Stem length (cm)
Stem length significantly differed among treatments. Varieties and treatments both revealed highly significant differences. While, interactive response among treatment and varieties were non significantly different (Table 1). IAA increased stem length as 18.61%. Under stress of low and high lead stem length was declined as 38.61 and 46.49% respectively. IAA alleviated the toxic effect of lead, therefore, stem length reduction was limited to 17.15 and 20.34% respectively (Table 2).
Root length (cm)
Highly significant differences were observed in root length by treatments, varieties and also by their interactions (Table 1). IAA increased root length upto 14.46%. Low and high lead decreased root length by 45.96 and 59.45% respectively, IAA mitigated toxic effect of lead. Hence, reduction by metal was 11.18 and 28.05% respectively (Table 3).
Leaf area (cm2)
Results revealed that variety, treatments and their interactions highly significantly different (Table 1). Leaf area was increased by IAA treatment (53.54%). Low and high lead treatments reduced leaf area as 38.61 and 62.20% respectively. IAA alleviated lead stress effects and limited reductions to18.50 and 44.88% respectively (Table 4).
Nitrogen (N) contents (mg/g)
The data related nitrogen contents showed that highly significant differences were found among different treatments. Varieties and collective response in varieties and treatments showed non-significant differences (Table 1). Increased nitrogen contents (0.09%) were observed by IAA treatment. Low and high lead treatments decreased the nitrogen values 23.25 and 29.96% respectively. IAA ameliorated the lead stress. Therefore, reductions by metal treatments were lowered to 7.90 and 21.83% respectively (Table 5).
Phosphorus (P) contents (mg/g)
The data revealed that phosphorus contents showed that treatments, varieties and their interactions showed non-significant differences (Table 1). Increased phosphorus contents (6.04%) were observed by IAA treatment. Low and high lead treatments decreased the nitrogen values as 25.11 and 27.90% respectively. IAA ameliorated the lead stress therefore phosphorus was reduced up to 13.48 and 23.23% respectively (Table 6).
Potassium (K) contents (mg/g)
The data related to potassium contents showed that varieties revealed significant differences while treatments and their interactions with varieties treatments showed non-significant differences (Table 1). Increased potassium contents (4.14%) were observed by IAA treatment. Low and high lead treatments decreased the potassium values 12.99 and 26.66% respectively. IAA ameliorated the lead stress therefore metal induced reductions were limited to 2.84 and 6.70% respectively (Table 7).
Well grown plants of mung bean with adequate amount of nutrients provide more energy in term of food and fodder. Growth was reduced in stem, root and leaves by Pb and enhanced by IAA (Table 2-4). Growth reduction might be owed to a decline of water potential (Atteya, 2002). Water contents of metal stressed plants are lowered by enhanced resistance in its flow (Poschenrieder
et al.,
1989) or it might be due to metal induced change in cell wall structure (Poschenrieder
et al.,
1989). Growth and morphology of mung bean is influenced by plant growth promoting rhizobia (PGPR) and other external factors
(Neha et al., 2021). Plant growth regulators can influence the productivity of mung bean
(Bhadane et al., 2021).
Growth reduction might be due to metal induced chlorophyll decrease by denaturation of its biosynthetic enzymes
i.e., 6-amino laevulinic acid dehydratase and porphobilinogenase by metal
(Hampp et al., 1974). Lead toxicity affects the rate of photosynthesis
(Carlson et al., 1975); changes in the thylakoid structure
(Fodor et al., 1996); reduction of mitochondrial cristae (Samardakiewicz, 2000) and phosphorylation process (Wozny, 1995).
Reactive oxygen species (ROS) production by metal lowers concentration of osmotica such as carbohydrates and amino acids
(Zhang et al., 1999); causes protein and lipid oxidation/ degradation of mitochondrial membrane and inhibition of photosynthetic ETC (Kappus, 1985). Peroxidase reduction by ROS results in shoot growth retardation (Stoeva and Bineva
, 2003). However, IAA treated plants showed better expression in all above parameters.
Lead exerted a negative impact on N, P, K content in lead treated mung bean plants (Table 5-7). Lead reduces the uptake and transportation of mineral nutrients in plants (Goldbold and Kettner, 1991).
Saygideger et al., (2004) observed that high level of Pb could decrease the nitrogen contents in
Typha ceratophyllum. The decline in nitrogen concentration due to Pb may be as a result of moisture stress which is created by Pb (Burzynisky and Grabowski, 1984). Application of Pb decreases the nitrogen and phosphorus contents
(Kibria et al., 2009). According to Orhue and Innch (2010), concentrations of phosphorous and potassium were significantly decrease in
Celosia argentia by treatment of Pb. According to Blatt (1993), transport of ion is regulated by auxin. Auxins cause an increased in concentration of K ion in wheat grain and leaves (Wierzbowska and Bowszys, 2008). Response of the varieties differed to IAA and metal. Yield varies with genetic makeup of mung bean (Priya and Ratna Babu, 2021;
Salman et al., 2021)