Page 179 - AJWEP-22-6

Zn accumulating behavior of L. uncinatus

with increasing Zn supply levels, as expected. At the Zinc treatments appeared to have a stimulatory effect
600 mg/kg treatment, root dry matter was reduced by on plant dry matter yield, as IT values for Zn supply
57% compared to control plants. levels of 200, 400, and 600 mg/kg were 146%, 134% and
The negative effects of toxic elements on root growth 150% respectively. Two fundamental mechanisms have
are well documented. For example, Luo et al. reported been reported for plant tolerance to toxic elements: Metal
38
that elevated Zn levels inhibited the growth of Jatropha exclusion and metal detoxification. In the exclusion
46
seedlings by disrupting normal cellular metabolism and pathway, plants restrict metal absorption into the roots,
inducing visible injuries and physiological disorders. thereby preventing translocation and accumulation in aerial
Moreover, root growth was identified as the first visible tissues. By contrast, hyperaccumulator species actively
47
site of damage under excessive Zn, due to reduced cell take up toxic elements and tolerate them through internal
division. Additionally, cell walls have been reported detoxification mechanisms. Several hyperaccumulator
39
to rupture under physical stress when their elasticity species have been identified for Zn. To cope with excess
is significantly reduced by Pb and Cd exposure. Zn in the cytoplasm, plants may employ one or more
40
Significant decreases in plant biomass production of the following pathways: (i) Reduced accumulation
have also been reported in Lupinus ballianus and across the plasma membrane, (ii) sequestration in
41
Lupinus termis when grown either in 100% mine subcellular organelles, (iii) precipitation as insoluble
waste substrates containing 3,780 mg/kg Zn or in soil- salts, (iv) binding of Zn to low-molecular-weight
filled pots supplemented with 100 mg/L Zn solutions, organic compounds, and (v) removal through the plasma
respectively. 42 membrane into the apoplast. 48
Shoot dry matter yield per pot ranged from 1.90 g The IT values obtained in this study were compared
to 3.36 g. A significant increase in shoot dry matter with those reported in other investigations (Table 3). The
was observed compared to the control, and total plant results indicate that Lupinus species (both L. uncinatus
biomass followed the same trend. Similar increases in in the present study and L. albus ) exhibited a high
32
plant biomass in response to heavy metal treatments capacity for Zn accumulation and efficient translocation
have been reported by other researchers for Mn and to aerial tissues, particularly the stem, and consequently
copper, as well as Cd. 44,45 demonstrated higher tolerance indices compared to other
43
hyperaccumulator plants. However, these comparisons
3.2. Metal tolerance should be interpreted cautiously, as the experimental
In this study, we employed the index of tolerance (IT) conditions differed among studies in terms of exposure
to evaluate the ability of L. uncinatus to withstand Zn duration, soil pH, texture, and growth medium.
treatments after 2 weeks of growth in contaminated Further research is required to directly compare the
soil. Figure 1 illustrates the tolerance of Lupinus plants effectiveness of different plant genera in phytoextraction
under Zn exposure. An IT of 50% represents 50% of of heavy metals. To date, only a few species have
optimum plant growth and is considered the minimum been reported in the literature as potential soil Zn
acceptable biomass for plants grown in the presence of hyperaccumulators, notably those belonging to the
toxic soil elements. 37 genera Thlaspi and Brassica spp.; however, confirmation
under standard growth conditions remains necessary.
The high metal IT values observed in this study
indicate that L. uncinatus has considerable potential
for application in Zn phytoremediation. However,
biochemical mechanisms conferring metal tolerance
and uptake are both species-specific and metal-specific.
A deeper understanding of the physiological and
biochemical characteristics of Lupinus species that
enable them to tolerate excessive concentrations of
metals is essential to fully harness their phytoremediation
potential.

Figure 1. Index of tolerance exhibited by Lupinus 3.3. Plant accumulation and transport of zinc
uncinatus exposed to different zinc supply levels for An unresolved issue in phytoremediation, apart from
2 weeks (n = 4) tolerance, is the uptake and internal distribution

Volume 22 Issue 6 (2025) 173 doi: 10.36922/AJWEP025140101