Fruits per Plant
Data on 30 days, 45 days and 60 days after transplanting were recorded (Figure 3). At

Fruit Yield per Plant
A large disparity in fruit yield among the four treatments was found (  Note: 5% level of probability. T 1 = control, T 2 =0.5 mM, T 3 =2 mM and T 4 =4 mM.

Dry Matter
The result revealed that there was a significant variation among the treatments ( Figure 5). The highest dry matter (7.22%) in tomato was recorded from T4 treatment whereas the minimum dry matter (5.85%) was observed in T1 treatment where no antioxidant was applied.

Malondialdehyde (MDA) content
A statistically significant variation was observed in MDA of tomato fruit at storage for different treatments (